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P L I C A T I O N S

11

e c t r i c a

I

o n s t r u c t i o n

D E D I T I O N

K.

Clidero

th

H.

Sharp e

'

"3

•da



Copyright © 1991 Irwin Publishing

No par t of this book may be rep rodu ced

or transm itted in any form or by any

me ans, electronic or m echanical, includ

ing photocopy, recording or any infor

mation storage and retrieval system now

known or to be invented, without per

mission in writing from the publisher

excep t by a reviewer wh o wishe s to

quo te brief passag es in con nec tion w ith

a review written for inclusion in a maga

zine,

newspaper, or broadc ast .

First Edition p ublish ed 1975

SI M etric Seco nd Edition pu blished 1979

Third Edition published 1991

Edited by Kate Revington

Designed by Jack Steiner G raphic Design

Typ esetting and illustrations

by Trigraph Inc.

Cover photograph by Birgitte Nielsen

Canadian Cataloguing in Public

Data

Clidero, Robert K.

Ap plications of electrical cons

3rd. ed.

Includes index.

ISBN 0-7725-1719-3

1. Electric engin eering. I. Sha rp

Kenneth H. II. Title.

TK452.C551991

621.3 C91-

ISBN-13:

978-0-7725-1719-7

ISBN-10: 0-7725-1719-3

Printed and bound in Canada

Published by

Nelson

1120 Birchmount Road

Toronto, Ontario M1K5G4

1-800-668-0671

www.nelson.com

http://www.nelson.com/

http://www.nelson.com/



CHAPTER 12:

Aluminum-Sheathed Cable/142

Construction, sizes, preparation,

installation techniqu es, and applications

CHAPTER 13:

Mineral-Insulated Cable/151

Sizes, preparation, handling, and

applications

CHAPTER 14:

Conduit Wiring/162

Rigid, flexible, thinwall, and plas tic

cond uit, tools, related eq uipm ent, sizes,

allied fittings, and regulations

CHAPTER 15:

Residential Service Wiring /199

Types, sizes, grounding, related

equipment, installation methods, and

regulations

CHAPTER 16:

Industrial Servic es/ 229

Wiring diagrams, 3 phase syste m s, 3 and

4 wire systems, m eter con nections,

grounding, circuit breakers, regulations,

ground fault protection d evices and

their operation

CHAPTER 17:

Fuses

/ 249

Types, sizes, and ratings

CHAPTER 18:

Residential Electric Heating / 266

Types, sizes, insulation, heat load

calculations and cost analysis

CHAPTER 19:

Discharge Light Sou rces/ 301

Fluorescent lighting; high-intensity

discharg e lamps, including the mercury

vapour, metal halide, and high-pressure

sodium; tungsten-halogen lighting; lamp

cons truction; circuit diagrams; and

applications; energy conservation and

lamp m aintenance

CHAPTER 20:

Mo tor Control / 334

Motor protection, across-the-line

starting, reduced voltage starting,

starte r construction and o peration,

magnetic starters, and circuit diagrams

for control circuits, overload protection

devices, typ es, and ratings

CHAPTER

21:

Fastening De vice s/ 376

Screw fasteners, wood and metal types,

bolt strength; masonry fasteners, types

and methods of installation; drilling

device s; hollow-wall fa steners ;

powder-actuated fasteners, associated

tools, acce ssorie s, and regulations

CHAP TER 22 :

Tools of the Electrical Trade / 406

Hand d river s; pliers; cutting, striking,

and m easuring too ls; safety devices;

pow er tools, electric and cordless typ es;

motor operation; power tool

maintenance, selection and users' safety

Glossary of Electrical Terms / 436

For Reference / 437

Inde x/ 438



Preface

A

s classroom tea che rs, we are aware

of the need for student textual

materials that explain the non-mathe

matical theory behind electrical devices

and equipment.

Drawing on our experience as jour

neymen electricians and high school

teachers, we have aimed, in this text, to

explain as simply as possible modern

electrical products and their applica

tions in electrical c ircuits. We hav e also

tried to downplay the use of complex

technical terms and to em phasize th e

reason s for electrical installation pra c

tices. This

Third Edition

has been given

extensive review not only by us but b y

the manufacturers of illustrated prod

ucts. Always, our intent h as be en to p ro

vide read ers with th e most recen t and

up-to-date changes in product design.

Many chapte rs have been

lengthened by the insertion of new prod

uct and technolo gy information. New

illustrations provide a clear understand

ing of recent chang es in both technology

and w iring co de s. Also, a new cha pte r

(Chapter 22) provides read ers with a

fuller u nde rstan ding of the specialized

tools used in the electrical industry.

Since the electrical industry has not

yet adopted the SI (me tric) sys tem of

measurement, the commonly used impe

rial measure tables ap pea r with m etric

equivalents through out the text. The

text accurately reflects an industry in

transition.

It is our hope that high school stu

dents, appre ntices, electricians, and t he

genera l public will find th is tex t a useful

tool for understanding how electrical

theo ry is transla ted into practical term s.

We would like to than k all thos e per

sons and organizations who se co-opera

tion mad e this text poss ible.

Robert K. Clidero

Kenneth

H.

Sharpe



E

lectrical power is supplied to the

hom e by th e local hydr o utility.

Because there are so many appliances

available today, two voltages are

needed. Lighting and receptacles for

such sm all appliances as radios, toast

ers, teakettles, frying pans, and electric

drills require a 120 V supply. Large

appliances, such as electric stoves,

clothes driers, some air conditioners,

and electric heaters, operate on 240

V

On the North American con tinent, a

frequency of 60 Hz (cycles) is th e s tan d

ard. The frequency of an alterna ting cur

rent sy stem is the num ber of pu lses of

current that pass along the con duc tors

in one secon d. On a 60 Hz system, there

are 120 pulses per seco nd. One p ositive

and one negative pulse make up one

cycle,

or

hertz.

(See Fig. 1.1) Residential

V2 I*:

cycle

negative

FIGURE

1.1

pulses

The Three

Wire

Distribution

System

voltages ope rate on a

single-phase

sys

tem. Both single-phase voltages com e

from a transfo rme r tha t h as a single pri

mary winding.

O btaining T wo Voltages

From T hree W ires

When two dry cell batteries of 1.5

V

each are connected in series, 3 V are

obtained. (See Fig. 1.2) By connecting a

wire midway betwee n th e two cells, a 3

wire system providing two voltages is

created. The distribution transformer

Three alternating current

FIGURE 1.2 Tw o voltages from 3 wires

Applications of Electrical Construction



used to supply a house or group of

hou ses is wired in the s am e m anner.

Distr ibut ion Transformer

The local hydro utility use s

a

ser ies of

transformers to lower its voltage s in

stages from the power station

to

the res

idential street. Each locality may differ

slightly in the actual v oltage tha t arrives

at the distribution transformer on

the

street. One comm on voltage is 2400

V.

(See Fig.

1.3)

secondary

wind ing

live wire

—<

pr im ar y w ind ing

2400

V

^ T T x

^

r ound

.

neutral

w i r e

1 2 0 V — f - 1 2 0 V -

240 V

_ laminated

core

t ransformer

rat io 10:1

— l ive wire

FIGURE

1.3

Distribution transformer circuit

diagram

High-tension

(high-voltage)

lines

sup

ply the p rima ry coil

of

the transformer

with 2400

V

This transformer reduces

the voltage on

a

10:1 ratio , giving

a

secondary output of 240

V A

wire is con

nected to th e midway point of the secon

dary winding, dividing its 240 V in half.

This middle,

or

neutral, wire provides

two voltages on a 3 wire system.

The two outer w ires of the secon

dary winding are known

as

th e live

wires. It should be noted th at in a resi

dential wiring system, the neutral wire

is

white

or

grey

in

colour, while the

live

wires are usually

black.

For safety pur

poses, th e live w ires are sw itch con

trolled and have fuses connected

in

series with them . The neutral wire (also

called th e

grounded,

identified conductor)

is grounded (conn ected to the earth ) at

the transformer and in the residential

main switch box.

Residential Overhead

Supply System

Figure 1.4 show s the me thod used

to

supply power to many

of

the h ouses

in

a

community. In some areas, a fourth wire

is brought from the hydro pole to the

house for the purpose of supplying a

flat-rate, hot-water heater system. (This

is cove red in more detail in Chapter 15.)

Residential Underground

Supply System

Modern community planning has led

to

the development

of

an underground sup

ply system in which wires

and

cables

are

placed below ground. The main advan

tage of this system is to give th e comm u

nity an unc lutte red look. Figure 1.5 shows

one variation of this type of system.

S witching the L ive Wire

On reaching the house, the hyd ro supp ly

lines pas s through t he

kilowatt hour

meter.

(The amount

of

power used

is

recorded on this m eter in kilowatt

hou rs.) The supp ly lines are the n carried

into the ho use by a conduit, which takes

them directly to the main disconnect

switch. As Figure 1.6 shows, the supply

lines are conne cted

at

the top

of

the

switch, which is stand ard practice . The

upper portion

of

the sw itch is called

the

line side. Most manufacturers have the

word line printed somewhere near

the

line termin als.

Should an electrical em ergency arise,

turning this switch

off

will disco nne ct

the pow er supply to all parts of the

hou se. Power may

be

restored by turn

ing th e main switch on again. Once th e

The Three Wire Distribution System



high tension pr imary l ines

(2400 V)

transformer and

neutra l grounded

N O T E :

To save cost of materials and wire,

the earth (ground) is used as a return

path for the primary circuit.

FIGURE 1.4 T ypical 3 wir e distribution system

distr ibut ion t ransformer

outdoor meter

service conduits -»

service mast

outdoor meter

\

service conduit

grade le

t

1 m m i n i m u m

i

hydro supply l ines (120 V/240 V) •

high tension primary lines (2400 V)

FIGURE 1.5

Underground distribution system




meter

service mast

service conduit

basement wa

live wire (line)

switch blades

operating

handle

ground wire

for

mast

box ground

cable clamp

neutral wire

g ro u n d w i re to cold-wa ter pipe

RGURE 1.6 Electrical connections in the main disconnect switch

main

switch h as been

pulled, or

turned

off. all co nt en ts

of

the m ain switch box

are

safe to hand le, with the e xcep tion of

the two terminal connection s th at

receive the incoming hydro supply lines.

Fuses may

be

replaced

or

checked,

repairs to the sw itch made,

and

any of

the wires

at

the bottom,

or load,

side of

the switch may be handled

in

safety.

Fusing the L ive W ire

The purpose

of

any fuse is

to

limit th e

amount

of

electrical

current (amperes)

that can pass through

a

given w ire.

If

more current

is

pass ed through the wire

than

it

is designed

to

carry, the wire wil

heat up and eventually start

to

burn

the

insulation covering it.

A

fuse is design ed




•

to heat up and melt

before

th e w ire it

protects is damaged.

The fuses in the main d isconn ect

switch are designed to protect those

con ducto rs going from the

load

s ide of

the switch to the

distribution panel.

The

voltage rating

of the fuse is m atche d to

the v oltage of the supp ly system , while

th e current rating of the fuse is ma tched

to the curren t carrying capacity

(ampacity) of the wire.

The amount of current entering the

ho use on one of the live wires must

leave the hou se on the othe r live wire

an d/o r the neu tral wire. Therefore, a

fuse is need ed on each of the live wire s.

Figure 1.6, on page 5, show s th e location

of the fuses in the main disconnect

switch.

W hy the N eutral W ire Is

Not Fused

W hen the 3 wire distribution sy stem first

ca m e into use, a fuse was placed in

series with the ne utral wire as well as

with the live wires. This practic e w as

soon d iscovered to be dangerous.

A 120

V

lighting circuit was protected

by a fuse on th e live wire and o ne on the

neutral w ire. Since both w ires were the

sam e size, both fuses w ere of the sa m e

current rating.

If

a fault c ausing a sh or t

circuit condition occurred and excessive

cur ren t sta rte d to flow, th e fuse would

open the circuit and prevent damage to

th e wire. Since both fuses in th e circu it

we re the sam e size, several things could

happen:

Situation A.

Both

fuses could blow at the

sam e time and preven t any further cur

ren t flow. Both the live and ne utral wires

would be safe to hand le, and repairs

could b e ma de to the circuit without fear

or dan ger of electrical sh ock . (See Fig.

1.7)

Situation

B. The fuse on t he

live

wire

could blow. Both fuses are rated the

same, but there could be some small di

ference in their con struction tha t would

mak e on e fuse we aker than th e other,

causing it to open first. If this happened

the wires would b e protected by the cu

rent flow being cut: the circuit would be

safe t o work o n. (See Fig. 1.8)

Situation

C.

The fuse on th e neutral wir

could blow. Th ere is no w ay to tell in

advance which fuse might be weaker.

Chance alone would determ ine w hich o

the two fuses would be the on e to blow

first.

If

the neutral fuse burned out first

no further curren t flow would dam age

the w ires. (Since the cu rrent entering a

circuit is the sam e as the curren t leav

ing, th e neu tral fuse could open t he cir

cuit a s w ell.) The live wire, however,

would still be intact.

A

person (if

grounded) attempting to repair the cir

cuit could receive a 120 V shock from

the live wire. Th e ch anc es of receiving

such a shock a re high, beca use all elec

trical boxes in m odern wiring sy stem s

are ground ed an d bec aus e plumbing fix

ture s, damp c on crete floors, etc., are

com m on in th e hom e. (See Fig. 1.9)

To eliminate th is dang er of shock , a

fuse is no longer installed in th e neu tra

wire.

Modern service installations are

designed to fuse only the live w ires.

Grounding the Neutral Wir

The m ajority of electrical service p arts

wiring boxes , cond uits , and sim ilar fit

tings are m ade of metal. Sometimes, wi

comes in contact with metal boxes—

perha ps insulation on condu ctors w as

damaged during the initial installation o

the circuit or becam e worn over a

perio d of yea rs. A grounded system is,

therefore, needed.




o-

fuse b lown

J

5

-

live wire

120

V

ground fuse b lown

FIGURE 1.7 Both fuses blow (S ituation A ).

neutral wire

short circuit at lamp

no shock

person grounded on concrete f loor

O-

fuse b lown

J>-

l ive wire

120 V

0

^ - - - c T \ j > -

grou nd fuse intact

neutral wire

HGUR E 1.8 The fuse on the live wire blow s (S ituation B).

short circuit at lamp

no shock

person grounded on concrete f loo

0 -

fuse intact

live wire

120 V

/~\

neutral wire

O - f -

o o

ground fuse b lown

RGURE 1.9 The fuse on the neutral wire blows (Situation C).

.short circuit at lamp

120 V s hock

person grounded on concrete f loo

Service masts,

which rise above the

roofs of many single-storey h ou ses , can

be targets for lightning during

thunder

storm s. To prevent thes e metal co ndu its

from attra cting lightning, they and thei r

boxes are grounded . Steel rods are

driven into the earth or wire fastened

onto cold-water pipes where they enter

houses.

If on e of the tw o live wires in th e 3

-*ire

system com es in con tact with a

grounded service box, many dangerous

possibilities arise. Anyone can becom e

grou nde d in a hou se . For exam ple, if th e

seco nd live wire of the 3 wire system

comes in contact with the frame of a

faulty power tool and if the first live wire

touc hes t he metallic service box, a

grounded pers on could receive a 240

V

shock—strong

enou gh t o kill.

A

person

trying to fix a light over th e k itchen sink

could receive a 240

V

shock by touching

th e sink and th e secon d live wire in th e

fixture. Cleaning a laundry room fixture




fuse

2400

V

l ive wire

t

240 V

neutral_wire_

t

120 V

J

person rece

240 V sh

accidenta l groun d

on

l ive wire

FIGURE 1.10 Accidental grounding of the live wire creates a 240 V shock hazard.

fuse

2400

V

l ive wire

t

240 V

_neutral_wire_

- ^ -

intentional

ground 120

V

I

fuse

person rece

120 V sh

person rece

120

V

sh

FIGURE 1.11 Grounding the neutral wire limits the shock hazard to 120 V.

with

a

dam p cloth while standing on the

basement floor might also result in

a

240 V shock . (See Fig. 1.10)

In mod ern s ervice installations,

the

main switch box is grounded and

a

termi

nal block is placed in th e lower portion

of the sw itch, wh ere the neutral w ire

could also be intentionally grounded .

With the neutral wire groun ded,

the

maximum shock

a

perso n can receive

from any o ne live wire is

120

V. T his

means that a grounded person working

with power tools, repairing equipm ent,

or cleaning fixtures can receive no more

than the voltage between the neutral

and

a

live wire, th at is, 720

V

Under cer

tain co nditio ns, this voltage can kill, but

th e da nge r is greatly redu ced . (See Fig.

1.11)

If

one of the live wires acc identally

touches a metal box or fitting with the

neutral wire ground ed,

a

short

circuit

resu lts. The fuse on th e live wire blow

and pr otec ts the circuit. The neutral

wire is safe to han dle even wh en

a

per

son is grounde d, since th ere is no volt

age difference b etwe en

it

and ground.

Unbalanced System

When

a

distribution panel

is

installed

a hous e, some attem pt is usually m ade

to distribute th e load evenly

on

each o

the live wires supplying the panel.

It

is

rare, however, for a dwelling to hav e t

same number of lights or devices turn

on for the load

to be

balanced

on

each

side of th e panel. Th e

neutral

wire in t

system is important here, because it

returns the unbalanced amount of cur

rent to the transformer.

If the neutral wire is broken or

disconnected in any way, th ere is dan

to the electrical equipm ent

in

the circ

Applications

of

Electrical Construction



Assuming that eac h individual load

device

draws the same current, the side

x

the system with the g reatest nu m ber

* devices turned on will have the

neatest number of parallel circuit paths.

ma parallel circuit, the m ore paths the re

are.

the lower the total res istance of th e

circuit. The difference in electrical

lesistance between the two sides of the

panel is determined by the nu mb er of

devices operating on each side .

If the n eutral w ire is d isco nne cted ,

there will no longer be a

120 V

circu it.

Th e two sides will now be

in

series with

each o ther and have an applied voltage

•& 240

V Since voltage is divided in a

series circuit, the side of th e panel w ith

fewer devices turned on (and, therefore,

higher resis tan ce) will receive a vo ltage

auch

higher than norm al. The o ther

side of the panel, with its lower resist-

• c e ,

will receive the bala nce of th e

240

V.

Light bulbs will glow muc h m ore

brightly with the increased voltage, and

sensitive equipment, such as stereos

and television sets, may be seriously

damaged. When connecting service con

duc tors, therefore, the

neutral

wire must

be disconnec ted last and reconnected

mrst,

when pow er is to be restored .

The danger of an unbalance d condi

tion is an oth er reaso n for never fusing

the neutral wire.

A

blown fuse on the

neutra l wire will result in an u nbala nced

voltage situation.

As current passe s through a circuit,

each lamp forms part of the circuit and

offers som e resistance to the current

flow. (See Fig. 1.12) Three factors are

involved in curre nt flow: line

voltage,

amperage, and resistance. The value of

each factor is determined according to

Ohm's

Law:

Current =

Voltage

Resistance

In term s of un its, th e Law can be

expressed as follows:

Amperes =

Volts

Ohms

As a mathe ma tical formula, it is state d in

this way:

" I

To mak e calculation easier, each

lamp shown in Figure 1.12 is the same

size,

receives

120

V, and draw s

1 A

of

curren t. The resistanc e of o ne lamp is

found by using Ohm 's Law:

" * \ *

4 A

I

m •

1 2 0 V

group 1

X

\ -

2 A

120 V

-o o o 9

< <

group 2

2 A

RGURE 1.12 Each lamp is the same size (amperage). T he current flows as show n by the

The T hree Wire Distribution System



Transposed, this equals

since

R

rep resen ts Resistance, which is

measured in Ohms.

R

(Ohms) =

E

(Volts)

/ (Amps)

Therefore, the resistance of one lamp

.

120 V

equals

I Pi.

That

is,/?

equals 12 0ii .

The resistance of one lamp is 120 ii.

The total resistance of all lamps of

the same size in a parallel

circuit

is equal

to the res istanc e of one lamp divided by

the number of lamps in the circuit.

Re sistanc e of the lam ps in Group 1:

120

i i

R

= = 30 i i

4 (lamps)

Res istance of the lam ps in Group 2:

120 i i

R = =

60

i i

2 (lamps)

When th e neutral wire is broken, the

lamps in Groups 1 and 2 are in series

with e ach other. (See Fig. 1.13) T he total

resistance tor the whole circuit is now

the sum of the resistances in Groups 1

and 2 wh ich is 30

ii

+

60

i i =

90

ii.

Since the neutral wire is broken, the

line voltage is now 240

V,

and the total

current in the circuit is

.

E

240 V

9

„ .

/ =

J?

=

"90ii-

= 2

-

6 7 A

Th e voltage in a series circuit is

divided between t he groups of lamps,

according to Ohm's Law:

'

= 1

Transposed, this equals

E

(V) = / (A) x

R

(i i)

The voltag e of Group

1

is

E =

2.67

A x

30

i i

= 80.1V

This low voltage will cau se th e lam ps in

Group 1 to glow dimly.

The v oltage of Group 2 is

E

= 2.67 A x 60 ii

= 160.2

V

side 1

240

V

o —

side 2

\r

2.67

A

neutral broken

S\j,

2.67 A

group

30 Q

80.1 V

\ *S s / \ i / group

- 6on

' T f

s /

Tf

N

160.2

V

FIGURE 1.13 Each lamp is the same rating (wattage). T he current flow is altered wh en the

neutral wire is

broken.

10




This higher voltage will cause th e la m ps

in G roup 2 to glow more brightly than

usual and may cause them to burn out.

F o r R e v

i e w

1. What voltage is used in houses for

portable equipment? for heavy-

duty equipment?

2. Which electrical frequency is used

most on the North American conti

nent?

3.

Kxplain how two sepa rate voltages

are obtain ed from the 3 wire distri

bution system. Include a diagram.

4.

What does the term

neutral

mean

when applied to a conductor?

5.

What is the purpose of identifying

the neutral wire?

6. What are the th ree differences

between the neutral and live wires

of a circuit, other than colour?

7. Explain why (a) the neutral wire is

grounded, and (b ) the neutral wire

is never fused.

8. What method is used to ground

the neutral wire in a house?

9. Why are the incoming hydro sup

ply lines connected to the upper

terminals of the main switch?

10.

What voltage is available b etwe en

(a) two live wires? (b) a live and

neutral wire? (c) a live wire an d

ground? (d) the neutral wire and

ground?

The T hree Wire Distribution System



• ^

T

he flow of electrical cu rren t in th e

vario us circu its of a building m ust

be co ntrolled. This is don e by using a

variety of switches capable of opening

and closing the circu its.

Switches are divided into two main

catego ries according to the m ethod of

installation:

Category 1.

The

surface

type of switch

is m ou nted on th e face of th e wall, with

the entire body of the switch visible.

(See

Fig. 2.1) '

o

GO

1

C O

FIGURE 2.1 S urface-mounted switch

Category 2.

The

flush

type of switch

unit is mounted within an electrical box.

Light ing-

Control

Switches

FIGURE 2.2 Flush-mounted switch

This box is recesse d in to the wall, so

that only the operating h andle of th e

switch is visible. This typ e of switch

looks neater and is used more exten

sively. (See Fig. 2.2)

Operating Mechanisms

Th ere ar e m any different typ es of

switches to con trol a wide variety

of

electrical devices. Just as there are

many switches, there are also many dif

ferent type s of operating mec hanism s to

suit individual circuit n ee ds . Figure 2.3

shows some of the m ore common opera

ting mechanisms.

12

Applications of Electrical C onstruction



wal l -

mounted

toggle

rocker

push

button

key

operated

panel-

mo u n te d

toggle

pull chain

R G U R E

2 .3

C o m m o n s w i t c h o p e r a ti n g m e c h a n i s m s

rotary

Internal Construction

The basic function

of

th e sw itch is

to

open and close a circuit. To do this the

switch ha s a combination of fixed and

mtoveable co ntac ts, which are usually

made

of

bra ss. Figure 2.4,

on

pag e 14,

shows two types

of

designs and

methods for moving the contac ts.

Switches designed

to

carry

a

high

current have larger and stronger con

tacts than those of switch es designed to

ope rate only one or two lights. N early

all,

however, h ave s om e form

of

spring

inside to open and close the contac ts

quickly. If the contacts are slow

to

open

and close, there

is

danger

of

the current

forming an arc—a spark jumping ac ross

the con tacts as they

part—resulting

in

heat damage and possibly contact

burning.

The main differences between a high

quality (expensive) and a low-quality

switch are the size and strength

of

the

con tacts and spring. Take care to

choose a switch capable of handling the

intended load on the circuit.

Lighting-Control Switches

1



toggle handle (Bakelite)

terminal screw (brass)

blade contact (brass)

body

or

case (Bakelite

or

porcelain

plaster ear (removable

mounting bracket (steel)

jaw contact (brass)

spring assembly (steel)

toggle handle mo unt in g bracket

4

spr ing

- contact poin ts

rD <-

terminal

N O T E : A

semisilent-type

switch does not

us e a b lade and jaw contact system.

Contact points

are

used.

FIGURE

2.4

Internal construction

of

a

single-pole switch

Switch Terminals

High-quality switch es a re also recog

nized by their large-headed, brass termi

nal screw s.

In

addition, they have well-

designed terminal bases with good wire

containment features. Some manufactur

ers provide a

push-in

type

of

terminal

by

which the terminal screw ho lds the wire

in a vise-like grip. (See Fig. 2.5) S witch es

that m ake sole use of the push-in

method of holding the wire may give

trouble

at

their terminal conn ections

in

years to come, thoug h. The installer

should consider more than the ease with

which

the

switches

can be

installed

in

the circuit.

Switch Ratings

Manufacturers usually place electrical

CAPTIVE MOUNTING

SCREWS FIT ALL BOXES

ON AC SWITCHES 1ME

wine

GAGE SHOWS

MOW EAR TO STRIP WIRES

S C R E W

RETAINING

O V A L H O L E RERMfrs

ADJUSTMENT IN CROOKED

Box

TERMINAL SCREWS FOR

SIDE

AND

OR

BACK

WttING

MOLDED UREA OR

PORCELAIN BODV

O N AC SWITCHES. COLOR

OF FRONT INDICATES

AMPERAGE

FIGURE

2.5

Rear vie w

of

a switch showing

2 types

of

terminal connections

ratings on th e m ounting bracket of the

switch. There are six possible ratings to

assist

a

person

in

matching the switch

t

u

Applications

of




nting bracket

power rating

iting

marks

amperes

manufacturer's

emblem

Canadian

Standards

Association

approval

alternating

current

RGURE 2.6 Typical switch ratings

die job: voltage, amp eres, test labora

tory appro val, "T" rating, AC or DC,

and pow er. (See Fig. 2.6) The first th re e

ratings must be placed on all sw itche s,

rhe second three— "T" rating, AC or DC,

and power—are marked on switches

designed for special applications.

Voltage. This rating refers to th e

electrical press ure the switch can

control safely. Lighting switches should

have a rating of 120 V to 125 V for

control of

one

live wire and 240 V to

250 V for con trol of

two

live wires.

Am peres . This rating refers to the

ability of the contacts to carry current.

The

higher

the cu rrent rating, the

more

load can be controlled by the sw itch.

The

curre nt ratings in crea se in units of

live

(for

exam ple, 10 A,

15

A,

20 A, etc.).

Test Laboratory Approval.

All

electrical products for sale or use in

Canada must be submitted to the

Canadian Standards Association (CSA)

for testing and approval. Since Canadian

standards often differ from the stan

dards

of

other countries, products mad

elsewhere m ust still be tested by the

CSA. For example, pro du cts m ade in

the

United States and tested and approved

by the American paren t

of

U nderwriters

Laboratories bear the mark

UL or Und

Lab.

If the se pro du cts a re

to

be sold

or

used

in

Canada, they must be retested

by the

CSA.

If appro ved , bo th the CSA

and Underwriters' approval marks may

be placed

on

the pro du cts. The CSA

mark is

a

guarantee to the user that

the

manufacturer's ratings are correct.

"T"

Rating. Incandesce nt lamps

(standard househo ld lamps) have

a

tungsten filament. When the lamp is off

an d

at

normal room tempe rature,

the

filament's electrical resistance is very

low. The low resis tanc e

of a

cold

filament allows

a

high inru sh of

current—eight to

ten tim es' the norm al

operating

current—to

flow into the lam

for th e length of time it takes to reach

full brilliancy. Once th e lam p is at

operating temperature, filament

resistance is high and normal current

flows through the lamp. Switches

designed to control a group of

incandescent lights must have

heavy-duty contacts and springs to

withstand these operating conditions

safely.

AC or DC.

Alternating current

(AC) is

used for

residential

installations, and

many switches produced for household

us e will be marke d acco rdingly. Som e

industrial

equipment, however, is

designed to operate on

direct current

(DC). Sw itches for control of this

equipment must have a direct c urrent

rating.

Once an arc

is

started between

direc




current switch contacts,

it will follow th e

contacts, continue to burn, and destroy

the switch within seconds. (Arcing

between alternating current switch con

tacts is usually less severe and damag

ing.) Switches d esigned for direct cur

rent use, therefore, must hav e strong

contacts and springs, together with ade

qua te insulation.

Power. Switches are also used to

control electric motors. A motor

requires thre e to five times as mu ch

curren t when start ing as i t doe s when

running. Therefore, when a large motor,

suc h as tha t of a refrigerator or air

conditioner, starts up, room lights will

dim briefly.

To be capab le of handling high-

curre nt situations, a switch must b e

equipped with sturdy contacts and a

strong spring. Since mo tors a re rated in

watts,

the power rating tells the installer

the maximum size of motor the switch

can control safely.

Dimmer Switch Rat ing

This ty pe of switch con sists of an elec

tronic circuit sensitive to the amount of

load placed on it. When installing a dim

mer switch, take care not to exceed t he

wattage rating on the unit. The total

wattage of the lamps being controlled by

the dimmer must not be greater than the

wa ttage rating marked on the sw itch.

L i g h t i n g - L o a d

Calculations

To determ ine th e am pere rating of a

lighting circuit, add th e wa ttage of all th e

lamps to be controlled by the switch;

then, divide the total by the circuit volt

age to calculate the amp erage (current

flow) for the circuit.

For example, if a room has six light

fixtures equipped with 100 W lamps on

120

V

circuit, the to tal wa ttage is 600

W

(6 lights x 100

W ).

The curre nt flow is

600 W divided by 120 V which is 5 A.

A

10 A,

"T"-ra ted, 120

V

switch would,

therefore, be adequate for this installa

tion. The cu rren t ratings for fluorescent

lights,

however, are usually marked on

th e ballast of each fixture. Adding th es e

am pere ratings will determ ine the cur

rent flow without further calculation

being necessary.

S witch Test E quipment

Switch m echanism s are usually com

pletely enclosed, and the internal con

nections are hidden from view. Simple

test equipment for locating the internal

connections can be made, however.

Both of the testers described in the fol

lowing paragra phs may be checked by

touching th e test clips together.

Series-Lam p Tester. Figure 2.7 sho w s

tester made from a lamp socket, light

bulb, and line cord. If, after the clips are

fastened to the switch terminals, the

lamp is on, there is a com plete, or

closed, circuit.

Safety Note:

This tester should not

be used on a switch con nected to a cir

cuit with its own s our ce of voltage su p

ply. Also, th e o pe rato r m ust be careful

not to touch t he me tal portion of the tes

clips, since this unit op er ate s on 120 V.

Buzzer Tester. Figure 2.8 show s a

tes ter ma de with a pair of dry cell

batteries and a small buzzer or bell,

which rings when the circuit is closed.

This simple unit is portab le and may be

carried in a tool box.

16




N O T E :

Spl ice wires.

Insulate wi th tape.

1

lampholder

l ine cord

plug cap

F I G U R E 2 . 7 S e r i e s - l a m p t e s t e r (120 V d e v i c e )

binding jumper

posts

y

f lexible cord

f r ic t ion tape

R G U R E 2 . 8

B u z z e r t e s t e r ( b a t t e r y -

p o w e r e d )

s ingle-pole switch

double-pole switch

3 way switch

o-

» o-

<yTo

^t

Switch Wir ing Symbols

A

system of electrical sym bols is often

used to represent various types of

switche s on wiring diagram s. Figure 2.9

shows symbols comm only used on elec

trical draw ings.

Switch Appl icat ions

Switches are available in a variety of

types for a variety of u ses . Single-pole

and double-pole switche s are used to

control lights or equipment from one

4 wa y s wi t c h

electrolier (tr i l i te)

(2 circuit switch)

electrolier

(3 circuit switch)

>£

F I G U R E 2 . 9 S w i t c h w i r i n g s y m b o l s

S E

S E




location. Three-way switches are used to

con trol lights in area s such a s room s

with two e ntran ces, hallways, or stair

ways wh ere it is conv enient to hav e con

trol from either of two locations. Four-

way switches are used where multiple-

switch control is needed, for example, in

large houses, apartment buildings, or

office buildings that have large rooms

with three or more entrances or stair

ways rising thre e or more stor ey s.

Single-Pole Sw itch. As th e most

commonly used switch for residential

and commercial lighting circuits, this

switch is also appropriate for fractional

kilowatt motors, portable appliances,

portable tools, etc.

The single-pole unit is designed to

control a 120 V circuit (on e live wire)

from one location. The two terminal

screws and the indicating marks (on and

off) on th e opera ting hand le make it

easy to recognize. (Some man ufacturers

use a small dot on the operating handle

to indicate the on position.) This switch

is available in a varie ty of styles and

operating mechanisms, with current rat

ings to suit any installation for which it

was designed.

When installing a single-pole switch

with a toggle or rocker mec hanism,

standard procedu re is to moun t the

switch with the operating h andle in the

up po sition (when the switch is turned

on). Figure 2.10 show s by sche m atic dia

gram a single-pole switch controlling tw

lights. Figure

2.11

shows how to c onnec

this sw itch in a residential w iring circui

live

120

V

- ^ .

o

.

neutral

FIGURE 2.10 S chematic wiring diagram

showing 2 lamps controlled from one location

switch box

off

posit ion

15 cm

wir e

octagon box

to dis t r ibut ion panel N O TE : Groun d wires are not sho w

FIGURE 2.11 C able wiring diagram showing 2 lamps controlled from one location

18




o

live

Si

120 V

lamp of f

safe:

no shock

person grounded

o -

-

neutral

c-

live

120

V

lamp off

o

-

»

i

neutral

• ^

danger: 120 V shoc

person grounded

RGURE 2.12 The danger in conn ecting a sw itch in the neutral wire

Remember that only the live wire is

connected to the switch. (See Chapter 1)

Figure 2.12 shows the danger of using

the ne utral wire, or groun ded , identified

conductor, to contro l the circuit. In

either case , th e light may be turn ed off,

but the live wire is still dan gero us at th e

light fixture.

Double-Pole S witch . This switch is

available in a variety of cu rren t ratings ,

but m ost often in the heavy-d uty ran ge,

ft is meant to control such energy u sers

as electric heate rs, air conditioners, and

some motors operating on 240

V.

Two

live wires and a switch cap able of

opening both live conductors of the

circuit simultaneously are required. The

double-pole switch, much like a pair of

single-pole switche s in the sam e case, or

body, is easily recognized by th e four

terminal screw s and t he indicating

marks on the operating handle.

When installing a d ouble-pole

switch, take care to co nnect the circuit

conductors to the proper terminals. This

preven ts short-circuit damage to the

switch contacts. Figure 2.13 shows by

schem atic diagram a double-pole switch

controlling an electric hea ter.

Figure 2.14 show s an im prope r con

nection, which will damage the switch

badly the instant it is turned on.

heater off

W - i

on posi t ion

FIGURE 2.13 S chematic wiring diagram of a

double-pole switch


1



live

c—

240

V

live

heater

• £ .

A M A - i

short c i rcui t when switch

contacts close

FIGURE 2.1 4 C ontact dama ge results if a

double-pole

switch is connected improperly.

live

c —

240

V

o-

live

person receives 120 V shock

heater

this wire not control led by switc

FIGURE 2. 16

N ever use a single-pole

sw itch on a 240 V circuit.

to panel

red wire

box

gr ound

screws

s wi t c h

box

cable

connector

NOTE: Both wires in th is c ircui t are al ive and should be

coloured accordingly. The modern cable containing

one red and one black w ire sho uld be used.

FIGURE 2.15

C able wiring diagram of a

double-pole switch

Figure 2.15 sho ws how to con nec t

this sw itch in a residential wiring circuit.

Safety Note:

Rem ember tha t a sin

gle-pole switch must not be used on a

240

V

circuit. Figure 2.16 shows the dan

ger of such a connection.

Three-Way Sw itch. These switches

are u sed in pairs , usually on

120 V

circuits. They c ontrol on e live wire in

order to provide indepen dent control of

a light or group of lights from either

of

two locations.

A

3 way switch is easily

recognized by its three term inals, one of

which is marked as a line terminal, and

by its lack of indicating ma rks. (The

word line may be printed be side the ter

minal, or the term inal may be coloured

for easy recognition.)

The internal design of th e 3 way

switch allows current to flow through

th e switch in either of its two po sition s.

For this reason, the switch h as no on/o

ma rks on the operating ha ndle. The cir

cuit is controlled by using two sw itches

as a tea m . Figure

2.17

shows the interna

switch positions and also how on e term

nal—the

common, or

line, terminal—is

used for both switch positions. Figure

2.18 shows b y schem atic diagram 3 way

switch control of one light.

This switch is available in a va riety

of styles and op erating m echanism s,

with current ratings to match the load

being con trolled. Figure 2.19 sho w s ho w

to connect this switch in a residential

wiring circuit. The two con duc tors run

ning between the switches are often

called travellers, or messenger w ires. If

the need a rises, this switch may also be

posit ion 1

posi t ion 2

0

S

0

©

• — ©

0

t

—

l ine termin al

FIGURE 2. 17 Internal connections of the 3

way switch

20

App lications of Electrical Co nstruction



n

—v

Z

ravellers

•23

V

light on J

-

= Jtral

RGURE2.18 S chematic wiring diagram

.ving 1 light controlled from tw o locations

live

o n

line

s t c ^

=>3 O .

Do not use

this termi nal.

120 V

lamp on

,

o - - - -

neutral


showing how a 3 way sw itch can be used

safely in place of a single-pole sw itch

line terminal

N — ^ black

/

lamp

to distribution

panel

RGURE 2.19 C able wiring diagram of 3 way switch control

used safely as a

single-pole

sw itch. Fig

ure 2.20 shows by schem atic diagram

such a circuit.

Four-Way Sw itch. Multiple-switch con

trol in large rooms or buildings is

achieved by using 4 way switches in

com bination w ith a pair of 3 way

switches in 120

V

c ircuits. This com bi

nation is particularly useful in suc h

areas as large room s with thre e or m ore

entrances and stairwells in buildings

of three o r m ore sto rey s. Control of

the light from a ny of the sw itch pos itions

may be obtained by operating any one

of the switches in th e grou p.

The 4 way switch is a non-indicating

switch, bec aus e the lights can b e con

trolled by any one switch in th e circuit.

It can be recogn ized by its four term inals

and lack of indicating marks on the oper

ating handle. Without pro per test equip

men t, th e only way to tell th e difference

between the 4 way and the double-pole

switch is to rem emb er that th e 4 way

has no indicating marks, while the

double-pole switch d oes.

The 4 way switch is available in a

variety of styles and operating mecha

nism s. It is thus a ble to suit any a pplica

tion. However, becaus e the internal

mechanism is more complicated and

the re is less consu me r de man d for it, th

4 way switch m ay be more expensive

than other types.

Figure

2.21

show s th e internal switc

pos itions , and Figure 2.22 sho ws by

schematic diagram control of a light

from th re e loc ation s. Figure 2.23 sho w s

control from five locations, and Figure

2.24 show s how to con nect this switch i

a wiring circuit.

Ughtlng-Control Switches

2



posit ion 1 posi t ion 2

0

X

0

FIGURE

2.21

Internal connections of the 4

way switch

c

'

J (-travellers-,

\ > -

live

o—i^^—o

o

1 o

ne

120 V

l ight on

o

neutral


showing

1

light controlled from three loca

tions

.travellers

live O——

<S

„ t^—

l ive

120 V

l igh t on ,

o

- - - -

neutral


showing 1 light controlled from five locations

Electrolier Switches

Two-Circuit Electrolier. T he

2

circuit

electrolier is mo re comm only known as

the trilite switch . Used with th e d ual

filament lamp , it prov ides thre e levels of

light (low, me dium , and h igh) for m any

table lam ps, floor lam ps, pole lamp s,

and hanging, or swag, lam ps. (See Fig.

2.25) Th e switch u nit and bulb in

combination give this circuit its

versatility.

The trilite switch h as thre e termi

nals,

o r leads, and is almost always a

rotary switch. It usually ha s no indicat

ing ma rks, since the installer may use

either of the two line term inals, depe nd

ing on the choice of seq ue nc e. Trilite

switches are used mainly for

120 V

lighting un its.

Figures 2.26 an d 2.27 sho w th e four

positions of the trilite switch. One termi

nal, called th e common, or line, terminal,

is use d in all th re e of th e on positions.

To tu rn th e bu lb off, th e bla de s of th e

switch are simply moved away from the

line term inal.

A

lam p with a switch a s

show n in Figure 2.26 ope rate s in a high,

medium , and low sequ enc e. If the switch

is con nec ted w ith the line termina l as

show n in Figure 2.27, howe ver, the lamp

will ope rat e in a low, me dium , and high

sequence.

to dis t r ibut ion

panel

FIGURE 2.24 C able wiring diagram showing 3 way and 4 way sw itch control

22 Applications of Electrical Co nstruction



switch

switch

table lamp

swag lamp

floorlamp

rotary tri l ite switch

V

switch

O

pole lamp

R G U R E S 2 . 2 5 A A N D B T y p i c a l 2 a n d 3 c i r c u i t e l e c t r o l ie r s w i t c h a p p l i c a t i o n s

terminal

h igh medium low

R G U R E 2 . 2 6 T r i li te s w i t c h p o s i t i o n s f o r h i g h t o l o w s e q u e n c e




of f low m e dium

FIGURE 2.27 T ril ite sw itch positions for low to high sequence

high

Trilite bulbs are available in three

sizes, or wattage ranges. The largest has

a mogul base equipped with 100 W and

200 W filaments. Both filaments opera

ting together provide 300 W of light in

the high position. The other two bulb

sizes use a

medium

base and are availa

ble in 50

W-100 W-150

W and 40

W-60 W-

100 W combinations. These units are

popular for smaller light fixtures.

Figure 2.28 shows the sw itch and

socket assembly wired as a working unit.

Some table and floor lamps are manufac

tured with a switch built into the socket

assembly. The only connections

required are for the live and neutral

wires in the lamp's cord. The switch may

be purchased as a separa te unit for con

nection to two independent light sock

ets,

as shown in Figure 2.29. This type o

connection may be installed in fixtures

using two standard light bulbs, rather

than the trilite bulb.

200 W f i lamen

100 W

f i lame

to centre contac

to r ing conta

ring

conta

centre conta

silver scre

120 V

centre contact scre

FIGURE 2.28 S chematic wiring diagram showing a 2 circuit electrolier switch

24

Applications of Electrical Con struction



Three-Circuit Electrolier.

There are

two typ es of 3 circuit electroliers. The

alternate typ e (See Fig. 2.30) puts on e

bulb on at a time and may be use d for

pole lamp s or other decorative units.

The consecutive type (See Fig. 2.31) is

often fitted into po le or swag l am ps. All

three lamps may be on at the sam e time.

Dimmer Switches

Lighting no t only illumina tes, it can cre

ate m ood s, as well. For exam ple, dim

ming lights in a dining area can cre ate a

more intimate atm osph ere. Two types of

dimmer switches, the high-low and the

infinite, are commonly used in hom es

and function on electronic circuitry.

Their operating methods are described

below. Othe r dimm ers functioning on

electrical resistors alone prod uce a great

deal of he at, wh ich is difficult to d issi

pate, and so are not desirable for hom e

use.

High-Low.

This two -stage , flush-

m oun ted, wall switch usually has a

toggle action. When the operating

handle is in the up position, the

neutral


and alternate switch positions for a 3 circuit

electrolier

typical applicat ion


and typical application show ing a 2 circuit

electrolier switch using 2 standard light bulbs

o—

l ine terminal

120 V

o-

consecut ive switch

posit ions

6h

49-

all l ights on

—©-:

neutral

FIGURE 2.31 S chematic wiring diagram an

conse cutive sw itch positions for a 3 circuit

electrolier

Lighting-Control Sw itches

2



stan da rd light bulb in th e fixture glows

at full brilliancy. When the operating

handle is placed in the down position,

the bulb glows at the lower level of light.

The light is turned off by moving the

handle of the switch to a centre position.

(See Fig. 2.32)

This switch is wired in a way sim ilar

to any single-pole switch. Take care to

install a switch of sufficient wattage rat

ing to ha ndle the lighting load of th e

circuit.

Infinite Dimmer Control.

This unit

mo unts in a standa rd electrical switch

box and can replace any standard

flush-mounted switch. The majority are

wall-mounted; however, units built into

light sockets for table lamp and floor

lamp applications are available. Both

single-pole and 3 way units are m ade.

The standard light bulbs used are turn ed

on or off by press ing th e con trol kn ob.

(See F igs. 2.33 and 2.34) Any level of light

from off to full brilliancy can be obtained

by rotating the control knob .

The dimmer switch is usually

equipped with leads for connection to

the electrical circuit.

case

/

terminal screw

FIGURE 2.32 High-low dimm er switch

high

Safety Note:

Take care to en sure

that th e total wattage of th e circuit load

does not exceed that marked on the

switch.

FIGURE 2.33 Infinite dimm er sw itch

FIGURE 2.34 A heavy-duty dimmer switch

equipped with an aluminum heat-sink for

proper dissipation of heat (right) compared to

a standard 600 W dimmer switch. The heavy-

duty dimmer switch can be used on lighting

circuits

up

to

1000W.

26




F o r R e v

i e w

1.

What is the pu rpo se of a switch in

a circuit?

2.

List and describe the two main

types of switches, according to

method of installation.

3. List seven operating mechanisms

used in lighting switch es.

4. List the p art s of a switch, a nd

state the purpose of each.

5.

Define

arcing,

and describe its

effect on a switch.

6. List the six electrical ratings that

may be marked on sw itches.

7. Why do manufacturers mark elec

trical ratings on switches?

8. Explain the function of the Cana

dian Standards Association and

the American parent Underwrit

ers '

Laboratories.

9. An oil bu rne r ha s a 560 W motor

ope rating on 240 V. It it d raw s

6.9 A, what ty pe of switch is

needed to control the motor?

Which electrical ratings should

appear on the switch?

10. A room is equipped with twelve

120

V

light fixtures, each having a

100 W bulb. What type of switch is

required to control these lights?

Which electrical ratings should be

marked on the sw itch?

11. Explain how to use a series-lam p

tester to locate a switch's internal

connections.

12.

Explain why th e neu tral w ire

should never be used to control a

circuit.

13.

Explain why a single-pole switch

should nev er be used to control a

240

V

circuit.

14.

Can a double-pole switch be used

safely to con trol a

120 V

circuit?

Explain, with the aid of a diagram.

15. Explain why care m ust b e taken

when connecting a double-pole

switch to a 240

V

circuit.

16. List three places in a home where

3 way switch control would be

useful.

17.

Show by diagram a

3

way switch

being used to replac e a single-pole

switch.

18.

What is th e nam e of the two con

ductors that connect 3 way

switches to one another?

19. List the ty pes and quan tities of

switches required for stairway

lighting with co ntrol from each

storey of a six-storey building.

20. List three a pplication s of

2

circuit

electrolier (trilite) switch control

in the home.

21 . Which terminal of the electrolier

switch must be located to deter

mine lighting se quenc e?

22. Explain why you think it would be

desirable to be able to change th e

level of light in a room.

23. Explain how a trilite lamp pro

duces three levels of light.

24.

What is the advantage an infinite-

dimm er control switch has over a

trilite switch?

25. Explain why care must be taken

not to exceed the wattage rating

on a dimmer switch.

Lighting-Control Switches 2



a

•

T

here are many types of lampholders

used for residential and commercial

lighting installations. This cha pte r cov

ers only the screw-base type.

Screw-Base Sizes

Th ere are five stand ard screw-base

sizes, each of wh ich has a partic ular

are a of us e. (See Fig. 3.1)

i f

in iature

9

intermediate

candelabra

m edium

m ogul

FIGURE 3.1 S tandard screw-base sizes

Lampholder

Mogul. As the largest of the screw-

base units, the mogul is used in reside

tial trilite lamps and in commercial are

such as parking lots, service garages,

and warehouses where larger light bul

are employed.

Mo gul-base light bu lbs rang e in siz

from 300

W

to 1500 W, which th e Cana

dian Electrical Code ha s set as th e max

mum size for incan descen t-bulb mogul

sock ets. Because 1500 W bulbs produc

a great dea l of he at as well as light,

mogul-base sock ets are usually heavy-

gauge br ass with a porcelain covering

withstand the heat .

Bulbs for the m ercury va pou r type

lamp exceed 1500 W They are also

equipped, however, with mogul bases.

Medium.

This is th e mo st comm on

residential socket size. Standard

incandescent light bulbs from 7.5 W to

300

W

are equipped with m edium base

as is the

125 V

plug fuse for the

distribution panel. Any comm ercial

lighting installation using a b ulb size of

up to 300

W

is also equippe d w ith a

medium-base soc ket .

The Canadian Electrical Code

requ ires tha t no lam p in excess of 300

be used in medium-base lam pholders,

unless th e lampholder is made of heat-

resisting material. The Code also

28




requires that all medium-base lamphold

ers ha ve an electrical ratin g of 660

W

and 250 V. This regulation is design ed to

protect the use r by ensuring safe opera

tion for the ra nge of bulb s available.

Intermediate. This sock et is use d for

such purposes as outdoor Christmas

tree lights, show case and aquarium

lighting, sewing-m achine lam ps, and

appliances such as electric stoves. The

intermediate socket has an electrical

rating of 75 W an d 125 V.

Candelabra. As the smallest screw-

base lampholder that may be connected

directly to a 120 V circuit, th e

cand elabra has an electrical rating of

75 W

and

125

V. Decorative lighting takes

full ad van tage of this sm all socke t. The

light bulbs use d in it are pro du ced in a

wide variety of sh ap es , often simulating

the flames of can dle s. They are ideal for

indoor Christmas tree lights and crystal

chandeliers.

Miniature.

This is the sma llest

screw-base lampho lder in the standa rd

group. It is used for dial-illuminating

panel lights in radio or television se ts.

One type of Ch ristm as tre e light string

also uses th ese so ckets in a

120 V

series

circuit. The voltage is divided am ong th e

num ber of lights in th e string, so tha t,

for example, if there are eight lights,

each light receives approximately

15 V.

This lampholder does not carry a

centre contact

brass termin al (live wire) — conne cting rivets

F IGU R E 3. 2 L a mpho lder c ons t ruc t ion

120 V rating due to the limited spa ce for

contact separation inside the socket.

Adapters

An ada pter is a device that can be used

to red uce socket size so that the lamp

hold er will acc ep t a bulb with a sm aller

base. The adapter has an external thread

to fit the socket being reduced and an

internal thre ad to fit th e sma ller bas e of

the bulb. Also, the re are ad apte rs that

allow a lampholder to acce pt two bulbs

rather than one and/or a plug from an

extension cord.

Safety

Notes: When using these

devices, take care not to place a load on

the lampholder in excess of its electrical

rating. Also, wh en an exten sion cord

adapter is being used, remember that no

effective ground connection is availa

ble—the protection normally offered by

a grounded tool or device is lacking.

Remember, too, that it is dangero us to

attem pt to increase socket size by using

adap ters, because the heat and current

from the larger bulb may damage the

smaller socke t.

Lampholder Construction

The basic com pon ents of all lamp holder

are similar (Fig. 3.2). The lampholder

body, however, may be made of different

materials, such as Bakelite, rubber, por

celain, brass, or aluminum. (See Fig. 3.3)

socket (or screw shel

lampholder bod

silver-coloured terminal

neutral wire "identified")

Lampholders 2



FIGURE 3.3 C omm on medium-base lampholders

Lampholder Swi tch

Mechanisms

Lampholders with built-in switch mecha

nisms are called key types. (See Fig. 3.4)

This term came into use when lamphold

ers had orna te, rotary switch handles

similar to door

keys.

Lampholders with

out switches built into the socket assem

bly are called keyless types. (See Fig. 3.5

30




55

=8

E

>•

RGURE 3.4 A push-through switch socket

C/J

•8

RGURE 3.5 A keyless lampholder

Circuit Connection

The terminals on lamph olders are

colour-coded to make the c onnection of

the circuit con du cto rs easier. (Most of

the lampholders mentioned in this chap

ter are designed for

120 V

circuits and

make use of this colou r co de.)

A 120 V circuit has a live and a neu

tral wire, each of which m ust be con

nected to the p rope r terminals at the

socket. One terminal is a natural brass

colour and is to receive the black live

wire.

(Inside, this bras s terminal joins

with the centre contac t.) The

white

neutral wire is fastened to th e "identi

fied," silver<oloured term inal. This ter

minal screw is joined to th e screw shell

of th e lam pho lder. (See Fig. 3.2)

Note: The Canadian Electrical Code

requires that a terminal intended

solely for the con nectio n of a neutra l

wire must b e identified by a tinned fin

ish, a nickel-plated finish, or by means

of som e distinguishing m ark.

It is im porta nt to us e this m ethod of

connec tion in order to avoid the dan ger

of shock. A perso n cha nging light bu lbs

or cleaning a light fixture with a d am p

cloth could easily touch the screw shell

and become grounded on the bathroom

or k itchen sink. If the sc rew shell is alive

the perso n could receive a 120 V shock.

If, how ever, there are pro per wiring con

nections, the only live par t of the so cket

is th e centre contact, which is not easily

touched by accident.

1 P ull-C hain Insulators

>-

I Th e Canadian Electrical Code requ ires

J

tha t lam pho lders with pull-chain switch

mechanisms have insulating links in

their chains. This regulation is designed

to prevent a perso n in contact with

ground from receiving a 120 V shock if a

defective switch unit makes the chain

alive. (See Fig. 3.6)

Location of Lampholders

Section 30 of the Ca nadian Electrical

Code outlines the location of lamphold

ers.

The se guidelines are subject to fre

quent change, because new products

Lampholders

S



2

£

I

>-

u

FIGURE 3.6 A pull-chain lampholder

and m aterials are constantly being intro

duc ed. When planning an installation,

make s ure to ob tain the latest edition of

the Code.

F o r R e v i e w

1. List th e five stan da rd screw -base

lampholder sizes, and give one

practical application for each.

2. W hat is the w attage rating for

incand escent lamps for the largest

screw-base lampholder?

3. Which electrical ratings for screw-

base

lampholders

are required by

the Canadian Electrical Code?

4.

W hy is bulb size for th e m edium-

bas e socket limited to 300 W?

5. List two type s of ad ap ters used

with light sockets.

6. What precaution is necessary

when using an adapter?

7. List the ty pes of lam pho lder

switch m echanism s. What is

mean t by the term keyless?

8. Explain

how

and why the conduc

tors from a 120

V

circuit must be

connected to a lampholder.

9. Why is an insulating link requ ired

in the c hain of one typ e of sw itch

mechanism?

10. W here can information be found

regarding th e installation of lamp-

holders?

32

A ppl icat ions of E lectr ica l Construct ion



Receptacles

T

he receptacle is the m ost

widely used electrical device,

bec ause it is the point in a circuit at

which power may be taken to supply

lamps, appliances, or portable plug-in

devices. The residential recep tacle

delivers 120 V to any electrical device

plugged in to it. Every mo dern hom e is

equipped w ith a num ber of duplex

receptacles.

Receptacles are available in a variety

of quality and du ty ran ges. Light-duty

receptacles, frequently sold as

standard

or re sidential grade, may be used in

living-rooms or bedrooms, where a table

lamp

or radio will be the largest curr ent-

dem anding device plugged in. The

slightly b etter quality medium grade

receptacles stand up to somewhat more

frequent use in kitchens and utility

rooms. Heavy-duty rece ptacles, known in

the electrical industry as premium speci

fication grade, or often simply specifica

tion grade,

are much better designed and

con structe d. They are most suitable for

use in kitchen are as, wo rkshop s, and

industrial/commercial settings. Electric

frying pa ns, teakettle s, and ot he r fast-

heating appliances requiring a current of

12 A to 15 A benefit from being plugged

into heavy-duty rec epta cles : if a light-

duty receptacle were installed for such

appliances, it would he at up , the con

tacts would become soft and lose their

ability to grip the plug firmly, and dan

gerou s overh eating w ould follow. The

result would be damage to the recepta

cle, wiring, and plug.

Careful ad van ce plann ing is nec es

sary in order to prevent overloading of

receptacles. For trouble-free service, the

duty range of the receptacle should be

ma tched to the type of appliances

expected to rely on the outlet.

N um ber of O utlets on a

Circuit

Section 26 of the Canadian Electrical

Code outlines regulations for the instal

lation of recep tacles. The num ber of

outlets per circuit, the location, and the

number of outlets required for a given

room or location are discussed in detail.

With products and building standards

constantly changing,

only

th e Code can

be relied upon to provide a ccura te, up-

to-date information.

Receptacle Construction

There a re many sha pes and styles of

receptacles, but each has basic similari

ties

J"igure

4.1 shows the standard,

duplex, "U" ground receptacle found in

the modern home. This receptacle is

Receptacles 3



l ive terminals (brass)

live slot

mount ing bracket

plaster

ears

(removable)

neutral slot

Bakelite case

cover mount ing screw

ground slot

mount ing h

grou nd terminal (gre

' "neutra l terminals (s i lver)

N O T E : A l l mo unt ing screws are #6-

FIGURE 4.1A Typical N E MA " U " ground receptacle

FIGURE 4.1B A 15 A , 125 V, specification

grade,

heavy-duty receptacle in NEMA

" U "

ground configuration

also widely used in office buildings,

stores,

and industry.

It

prov ides a firm

electrical connection for

120 V

equip

ment, toge ther with ground protection

for portable equipment.

Receptacle Combinations

Receptacles are available in single,

duplex, and

three-plug

units. The mo st

com mo n of all is the duplex receptac le,

which is designed to receive two electri

cal plugs. Some duplex units have one

half as a "U" ground and the other half in

a different sh ap e. Also, the re are rec ep

tacles team ed w ith switches, which

allow a light to be turned off either in t

room or at the receptacle itself.

Receptacle and Plug

Shapes

Figure 4.2 show s so m e of the configura

tions (shapes) of receptacles and plugs

that are available. There are many oth

ers made for specialized use. This

chapter discusses only the more

common ones.

Old-Style Two Prong.

Many building

con struc ted during the 1940s and

1950

were equ ipped with this unit. Th e main

disadvantage is the lack of ground

protection.

"U"

Ground. This recep tacle acce pt

both the 2 prong plug and th e 3 prong

"U" groun d plug. If th e g round prong is

remo ved from th e 3 prong plug, it will

still fit th e rec epta cle in one direction

only. Careful inspe ction of the rec ept ac

34 Applications of Electrical Construction



old-sty le 2 prong

"U "

g r ound

3 prong twist - lock* direct -current* 240 V tan dem

©

©

©

©

©

©

drier recep tacle 30 A , 125 V / 250 V*

* polarized receptacles

FIGURE 4.2 Receptacle and blade patterns (configurations

range receptacle 50 A , 125 V / 250 V*

will show th at th e live and neutral slots

are different sizes to prevent inter

changing th e co nn ectio ns. (See Fig. 4.3)

Crow's Foot.

This plug was an early

attempt to provide ground protection in

a recep tacle. Unfortunately, the sh ap e of

the 2 prong plug could be modified with

pliers, allowing it to be fitted into the

receptacle. Also, the crow's-foot plug

often had its ground prong removed and

blades resh aped for use in standard 2

prong receptacle s. Ground protection

was lost in both cases. It became obvi

ous a change in design w as n eede d.

Twist-Lock.

This rece ptacle is

available in 2, 3, and 4 prong units. Its

major advantage is that the plug can

not be pulled out of the receptacle

accidentally. The 3 and 4 prong units

provide ground protection.

Receptacles

3



FIGURE 4.3 A specif ication grade " U "

ground receptacle

FIGURE 4.6

receptacle

A 250 V tandem

" D "

ground

FIGURE 4.4

A

250

V direct current " IT

ground receptacle

FIGURE 4.5 A 125

V direct current "IT

ground receptacle

Direct-Current. The main use for this

recep tacle is to keep the positive and

negative conductors from being

interchanged in DC system s. Some

models have ground protection.

(See Figs. 4.4 and 4.5)

Tandem.

Air conditioners, motors,

and heaters of 240 V make use of th is

=3

e

g

o

FIGURE 4.7

receptacle

A 250 V

15

A, single tandem

unit. It is equipped with a ground prong

and is used primarily on 240 V circuits,

where its blade shape prevents

120 V

units from being plugged in.


Range and Drier Receptacle.

Each

time an electric range or clothes drier

is connected to the cable in a house

or apartmen t building, the cable is

shortened slightly. Sometimes the cable

is shortened to the point where it can n

longer be used . The heavy-duty range

and drier plug and receptacle were

designed to prevent this from happening

They allow the range and drier to be

pulled out from the wall for spring

cleaning or simple removal.


36




\ ..." -

J L

i

IV)

•a

e

CO

FIGURE 4.8 A residential electric drier

\) receptacle

Commercial and industrial applica

tions often require voltages and c urr ent s

other than t ho se found in residential

applications. To prevent accidental

smatching of cord s and rec eptac les, a

•*ide variety of recep tacle configurations

has been ap proved by the Canadian

Standards Association (CSA). These can

be seen in Figures 4.10A and 4.1 OB o n

pages 38 and 39.

Receptacle Grounding

Receptacles equipped with a

ground slot

are designed to provide safety for the

person using the equipment connected

to the rece ptac le. If a fault occ urs in an

electric drill, for exam ple, th e cu rren t

will

travel to t he frame of th e drill, the n

back along the ground conductor to the

distribution panel. The circuit fuse in the

panel will blow a nd prev ent th e drill's

user from receiving a shock .

If

there is

no ground protection , however, the us er

could receive a 120

V

shock as the current

flow pa sse s from th e tool's frame thro ug h

the oper ator on its way to groun d.

The ground-equipped receptacle has

FIGURE 4.9 A residential electric range

receptacle, rated at 50 A

a green,

hex-shaped terminal screw

for

connection to the grounding circuit of

the electrical box that s upp orts the

recep tacle. The ground w ire in a non-

metallic or armoured cable wiring sys

tem runs between th e ground terminals

of the distribution panel, those of the

receptacle box, and the receptacle

itself.

A

metal conduit system carries the

ground connection from the distribution

panel to the receptacle box within its

metal easing.

A

flexible conduit system

usually requires a sep ara te, green, insu

lated conductor to be pulled into the

conduit to realize the same purpose.

These are Canadian Electrical Code

requirements.

Isolated Grounding

Receptacles

Some sensitive electronic equipment

such as cash registers, com puters, and

medical instruments will perform poorly

if any electromagnetic interference

passes through their regular grounding

circuits. However, special re cepta cles,

Receptacles



125 V

15 ampere

D Qw)

5 - 1 5 R

20 ampere

5-20R

30 ampere

7 \

(

0

•aw)

5-30R-

50 ampere

[

D

Qw)

5-50R

60 ampere

S

'•a

B

o

•

i

a

o

a

250 V

6 - 15R

©

6-20R

o

-30R

6-50R

277 V

A C

7 - 1 5 R

7-20R

U

^

7-30R

v

ft

# y

7-50R

24

347 V

A C

24-15R 24-20R

24-30R

24-50R

if

9

P

14

125

V /

250 V

1 4 - 1 5 R

1 4 - 2 0 R

1 4 - 3 0 R

14 - 50R

1 4 - 6 0 R

15

3 0

250 V

1 5 - 1 5 R

1 5 - 2 0 R

1 5 - 3 0 R

1 5 - 5 0 R

1 5 - 6 0 R

NO TE : 3 0 refers to a 3 phase system. The "Y" symbo l s igni f ies a 3 phase, 4 wire W ye-connected system

FIGURE 4.10A CS A configurations for non-locking cord caps and receptacles




15 ampere 20 ampere 30 ampere 50 ampere

60 ampere

L5

125

V

c

'•&

c

3

O

o>

V

CO

o

a.

L6

250 V

L7

277 V

A C

L8

480 V

A C

L9

600 V

A C

_c

c

D

O

5 >

Q>

L14

125 V/

250 V

L15

3 0

250 V

L16

3 0

480 V

L17

3 0

600 V

L21

3 0

208Y/120V

<B

P

g

9- o>

L22

3 0

480Y/277 V

20R

L22 \

Z

0

L23

3 0

600Y/347

V

( < 3

G O

0 /

50R

N O T E :

30 refers to a 3 phase system. T he "Y" symb ol s ignif ies a 3 phase, 4 wir e Wye-connected system.

RGU RE 4.10B CS A configurations for locking cord caps and receptacles

Receptacles



with ground terminals electrically iso

lated from mounting straps/brackets,

can overcome this problem. Such recep

tacles have separate, insulated ground

wires that provide grounding pa ths sep

arate from normal grounding circuits.

Bothersome malfunction of equipment is

thus p revented. These receptacles,

marked by the manufacturer, are fre

quently produced in a bright orange

colour for easy recognition.

Split Receptacles

Duplex units are designed so that the

bridge linking the two terminal points

on the one side can be removed. This

separates electrically the upper and

lower portions of the receptacle from

each other. (See Fig.

4.11)

Dividing the

receptacle electrically has two major

advantages.

One is that half of a receptacle placed,

for example, in a living-room may be

controlled by a wall switch. This allows

a lamp to be turned on without entering

the darkened room. The other half of the

receptacle may be made alive all the

time, for use with radios, televisions, or

other appliances in the room. Figure 4.12

shows a diagram of such a circuit.

The second major advantage is for

use of appliances in the kitchen area.

Splitting th e receptacle allows two

separa tely fused circuits to be run to

one receptacle at the counter. This

permits two high current-consuming

devices to be plugged in to one recepta

cle without overloading the circuit. Wi

out a split receptacle, using two appli

ances, such as an electric kettle and

frying pan, in the sam e outlet would no

mally blow a 15 A fuse. Adequate prote

tion for the circuit conductors is not lo

when the split receptacle system is

used . Figure

4.13

shows a wiring diagra

of such a circuit.

Replacement of

Receptacles

While most receptacles deliver years o

trouble-free serv ice, replacements are

sometimes necessary. When receptacle

no longer hold the plug firmly or heat

up during use, a new unit should be

installed. Units are available in a variety

of styles and colours to suit any room's

decor, but attention must be paid to th

receptacles' electrical ratings to ensure

safe operation.

removable bridge

i—r

terminal

FIGURE 4.11 Receptacles can be "s p l i t " by removing the bridge.

40




l ive wire

lamp plugs

In here

br idge

' left

intact

br idge removed

120 V

neutra l wire

TV plugs in here

RGURE 4.12 W iring diagram show ing a split-switched receptacle

teakett le plugs

here

bridge

' left

intact

live w ires

bridge removed

yy

15 A fuse

common neutra l wire

1 = 1

frying pan plugs in here

SURE 4.13 W iring diagram show ing a double-fused split receptacle

NEMA Receptacles

The National Electrical Manufacturers'

Association (NEMA) is an Am erican

organization dedicated to standardizing

electrical dev ices. Through its efforts, a

radio of any m ake can now b e plugged in

to a receptacle in any town in N orth

.America

and be expected to op erate sat

isfactorily. Receptacles have been stan

dardized in mo unting techniq ue and slot

placement. R eceptacles, wall plates, and

receptacle boxes from most manufactur

ers are completely interch angeab le.

The Electrical Electronics Manufac

tu re rs ' Association of Can ada (EEMAC)

is the Canadian equivalent of NEMA.

Polarized Receptacles

The crow's-foot, DC, and twist-lock

recep tacles are examples of polarized

units. They accep t

only

their own style

of plug and the plug can be inserted in

only one way—a

necessary feature in

circuits where it is dangerous to inter

change a ny of the circuit co ndu ctors .

Receptacles

4



Plaster E ars

Many receptac les are equipped with

small extensions to the mounting

bracket called plaster ears. When a

receptacle is installed in a building with

plastered walls or wood panels,

plaster

ears are ve ry useful.

Plaster

around the

receptacle box often crumbles, leaving

a

space with little

or

no support

for

the

receptacle. The

plaster

ear extensions

provide extra length and width to the

moun ting bracket, making possible a

sec ure , flush m oun ting. (See Fig. 4.14)

Receptacle installations in surface

wiring boxes, suc h a s th e utility box

or

FS fitting, do nor require plaster ears.

(See

Fig. 4.15)

Removal

of

the ears

is a

simple mat

ter. Bend them back and forth several

times w ith a pair of pliers.

Ground Fault Interrupter

Receptacles

Modern wiring regulations require out

door receptacles

to be of

th e Ground

Fault Interrupter

(GF1) typ e. C onsult th

Electrical Code for your area to deter

mine exactly wh ere the se units must

be

installed. The

GFI

receptacles are

designed to protect users of portable

tools and equipment from electrical

shock, which can occu r if the tool or

equipment becomes faulty. Each year,

m any pe ople are killed

or

endangered

b

the p ortable electric devices that have

developed internal defects or insulatio

breakdowns.

It

is not always obv ious

to

the operator that this breakdown has

occurred until the device is plugged in

and

a

shock received.

Normal fuses and circuit breakers

will no t blow

or

trip unless the curren t

flow to ground (earth) exceeds the

ampere rating

of

the protection device

They are designed

to

protect

a

circuit's

wire, NOT th e pe rson using the circuit.

GFI rece ptac les are designed to detect

small leakage cur ren ts when the y de

velop and trip open t he circuit to prote

the person using that circuit. Currents

as low as

5

mA (0.005 A) can

be

sensed

by the unit when it is pro perly installed

#6-32 mount ing screw

bare ground wire

15 cm wire

m m

chipped or broken plas

near b

plaster w

sect ional

plaster

Plaster

reaches solid mater

FIGURE 4.14 Flush-mounting a receptacle using

plaster

ears

42 Applications

of




wires

conduit

V o n w ire

5-32 mount ing

FS condu it f i t t ing

(cast a luminum)

plaster

ear removed

RGURE

4.15

S urface-wiring a receptacle

it plaster ears

Dam pness in the tool, metal shav

ings,

or rough handling can cause the

nitial

breakdow n in th e insulation of th e

tool or eq uipm ent. Standing on a con

crete floor, ou tdo ors on g rass or ea rth,

or on m etal plum bing or frame un its of a

building will place th e o pe rato r in con

tact with the earth or ground.

An electrical shock can hav e serious

effects o n a person w ho is subjected to

L The human body does not allow a

current to flow due to its normally

high electrical resistance. However, very

small amounts of current can cause pain

or upset bodily functions such as

breathing and heart beat.

The unit of measurement for this

dfecussion will be the milliampere. One

milliampere of curre nt is equ al t o

0.001 A. A person will feel a slight shock

if 5 mA of current flow through the

body—not enough to harm, but suffi

cient to know a shock haza rd e xists.

At between 10 mA and 15 mA of cu r

rent

flow, m uscular freeze

may occur,

preven ting th e op era tor from letting go

of the tool b eing us ed. At th e 50 mA to

100

mA

level, he art fibrillation and de ath

occur. As can be seen by th es e figures, a

normal 15 A circuit fuse would be of no

value in protecting a perso n u sing the

circuit. Chap ter

16

explains the w orkings

of ground fault d evic es in m ore d etail.

One of the features of the Ground

Fault Interrupter rec eptac le is that onc e

connected to a circuit, any receptacle

connected

after

t he

GFI

unit will also

offer ground fault protection to the cir

cuit. Outdoor receptacles, garages, bath

rooms, pool areas, workshop s, laundry

rooms, and num erous other locations

can well take adva ntage of the p rotec

tion offered by ground fault interrupters.

(See Figs. 4.16 and 4.17 for typ ica l GFI

receptacles.) Great care must be taken

to connect the leads of the receptacle

according to the manufacturer 's

FIGURE 4.16 Front vie w of a GFI receptacle

Receptacles

43



instructions. If connected incorrectly,

the GFI recep tacle will not prov ide th e

pro tect ion d esired . Figure 4.18 illus

trates a typical wiring diagram.

Some manufacturers produce a GFI

receptacle that uses terminal screw con

nections rather than connection leads.

The choice of connection m ethod is then

left to t he installer. Figure 4.19 illustr ates

a typical comm ercial-duty, specification

grade GFI, suitable for both vertical and

horizontal m ounting.

GFI receptacles are equipped with

test and reset butto ns. The unit should

FIGURE 4.17 Rear vie w of a GFI recep tacle, FIGURE 4.19 A comm ercial-duty, specifica-

show ing the connection leads tion grade ground fault protection receptacle

and cover plate

splice

black lead

GFI

receptacle

green lead

splice

f \ V U U \ U V

CZI

I—I

a

test

I

|

reset

C

black wires

/ \ to next receptacle

i

•

Insulate ends of red and

•

grey if no othe r receptacles

are to be connected.

B [

standa rd receptacle

gr ound

white lead

neutral wire

o

"splice grey

lead

splice

\ /

whi t e w i r es

gr oun

to next receptacl

to next receptac

FIGURE 4. 18 C onnection diagram for a GFI receptacle installation

44




in

fiGURE 4.20 A typical electric shaver outlet

be tested at least once a mo nth by pres s

ing th e test butto n on th e face of th e

rece ptac le. This simulates a ground fault

in the circuit and the relay within t he

receptacle should react and open the

rrcuit. The reset button will at this time

protrude from the face of the receptacle,

indicating successful operation of the

unit. Pressing the reset b utton back into

place will reactiva te the relay in th e

recep tacle for further us e. This simple

test assu res the owner tha t the unit is in

proper working order.

Prior to recent GFI developm ents,

electric shave r recep tacles tha t isolated

the supply voltage from t he shav er w ere

available. This eliminated the sh ock haz

ard present wh en electric shaving equip

ment was used near plumbing fixtures.

These recep tacles were, however, too

small (electrically) for use with m od ern

hair dr ier s. (See Fig. 4.20)

Hospital Grade Grounding

Receptacles

Receptacles in hospitals and oth er m edi

cal facilities are often subjected to

severe use and mechanical ab use. When

an emergency oc cu rs or a life is at sta ke,

time becom es im porta nt. Medical staff

will frequently move plugged-in pi eces of

green dot

FIGURE 4.21 A 125 V " U " ground recepta

cle of hospital grade, identified by a green dot

on the lower face

equipment about, causing unintentional

abuse to both the cord connector and

receptacle.

Hospital grade receptacles are made

from a

heavy-duty,

abuse-resistant ther

mo plastic, capab le of w ithstanding

impact d amage, while resisting the tend

ency to crack or break. The possibility of

sho rt circuits is reduced by having a

thick-walled, mou lded ba se of similar

material. A one-piece, integral groun ding

contact ensures proper grounding of the

circuit and equipment being used. Hos

pital grade rec eptac les ar e identified by

the green dots on the ir faces, visible

even when their cover plates are

insta lled . (See Fig. 4.21)

Receptacle Covers

Indoor receptacles use standard-sized

metal or plastic covers when installed in

resid entia l c ircu its. (See Fig. 4.22) When

covers are used outdoors or in other

dam p areas, they should be the type

that provides easy access to the recepta

cle but keeps out weather-m oisture and

dirt. (See Fig. 4.23)

Receptacles

4



3

0)

FIGURE 4.22 Indoor receptacle and cover

FIGURE 4.24 C ombination sw itch and

receptacle unit

device in another area of the room or

building . See Figure 4.24 for a typica l

unit.

FIGURE 4.23

cover

Weather-resistant receptacle

Combination Units

When installation sp ac e is limited, a unit

that allows an installer to locate the

switch and rece ptacle in the sam e single

gang box is recom m ended . The switch

can either control the receptacle portion

of the unit, a light fixture, or a no the r

F o r R e v i e w

1. W hat duty ra nge of rece ptacle

should be selected for kitchen

use? Why?

2.

Where in the home may light-duty

receptacles be safely installed?

3. Where can information be found

regarding the num ber of recepta

cles required for a room?

4. E xplain wh ere th e live, neutral,

and ground wires are connected

on a duplex "U" ground

receptacle.

5.

List two us es for a switch and

receptacle combination unit.

6. What is the main disad van tage of

the old-style 2 prong receptacle?

7. Would an extens ion cord fitted

with twist-lock units be an advan

tage on a constru ction job site?

Why?

8. Explain the purpose of the ground

slot on a receptac le.

9. Where does th e ground in a recep

tacle originate?

46




10.

How is the g round circuit carried

in a conduit system ?

11.

What is the d ang er in using a po r

table electric tool that has had the

grounding prong removed from its

plug? Explain.

\2 .

List two are as for use of split

receptacles in the h om e.

[13.

What are the adv antage s of using

split receptacles?

11

What is a

NEMA

receptacle?

Explain.

ist three examples of polarized

receptacles.

16.

What are

plaster

ears? W here and

why are they used?

17.

What type of receptacle is recom

mended by the Electrical Code for

use in outdoor areas?

|18.

What advantage has a

GFI

recepta

cle over o the r ty pes of

receptacles?

19.

Why will a norm al fuse or c ircuit

breaker not protect a person using

portab le tools on a circuit?

120.

Why is it imp orta nt for a

GFI

unit

to detect leakage currents as low

as 5

mA?

Receptacles

4



Conductors

O

ne of the most imp ortant pa rts of

any electrical system is the co ndu c

tor that makes up the wiring circuit.

Most con duc tors are rarely check ed

after the installation h as been appro ved.

For this reason and o ther s, the ch oice of

conductor is an important feature of cir

cuit design.

Conductor Materials

Conductors used for residential and

industrial wiring circuits are usually

m ade from co pper, aluminum, or steel. If

exposed to the air, thes e metals co mb ine

with the oxygen. This

oxidation

pro

duc es a layer of oxide on th e surface of

the conductor. If a conductor is allowed

to oxidize at the terminal point or splice,

the current-carrying ability of the termi

nal will be seriously reduced. That is

because the oxide layer does not con

duct electricity.

Copper.

Co nduc tors are often m ade of

copper, because it is an excellent

condu ctor, easy to work with and

hand le, and do es not oxidize as mu ch as

aluminum o r steel. Copper is also u sed

in electronic circuits bec ause it solders

readily, ensuring a secure electrical

connection. Copper has beco me

expensive, however, and a sub stitut e is

being sought.

Copper w ire

splices

must be mad

secu re to preven t the oxide coating f

reducing the current-carrying ability

the splice.

Aluminum.

Aluminum is lighter th

cop per but not as good a condu ctor.

obtain the same current-carrying

capacity, therefore, an aluminum

con duc tor mu st be slightly larger tha

one made of copper. Also, aluminum

oxidizes rapidly. The aluminum oxide

acts as an insulator and reduces

electrical c urr en t flow.

Using aluminum po ses two othe r

major proble ms . One is

electrolysis,

which is the chemical breakdown of

metals reacting with one another. Alu

num will react with some metals in th

way. The p roce ss is accelerated by m

ture and th e flow of curre nt in the con

ductors. Approved connection devic

resist this proce ss, and s o approv ed

minal splice connectors should be us

Also,

antioxidant chem icals

to preven

oxidation of th e wire are available.

Th ese chemicals a re usually applied

with a brush, forcing the chemical in

the stran ds of the cab le. Figure 5.1 il

trates a typical chemical available fo

this purpose.

The second major problem with a

minum conductors is that the connec

48




RGURE 5.1 A ntioxidant chemical for use on

num conductors

nints lose their grip.

A

terminal screw

can be tigh tened firmly, but in a few

days,

the aluminum will accept th e new

shape into which it has been forced.

fhis

reduces the pressure of the termi

nal

screw on the wire, and th e aluminum

lo w s in to the new shape. This

flow—

called

cold flow—results

in a loosened

conne ction. As a result, the terminal

connec tion will overheat, causing dam

age to the connec tion and insulation.

If han dled prope rly, aluminum is an

c&ctive

cond uctor that provides many

years of servic e. It is not of much use ,

however, for circuits where solder con

nections are necessary, because alumi-

•um cannot be soldered simply.

Steel. Steel is the stro ng est of th e

three metals and is used mainly as a

supp orting material. For example, alumi

num and copp er cables are often wound

around a steel centre core for outd oor

wiring. Con ductors m ade this way can

withstand a great deal of stress. Also,

electric railway or subway syste m s often

use steel rails as the con duc tors in their

supply system . The rails are som etimes

made of special steels containing a small

amount of copper to improve the cur

rent-carrying ability of th e rails.

While the metal conduit and boxes

are

not

used to carry current for the

operation of electrical equipment, steel

enclosures

are

used to complete the

groun ding circuit. In rural serv ice instal

lations, for example, two steel rods are

often driven into the ground to provide

a ground connection w here there is no

metal water supply system to the

building.

Conductor Forms

Co nduc tors used for residential and

industrial wiring circuits are made in the

form of wire, cable, and cor d.

W ire. W ire, wh ich is a single, solid

strand, is the least flexible form of

conductor.

Copp er wire is usually m ade by

drawing

a soft co pp er rod, which is from

6 mm to

13

mm in diameter, through a

series of doughnu t-shaped metal blocks

called

dies.

Th e hard cen tre of each die

ha s a hole slightly

smaller

than the hole

of the die through w hich the rod h as jus

been draw n. As the rod p ass es throu gh

the dies, it is reduced in diame ter and

lengthened.

The wire ten ds to hard en after p ass

ing through several dies. This hard-

drawn copper is used for some outdoor

wires bec aus e it is quite strong.

If the diam eter n eed s to b e m ade stil

Conductors

4



low voltage thermos tat (LVT) contro l wire 2 conductor

C A N A D A WtRK

annunciator wire

blast ing wire

asbestos-insulated stove wire

low voltage con tro l wire (LVT) 3 conductor

P O L H T M Y L H I B L I N K WI RR

polyethylene l ine wire

thermoplast ic- insulated wire

FIGURE 5.2 Typical insulated wire s

50




therm oplast ic- in sulated , weather- and heat-resistant cable

therm oplas t ic- insu lated, weather- and heat-resistant cable

f lexib le we ld ing cable

E XE LE NE 6 0 0 V O L T S

service entrance cable

* #

, m

^ ^^^"A ^ 4.

,

* ^ , % ^ ^ ^ . ^ f c ^ - .

,

* ^ - ^ % *.

armoured cable

•™*—

turn**,

nonmetallic sheathed cable

CURE 5.3 T ypical insulated cables

Conductors



lamp cord

n

/i

HPN (chlorinated polyethylene) heater cord

^ ^ r "J*?^™?

wffrf:JL

,B

/3 SJTW outdoor cord

TYPE SJ 300 VOLTS

light-duty cord for small motors and tools

heavy-duty, type SO power supply cord

FIGURE

5.4 Typical light- and heavy-duty

insulated

cords

52




smaller, th e wire is first p ass ed throu gh

•

annealing

oven, which heats and

oftens it. The wire can then be further

edu ced to any size required. The

me aling process m ay have to be

irpeated several times. The wire may

asso be insulated w ith a varie ty of

•aterials. (See Fig. 5.2 on page 50.)

Aluminum wire is produced in the

way.

Cable. A cable is a

compound

mductor

m ade of a num ber of str an ds

*

wire. Some are twisted tog ether to

farm a large conductor before being

iasulated.

This typ e is usually u sed in

circuits w he re th er e is a large flow of

current.

Others are assembled and

placed under a common cover after each

•ire has been insu lated. This type is

ased extensively for the wiring

of

ildings . (See Fig. 5.3 on page

51.)

A

cab le is mo re flexible th an a wire of

i

same size.

Cord. The cord 's con duc tors are

Bade

of man y str an ds of fine wire

risted together. The cord is ma de of

•JPD

or m ore separately insulated

iductors

assembled within an

iting

jacket. It is th e m ost flexible

i

of condu ctor an d is used to supp ly

ait

to hand-held app liances and

rtable to ols, where freedom of

ovement

is importa nt. Appliance and

I

cords som etimes have a third

iuctor (with green insulation),

:h is used for grounding. (See Fig.

•

inductor Sizes

iductor

sizes are me asured and listed

i

two ways. One meth od is based on the

^•erican

Wire Gauge. The oth er is

fcased on area.

FIGURE 5.5 A merican W ire Gauge used to

measure size of solid conductors (wires)

Am erican Wire Ga uge (AWG). This

gauge is used to m easure only

solid

co nd uc tors (wire). The outer edge of th e

gauge has slots, which are num bered.

The

smallest slot

into wh ich t he w ire wil

fit is the

gauge number

of the wire . (See

Figs. 5.5 and 5.6) The

AWG

can m easure

wire from No. 36 (the sm allest size) t o

No.

0 (the largest size).

wire

gauge

wire in slo

gauge number

FIGURE 5.6 Using the A merican W ire

Gauge

Conductors

5



Wire produced for special applica

tions c an be as small as No. 44, however,

and as large as

No.

0000 (4/0 ). The

small, hair-like wires a re used in the

windings of electric motors and similar

equipment.

Area of Cross-Section.

Th e size of a

larger conductor is determined by

calculating the conductor's cross-

sectional area. When a com pound

conductor, such as a cable, is to be

mea sured, calculate the area of on e

strand , then multiply the area of tha t

strand by the number of strands in the

cable . Traditionally, the a rea of cro ss-

section has been referred to as the

circular mil area. However, und er th e

metric system, the cross-sectional area

is m easured in squa re m illimetres. (The

symbo l is mm

2

.) The cross-sectional area

is obtained by using the

formula A = n

x

r

2

, where

A

is area, r is th e rad ius of t he

con duc tor in millimetres, and

it

is a

constant (3.14).

Non etheless, the term

MCM

still

applies to p articula r size s of wires. Used

for large co nd uc tor s (over 4/0 in size), it

refers to thousands of circular mils. A

con duc tor with a diam eter of a

thousandth (0.001 in.; 0.002 cm ) of an

inch has a diameter of 1 circular mil.

(See Fig. 5.7A) C ond ucto rs larger tha n 1

mil in diameter must be measured with a

micrometer to determine their diame

te rs in mils. If, for example, a N o. 6 AWG

co nd uct or has a diam eter of 0.162 in.

(0.411 cm), its diam eter in mils is 162.

Circular mil area is calculated by sq uar

ing the diam eter in mils: this AWG con

du cto r would b e 26 240 circular mils.

Determining the circular m il area s of

large conductors is more complicated,

becau se such condu ctors are usually

stranded to improve their flexibility.

Stranded

con duc tors a re mad e up of

severa l row s of st ran ds as follows. Ro

is a single stran d. Row

2

co nsi sts of 6

stra nd s twisted over the to p of row 1.

The third row would con tain

12

stran

wrapped in the opposite direction to

tho se of the seco nd row.

A

fourth row

would have

18

strands, wound in the

opp osite direction to thos e of the thir

row. Each new layer or row of str an ds

add ed to th e con duc tor will contain s

more strands than the previous row.

(See Fig. 5.7B) Th e num ber of str an ds

mu st be calculated to arrive at the co

ductor's total circular mil area.

The next step is to determ ine the

diam eter of one stran d, using the sa m

method you would for small conducto

1 circular mil

FIGURE 5.7A Diameter of conductor in

circular mils

row 4, 18 str

row 3,12

str

row 2, 6 str

row 1, 1 s

FIGURE 5.7B A multi-stranded conducto

w ith 4 rows and 37 strands

54




Cable stran ds are frequently produ ced

ID diameters that suit cable size and

design more than stand ard wire gauge

sizes and d im ensio ns. If a cable ha s a

single-strand

diam eter of 0.116 in.

(0.294 cm), the stra nd's diam eter would

be 116 mils. The circular m il area of th e

strand would be

13

456 circu lar mils

(116

K 116). The size of the com plete cab le, as

shown in Figure 5.7B, would be found by

multiplying 13 456 x 37 strand s. This

497 872 circular mil cab le wou ld b e con

sidered a 500 000 circular mil cable by

Electrical Code tables—a 500 MCM

cable.

Tables 5.1 and 5.2 show th e m etric

sizes of various types of co nd ucto rs.

Bear in mind, however, that the current

edition of the Canadian Electrical Co de

and much of the electrical industry still

•efy on the imperial syste m of m easure-

saent. Tables 5.3 and 5.4 sh ow the impe

rial dimensions and sizes of bare copper

•ire

in both solid and stranded

configurations.

Wire Size Uses

Wire and cable for buildings are m ade in

wen gauge sizes, such as Nos. 14,12,10 ,

L

etc. Odd gauge sizes, su ch as N os. 15,

1,9, etc., are not used for building

wire and cable becaus e the re is not

enough difference in current-carrying

capacity (ampacity) to make production

of thes e odd sizes worthw hile.

No.

10 gauge wire is the larg est single-

strand conductor allowed under a termi-

aal

screw b y the Canadian Electrical

Code. Larger con duc tors must be

taserted into a compression-type fitting,

called a lug. (See Fig. 5.8) S ince w ire and

cable for buildings need to be flexible,

con duc tors for this use are usually

strande d w hen m ade in sizes larger than

No.

10

gauge.

mount ing hole

cable

FIGURE 5.8 Me tho d for installing cable in a

jug

Wire for motors, transformers, and

oth er m agnetic equipm ent is mad e in

both odd and even gauge numbers,

beca use wire size for these uses is more

critical. Co ndu ctors with large cross-sec

tional areas are used for industrial appli

cations w here a large amount of curre nt

must be carried.

Conductor Insulation

There are conductor insulators made fo

a wide variety of uses and situations.

The more common types are thermo

plastic, rubber and cotton, neoprene,

asbestos, varnish, glass over thermo

plastic, and c ros s link.

Therm oplastic. This is one of the

most common insulators used for

residential and industrial wiring.

Thermoplastic is an excellent insulator,

bu t it is sensitive to ex trem es of

tem perature. At high temperatures, it

m elts. At lo w temp eratures, it becom es

brittle and cracks if handled roughly.

Weatherproof and heat-resistant

therm oplastics are available, however.

Thermoplastic weatherproof insulation

is called

TW .

The

TW-75

type is

Conductors 5



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i n i n i n

co c n CN

i n i n i n

c o m r -

o o o

i n

c o t *

o o i n

r - « - c o

o

i n i n

O CO 1

t -

i - CN

•»om

N C O C O

o d d

o r - r-

(6

r- i

c d

i n o o

1 C D I D

o o o

o d d

« -

i n i n

M (B *

£ 8 g

r

i n i n I D

•-

co m

p

i n

o

o * - CO

i n o i n

•<J

r-

en

g § §

o o o

CO CO

i -

« - * - CM

o

o

o

O ^ CN

CN

<N

CO

o o o

8S3

CO — O)

CO « * <»

o d d

*P "* **

CO O CN

«—

w-

Q Q O

fi

SB 9

o o O

o d d

i n ur>

p

m cs

f-

o i n i n o

C N c o m c o

*— *—

o o o o

CO

t -

t CO

*- C N C N C N

o

i n

o o

m

r-»

O c o

t—

i— CN CM

o

m

o o

co co • - co

C N C N C O C O

o o i n i n

r- o * t cn

* - CN CM CN

o o

m

o

W O C O ' J

C N C O C O ^

i n o i n o

o> cn o i n

c o

T

c o

r v

p i n o i n

0 >

C M

Q « -

i n

r-

c n

t -

c o r^ C N

co

i n i n p p

O O O O

TT i n CO CN

c o

^ i n tv

T- ^ ^>

§ § § §

o o o o

d d o d

p p p o

C N C N C N

CN

© © o o

? CN O T »

i n o o o o

o c o i n r- • -

C N C N C N C N C O

m o i n m i n

- - i n a >

C M

c o

c o c o c o •«» r r

i n m

o

m

o

i n c o

T -

c o c o

CN CN CO CO CO

i n i n i n i n o

- t ^ i n i n c o

i n i n o o o

i n

T - P-

c o

- *

c o » * * » m c o

o

i n

o

i n

o

c o

^

o c o

i n

i n c o

r» - r -

<r>

i n o i n o o

o >

c o < N

c n

»—

c o o C N c o

r-»

.—

t—

r-

t—

o i n o i n i n

c o

r - C M

c o t

c o i n c o o i n

t— i- r-

CN CM

co •— co

«—

cn

-.

cq cq cn cn

d d d d d

CN CO co

p

• -

0 > d ^ t o i n

r- C M C N C N C M

i n i n i n i n i n

c n cn cn cn cn

o o p p p

d d C> <D G

-T ' t ' t ' J * t

C N C M

CM

C M C M

g § 8 §

56 Ap plications of Electrical Con struction



T A B L E 5.2 D ime n s io n s a n d re la te d d a ta for b a re co p p e r a n d a lu m in u m s t ra n d e d co n d u cto rs

S tra n d e d Bare C o p p e r a n d A lu m in u m C o n d u cto rs

C o n d u c t o r

S i ze

AWG cmil

14 4110

12 6 530

10 10380

8

16510

6 26 240

4 41 740

3 52 620

2 66 360

1 83 690

1A> 105 600

2/0

133100

3/0 167 800

4/0 211 600

250 kcmil

300

350

400

500

600

750

1000

1 260

1 500

1 750

2 000

A rea

m m

J

sq.

i n .

2.08 0.003 23

3 31

0.00513

5

26

0.00816

8.37 0.012 97

13.30 0.02061

21.15 0.032 78

26.66 0.041 33

33.63 0.05212

42.41 0.065 73

53.51 0.082 91

67.44 0.104

5

85.03 0.1318

107.22 0.166 2

12668 01963

152 01 0.235

6

177 35 0.274

9

202 68 0.314 2

253.35 0.392 7

304.02 0.471 2

380 03 0 589 0

50 6 71 0 .7854

633.38 0.981

7

760.06 1

178

886.74 1.374

1013.42 1.571

Mo

of

Wi res

(a), (b)

7

7

7

7

7

7

7

7

19(18)[18|

19(18)1181

19(18)1181

19(18)1181

19(18)1181

37(36)1351

37(36)1351

37(36)135]

37(36)1351

37(36)1351

61(58)1581

61(58)158]

61(5811581

91

91

127

127

Wi re

D i ameter

m m in.

0.61 0.024 2

0 77 0 030 5

0.98 0.038

5

123 0.048

6

1.55 0.061

2

1.96 0.077 2

2.20 0.086 7

2 47 0.097 4

1.69 0.066

4

1.89 0.074

5

2

13

0.083

7

2.39 0.094 0

2 68 0.105 5

7 09 3 082

:>

2

23

0.090

0

2 47 0.097

3

264 0 .1040

2.95 0 1162

2.52 0 099 2

2.82 0.1109

3.25 0.128 0

2.98 0.1172

3.26 0.128 4

2.98 0.117 4

3 1 9 0 . 1 2 5 5

N omi na l Conductor D i ameter

Compressed Compact

R ound R ound

m m in . mm in.

1.80 0.071

2.26 0089

2.87 0.113

3 6 1

0.142

4 5 5

0.179

5.72 0.225

6.40 0.252

7.19 0283

8.18 0 322

9.19 0.362

10.31 0406

11.58

0.456

13.00 0.512

14.17 0558

15.52 0 611

16.79

0661

17.93 0.706

20.03 0.789

2268 0.866

24.59 0.968

28.37

1.117

3175

1.250

34 80

1.370

37 59 1.480

40 21

1.583

3.40

0.134

4 29 0.169

5 4 1 0.213

605 0.238

6 81 0.268

759 0.299

8 5 3 0 3 3 6

9.55 0.376

10.7 0.423

12.1 0.475

13.2 0.520

14.5 0.570

15.6

0.616

167 0 .659

18.7 0.736

20.7 0.813

23 1 0 908

26.9

1.060

A p p r o x i m a t e N e t W e i g h t "

ko/IOOOm

A l u -

C o p p e r minum

18.9

30 0 9 1

47.7

14.5

75.9

231

121

36.7

192 58.3

242 73.5

305 92.7

385

117

48 5

147

611

186

771 234

97 2 296

1 149 350

1 37 8

419

1 60 9

489

1 83 8

559

2 298

699

2 758 838

3 447 1048

4 595 1 396

5 743 1 750

6 892 2 100

8041 2440

9 190 2 790

Ib . / IOOOft .

A l u -

Copper m i n u m

12.7

20.2 613

32.1 9 75

51.0 165

81.1 24 6

129 39.2

163 49.4

205

62.3

25 8

78.6

32 6

99.1

41 1

125

518 157

65 3 199

772

235

92 6

282

1 081

329

1 235 376

1 544

469

1 854 564

2 316 704

3 088

938

3 859 1 174

4 6 3 1

1410

5 403 1 640

6 175 1 880

A verage D C R es i s tance" '

25 C

a/iooo m

A l u -

Copper mi num

8.61

5.42

889

3.41

5.59

2.14

3.52

1.35 2.21

0.848 1 39

0.673 1.10

0.533 0875

0.423 0.694

0.335 0.550

0.266 0.436

0.211 0.346

0.167 0.274

0.142 0.232

0.118

0.194

0.101

0.166

0.088 5

0.145

0.070 8 0.116

0 059 0 0.096 7

0.047 2 0.077 4

0.035 4 0.058

0

0 028 3 0046

4

0 0236 0 038

7

0 020 2 0 033 2

0 017 7 0 0290

12/1000

ft.

Alu

C o p p e r m i n u

2 6 3

1.65

2.71

10 4

1.70

0 653

1.07

0 411 0.674

0258 0 .424

0.205 0 336

0 1 6 3 0 2 6 7

0 129

0.211

0.102

0.168

0 081 1

0.133

0 064 3 0.105

0.051 0 0.083 6

0.043 2 0.070

8

0.0360 0.059

0

0.0308 0.050

6

0.027 0 0.044

2

0.0216 0.0354

0.018 0 0.029 5

0.014 4 0.0236

0.010 8 0.017 7

0.008 63 0.014

2

0.00719

0.0118

0.00616 0 .0101

0 005 39 0.008 8

(a) Reduced number of wires for copper compact

standings

shown in ( ) parentheses.

(b) Reduced number of wires for alumnum compact strandings shown in I I parentheses.

(c) Approximate weights and average DC resistances are considered to apply to

ail

types of strands.

Conductor data and metric equivalents in this table are based where possible on

EEMAC

recommendations current at time of compilation, otherwise on published

ICEA standards.



TABLE 5.3

Size

A W G

0 000

0 0 0

0 0

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

2 0

22

D i m e n s i o n s , W e

Diameter

mil

460.0

4 0 9 . 6

364.8

324.9

289.3

257.6

229.4

204.3

181.9

162.0

144.3

128.5

114.4

101.9

90.7

80.8

72.0

64.1

57.1

50.8

45.3

40.3

35.9

32.0

25.3

ghts, and Resistance of Bare Copper Wire, Sol id ,

A W G S i zes

Area

cmil

211 600

167 800

133 100

105 600

83 690

66 360

52 620

41 740

33 090

26 240

20 820

1 6 5 1 0

13 090

10

380

8 230

6 530

5 180

4 1 1 0

3 260

2 580

2 050

1 620

1 290

1 0 2 0

640

Weight

lb. /1000ft .

640.5

5 0 7 . 8

402.8

319.5

253.3

200.9

159.3

126.3

100.2

79.44

6 3 . 0 3

49.98

39.62

31.43

24.92

19.77

15.68

12.43

9.87

7.81

6.21

4.92

3.90

3.10

1.94

Resistance

ii/1000 ft.

20°C

Annealed

Wire

0.049

0

0.061 8

0.077

9

0.098

3

0.124

0.156

0.197

0.249

0.313

0.395

0.498

0.628

0.793

0.999

1.26

1.59

2.00

2.52

3.18

4.02

5.05

6.39

8.05

10.1

16.2

thermo-plastic,

weatherproof,

and heat-

resistant. Some of the h eat prod uce d by

equipmen t such as electric hea ters ,

stoves, and light fixtures travels back

through the conductor, damaging the

insulation. TW-75 is cap able of w ith

standing such hea t .

Rubber and Cotton.

Homes wired

with the knob and tube system have

conductors covered first with a layer of

rubber and then an outer braid of cott

for extra prote ction. Also, the co pp er

wire is coated with tin to prevent prem

ture o xidation of the copper, b eca use o

the su lphur conten t of the rubb er. Thi

form of insulation is rarely used for mo

ern w iring system s.

Neoprene.

This is a spec ial typ e of

rub ber insulation used widely on

heat-proof line cords for such

58

Applications of Electrical Cons truction



TABLE 5.4 D ime ns ions , W eigh t s , and R es is tanc e of Bare Coppe

Size

AWG or cmil

2 000 000

1

750 000

1

500 000

1 2 5 0 0 0 0

1 000 000

900 000

800 000

750 000

700 000

6 00 000

500 000

450 000

4 00 000

350 000

300 000

250 000

0 000

000

0 0

0

1

2

3

4

5

6

7

8

9

10

St ran

Overall

diameter

mil

1 6 30

1 526

1 411

1 288

1 152

1 094

1 031

9 9 8

96 4

891

813

772

726

6 79

6 29

574

552

492

414

36 8

328

292

26 0

232

206

184

164

146

130

116

ded, A W G a n d c m i l

Number of

Strands,

Class B

Stranding

127

127

91

91

61

61

61

61

61

61

37

37

37

37

37

37

19

19

19

19

19

7

7

7

7

7

7

7

7

7

Sizes

Weight

lb /100 0 f t .

6175

5 403

4 631

3 859

3 088

2 779

2 470

2 3 1 6

2 161

1853

1 544

1 389

1 235

1 081

925

772

653

518

411

326

259

205

162

129

102

80. 9

64.2

51. 0

40. 4

32.1

r W i re ,

Resistance

fi/1000ft.20°C

Annealed W ire

0.005

29

0.006

05

0.007

05

0.008 46

0.010 6

0.011

8

0.013 2

0.014 1

0.015 1

0.017 6

0.021 2

0.023

5

0.026

5

0.030 2

0.035

3

0.042

3

0.050

0

0.063 1

0.079

5

0. 100

0. 126

0. 159

0.201

0.253

0.320

0.403

0.508

0.641

0.808

1.020

keat-producing

appliances as teakettles,

Irying

pans, and soldering irons. Since

•eoprene

is also oil-resistant, it can be

•sed

on extension cords for service sta

tions. The abbreviation for heat-proof

•eoprene

insulation is HPN.

Asbestos.

At one time, major

appliances such as electric stoves used

asbestos-insulated wires for the

heat-proof insulation required for their

internal circuits. For example, asbestos

insulation was used for connections

Conductors 5



between elements and control switches.

It also appeared in the cords of certain

appliances such as soldering irons and

toasters.

It has been established that asbestos

fibres can harm persons who breathe

them in over a period of time. As a

result, manufacturers no longer produce

asbestos-insulated wire, which can still

be found in older equipment in both

homes and industries.

Varnish. Copp er wire with a baked-on

varnish insulation is used extensively for

motor windings. The high quality of the

insulating varnish me ans that the

insulation can be very thin, allowing

spa ce for the m any windings req uired.

This type of insulation has a

tem pe rat ur e rating in exce ss of 200°C. Its

abbreviation is V.

Glass over Thermoplastic.

Conductors

supplying recessed fixtures require a

heat-resistant insulation because there

is little, if any, air circu lation to cool the

conductors .

GTF

(glass an d

thermoplastic for fixtures) is used for

this purpose.

Cross Link. This ma terial is

thermo-setting

and will no t m elt. It ha s a

higher tempe rature rating than TW and

is now widely used for building wire.

Ampac i ty

The p urpo se of a con duc tor is to ca rry

cur rent from on e place in a circuit t o

another.

Ampacity

refers to the ability of

a conductor to carry current. (See

Tables 5.5 and 5.6)

The am pacity rate of a con duc tor is

determined by its material, size, and

insulation.

M aterial. The material of which the

cond uctor is made determines how

easily it will carry cur rent. For exam pl

copper is a better condu ctor than

aluminum and will therefore carry mo

current.

Size. The larger the condu ctor, the

m ore curre nt it will carry without

heating. Since conductors are often

enclose d in cond uits and b oxes, take

care to use co ndu ctors of large enoug

size and to prov ide sufficient sp ac e fo

air c irculation. By doing so , you will

avoid conductor overheating and thus

prevent da ma ge to the insulation.

Insulation. A

conductor with

insulation cap able of withstanding he

will have a higher ampacity rating tha

con du ctor of the sam e size with a low

insulator tem perature-rating. W ires w

heat-resistant covering

can b e co ntain

in a more confined area than normal

cond uctors, without heat damage to t

insulation.

The voltage of the circuit will also

affect th e cho ice of insulator. The con

ductors must be insulated from each

other as well as from ground, and the

insulation must be capable of withsta

ing th e electrical pr ess ure of the circu

Under high-current con ditions, the

cur rent flows mainly along the surface

the conductor. This is known as the s

effect, and steel-core conductors can

used in such situations to combine

strength and ampacity, because the

outer section of the conductor carries

the bulk of the current.

Conductors must be handled care

fully to prevent surface nicks and

scr atc he s. The condu ctor will heat at

the point of a surface nick, because th

nick will have reduc ed the cross-sec

tional area. If th e nick is de ep enou gh,

60




TABLE 5.5 Allowable Ampacities for Not More Than 3 Copper Conductors

in a Raceway or Cable

1 Based on A mbient T emperature of 30°C

Allowable Ampacity

Size

AWG

MC M

Col.1

14

12

10

8

6

4

3

2

1

0

0 0

000

0 000

250

300

350

400

500

6 00

700

750

800

900

1 000

1250

1

500

1

750

2

000

60°C

TypeTW

Col.

2

15

2 0

30

4 0

55

70

8 0

100

110

125

145

165

195

215

240

26 0

280

320

3 5 5

385

400

410

435

455

4 9 5

520

545

560

75°C

Types

RW-75,

TW-75

Col.

3

15

2 0

3 0

4 5

6 5

8 5

100

115

130

150

175

200

230

255

285

310

335

380

4 2 0

46 0

475

490

520

545

590

6 25

6 50

665

8 5 - 9 0 C

Types

R-90,

RW-90,

T-90 Nylon,

Mineral-

insulated

cable.

Paper

Col.

4

15

2 0

30

4 5

6 5

8 5

105

120

140

155

185

2 1 0

235

26 5

295

325

345

395

4 5 5

4 9 0

500

515

555

585

6 45

700

735

775

110°C

Col.

5

3 0

3 5

4 5

6 0

8 0

105

120

135

160

190

215

245

275

3 1 5

345

390

4 2 0

4 7 0

5 2 5

56 0

580

6 00

—

6 80

—

785

—

840

125°C

Col.

6

3 0

4 0

50

65

8 5

115

130

145

170

200

240

26 5

3 1 0

3 3 5

380

4 2 0

4 5 0

500

545

6 00

6 2 0

6 40

—

730

—

—

—

—

200°C

Col.

7

3 0

4 0

5 5

7 0

9 5

120

145

165

190

225

250

285

340

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

W information of condit ions that may change the values in

.table, see the corresponding table in the Canadian Electrical

Based on Canadian Electrical Cod

Conductors

6



•Ere

may be

serious heat damage

to the

•rounding insulation.

Electrical Resistance

Barrent does

not

flow through

a

conduc

tor by itself. Electrical pre ssu re (volt

age) must

be

applied

to

force

the

current

n g the conductor. There is always

form

of

resistance

to

cur ren t flow

the conductor. This resistan ce

is

sured

in

ohms.

Resistance

is

determined by

the con-

tor's diameter, length, tem peratu re,

i material.

The

smaller

the

diameter,

1

longer the length, and the higher the

anperature,

the

greater

the

resistance

b f l b e .

Resistance

has

little,

if

any, effect

on

lectrical performance

in the

average

sidential

circuit. In

tall

buildings,

•pawling industrial com plexes,

or

street lighting, wh ere cond ucto rs must

fravel long distan ces , however, resist

ance is an important factor. Considera

ble voltage

may be

lost

in

delivering

the

|narrent

to the end of the

circuit.

The

result is dimming lights

and

less efficient

dectrical m otors. Voltage drop

is

reduced by increasing

the

diameter

of

Ibe wire used

in the

circuit. Tables

5.3

and 5.4 provide a comparison of the vari

ous resistances

for

solid

and

stranded

wires.

F o r R e v i e w

1. What two m aterials are most com

monly used

for

electrical conduc

tors? Why?

2. Define oxidation,

and

describe

its

effect

on

metal conductors.

3. Describe

the

process

for

produc

ing wire.

4.

Why are

cables

and

cords made

from many strands

of

wire?

5. What is the name of the gauge

used

to

measure solid co nduc

tors? W hat sizes of wire can this

gauge measure?

6. What m ethod

is

used

to

measure

the size

of

large cables?

7. A cable consists

of

19 stra nd s.

Each strand has a metric diameter

of 2.388 mm . What

is the

gauge

number of the cable?

8. A cable cons ists

of

37 stran ds,

each having a diameter of 80.8 mil

What

is the

gauge numb er

of the

individual strand? Calculate

the

nominal size

of the

cable

itself.

9. List five

or

more m aterials com

monly used

for

insulating condu c

tors.

10. Define ampacity, and list and

explain

the

factors that affect

it.

11. Why should circuit voltage be con

sidered when selecting

a

conduc

tor?

12. Explain why cu ts

or

other damage

to conductors should

be

avoided

during installation.

13. List

and

explain

the

factors tha t de

termine

a

conductor 's resistance.

14.

What

is the

effect

of

conductor

resistance on circuit voltage? Give

examples.

15. Calculate the resistance of 152 m

of

N o.

14 AWG solid bare co pper

wire.

Conductors 6



A

ny electrical device that is designed

to rec eive its electrical supp ly from

a receptacle will be fitted with a line

cord. Cord fittings attached to the line

cord are used as a convenient m ethod

for connecting the d evice to the power

source.

Male and Female Plug Caps

Th ere are two m ain type s of cord fit

tings, or plug caps: male and female.

Both are produced with the same blade

shap es, as described in Chapter

4.

(See

Fig. 4.2)

The

male

plug cap is designed to be

inserted in to the slots of a receptacle.

(See Fig. 6.1) It is usually a tta ch ed to the

end of line cord s on elec trical appli

ances, lamps, and pow er tools.

U

o

•a

E

to

Cord

Fittings

FIGURE 6.2

body)

Female plug cap (connector

FIGURE

6.1

Ma le plug cap

The

female

plug cap is designed to

receive th e m ale plug cap. (See Fig. 6.2)

It

is attac hed to one end of an extension

cord, which has a male plug cap on the

other end. Usually, both have the same

blade shape.

Uses for Heavy-Duty Cord

Caps

Mobile hom es (trailers), electric stov es

and clothes drie rs require heavy-duty

cord caps for their power supply. In

industry, cord fittings with current and

voltage ratings other than the usual

10

to 15 A, 120 V residential ratings are

often required. Some examples are cord

ca ps for welding ma chin es, floor finishe

battery chargers, and marine shore line

64




g Cap C onnection

Plug caps are often damaged by care

lessness. For example, many people

emove plugs from rece ptac les by tug-

0og on co rds . Figure 6.3 show s how line

sords

and plug caps are connected so

hat

the strain from pulling on the c ord

•til

be absorbed by the blades rather

ban by the ter min als. To preve nt loose

strands of the flexible cord from slipping

out of the terminal connection, the

strands are twisted together and then

sound clockwise around the terminal

screw. Soldering the g rou ps of twisted

strands before assem bly also helps

Bake the electrical connection secure.

3

Wi r e "U" Gr ound

Plug Cap

DTE Solder all

randed

wire and

•>d clockwise

ound

terminals.

neutral wire

(white)

silver

termina

ground wire (green)

green terminal

ve

wire

(black)

brass terminal

K3URE6.3

:ap

Me thod for connecting cord to

An

underwriter's

knot used to be tied

n the cord to prevent t he cord from being

pulled out of the cord cap . But stre ss

• as

placed on the cord's insulation. As a

result, a knot is seldom used with m od

em plug cap s in which conducto r space

is

limited. Instead, ind ustrial or heavy-

duty plug caps are now equipped with

metal

or plastic

clamping devices

to hold

the co rds in th e plug c ap s. (See Fig. 6.4)

These devices are particularly useful on

construction sites , where extension

x>rds and cap s are w alked on, driven

over, and trea ted roughly.

cord c lamp

plug cap

cord

pr ongs

FIGURE 6.4 Industrial (heavy-duty) plug cap

equipped w ith cord clamp

Dead-Front Plug Caps

To promote the personal safety of porta

ble equipmen t users , th e Canadian Elec

trical Code now requires that all new

plug caps be of

dead-front

construction.

A dead-front plug cap h as pron gs and

terminals assembled as a removable

unit. (See Figs. 6.5, 6.6, and 6.7) The co rd

con nects to the rear of the unit. The

front, w hich is the expose d portion of

the plug cap , is free of term inals, con

ductors, and insulating disc.

The dead-front plug cap represents a

significant improvement over the many

older, plug cap m ode ls it is being used to

replace. On older models, the insulating

disc

of the m ale plug cap fits se par ately

over the prongs where the cord has

been connected. The disc's purpose is to

Cord Fittings

6



FIGURE 6.5 L ight-duty, dead-front plug cap

in the

" U "

ground configuration, black neo-

prene body

preven t loose stran ds or termina ls from

coming in contac t with the cover plate

the receptacle. But if the cover plate is

made of metal and no insulating disc is

prese nt, a short-circuit flash can occ ur

as the plug is inserted in to the recepta

cle. The hand of the person plugging in

the cap may be burned .

The safer dead-front plug caps are

pro du ced in all cord c ap configuration

and in both residential and industrial

grades.

Room y wi r ing c ham ber pr o

v ides ample space for wir ing .

Ribbed nylon housing of fers

secure, non-slip hand

ho ld.

W ir ing entrance holes are

angled to permit "s t raight

conductor insert ion.

Broad gr ipping area accommo

dates wide range of cable

diameters.

Grip is an integral part of

mo ulded device. Jaws of fset

cable slight ly to prevent slip

page of inner wires.

Dead front

el iminates need

Each indiv idual wir ing

|

insula t ing disc,

terminal is

completely

enclosed in its own

separate cham ber. C lear polyca rbona te perm

visual inspect ion of termi

af ter wir ing.

FIGURE 6.6 Internal construction of a heavy-duty, dead-front cord cap show ing cord and

terminal connections

66




• p l i a n c e

P lug Caps

Jl

portable appliances, such as tea-

ttles,

frying pans, and percolators, are

i

made with removable cord sets.

e sets have plugs that are easy to

provide strain relief for the cord,

I resist heat. Figures 6.8 and 6.9 show

a

appliance plug and its cord co nnec-

ttons.

s

Bakelite

body

BGURE 6.8 A ppliance plug

spr ing

Some large stationary appliances,

such a s electric stoves and clothes

driers ,

are now being made with cord

sets . This allows larger units to be pulle

away from the wall for cleaning and

quickly disconnected from the power

sou rce for servicing . Figures 6.10 an d

6.11

show typical cord and c ap se ts for

use with large appliances.

FIGURE 6.10

plug cap

Typical 50 A range cord and

C UR E 6.9 A ppliance plug cord connection

FIGURE 6.11 Typical drier cord and plug ca

with a 30 A rating available in kit form

Cord Fittings

6



Electrical Ratings

Plug caps a re rated in volts and

am pere s. The rat ings of th e unit must be

matched to the requirements of the cir

cuit. If a light-duty un it is installed w here

a heavy-duty unit is necessary , the plug

will ove rheat. This can c ause dam age to

th e plug and /or recep tacle and the con

du cto r insulation. Look for th e CSA

stam p on the plug cap ; this is a guaran

tee that the manufacturer 's ratings are

correct.

Grounded Cord Caps

As explained in Chapter 4, there is a

need for a ground prong on a male plug

cap and a correspo ndin g slot in the

ma tching female plug cap. These units

are placed on any tool or device th at

could deliver a shock to the operator if

th e device is used in an area where th e

operator could become grounded.

Faulty equ ipme nt often allows cu rrent to

flow to th e b ody o r frame of the tool,

then through the ope rator into the

ground. This prod uces a serious electr i

cal shock. The ground p rong and g round

wire can carry this stray or leakage cur

rent into the ground ra the r than have it

go through the operator. This can pre

vent electrical shock to the operator.

Figure 6.12 illustra tes male plug c ap s

with their rugged U-shaped ground

prongs, recommended for all portable

tools and equipme nt.

T wist-L ock C aps

Cords and conn ecto rs are often used in

high traffic are as. Movement by p erso ns

walking past c ord s or mov eme nt of

plugged-in equipmen t can cause cord

caps to accidentally fall out. To prevent

such inconveniences, a type of cord cap

tha t requ ires twisting to lock th e cap in

place after insertion has been produced

Such twist-lock caps are used quite fre

quently in industry and business. They

are available in many voltage and cur

ren t ran ge s, eac h with a slightly differen

blad e configuration. A typical 3 prong,

125 V, 15 A cord cap can be seen in

Figure 6.13.

FIGURES

6.12A

A N D B

Male plug

caps

w ith ground prong in dead-front plug design

FIGURE 6.13 T wist-lock, 125 V, 15 A cord

cap

68




>spital Grade C ord C aps

pital grade cord cap s are designed to

the most demanding needs of hos-

and health care facilities. Their

n bodies resist imp act, grea se, oil,

abrasion and ultraviolet radiation,

the cord grip action reduces strain

ring terminals and helps prevent

ightening of assem bly screw s.

-coded faces are clearly marked

amp erage and voltage ratings

—blue, 20 A— red), and individual

nnelled wire wells acc ept up to

) AWG con du cto rs. Figure 6.14

ates hospital grade caps and

tors .

F o r R e v i e w

1. Describe th e two m ain types of

cord fittings.

2. List five common cord cap blade

shapes.

3.

What may happen if a plug is

removed from a receptacle by pul

ling on the cord?

4. Why are the co ndu ctors taken

around the blade of the plug cap

before securing them to the termi

nal screw?

5. What is the purpose of soldering

the cord strands before winding

them around the terminal screw?

6. Why are heavy-duty plug caps

equippe d w ith clamping dev ices

for the co rds?

7. Describe the insulating disc, and

explain its purpose.

8. What is the p urpo se of th e dead -

front plug cap?

9. List two rea son s why large appli

ance s are being fitted with cord

sets.

10.

List the electrical ratings that

must be marked on plug caps.

JRE6.14 Hosp ital grade nylon plugs

I connectors

Cord Fittings

6



M

ode rn wiring system s require an

electrical outlet box at each point

in th e circuit whe re a switch, lamp-

holder, rece ptacle, or splice is loca ted.

Section

12

of the C anadian Electrical

Code provide s an up-to-date sum ma ry of

installation procedures.

Most electrical boxe s are mad e

of

galvanized or cadmium -plated steel.

Nonmetallic wiring systems may use

boxes m ade of

Bakelite.

This heat-resist

ant material cannot be used for metallic

wiring syste m s be ca us e it is quite fragile

and n ot able to withstand th e strain of

metal box connectors.

W here there is mu ch m oisture, boxes

may be m ade of

brass

or

everdur.

These

nonrusting, high-corrosion-resistant

ma terials prevent box damage from

chemicals or moisture in the surround

ing air.

There are several types of boxes for

various uses: the octagon, pancake,

square, sectional plaster, utility, and con

crete-masonry-tile.

Octagon Box

This typ e of box usually supports light

fixtures or serves as

a junction

point for

wire splice s. It can also be use d with

special covers as a supp orting box for a

switch or receptacle.

Electrical

Outlet

Boxes

Dimensions. Octagon boxes are

available in two diam eters. The 10 cm

diameter box is the most common.

Boxes with d iam eters from 8 cm to 9 c

are available for applications where th

box size is limited . (See Fig. 7.1)

10 c

w id e

x 4

dee

FIGURE 7.1 T ypical octagon box

FIGURE 7.2 O ctagon box extensions

70




Note: Check the Canadian Electrical

Code requ irem ents for your area .

Another important box dimension is

depth. This measurement determines

tbe amount of conductor space within

the box. The m ost comm on d epth is

4 cm.

A

box 5.5 cm in de pt h is available

br installation where m ore con duc tor

space is required.

Box extensions are designed to

mo unt directly on th e to p of an ex isting

octago n box. They are simply octag on

boxes without bottom s to provide an

increase in con ducto r spac e when

required. (See Fig. 7.2)

Covers. The re are many type s of

octagon box cove rs, allowing the box to

ser ve many pu rp os es . (See Fig. 7.3) Box

cov ers and extension boxes are fastened

with two

No.

8-32 round-head machine

screw s, which are provided with eac h

box.

Octagon Concrete R ings. Th ese rings

are used in buildings wh ere the bo xes

and wiring system are installed before

th e c on cre te is poure d. (See Fig. 7.4)

They are available in d ep ths of 4 cm t o

15 cm. There can be a cover on either

end of th e ring. Figure 7.5 show s a

con crete ring installation.

FIGURE 7.4 Typical 10 cm octagon con

crete ring (C over screw may be wax-pro

tected.)

CURE 7.3 O ctagon box covers

Knockouts.

Knocko uts, or

KOs,

are

removable and provide for the entrance

of wire, cable, or conduit to the box.

Described in App endix

G

of th e

Canadian E lectrical Code, they are m ade

in comm on trad e sizes, for examp le,

13 mm, 20 mm , or 25 mm. A 13 mm

knockout is designed to accept a condui

with an internal diam eter of 13 mm . The

Electrical Outlet Boxes

7



concrete r ing box cover locknut

#8-32 machine screw

conduit poured

conductors concrete

FIGURE 7.5 Concrete ring ceiling installation

45 cm offset hanger

bar

box with

mounting bracket

FIGURE 7.6 Mounting bracket and hanger bars

D o 6 6

o

o

45

cm

straight hanger

bar

actual diameter of the knockout is

approximately 22 mm.

Methods of Mounting.

Octagon boxes

can be used with either a surface or

a

concealed wiring system . There are

screw ho les in the bottom of th e box for

fastening the box on the surface of a wall

or ceiling. Concealed wiring m ethods

allow for severa l mounting techn iques.

Figure 7.6 shows the mounting-bracket

and hanger-bar assem blies. Figure 7.7

shows three ways of supporting the

boxes.

Pancake

Box

This 10 cm round box is used primarily

with an ou tdoor porch light. (See

Fig. 7.8) Its 1.3 cm depth allows a fixtu

to be mounted over it without the box

being seen. Also, when a fixture must b

installed on a finished wall, the use

of

a

pancake box eliminates the need to

make a hole in the wall. (See

Fig.

7.9)

Conductor spac e in the box is limited t

two wires, and access is through

knockouts in the back of the box.

Square Box

The square box is used primarily as

a

junction

box for surface and concealed

wiring system s. (See Fig. 7.10) There ar

special covers that perm it this box to

support switches, receptacles, and pilo

lights. (See Figs. 7.11 and 7.12)

72




45 cm offset hanger bar

knockout

plaster

knockout

plaster

~

i

outlet box on 2 cm

thick wood strip

v x

:• > \ w

-£zZ>

.jH >V\'.iW\

knockout plaster

nails

CURE 7.7 Me thod s for suppo rting

Bagon boxes

BGURE 7.8 Typical 10 cm round pancake


l ight

f ixture morta

jo int

f ixture bracket

p lug

and scre

pancake box

FIGURE 7. 9

Installation of a fixture on a

pancake box

FIGURE 7. 10

S quare boxes

Dimensions. Square boxes are ma de i

two sizes. The

10

cm width is the m ost

common. A box 12 cm w ide is also

available.

The standard square box depth is

4 cm.

A

box 5.5 cm in d ep th is also avail

able.

When extra conductor space is

needed, extension rings ma de for t he

squ are box are used . Box cove rs and

extension rings are fastened with two

No.

8-32 round-head machine screws.

Knockouts in a combination of

13

mm,

20 mm, and 25 mm sizes are available.

Figure 7.13 show s an e xtension box.

7




luires

that th e front of the box b e

h with the surface of walls finished in

lbustible

materials, such as wood

Belling. (This is a precautio n to pre-

a flash fire in the box from spread -

[to the surrounding m aterial.) The

:

may be reces sed up to 6 mm in walls

[plaster or m asonry.

Construction.

Most sectiona l plaster

nxes are ma de of galvanized steel,

kelite,

or phenolic, boxes are available

use with nonmetallic wiring system s.

The sides of the metal boxes are eas-

removed for

grouping,

or ganging

ler,

a series of b oxe s. (See

7.15) This feature allows an installer

mt

quickly assem ble a box capa ble of

••pporting any num ber of switche s or

eceptacles. Sectional boxes m ade by

e man ufacturer may not link up with

hose mad e by another. When assem -

fcg

a gang unit, therefore, take care t o

elect boxes of the sam e type.

• • t e n s i o n s . The stand ard sectional

i

is 5 cm w ide and 7.5 cm in heigh t.

i de pth of the box varies with th e

nt of cond uctor spa ce

required,

stand ard dep th is 6.5 cm. Units

7.5 cm, 5 cm, and 4 cm in dep th are also

available.

Co vers. Covers for this box are m ade

primarily for switches or receptacles. A

blank

co ver is used w hen th e box is to

serve as a junction point for splices

in the w ires.

Plaster

boxes have two

No.

6-32 thread ed mou nting lugs

space d 8 cm apa rt, which accep t any

manufacturer's switch or receptacle.

The covers are usually fastened to the

switch or recep tacle with

N o.

6-32

machine screws. (See Fig. 7.16)

FIGURE 7.16 S ectional plaster box covers

O

Ml ' lt§l

o

IRE 7.15

Sectional plaster boxes for ganging


7



Gang cove rs are used for m ultiple

switch or receptacle units mo unted in

grouped boxe s. Sectional boxes a re

som etime s used to enclose pilot lights,

which indicate wh en a piece of electrical

equipm ent is operating. Covers for this

pu rpo se are also available.

Bakelite, or phe nolic, is usually used

in the m anufacture of cove rs.

It

is a good

insulator, heat-resistant, easily moulded,

and generally low in cost, making it ideal

for th e pu rpo se. B rass, aluminum, stain

less steel, and galvanized steel covers

are produced w here a stronger or m ore

decorative cover is needed.

Method s of M ounting.

Sectional

plaster boxes can be suppo rted in

severa l way s. Figure

7.17

show s a group

of boxes equipp ed with m ounting

bra ck ets. Figure 7.18 shows ho w single

or ganged units can be supported.

W hen a bo x mu st b e installed in a fin

ished wall, a special purpose unit can be

used . This sectional box is equipp ed

with an expanding bracke t that will pa ss

throu gh a pre-cut hole in the wall,

expand , and grip the plaster when a ten

sion bolt is tightened. The cab le mu st be

fastened securely to the box before the

box is inserted into the ho le. Once the

bracket has expanded, it cannot be

rem ove d easily. (See Fig. 7.19, page 78.)

A second me thod of mounting sec

tional boxes in existing walls depends on

the use of the recently developed swing

arm.

After c utting a hole in th e wall to .

accep t th e new box, the installer con

nects the cable to a built-in cable clamp

in the usual m anner and inserts the box

into plac e in th e wall.

Plaster ears

pre

vent the box from falling through the

hole, while adjustm ent of a spec ial screw

brings th e swing arm into a holding posi

tion on th e inside of the

wall.

Further

use of the special screw tighten s the

o

0

\ °

•*•

0

O

slfcP

J o

IISII

RT^s^,

0

0 °

c0°

FIGURE 7.17 S ectional plaster boxes wit

mounting brackets

76

Applications ol Electrical Construction



Na i l Mo u n t in g

Scre w Mo u n t in g

Side Bracket Mounting

H

Gang Mount ing

plaster

box

wood screws

5cmx

10 cm

stud

2 cm w o o d s t r ip

CURE 7.18 Methods for mounting sectional plaster boxes

ing arm for secure holding

of

the box

the wall. (See Fig. 7.20)

•teel S tud A ppl icat ions

tment

buildings, office complexes,

othe r comm ercial buildings

fre-

ently

contain parti t ions constructed

lith steel studding rather than the tradi

tional wooden uprigh ts. Special boxes

have been designed for u se in these

areas. (See Fig. 7.21)

S ectional Box A ccessories

Renovations

to

existing buildings often

require the resurfacing of walls and par

tition s. When new dry wall or similar


77



plaster

ear

expanding

bracket

expanding bracket

sect ional

plaster

box

t ens ion

bolt

precut

opening

plaster

ear

lath and

plaster

FIGURE 7.19 Me thod for mo unting a sectional plaster box in a finished wall

s wing

arm

1/2 in .

(13

m m )

knockout

cable

entries

(2 each end)

wall panel

t igh t en ing

screw

cutou

templates

suppl ied

in each

carton fo

m a x i m u m

bear ing

surface

adjustable

for 1/8 in

(4 mm

to 3/4 in

(19 mm

dr y wal

t ightening

screw

yy CERTIFrEO „

FIGURES

7.20A

A N D B A swing-arm box designed for use in existing walls

78

Applicat ions of Electr ical Construct ion



I

the wrap-a-round box at

3

height and hold f lat

•ne steel stud.

Fold both ends of the wrap -a

round bracket around the stud

flanges.

Fold the wrap-a -round bracket into

the steel stud using your f ingers.

No special tools required.

u

-

-"

a

-

-

~

y

—

z

-

•

-

t

0

u

-

3

The wrap-around bracket and the

steel stud f langes should be

cr impe d together w ith

pliers to secure the box in

posit ion.

Improv e the insta l la t ion by adding

screws to the fron t and rear

f langes.

GURE 7.21 S tep-by-step mounting procedure for mounting steel stud boxes

aterial is added to the surface of a wall,

le

existing boxes are automatically

scessed, making conne ctions with new

evices, such as switches and recepta-

les.

awkw ard. A box exten sion th at fits

a

the front of th e previous ly installed

OK

is now available. This extension pro-

Ides the required m etal barrier

etween

the wall material and the con

du cto rs. It also provides a secure mo unt

for new switches or other devices. (See

Fig. 7.22)

Current regulations in the hom e insu

lation field require the installation of

som e form of vap our ba rrier around out

let boxes when they are m ounted on out

side walls. A fast, convenient way of pro

viding this vapour barrier is to ch oo se


7



new wal l sur face

old wall surface

S B EX

new

wall ••

surface

old wal l

surface

switch box switch bo

/'/' "i &

* " " s B E x " "

FIGURE 7.22 Installation of SBEX switch box extension wh en resurfacing old walls in existi

buildings

som ething from th e new line of tran spa r

ent, tough, resistant plastic pro duc ts

tha t will stan d u p to extrem e cold. The

plastic is moulded into single and 2 gang

box sh ap es . The larger, 2 gang units can

also be used to en close squa re or octa

gon b oxe s in the 4 in. (10 cm ) size. (See

Fig. 7.23)

Utility Boxes

This versatile box is used to support

receptacles, switches, and pilot lights in

surface wiring sys tem s. Its roun ded

corners and smooth exterior design

make it an ideal unit for surface wiring

system s with cable or condu it.

Construction. The utility box is

usually m ade of galvanized or

cadmium-plated steel. (See Fig. 7.24)

Dimensions. Standard utility box

widths vary between 5.5 cm to 6 cm

80

depen ding on the manufacturer. T he

length of the box is a stan dard 10 cm.

The d epth is usually 4 cm. A unit 5 cm

depth is available.

Covers.

Utility box cov ers are usual

ma de of plated steel. Bakelite cove rs

should not be used because the sharp

corn ers break easily whe n used with

surface wiring materials.

Most utility box cov ers a re m ade f

recep tacles and sw itches. However, p

light and blank co vers are also availab

(See Fig. 7.25)

M ethods of M ounting. There are

several units with mounting b racke ts

attached. (See Fig. 7.26) Holes are

provide d in th e back of the box for b o

or screws when the box is mounted

directly on a surface. The devices are

fastened to the box with No. 6-32

machine screws.

App lications of Electrical C onstruction



r use with any

anx 7.5 cm

I • := box up to

For use with all two

gang device boxes

up to 7.5 cm and 10 cm

square or octagonal

boxes in either shallow

or deep configurations

Installat ion Procedure

1. Remov e the necessary pry-ou ts fro m the

metal box. Place the metal box inside the

vapour barrier. Adjust the front of the metal

box at the required distance for f lush

mo u n t in g w i th d ryw a l l .

2.

A t tach the metal box with i ts vapour

barr ier to a stud with nai ls or screws.

3. P uncture the box 's vapour barrier wi th a

square head screwdriver where the pry-

outs have been removed. Push the cable

(nonmctailic sheathed cable) through the

hole in the vapour barr ier. T hen, fo l lo w

usual wir ing procedures.

a) Unskinned cable will penetrate a box's

vapour barrier and metallic device boxes

easier than skinned cable. Cable can be

skinned after entered in the box and

pulled back to its proper length.

b) Insulation paper mus t be placed behind

the f lange of the vapour barrier so that

the front surface of the f lange will seal

effectively.

BGURE 7.23 P reshaped, plastic vapour barriers provide adequate protec tion from m oisture

:o pass through an outlet box.

5.5 cm to 6 cm

wide

10 cm long

4 cm to 5 c m

deep

I

• C U R E 7.24 Typical utility box and extension FIGURE 7.25 Utility box covers


81



I

a m

r^®

9>j

f

FIGURE 7.26 Utility boxes w ith mo unting

brackets

Concrete-Masonry-Ti le

Boxes

Industrial and commercial buildings

made with poured concrete or other

ma sonry m aterials require a box that

can be set directly into the material

during

construction. These boxes are

intended to be used with concealed

metallic

w iring sy ste m s. (See Fig. 7.27)

Construction. Concrete-masonry-tile

boxes are usually made of galvanized

steel.

Dimensions. A single-gang unit is 5 cm

wide and 9.5 cm in height.

It

is also

available in a multi-switch unit c apa ble

of supporting five switches or

receptacles.

Covers.

Covers are m ade for single or

group installation of switches,

receptacles, and pilot lights, or

combinations of all three.

M ethods of M ounting. These boxes

are held in place by the co ncre te o r

m ortar of the m asonry wall . When t he

© er c? cr

<s>"

o <=»

ooQoo ooQoo

o°o o°o

o"p'P p P £>

FIGURE 7.27 C oncrete-masonry-tile box

building is made with poured conc ret

walls and floors, the boxes may be w

into position to hold them securely

while th e conc rete is being po ured.

Electrical boxes provide access for co

du ctor s in two ways. The removable

disc,

called th e knockout, allows con

and/or cable connectors in trade size

13 mm, 20 mm, and 25 mm internal di

eter to be fitted to the box.

Boxes designed for use with nonm

tallic or armoured-ca ble syste m s are

available w ith

built-in clamps.

These

cable clam ps eliminate the need for s>

arate connecting de vices and also

sho rten th e time required for this

ope

tion.

The rem ovable disc designed for

boxes equ ipped w ith cable clamps is

called the

pry-out.

A ppendix G of the

Canadian Electrical Code describ es t

82




knockout pry-out

Standard sizes are

13 m m 20 m m 25 m m

JRE

7.28 Typical knoc kout and pry-out

pry-out as "a knockout provided with a

slot in order that a screwdriver may be

inserted to pry out the knockout." (See

Fig. 7.28)

Th ere are se veral t ype s of built-in

box c on ne ctor s. (See Fig. 7.29) Built-in

cable cla m ps are usually found in octa

gon and sectional

plaster

bo xes. (See

Fig. 7.30)

standard

nonmetallic

sheath connector

o]

SI

©0

0

©

3 X

J

o

l O o

<

Q O

nonmetal l ic

sheath connector

(for use wi th 10 cm octago n

box with 4 cm depth only)

ar m our ed

cable connector

FIGURE 7.29 C able clamps

FIGURE 7.30 Boxes with built-in cable

clamps


83



Box Grounding

A

mod ern electrical wiring box prov ides

one or two m achine screws in the back

of the box for grounding p urp ose s. A

nonmetallic cable system has a bare

ground w ire within the c able. The

ground wire mu st be conn ected to one

of the screw s provided in the box. A

receptacle should have a conductor join

ing its ground terminal with the ground

screw in the box .

A metallic wiring system norm ally

relies on a secure metal-to-metal connec

tion with the b ox to com plete its ground

circuit.

Conductor Capacity of a

Box

The number of current-carrying conduc

tors contained in a box must be limited.

When too many conduc tors are con

tained in a box, the c on duc tors might be

forced into a sha rp edg e or m ounting

screw within the box. The sh arp edge

might penetrate the insulation on the

conductor, allowing the current to take

oth er than its intend ed path. If th e dam

aged c on du cto r is a live wire, a short-cir

cuit condition will occur and the circuit

fuse will blow. If for some reason the box

is not grounded, th e box and any metal

object in contact with it will become

alive and dangerous.

A seco nd, and equally im portan t,

reason for limiting the number of con

du cto rs in a box is overheating. Any con

ductor carrying current will produce

some heat as a side effect. The more cur

rent passing through the conductor, the

more he at will be pro du ced . The mo re

cond uctors there are in a box, the more

heat will be accum ulated within the box.

Once the cov er is placed on th e box,

the re is little or no a ir circulation to cool

the conductors. Modern conductor ins

lation is designed to withstand som e

heat, but it will become hard and brittl

if ov erhe ated for an extend ed period of

time.

Each size of cond ucto r req uires a

certain amount of free air space for co

ing. Th e C anadian E lectrical Code lists

the volume of air spa ce requ ired by

some of the common c ondu ctor s izes.

(See Table 7.1)

TA BLE 7.1 Space for C onductors in

Boxes

S ize of

C onductor

A W G

Copper or

A l u m i n u m

14

12

10

8

6

Usab le S pace W i th i n

Box

for

Each

Insu l a ted C onductor

Cubic

C ent i metres

2 5

29

37

4 5

7 4

Cubic

Inches

1.5

1.75

2.25

2.75

4.5

Based on the Canadian Electrical Code

The Canadian Electrical Code also

lists the air sp ac e available in stan da rd

electrical bo xes . (See Table 7.2) Mathe

matical calcu lation of the volu me of a

box (length x width x dep th) will not

give the s am e results a s listed in

Table 7.2. Because of the differences in

toleran ce du ring man ufacture of boxes

the E lectrical Code C omm ittee decided

on stand ard capa cities. Th e actual inte

nal dime nsions of a sectional plaster

box, for exa mp le, are slightly smaller

than th ose listed in catalogu es and

tables.

Calculation of Box C apaci

Table 7.2 lists a dev ice box 75 mm x

50 mm x 65 mm as hav ing 205 cm

3

of a

84




Box

Dimensions

Trade Size

O c t agon

.are

r

- . - d

Mas onry Box

T A B L E 7 . 2

Mi l l imetres

100x40

1 0 0 x 5 5

1 0 0 x 4 0

1 0 0 x 5 5

1 2 0 x 4 0

120x55

100x13

75 x 50 x 40

75 x 50 x 50

75 x 50 x 55

75 x 50 x 65

75 x 50 x 75

100 x 50 x 40

1 0 0 x 5 5 x 4 0

1 0 0 x 5 5 x 4 5

1 0 0 x 5 5 x 4 8

1 0 0 x 6 0 x 4 8

95 x 50 x 65

95 x 50 x 90

100 x 55 x 60

1 0 0 x 5 5 x 8 5

N u m b e r o f C o n d u c t o r s

Cubic

C e n t i m e t r e

Capaci ty

C opper or

A l u m i n u m

245

3 4 5

345

4 9 0

490

6 9 0

82

130

165

165

205

245

145

165

2 4 5

2 3 0

2 6 0

230/gang

3 4 5 / g a n g

3 3 0 / g a n g

3 6 5 / g a n g

14

10

14

14

2 0

2 0

2 8

3

5

6

6

8

10

6

6

10

9

10

9

14

13

14

n Boxes

M a x i m u m N u m b e r o f

Ins u la ted C onduc t ors

Size in AWG

12

8

12

12

17

17

2 4

2

4

5

5

7

8

5

5

8

8

9

8

12

11

12

10

6

9

9

13

13

18

2

3

4

4

5

6

4

4

6

6

7

6

9

9

9

8

5

7

7

10

10

15

1

2

3

3

4

5

3

3

5

5

5

5

7

7

8

6

3

4

4

6

6

9

1

1

2

2

2

3

2

2

3

3

3

3

4

4

4

rings to have the same value as the eq uivalent trade size box

the Canadian Electrical Code

pace.

Table 7.1 lists a

No.

14 gauge con-

fcctor as requiring 25 cm

3

of air sp ac e,

therefore, the number of

No.

14 gauge

•ductors

allowed in this box will be :

=

8.2

ir sp ac e in the box 205

Air spa ce of 1 conductor " 25

f cours e, only 8 con du ctors can b e put

I

the box.

Clamps, receptac les, sw itches, or

?r devices inside the box take u p

ie

of the free air sp ac e. Section 12 of

| Canadian Electrical Code state s tha t

each

device in the box,

one

conduc-

• must be subtracted from th e tota l

listed (in Table 7.2). For exam ple, th e

device box listed as having a capacity of

6 condu ctors would be limited to 4 con

du cto rs, if it conta ined a switch an d

built-in ca ble c lam ps.


Code explains in detail how con duc tors

entering and/o r leaving a box must be

counted to determine the total number

of conductors allowed. Always use the

latest edition of the Code, which is

revised regularly.

Since th e C anadian Electrical Code

and much of the electrical industry

use imperial measu rem ents, imperial




TABLE 7 .3 Imper i a l D i m ens i on s and C onductor C apac i t i es fo r E l ec tr ica l W i r i ng Boxes

Box

Dimensions

Trade Size

O c t a g o n

S q u a r e

Round

Device

Masonry

Inches

4x172

4 x

27s

4 x 172

4 x27s

4"/ux1Vfe

4'7iex278

4x72

3 x 2 x 1 7 2

3 x 2 x 2

3 x 2 x 2 7 A

3 x 2

x

272

3 x 2 x 3

4 x 2 x 172

4 x 27s x 17

2

4x27sx1

3

/4

4 x 2 7 8 x 1

7 B

4 x 2

3

/ e x 1 7

8

3

3

/4 x 2 x 2 7

2

3

3

A x 2 x 3V

2

4 x 2 7 4 x 3 7

8

4 x 274 x 3 7

8

Cubic

Inch

Capacity

Copper or

Aluminum

15

21

2 1

3 0

3 0

42

5

8

10

10

12.5

15

9

10

15

14

16

14/gang

21 /gang

20.25 /gang

22.25 /gang

Maximum Number of

Insulated Conductors

Size in AWG

14

10

14

14

20

20

28

3

5

6

6

8

10

6

6

10

9

10

9

14

13

14

12

8

12

12

17

17

2 4

2

4

5

5

7

8

5

5

8

8

9

8

12

11

12

10

6

9

9

13

13

18

2

3

4

4

5

6

4

4

6

6

7

6

9

9

9

8

5

7

7

10

10

15

1

2

3

3

4

5

3

3

5

5

5

5

7

7

8

6

3

4

4

6

6

9

1

1

2

2

2

3

2

2

3

3

3

3

4

4

4

TABLE 7 .4

W i r i ng Boxes and The i r C onductor C apac it ies fo r Use on 347 V S ys tems

Dimensions in Inches

347 V Boxes

3x274x272

4 x 27a x 1 Ve

4 x 274 x 27a

4x274x37s

Cubic Inch

Capacity

15.7

16.5

20.25 /gang

22.25 /gang

Maximum Number of Conductors in

Boxes

Size in AWG

14

8

9

11

12

12

7

7

9

10

10

5

5

7

7

8

3

4

5

6

m easu rem ents are provided in Table 7.3.

This tab le lists electrical wiring b oxe s

and their cond uctor capacit ies .

The trend tow ard using 347 V sup

plies for lighting circuits has affected

electrical wiring box es. Switches an d

other related devices must be

somew

larger to safely handle the higher

volt-




TABLE 7.5 Wiring Boxes and Their Conductor Capacities for Use on 347 V Systems

Dimensions

in

Mi l l imet res

347 V Boxes

~: • 55x65

• 0 0 K 60 x 47

Dx 55x60

x 55

x 85

Cubic Cent imet re

Capaci ty

268

282

330

467

M a x i m u m N u m b e r

of

Conductors in Boxes

Size in A W G

14

8

9

11

12

12

7

7

9

10

10

5

5

7

7

8

3

4

5

6

s.

and therefore the boxes supporting

closing the se switches m ust

be

brged. By doing so, the required cool-

air sp ac e is provide d. Tables 7.4 and

1st these boxes and their conductor

opacit ies .

o

r

R e v i e w

t materials are used for the

construction of electrical boxes?

Where and why are brass boxes

•d ?

I type of box is used for

Indoor light fixtures?

the sizes in which o ctagon

boxes are made.

Explain how sw itches

or

recepta

cles are fastened to the octagon

box.

When are octagon concrete rings

•d ?

kliere and wh y are pancake boxes

sually used?

xplain where and for what pur-

oses square boxes are used.

low did the sectiona l plaster box

• its name?

10.

What

is a

gang box? What

is it

used for?

11. Explain where and how the sec

tional plaster box special purpose

unit is used.

12. Why

is

Bakelite

not

recommended

for utility box covers?

13.

W hich boxes are used

for

build

ings ma de of poured concrete an d

block?

14.

State two reaso ns for using bo xes

with built-in ca ble clam ps.

15. What is a pry-out? How do es it

differ from a knockout?

16. How are boxes grounded in a con

duit system ? How are they

grounded in a nonmetallic cable

system?

17. State two reaso ns

for

limiting th e

number of conductors in a box.

18. Explain how th e volume and

the

condu ctor capacity of a box are

calculated.

19.

Calculate the num ber of conduc

tors allowed in a 10 cm octagon

box, 4 cm in depth, to be used in a

circuit w ith No. 12 gauge wi res.

20.

If the o ctagon box describ ed in

review pro blem 19 contains two

built-in clamps and

a

fixture stud,

how many wires are allowed,

according to the Canadian Electri

cal Code?


87



N

onmetallic-sheathed

cable

(NMSC)

is used more often in residential

wiring installations than any other wir

ing method. The Canadian Electrical

Code perm its this cable to be installed in

a building made of comb ustible material

or of wooden frame construction. It may

not

be used in other types of building

construction without permission from

the electrical inspection a utho rities.

Cable Construction

There are several basic types of nonme

tallic-s hea thed cab le. (See Figs. 8.1, 8.2,

8.3,8.4,

and 8.5)

Nonmetallic

cable for

dry locations (NMD) is used in norm al

residential circuits. Nonmetallic cable

for wet locations

(NMW)

is used in farm

buildings or similar struc ture s, w here

the re is usually more mo isture. NMW

cable can be buried directly in the earth,

providing ad equ ate protec tion is given

to the cab le.

Trade N am es.

NMSC was first

produ ced by the Rom e Wire and Cable

Company, which named its new product

Romex. T his nam e is still used often in

the trade s. Each company producing

NMSC, however, has its own pro du ct

nam e ending in "ex", e.g., Canadex from

Canada Wire and Cable Limited and

Philex

from Phillips Cables Limited.

Nonmetalli

Sheathed

Cable

Wiring

Types of Insulation. NMD-3

cable

been used for several years for res

tial

wiring. The n um ber 3 indicates

maximum allowable tem pera ture of

cable : 60°C.

This cable is not suitable, howev

for use with modern light fixtures. H

from th e fixture b ulbs often drie s ou

cable, making the insulation brittle

of little value. NMD-90 and NMD-90

cables with temperature ratings of 9

have now replaced

NMD-3

cable. T

cables can a lso be used to sup ply e

tric heaters, stoves, and clothes dri

Conductor Materials.

NMSC is

produced with copper or aluminum

co nd uct ors. Since aluminum is not

good a con duc tor as copper, one w

size

larger

m ust be selected when

aluminum conductor nonmetallic-

sheathed cable.

Conductor

Sizes.

NMSC

with cop

conductors is available in gauge No

12,10, 8, 6, and 4. The sm allest gaug

aluminum conductor cable produce

how ever, is No. 12. Cable for both d

and w et use is available with two o r

three insulated conductors and a b

ground wire.

88




HJRE8.1 NMD-90 cable

i 8.2 N ylon insulated N MS C

\E 8.3 Moisture-proof N MS C with copper conductors {Note: Kraft paper

omit ted;

extra

Applied to wires)

D R T -".OAMP 3 0 0 V O L T S

•BURE 8.4 T ypical 3 conductor, N o. 8 gauge range cable {Note: G round wire located betwe en

Tfeted

conductors)

CURE 8.5 A 2 wire (black, red, and ground) nylon Heatex NMD-7 cable for use with electric

circuits operating on 240 V

Nonmetallic-Sheathed Cable Wiring

89



Cable Installation


Code requires NMSC to be installed in a

loop system. This means that all cables

are run in continuous lengths between

the electrical b oxes.

Joints.or

splices in

the cable must be made in a box. (See

Fig. 8.6) All elec trical bo xes in the sys

tem must be accessible for inspection or

circuit repair after the building is com

pleted.

panel

switch

<i>

light

,

— ®

continuous cable between boxes

receptacle

F I G U R E 8 .6 L o o p s y s t e m

The knob and tube wiring system s

used before the loop system was devel

oped allowed splices at almost any point

in th e circuit. This and th e fact tha t t he

live and n eutral w ire of the s am e circuit

did not always travel side by side m ade

troubleshooting difficult even for the

experts.

Cable Supports

NMSC mu st be fastened to th e w ood en

me mb ers of a building by straps, sta

ples, or other approved devices permit

ted by th e CSA. (See Fig. 8.7) S taples take

the least time, but th e cable m ay be

damag ed if th e staple s are driven to o

deep ly in to the w ood . (See Fig. 8.8)

Straps may be secure d w ith screws or

nails.

Th e Canadian Electrical Code

steel staple aluminu m strap

FIGURE 8.7 C able suppo rts

incorrect:

cable damaged

FIG URE 8.8 Fastening cable wi th s taple

requires that a stra p or staple be plac

within 30 cm of every box. Doing so

preve nts any undu e strain on the cab

from pulling th e con du cto rs out of the

box. Cable sup po rts m ay be placed as

far as 1.5 m apart on the ru ns between

th e b oxes , bu t it is often a good idea t

place them closer together. Cable ins

lations are usually in service for many

years, and so neat and secure installa

tions are imp ortant.

Fastening a C able to a Bo

Safety Note: NMSC must be held

securely by the clamp or conne ctor a

the box. Do not overtighten the clamp

this might crush t he cable and create

short circuit.

Approximately 6 mm of oute r

she

should extend beyond the clamp to p

tect th e TW insulated wire from the

clam p. (See Fig. 8.9) Also, a minimum

15 cm of free, insulated conduc tor m

be available for connection to devices

Applications of Electrical Co nstruction



outlet

box

ground

screw

switch /

mo u n t in g

lug

\o

35

15

c m

free

conductor

cable strap

w i th in

30 cm

of box

KURE 8.9 Me thod for conn ecting cable to

^ ^ H b o x

fee box. Th e bare ground wire may b e

•rimmed after connecting it to the box

p o u n d screw or, in the case of a recepta

cle,

left long enoug h to co nne ct to th e

eceptacle

ground screw as well. Take

care to trim neatly exce ss kraft pap er

fcotn the cable in the box. The trimming

peduces

any fire hazard.

grade level

V

protective board

(preservative-treated)

N MW U Buried

in

the

Earth

The h eavy layer of TW insulation on th e

NMWU con du ctors makes this cable

suitable for use in underground runs

supplying garden or post lights. Take

care to protect the cable from garden

tools.

(See

Fig. 8.10)

Cable Protection for

Concealed Installations

The Canadian Electrical Code requires

tha t NMSC be kept at le ast 3 cm from the

oute r edge of any wood en mem ber.

Otherw ise, driven nails or screws su p

porting baseboa rd, plaster, wood pan els,

or other wall products may pierce the

cable. When a cable has been pierced

with a nail, the problem is usually not

discov ered until th e building is com

pleted and the circuit made alive. With a

finished wall concealing th e dam aged

T

NMWU

water-t ight connector

post l ight

concrete

15 cm sand layer

BGURE 8.10 P ost light installation using N M W U

Nonmetalllc-Sheathed Cable Wiring

9 1



water

Ufpipe

FIGURE 8.11

tion

cable,

it is

bo th difficult and costly

to

locate and repair the fault.

Normal procedure is to drill hole s in

the centre of the wooden me mb ers that

the cable must pass thro ugh . Water and

air circulation sys tem s in the walls will

often make it nece ssary to run the cable

closer to the ed ge

of a

wooden mem ber

than the required 3 cm. In these cases, a

steel plate is

fastened

to

the wooden

mem ber in front of the cable to protect

it. Often, the plate is a side of a sectional

plaster

box left over from a gang box

assem bly. (See Fig.

8.11)

Take car e not to

damage the cable

by

locating

it

too near

to a hot-water pipe or hot-air du ct.

Residential Cable

Appl icat ions

NMSC has a maximum rating of 300 V

and will readily acce pt the 120 V/240 V

supplied to a residence.

Most circuits in house s consist of

No.

14

gauge

NMSC

and should be f

at a maximum of 15 A. Kitchen rece

cles supplying cu rrent

to

frying pa n

teakettles, or similar ap pliance s can

No.

12 gauge NMSC fused at 20 A. Th

increase in cable size and am pacity

vides a margin of safety t o a circu it

operating very close

to

its c apacity.

Home electric heating syste m s often

have circuits consisting of No.

12

ga

NMSC. Hea t-sensitive fuses sho uld b

used

to

protect th ese circuits.

Clothes driers are supplied with

cond uctor, No. 10 gauge

NMSC,

com

monly called drier cable. Fuse prote

for this cable should not exceed 30

Heat-sensitive typ e fuses are the b es

Electric stoves use a 3 conductor,

N

gauge

range cable

fused

at

35 A

to 4

depending on the size of stov e. (See

8.4,

on

page 89.)

Cable Wir ing Diagrams

An important p art of any wiring sys

is prepa ration

of a

circuit diagram. T

diagram helps determine the sequen

which the devices are

to be

connec

and the number of wires required in

cable between the boxes.

Graphical symbo ls are used to s

plify the drawing

of

electrical de vic

a circuit. Th ese universal sym bols a

listed in Appendix F of the Canadian

Electrical C ode. (See Table 8.1) Cab

are represented by a single, solid lin

with

the

number

of

insulated wires

the cable shown by short d ashes ac

th e cab le line. For example,

a 2

wire

cable is shown as ft , and a

cable

as fff

.

Remem ber that nonmetallic-

sheathed cable is available in 2 and

wire co m binatio ns. Any wiring circu

must be completed using only the w

black, or red NMSC wires a vailab le.

92




TABLE 8.1

ELECTRICAL SY MB OL S FOR ARCH ITECTURAL P LANS

z

'2

I

i

©

;;

::

:,\<

a

O

©

I

• O

-®

- C E )

-©

<£

<t>

-©

a >

- 0

-©

-©

^ , 3

~ ^ 7 W P

=©s

®

®

s

S

2

s

3

G E N E R A L O U T L E T S

Out let

Blanked O ut let

Drop Cord

E lectr ical O utlet; for use only

when c irc le used alone might

be confused with columns,

p lum b ing s y m bols , e tc .

Fan O ut let

Junct ion Box

Lam pholder

Lampholder w i t h P u l l S wi t c h

P u l l S wi t c h

Outlet for Vapour Discharge

Lam p

Exit L ight O ut let

Clock O ut let (S peci fy Voltage)

NOTE: Symbols on the left above

refer to ceilings; those on the

right above refer to walls.

RECEPTACLES

Duplex Receptacle

Other than Duplex Receptacle

1 = S ingle, 3 = T r ip lex, etc.

Spl i t -Switched Duplex Receptacle

T hr ee-Conduc t or S p l i t -Dup lex

Receptacle

T hr ee-Conduc t or

Split-Switched-Duplex

Receptacle

Weatherproof Receptacle

Range Receptacle

Switch and Receptacle

Radio and Receptacle

Special Purpose Receptacle

(Described in Specif icat ion)

Floor Receptacle

S W I T C H E S

Single Pole Switch

Double Pole Switch

T hr ee Way S wi t c h

S . Four Way S wi t c h

S D

A u t om at ic Door S wi t c h

S E E lectrol ier S witch

S K

Key O perated S witch

Sp S witch and P i lot Lamp

SC B C ircuit Breaker

SWCB

We atherproof C ircui t Breaker

S M C M om e nt ar y C ontac t S wi t c h

Sue

Rem ot e C ont r o l S wi t c h

S

W

p Weat her pr oof S wi t ch

S F Fused S witch

SWF

We atherproo f Fused S witch

S P E C I A L O U T L E T S

X

a b c

-

eic A ny standard sym bol as given above

©a.b.c.ic.

w i t n t n e

addit ion of a lower case

e subsc ript letter may be used to

^ B , b . c . e t c . t .

. . . . ,

designate some special var iat ion o f

standard equipment of par t icular

interest in a specific set of

architectural plans.

When used they must be l is ted in

the Key of Symbols on each drawing

and, i f necessary, further described

in the specif icat ions.

P A N E L S , C I R C U IT S , A N D

M I S C E L L A N E O U S

• • L igh t ing Panel

M Power Panel

— Branch C ircui t; C oncealed in

Ce i l ing or Wal l

— Branch C ircui t; C oncealed in Floor

— Branch C ircuit ; E xposed

•—••

Hom e Run to Panel Board

Indicate number of circuits by

number of arrows.

NOT E: Any circuit without further

designation indicates a two-wire

circuit. For a greater num ber of wires

indicate as follows:

-H-h

(3 wires)

-ft—If-

(4 wires), etc.


93



architectura l symbols

w ir in g d ia g ra ms

- # -

< D

•HZhHjHKD^KD

* * < >

- # -

4 #-

- # -

white wire used to feed switch

<XD

7

Kt>KD^-n

FIGURE 8.12 C able wiring diagrams for single-pole sw itch

Figures 8.12,8.13, and 8.14 com pa re

architectural symbols

with wiring

diagrams of basic lighting circuits. Fig

ures 8.15 and 8.16 provide more complex

circuits designed to d evelop w iring

skills. You will dev elop a gre ater und er

stan din g of th es e skills if you take tim e

94

to draw and complete the circuits on

note paper. Use coloured pencils to in

ca te th e wires . Since a cable system o

wiring requires that all splices and co

nections be in a box, it is unnecessary

show the individual conductors

betw

the boxes.

A

single line is used to




architectura l sym bols wir in g d iagrams

< H

fe^€

-rtt-

<>*-©

< H-

<t> < D

•< tt

C)

< D

I O T E :

Receptacles alive at all t imes . S witch controls only the light.

?E 8.13 W iring diagrams w ith receptacles

present the ca ble in thes e circu its.

R

Fig. 8.12)

Figure 8.13 shows simple lighting cir-

•ts

with a duplex receptacle

added,

sceptacles are con side red to b e alive at

I

times, unless otherw ise marked on

the diagrams. Three-conductor cable is

required for some of the se circu its.

Th ree and 4 way switch-control cir

cuits are sh ow n in Figure 8.14. Three-

con duc tor cable is often used in this

typ e of circuit.

Nonmetallic-Sheathed

Cable Wiring



architectura l symbols

w ir in g d ia g ra ms

-#/-

line

• * © •

-#-

S

3

line

-tV-

-/rV-

£>

*V— L

\—>w-

line

<—#-

-fi¥-

-¥r¥-

• ' H Z h H Z M Z h K D

S

4

S

3

FIGURE 8.14 W iring diagrams show ing 3 and 4 way switch control

96




+-ft

7 7 ^

X - 7 ^

7 7 ^

+-6

/ / /

-7TT

7 7 7 ^

7 7 ^

JRE

8.15 Wiring diagrams using architectural symbols to show

2

and

3

w ire cables


97



«—

¥t

*—T¥-

W-

T 4 4 M <• V ^ - ( L V - 7 ^

PS

FIGURE 8.16 C omplex wiring diagrams using architectural symbols to show com binations o

lights,

receptacles, and assorted sw itching m ethods




ISC A ccessories

fat all electrical boxes are equipped

In

built-in clam ps. Distribution pan els

d

outlet boxes with 13 mm knock outs

•quire

cable connectors. (See Figs.

8.17

kd8.18)

IBURE8.17 Typical 3030 style N MS C con-

^wexpansion type)

HJRE 8.18 A luminum die-cast connector

•nut)

Some

15

cm of the cable's oute r

he ath is easily split with a cable ripper.

e Fig. 8.19) This simple metal tool

i

time and p reven ts damage to the

le

during the ripping pro ces s. Mod-

i NMD-90

cables are smaller and m ore

impact than the older cables with

aided

outer sheaths. Special cable

^pers have been developed just for

ten, but great care must be taken not

-fiage the nylon sleeve ov er th e PVC

groove cut by ripp

tooth of r ipp

cable ripp

FIGURE 8.19

NMSC for box

Cable ripper for preparation of

insulated wires. The need for care is

most obvious when ripping 3 wire cable.

Cutting pliers (diagonal

cutters)

are used

to trim off th e loos e end s of kraft pa per

and outer shea th.

F o r R e

v i e w

1. With wh ich typ es of building

materials may

NMSC

be used?

2.

What are the two basic typ es of

NMSC, and w here are they used?

3. What is the purp ose of the bare

wire in NMSC?

4.

Describe the loop system used

with NMSC wiring.

5.

Why do es the Canadian Electrical

Code require that all joints or

splices be m ade in a box?

6. List th e devic es that may be used

to su pp ort NMSC. How sh ould

these devices be spaced, and why?

7.

When fastening a cable to a box,

how much cond uctor should be

left free? Why?

8. Describe how

NMW-10

is run

under ground and connected to an

outdoor post light.

9. When running NMSC thro ug h

wooden m embers, what precau

tions should be taken? Why?

Nonmetallic-Sheathed C able Wiring

99



cl

< //

JJ-

V /

• 7 4 4 ^ -

^44^

S . A

Answers to FIGURE 8.15

Wiring diagrams show ing 2 and 3 wire cables

100




switched

receptacle

* - f r

S.A

rers to FIGURE 8.16 C omplex wiring diagrams showing combinations of lights, recepta-

, and assorted switching methods.

Nonmetallic-Sheathed Cab le Wiring

101



T

he Canadian Electrical Code once

required that joints and splices in

insulated conductors be soldered, and

then cove red with an insulating tap e

equivalent to the insulation on the con

ductor. Soldering the splice prevented

the weakening of the electrical connec

tion by th e action of oxidation. But it

was also time-consuming and could cre

ate other problem s. When large cab les

were connected, they were heated to a

temperature that often damaged the

insulation ne ar th e sp lice. Also, to dis

connect the condu ctors, more heat was

neede d to melt the solder. The num ber

of tools required and the cost of one

time-use materials made this system

unsatisfactory. Th e need for a conven

ient method of making electrical splices

resulted in the developm ent and

subsequent

CSA

approval of so lderless

connectors.

S olderless W ire

Connectors

One of the first solderless wire connec

tors co nsisted of a tapered porcelain ca p

with an internal screw thread. While por

celain is still used in the pro duc tion of

some heat-proof units, Bakelite and/or

nylon are now most often used in the

construction of wire connectors.

Solderless

Connectors

There are three m ain types of so

less wire conne ctors: twist-on, set-

and com pression . The name s for ea

refer to the system used to apply th

unit.

Twist-on Connector. This connec

has a cone-shaped, metal spring tha

threads itself around the conductor

the co nne ctor is rotated. Several

man ufacturers pro duc e this type of

connector, but th e operating princi

th e sam e. (See Fig. 9.1) The interna

spring design takes advantage

of

leverage and vise action to multiply

strength of a perso n's han d. Th us,

conductors are forced into a solid,

effective splice. (See Fig. 9.2)

Using the twist-on c onn ector is

of the quicke st ways of splicing and

lating electrical con du cto rs. It is su

for use with solid and/or stranded

ductors operating at 600

V

or less.

models have been approved for use

1000

V.

One variety of twist-on connect

features

built-in

wings to increase t

torsion a chieved by the installer w

joining con du ctors in the

No.

12,10

8

AWG

sizes. (See Fig. 9.3)

Besides such special features, t

twist-on c onn ector is made in a ran

sizes for splicing conductors from

102




••ne-retardant

isermoplastic shell

XJ|>

seated,

—r»re-wire

posit ive

grip

design

deep skirt,

wide throat

double-thick

protective cap

flame-retardant

thermoplastic shell

threaded entry

colour-

coded

square-edged

live-action

spr ing

contoured

w in g s

deep,

wide skirt

HJRE9.1 C utaway view of a twist-on

' sh owing the connec tor's internal

- d its effect on the conductors wh en

FIGURE 9.3 Wing-nut style of wire connec

tor for extra torque, or twisting

power,

while

splicing larger conductors in the No. 12 to

N o. 8 A WG range

• 3are wires and cut to length.

insulation

4

#

ends of wire

S tep 2. Insert wires an d rotate cap.

N O T E : Wires twist

together as cap is rotated

Step 3. Tighten cap fully.

N O T E :

No bare wire when cap in place

JRE 9.2 Me thod for installing a twist-on connector

Solderless Conn ectors 10



gauge up to N o. 8 gauge. Some manufac

ture rs use a num bering system to iden

tify the different sizes of their product.

Others have adopted both number and

colour codes for easy, visual product

recognitio n. (See Fig. 9.8 on page 106)

Set-Screw Connector.

This two-piece

connector is widely used in circuits

where equipment m ust be changed

frequently for maintenance purposes.

Th e simple set-screw design allows solid

and/or stranded condu ctors to be inter

cha nge d easily. (See Figs. 9.4 and 9.5)

S tep 1. Insert wires. Do not tw ist.

FIGURE 9.4 S et-screw connector

Set-screw connectors are made for

us e on c ircuits up to 600 V, with

appro val for use on so me lighting cir

cuits of

1000

V. They are designed to

splice con duc tors from

No.

18 up to No.

10 gauge in size.

Figure 9.6 show s typical app lications

of both twist-on and set-screw connec

tors . Both are for us e in electrical boxes

or enclosures only.

Com pression Connector.

Unlike the

mechanical (set-screw) connector, this

two-piece compression connector

requires a special

crimping

(compres

sion) tool to install the cond uctor-

retaining

sleeve.

The retaining sleeves

are made of copper and/or zinc-plated

steel. An insulating cap of plastic or

nylon is fastened over th e sleeve after

set-screw

insulat ion f lush

brass connector body

S tep 2. T ighten set -screw.

threads for insulat

Be sure insulat ion

does not slip

into connector body.

D

S tep 3. Install cap.

thr

insulat

Be sure threads are

at insulat ion end of splice.

FIGURE 9.5 Me thod for installing a set

screw connector

the conductors have been crimped

firmly. (See Fig. 9.7) This typ e is for

permanent installation, because the

ductor cannot be easily removed fro

the retaining sleeve.

Th ese un its are m ade for use on

cuits of 600

V

and may be used on l

ing fixtures up to 1000 V. The retain

sleeves are made for splicing condu

No.

18 up to N o. 6 gauge . The zinc-p

steel sleeves can be used only on co

con duc tors, due to the possibility

o

electrolysis acting on the se sleev es.

Some compression con nectors a

104




9.6 Typical tw ist-on and set-scre w connec tor applications

Solderless Con nectors 10



conductor retaining sleeve

indented cr imp insulat ing cap

FIGURE 9.7 Me thod for installing a com

pression connector

used to simplify the connection of

stranded conductors to a terminal

screw. These units prevent loose stra

from slipping out from und er th e term

nal screw and reducing the current-ca

rying capacity of the connection. (See

Figs. 9.9 an d 9.10) Special crimping

p

are needed to install thes e conn ector

on con du cto rs ranging from No. 18 to

No. 10 gauge.

FIGURE

9.8 C olour-coded w ire connectors

are available in a range of sizes from grey

(small) to blue and orange (medium) and to

yello w and red (large).

fork-tongue

insulated ring-tongue

FIGURE 9.9 Fork-tongue and insulated

tongue compression lug installations

FIGURE 9.10 C ompression tool and cnmp-on terminal lugs

106




:hanical C able

nnectors

:ting cab les p os es se vera l difficul-

: all stran ds m ust be held secu rely

hout damage to any, beca use damage

I

reduce the connection's conductiv-

e connection must maintain a firm

i

on the cable, com pressing the

Js

into a solid g roup th at will not

.

after a time; and t he con nec tor

be m ade of a me tal that will not

rage electrolysis betw een itself

the cable. Mechanical connectors,

, lugs, meet these requirements.

I Fig. 9.11)

There are several kinds of mech ani

zable connectors (see Figs.

9.12,9.13,

19.14), and service entranc e equip-

: for buildings mak es extensive us e

l. Figure 9.15, on pa ge 108, shows

blocks from a distribution panel,

i

neutral block is capable of co nnec t-

the

main neu tral cab le to the neu tral

;

of ev ery circuit within a b uilding.

Cable conn ecto rs are m ade in sizes

conductors of

No.

14 gauge up to

I MCM. Co nn ecto rs for ca bles larger

1000 MCM may be obtained from

i

manufacturers by special order.

FIGURE 9.12

cal connector

Typical 3 conductor mechani-

P reparation of the Cable. The

following pro ce du re is for installing

copper and aluminum conductors in

lugs.

Step

1

.

W hittle off th e insulation with

a knife, taking care not to nick any of th e

m ount ing ho le

^ ^ K 9 . 1 1 Typical lugs

Solderless Connectors

107



i

FIGURE 9.13 S plit-bolt connector

3

FIGURE 9.14

cal connector

A single conductor mechani-

strands. Do not circle the cable with the

knife, since this usually nicks the wire

stran ds, which reduces their strength

and conducting capacity.

Step 2.

Remove any

oxide coating

(a

dark dull coating) that is visible on the

bared portion of the cable. This is an

important procedure when using

aluminum cable, because it oxidizes

rapidly. Apply antioxidant chemicals t o

aluminum conductors at the same time.

Use a wire brush to apply the chemical

and remove oxidation.

branch c ircui t neutral wires

FIGURE 9.15 N eutral blocks for distributic

panels

Step 3.

Tighten the holding screw

once the cable has been fully inserted

into the lug. Allow several minutes to

elapse, and then retighten the holding

screw. The strands will have settled in

place, making a second tightening

necessary for a secure connection.

Compression Cable

Connectors

These solderless connectors are made

from a one-piece tubular form for inst

lation with a hand- or hydraulic-powe

compression

tool.

(See

Fig.

9.16) The

tubular forms are made from a high-c

ductivity, electrolytic copper. One en

(the tongue) is flattened and drilled fo

fastening to a terminal block. The con

nec tors are often electro-tinplated to

minimize corrosion.

The strand s of the cable are

compressed within the copper tube b

the compression tool until they form a

solid mass of copper. This process

ensures long life and maximum curren

carrying capacity for th e terminal con

108




( J

SURE 9.16 C ompression type solderless

and splice

nection. Th ere are thre e type s of com

pression tools: the hand-operated

mechanical type; the hand-operated

hydraulic type; and th e

motor-driven

hydraulic typ e. (See Figs. 9.17, 9.18, and

9.19)

Aluminum cables require special

attention when terminated with a com

pression-type solderless lug. Figure 9.20,

on page

111,

show s the correct proce

dure for terminating aluminum cables.

Figure 9.21, on page

112,

shows the

effect of a com pre ssion tool on a cable .

JRE 9.17 A hand-operated, mechanical type comp ression tool

JRE 9.18 A hand-operated, hydraulic type comp ression tool


109



FIGURE 9.19 A motor-driven, hydraulic type compression tool

110




1. C ar e fu l ly r em ov e ins u la t ion w i t ho ut n ick - S T E P 2 . Wi r e-br us h c onduc t or t o r em ov e any

•x j

conductor. oxid e.

STEP 3. A pply ant iox idant to prevent form at ion of STEP 4. T ighten mechanical connectors

securely,

surface oxide.

S T E P 5. C r im p c om pr es s ion t y pe c onnec t ors w i t h

proper die and tool the recommended number of t imes.

IE

9.20 P rocedure for termina ting aluminum cables


11



connector 1-piece

cannot sp l i t

indent anywhere on

circumference

cup-shape indent co ld-worked

retains form and provides secure gr ip

connector swaged to conductor

maximum effect ive deformation

obta ined for force exer ted

indents un i form

readily inspected

5^EZ

each strand compressed into close contact

wi t h connector and other strands

FIGURE 9.21 E ffect of compression tool on cable and lug

Figure 9.22 sho w s two ou tdo or ap pli

cations for solderless compression con

nectors. In both cases, installing solder

con nectio ns w ould be difficult and

inconvenient.

Insu lating T apes

Once installed, solderless cable connec

tors requ ire an insulating tape or other

covering to replace the insulation

removed during the making of the splice.

(See Fig. 9.23) Th is tap e o r cov ering

material must be capable of w ithstand

ing both the circuit voltage and the nor

mal wear and te ar on the cable. In other

word s, the covering material must hav e

the sam e voltage rating and p hysical

properties as the cable's original insu

lation.

Some splices requ ire severa l type s of

insulating m aterial to provide ade qua te

electrical protection . Common coverings

are friction tape, vinyl plastic, fibreglass,

and insulating putty.

Friction Tape. This basic cotton tape

has an insulating com pound impreg

nated into the weave. A low-quality

insulator, it sho uld not be used on cir

cuits above 120V.

Vinyl Plastic.

Th is excellent insulatin

prod uct, available in assorte d types a

colou rs, com es in several thicknesse s

and w idths. It adh eres readily to m ost

surfaces. A general purpo se vinyl tape

seen in Figure 9.24 is approx imately 7

thick and resists abrasio n, sunlight,

m oisture , alkalis, and many a cids. It h

CSA approval for use on cable splices

to 600 V and fixture and wire splices u

to a m aximum of

1000 V

at 105°C.

A more specialized type of vinyl ta

can be used where cold tem peratures

are e xpe rienc ed. It is slightly thicker, a

8.5 mils, and has extra pliability for

application at extremely low temp era

tures.

It also rem ains eas y to hand le a

normal tem pera ture s. Figure 9.25

illus

trates an application of this high-quali

112




JRE 9.22 T ypical outdoor uses for hand-operated, hydraulic com pression tools

Apply several layers tape.

Pull t ightly here.

compression connector

cable

JRE 9.23 Taping a splice

Solderless

Connectors

11



FIGURE 9.2 4

electrical tape

General purpose vinyl plastic

FIGURE 9. 26 High-quality, all we ather

i

FIGURE 9 .25

A pplication of vinyl plastic

electrical tape suitable for cold w eather

5

all we ath er tap e. Figure 9.26 show s a

ical form of it.

Sturd y vinyl 10 mil tape s can b e

where more abrasion resistance and

mechanical strength are required. W

widths are produced to speed up th

insulating of larger splice are as. Wh

temp eratures up to

105°C

are en cou

tered, a more heat-resistant tape is a

able. This tape co uld b e used in and

around electric motors and is equip

with a special oil resistant adhesive

vinyl backing m aterial.

EPR

Tape.

Ethylene propylene ru

tape is a 30 mil, nonvulcanizing mate

tha t ca n b e used for low voltage as w

as high voltage applications up to

69 000

V.

It can be stretche d upon

114




: 9.27 High and

low

voltage,

EPR,

sss rubber splicing tap e w ith a 130°C

ppfication

to ten t imes its normal

sigth, thu s forming a m oisture-tight

[taper

over the sp lice. (See Fig. 9.27)

Recent developm ents in tape tech-

togy have led to the production of an

• ape that d oes not require a separa-

liner between layers on the roll. The

prevented older-style tape from

ring tog ethe r on the roll. It was often

rard

to

handle

and

messy

to

clean

I after taping .

The new linerless tape has a unique

to dissipate any heat from the

;. Its

stable prop erties improve the

:al,

electrical, and phy sical

icteristics

of the tape up to a maxi-

i operating tem perature of 130°C.

self-bonding,

flame-retardant

tape

tinguishing

and

suitable

for use

previously restricted to spe-

products.

Ir eg la ss . This tape is used on splices

tere the tem per ature may reac h 130°C.

It has a pres sure sensitive, therm o

setting adhesive that m akes it suitable

for use in such high tem peratu re appli

cations as furnace c onnec tions, wa ter

heaters, etc.

Insulating Putty. Large co nn ect ors

requ ire good quality insulation that will

fill voids and pad any irregular shapes

produced by the con necto r. An electrica

grade , rubbe r-ba sed, self-fusing elastic

type putty is available in tape form for

the insulating of large con nec tors. It

should be used on low voltage circuits

(600 V or less) wh ere it will resist aging

and not dry out. Figure 9.28 illu stra tes

the proper m ethod

of

insulating

a

large

connector.

Another form

of

insulating pu tty

is

the vinyl mastic p ad. (See Fig. 9.29 on

page

117.)

These pad s consist of a self-

fusing, rubber-b ased com pound with a

strong adh esive. They mould around dif

ficult shapes and have excellent resist

ance to alkalis, acids, m oisture , and

varying wea ther cond itions. Figure 9.30

illustrates the proper m ethod of using

them.

Resin Splicing K its.

A

resin splicing

kit can be ob tain ed w ith sufficient

materials included to comp lete one

splice. A plastic mould, funnels, insu

lating and sealing com pound , and

pouring resin are included in the kit.

Figure

9.31,

on page 118, illustrates the

pouring of the resin into the m ould.

Th ese u nique "field splicing kits" can be

used for overhead, underground, or

direct burial applications up to 5000 V.

Figure 9.32 illus trate s

a

cutaway

of a

resin splice after the mould has been

removed. Th e kits are available in a

variety of forms to handle numerous

shapes and types of splices. Since the y

are produced in a variety of voltage


U



S T E P

1.

A pply f i rs t p iece of insulat ing putty.

STEP 2. O ver lap a second piece of insulat ing

putty.

STEP 3. Press and form put ty to shape

of

connect ion.

STEP 4. C omplete insulat ing process with layer of

vinyl plast ic tape.

FIGURE 9.28 Insulating a splice using self-fusing elastic putty

ratings, take c are

to

select the prop er kit

for th e splice

or

connection

to be

insu

lated.

If

prop erly installed, th e kit forms

a mo isture- and w ater-tight cover o ver a

splice tha t could take conside r

able time an d material to insulate in any

other manner.

A resin-pressure system of insulating

splices is cap able of insulating cables

up

to a

capac ity of 8000 V. To insulate

in this m anner, apply an open-weave,

spacer tape around the splice. Next, tape

an injection fitting into plac e, and do

a

final tapin g

of

vinyl plas tic. A liquid-tigh

mould forms. Now use

a

resin-pressure

gun

to

pu m p the insulating resin into

tf

wrapped splice. A tough, moisture-pro

insulation on th e sp lice will resu lt. Fig

ure 9.33,

on

page

118,

illustrates

the

s teps

in

making such

a

splice.

Electrical Coating. Occasionally

a

splice that has been taped

or

been in

service

for a

while may require a little

116




C

9.29 Vinyl ma stic insulating ma terial in roll and pad form at

M .

Remove backing.

STEP

2. P osi t ion pad .

? 3 . W r a p a r o u n d .

STEP

4. Insulat ion com pleted.

PRE 9.30 P roper technique for insulating with vinyl mastic pads


11



FIGURE 9.31

mould

P ouring resin into a splicing

STEP

1.

Apply an open

weave,

spacer tape to

splice.

FIGURE 9.32 C utaway view of a com pleted

resin insulated splice

extra moisture proofing or insulating. A

liquid, brush-on coating is available

to provide this extra protection when

required. Figure 9.34 shows this productbeing applied to a taped splice.

Coloured Tapes.

Vinyl tape is avail

able in eight, fade-resistant colours:

red, yellow, blue, green, white, orange,

brown, and grey. Tape in these colours

STE P 2. Install injection f it t ing and cover. S plic

area with plastic vinyl tape.

t

STE P 3. Force resin into splice with

resin-press

g u n .

Avoid excessive pressure to prevent bulgi

of tape.

FIGURE 9.33 Insulating a splice using th

resin-pressure system

118




•GUftE 9.34 A pplication of liquid insulating

• be used to replace coloured insula-

noved from a conductor before

Scing

or to identify and mark v ariou s

nrit conductors . It is app roved for u se

600 V

at 80°C and ha s similar quali-

i

to the oth er vinyl tape s available.

Jping a S plice

19.23

shows how to tape a splice,

lufacturers provide instruction

ts covering application methods for

: specialized m aterials.

When removing insulation, take care

I to nick the cab le, something which

wild produ ce sha rp edges or burrs in

stran ds. Burrs are potential weak

i

that might puncture the tape or

>lish electrical str es s in th e sp lice.

higher the circuit current and volt-

,

the greater the danger of splice

lage

from electrical stre ss.

Heat-Shrink Tubing

Special plastic tubing that protects

splices is now produ ced by the plastics

industry. This tubing has a program

mable memory which allows it to be

shrunk or reduced in diameter when

heated. Tubing of somewhat larger diam

eter than the splice to be insulated is

easily slipped over the connection area.

It is then heated with a hot-air blower

and sh rinks into a secure, one-piece

plastic layer over the splice.

Chem ical M ake-u p. A virgin plastic

material, such as polyethylene, is used as

the base for heat-shrink

tubing.

Such a

material must possess mechanical

strength and the capacity to resist

certain fluids and ultraviolet light. It

mu st also b e a high-quality electrical

insulator. The molecular structure of the

plastic is modified by blending additives

into it. These additives enh ance the

existing qualities of the p lastic and a dd a

few feature s, a s well.

One new feature is that the tubing

may soften und er heat, but not turn into

liquid. Under adve rse high tem pera ture

con dition s, such a s a fire or short cir

cuit, the plastic will not run off the

splice. Too much heat can, of course,

des troy th e tubing, bu t it will remain

in a rubber-like sta te until th e p oint of

destruction.

The second and mo st desirable fea

ture is the perfect elastic mem ory pro

duced by the radiation cross-linking of

the plastic m olecules. The tubing, sup

plied in an expanded (deformed) condi

tion, will shrink tightly over irregularly

shaped splices or objects when heated.

Different blends of the plastic pro

du ce a varie ty of tubing, making it useful

in higher temp erature areas, in cold

weather applications, and in or near cor

rosive ma terials or liquids.

Solderless

Connectors

119



Types of Heat-Shrink

Tubing

Two main types of this tubing are used

extensively in industry.

Polyolefin

tub

ing, a simp le, heat-shrin k tub ing, is one

of the m ost popula r type s for covering

splices or electrical conn ecto rs. (See

Figs.

9.35 and 9.36)

A

second type of tub

ing, known a s

dual-wall

tubing, has a n

outer tube of polyolefin and an inner

tub e of adhesive-type plastic wh ich will

form a perfect seal around the splice or

connection. This seal is capable of keep

ing out all dirt, moisture, va pou rs, etc .

Th e inn er sealing w all is simp ly a differ

en t blend of polyolefin having a dh e

sive/sealing pro pertie s. (See

Figs.

9.37

and 9.38)

t

FIGURE 9.35 P olyolefin, heat-shrink tubing

placed over a crimp-on connector

§

FIGURE 9.36 W hen heated the tubing will

shrink to form an insulating barrier over any

shape of connector or splice.

FIGURE 9.37 Dual-wall polyo lefin, heat-

shrink tubing, placed over a multi-conductor

splice

FIGURE 9.38 Dual-wall

polyolefin

tubing

I

capable of waterproofing splices and conn?

t ions to components.

Heat Source

The approved method of heating the

tubing is with a hot-air conv ection heat

blower as shown in Figure 9.39. Shrink

tem peratu res rang e from 80°C to 150°C

depending on the blend of polyolefin

being used. In the lower hea t rang es,

a standard hair dryer can shrink the

tubing.

When emergency situations arise

and a blower is not av ailable, a flame

from a m atch or oth er low-level flame

120




RE 9.39 Hot-air gun in use w ith heat

ing to activate the elastic memory

e can be used. Relying on a flame

uld

not be don e in general prac tice

•• e v er : care must be taken not to

ceed

the plastic's temp eratu re rating.

Fig. 9.40)

JURE 9.40 L ow temp erature flame being

eat-shrink tubing wh ere power is not

Appl icat ions

Due to th e simple application proc ess

and nea tness of the com pleted job,

many u se s have been found for polyole-

fin tubing. There are ten major c olou rs,

as well as clear plastic, available for t he

identification of conductors or connec

t ions. Colours with strip es a re also avail

able to provide an even greater n umb er

of identification com bina tions. This

high-quality insulating product can hold

conductors in groups for the separation

of circuits and easily cover co mp lex con

nectors or terminals. Heat-shrink tubing,

with its versatility, has bee n used exten

sively in mass transit vehicles such as

trains, m ilitary ships , aircraft and land

vehicles. Special vers ions of th e tubin g

are also being produced for use in space

satellites . (See Figs. 9.41,9.42,9.43,9.44,

9.45 and 9.46)

FIGURE 9.41 Flexible, general purpose tub

ing for ide ntification of cables

FIGURE 9.42 A dhesive-lined, sem i-flexible,

thinwall tubing w ith a high shrink ratio and

flame-retardant jacket


12



FIGURE 9.43 Heat-shrink tubin g used to

insulate and protect an electronic co mp one nt

FIGURE 9. 44 Heat-shrink tubin g used to

identify circuits and individual conductors in a

circuit

FIGURE 9.45 Heat-shrink tubing used to

enclose crimp-on term inal conn ectors

FIGURE 9.46 Bus-bars insulated and colo

coded with heat-shrink tubing

Ratings and Approvals

The tubing has both CSA and Underwr

e r s '

Lab oratories app roval for use in t

electrical industry. Various thicknesse

form protection for the many residentia

and indu strial voltag es in use, while te

pe rature ratings for continuous-duty u

range from -55°C to 135°C. Polyolefin

tubing would a ppe ar to be a great boo

to the electrical industry.

122 Ap plications of Electrical Con struction



o r R e v i e w

t two disadvantages of solder

ing and taping wire splices.

>t three ty pes of solderless wire

con necto rs. What is the maximum

circuit voltage for each?

L Why are crimp-on connectors

installed on small stranded con

ductors fastened under terminal

rews?

at arc the disadvantages of

npression connectors?

three reasons why lugs are

ful.

t the ste ps in fastening a co pp er

cab le to a terminal lug.

-t

the ste ps in fastening an alu-

um cable to a terminal lug.

why

should nicks on the stra nds

i cable be avoided when remov-

insulation?

^BThy must a mechanical co nne ctor

be retightened several minutes

after the first tightening?

Describe the methods for crimp

ing copper and aluminum com

pression con nectors t o a cable.

Which two types of protection

must electrical tape provide?

Why is it necessa ry to observ e the

temperature ratings of electrical

tape?

L

List three com mon type s of electri

cal tape.

L Describe how large, irregularly

shaped cable conn ectors are insu

lated.

L What are the advantages of insu

lating putty w hen covering large

or irregularly shap ed splices?

What advantages do resin splicing

kits have over more conventional

methods of insulating a splice?

17. Why must care be taken to select

an insulating product that has the

proper voltage rating?

18.

What are the advantages of using

coloured insulating tapes?

19. Why is it desirable to pull or

stretch the tape s as they are being

applied to the splice area?

20. Under what conditions would a

brush-on, liquid insulating mate

rial be used?

21 . Name the two main ty pes of heat-

shrink tubing in use throughout

the electrical industry.

22.

What advantage has heat-shrink

tubing ove r othe r forms of electri

cal insulation?

23.

List four different applications of

heat-shrink tubing in the care and

protection of electrical wiring cir

cuits.

24. How can heat-shrink tubing be

used in the identification of circuit

terminals and conductors?

25. What methods are used to reduce

the tubing to its final size after

installation on splices or termina

tions?

Solderless Connectors 123



Heat-Contr

Switches

E

lectrical cooking appliance s, su ch

as ovens, ranges, hot plates, and

com me rcial coffee-makers u sed in res

tau ran ts, use a variety of heavy-duty

switches to control their he ating ele

me nts. One common method for pro

viding different levels of hea t is to us e

two elements and conn ect them in

series/parallel combinations across

120

V

and 240

V.

The switches discussed

in this chap ter a re capab le of providing

the series/parallel connections required

for this m ethod of he at c ontrol.

Three-Heat, Single-Pole

This simple heat-control switch is used

primarily for rangettes and hot plates

operating at 120 V. Heat rang es are pro

vided by connec ting two eleme nts of the

sam e size (wa ttage) as follows:

Low:

2 elem ents in series on 120 V;

Medium: 1 element on 120 V;

High:

2 eleme nts in parallel on

120 V.

Figures 10.1 and 10.2 show the

switch, its internal con nection s, and wir

ing by schem atic diagram. The switch's

con nec tions can be tested with a series-

lamp teste r (describe d in Chapter 2).

Three-Heat, Double-Pole

This switch uses th e same series/paral

lel com binations of the tw o elements a

th e single pole version. Sw itches con

trolling 240 V (two live wires) mu st b e

cap ab le of open ing bo th live wires at I

switch. When th e switch is turn ed to

i

the re m ust be no voltage present at th

elements.

Figures 10.3 an d 10.4 show th e

switch, its internal conne ctions, and w

ing by schem atic diagram.

Five-Heat

More variations in heat are available b

using the 5 heat, dou ble-pole switch to

control two elements of the same size.

Two elemen ts, each rate d at 600 W on

240

V,

will provide heat as follows:

Low: 2 elem ents in series on 120 V

provide

75

W;

Low-Medium:

1 element on 120 V

provides 150

W;

Medium:

2 elem ents in parallel on

120 V provide 300 W;

Medium-High: 1 element on 240 V

prov ides 600 W;

High:

2 elem ents in parallel on

240

provide 1200

W.

124 App lications of Electrical Con struction



z

6

rotary knob

Bakelite cover

porcelain base

switch

h igh

m e d i u m

switch posi t ions

JRE 10.1 S witch positions

reference point

(to assist in

locat ing terminal)

off

pilot l ight

(circuit if used)

neutral wire

1 2 0 V

l ive wire

reference point

JRE 10.2 S chematic wirin g diagram for a 3 heat, single-pole switc h

Heat-Control Switches

125



^

L

1

3 N

^ J ^

L

t

h i g h m e d i u m

FIGURE 10.3 S witch positions for a 3 heat, double-pole switc h

reference

point

live

reference point

240 V

live

elen

FIGURE 10.4 S chematic wiring diagram for a 3 heat, double-pole switch

Figures 10.5 and 10.6 show the

switch's internal connections and its

wiring by schem atic d iagram.

Heat variations other than those

listed above can be obtained by using

elem ents of two different sizes. Also, a

safety pilot light indicates when the

switch is on in one of its five h eatin g

position s. Take care to use a 120 V lamp

for the pilot light. Lamps with

lower voltage ratings will burn out if cc

nec ted to this circuit. Lamps with

high

voltage ratings may b e too dim for

effe

tive use.

Seven-Heat

This switch looks m uch like th e 5 heat

switch, but has th e adv antage of two

extra heat-levels. Because of this great

126




^ t b - Q - O .

low

low-m edium m edium m edium -h igh h igh

JURE 10.5 Internal sw itch conne ctions (rear view) for a 5 heat sw itch

E 10.6 S chematic wiring diagram for a 5 heat sw itch

•ge of heat selection, the heat switch

B gradually replaced the o lder 5 heat

•itch design.

The seven heat-levels are obtained by

•eg

two different elements, each rated

1240 V. A

600

W

and an 800

W

element

combination provide heat as follows:

i- mer:

Both elem ents in series on

0

V

provide approx imately 87 W.

»rtion 6: One 600 W element on

» V provides 150 W;

ssrtion 5: One 800 W element o n

»V provides 200 W;

Position 4: Both elem ents in parallel

on 120 V provide 350 W;

Position 3: One 600 W elemen t on

240 V prov ides 600 W;

Position 2: One 800

W

elemen t on

240

V

prov ides 800 W;

High: Both elem en ts in parallel on

240 V provide 1400

W.

Figures 10.7 and 10.8 show th e sw itch's

internal conn ection s and its wiring by

schematic diagram.

Most mo dern ra nge s have a pilot

light terminal at the rear of the switch to

Heat-Control

Switches

127



simmer

position 6 position 5 position 4

Q

positio

position 2 high

FIGURE 10.7 Internal switch connections (rear view) for a 7 heat switch

120

V/240

V

o--

live

neutral

live

O N

h o -

O

L

2

1 2 3 4

0 0 0 0

element

,_yw\A

element

^ *

AAA/VH,

FIGURE 10.8 Schematic wiring diagram for a 7 heat switch

show whether the element is on.

An

ele

ment that has been left on may not glow

red but still be hot enough to burn a per

son touching it.

Infinite-Heat

Improvements in the design of electric

ranges created a need for a greater vari

ety in heat levels. The infinite-heat

switch, as the name implies, offers an

unlimited variation in heat level.

Although this switch is often

more ex

sive than other heat control switches

a single element requiring less wiring

offsets this initial cost.

Figure 10.9 shows by schematic

ing diagram the internal workings of

typical infinite-heat switch.

128




pi lot l ight terminal

l ine terminal

main contacts

bimetal s t r ip

heater coil

of switch

pilot l ight contact

l ine contacts

element terminal

N O T E :

S wi t c h

in off posit ion

RE 10.9 Schematic wiring diagram showing infinite-heat switch parts and circuit

Operation of Infinite-Heat Sw itch .

{cam

is fastened to the knob of the

tch. One of the

main

con tacts is on a

wnetal strip fitted in to a tension arm.

a the knob is turned slightly, th e cam

Ktuates the tension arm . The arm

Btates

on the pivot and closes the main

aontacts, thu s heating th e elem ent.

A h eater coil

is wound around the

aetal strip and conn ected in parallel

the element. The heat from the

eater coil warms the bimetal strip and

causes the strip to bend outwards. This

j>ens the circuit, and the hea ter cools.

:

strip contracts and closes the con-

ts .

This activates the element and

heater again.

The more the knob is turned , th e

•o r e it cau ses the tension arm to ex ert

pre ssu re on the con tact s. Therefore, it

takes longer for the heater to b ecom e

hot enough to actua te the bimetal strip

and open the contacts.

The single eleme nt o pe rate s at full

power each time the contacts are

closed, and the heat level is regulated by

the speed at which the main co ntacts

open and close. The num ber of opera

ting cycles in a given period of time a nd

the length of time the elem ent is on in

each cycle is controlled by the amount

the knob on the switch is rotated.

A pilot light terminal simplifies the

conn ection of a light to in dicate th e on

position. Figure 10.10 illustrates the

internal layout of a typical infinite-heat

switch.


129



permanent magnet (opens and

closes contacts quickly)

terminals

bimetal

str ip

control

k nob

shaft

tension

arm

FIGURE

10.10 Internal

layout of an infinite-

heat switch unit

Oven Control

The switch controlling th e he at level in a

modern oven also provides infinite-heat

:

control.

A

liquid expa nsion s ystem is

used to regulate th e on and off cycles

th e sw itch. Cycling of the switch is fu

ther regulated by

an

adjustable threa

shaft that operates like a cam. The tim

ing of the heating cycle determine s th

amount of hea t in the oven at a given

time. The liquid expansion system

replaces the heater coil found in th e

nite-heat sw itch. (See Fig. 10.11)

The oil-like material used in the bulb

the liquid expansion system sens es

th

oven tem perature, expands

according

and operates a diaph ragm device ins

the switch. Both the expansion and c

traction

of

th e liquid and th e movem

back and forth of the d iaphragm open

and close a se t of contac ts inside the

switch. These co ntac ts switch the ov

on and off at the proper rate

of cyc ling to obtain the temperature

selected by the p erson using the oven

The oven sw itch con trols two ele

ments inside the oven. The upper bro

element is turned on by rotating the

live

240 V

live

.2 6(g

diaphr agm 5(§?

> >

f

pilot

pi lot l ights

4

< 1

NOTE: Bulb located ins ide oven

between upper and lower elements

bu lb

broi l

}-©—'

-©

bake

broil

bake

r

copper tube

(gas-f i l led

or

oil-f i l led)

FIGURE 10.11 A liquid expansion system oven control switch

130 Applications

of




d the switch to the broil

position,

•anufacturers design the oven

o

that

it

will rem ain in

a

slightly

losition

for this operation. They

• l e n d

that broiling be done with

• e n door partly open to ensure

•en temp erature does not get hot

to cycle the c onta cts. The broil

twill

then remain

on,

necessitat-

1

food watching

if

burning is

to

ided. It is also com mon to have an

•ith an automatic preheat process.

i the oven is being pre heated , the

Element will com e on with th e bake

•L

The broil element will

be auto-

iy

turned off when oven

tempera-

s approx imately 40°C below th e

setting of the sw itch.

Men

tem pera ture will then

be

Bfat to its selected heat level by the

element and kept there as

the

h

cycles on and off during the

tag

proc ess. Having both eleme nts

gether provides a lot of heat and

he oven up to temp erature rather

ly.

The purpose

of

th e broil

ele-

then is

to

preheat the oven an d/or

food qu ickly. The lower bake ele

ment is used for normal heating of the

oven and is und er the con trol of the liq

uid expansion system

at

all tim es.

Pilot lamps are norm ally included

in

the oven circuit

to

indicate when the ele

ments are on and producing heat in th e

ove n. Figure 10.12 illustra tes th e internal

layout

of a

typical oven con trol sw itch.

Self-Cleaning Ovens

Ovens with a self-cleaning feature do

not req uire spilt or burnt food to be

remov ed from t he w alls and floor of the

oven through the use

of

stron g cleaning

materials. They thereby eliminate

a

tedi

ous and often messy process.

Continuous Cleaning Type.

This oven

uses its normal cooking temperature

to gradually reduce the b urned food

particles

on

its inner surfac es. An oven

cleaned this way doe s not appe ar to be

as clean as on e of the sec ond ty pe and

the proc ess takes m uch longer.

Pyrolytic Self-Cleaning Type.

This

oven, with its more efficient cleaning

bake terminal

-copper tube

line terminal

d ia p h ra g m me ch a n ism

10.12 Internal layout of an oven control switch


131



system, uses a high oven te m pera ture

over a sh ort er period of time to re du ce

food particles to an easily removable ash.

A pyrolytic oven relies on a co ntrol

switch-and-circuit that o pe rate s in much

the same manner as the temperature-

sensitive expansion system used in regu

lar oven switches. However, the control

switch-and-circuit has more functions to

perform than the expansion system.

The oven temp erature reaches approxi

mately 480°C during its cleaning cycle,

and as mentioned abo ve, reduces food

spill-overs to a small am oun t of ash

(muc h like a ciga rette ash ) in an ho ur

or two. This ash can then be easily

removed, leaving the oven clean and

read y for future us e.

Due to the much higher tempe ra

tures in this type of oven, the oil-like

material in the expansion s ystem is

replaced w ith helium ga s.

A

larger bu lb

accommodates the amount of helium

required to ope rate the diaphragm in the

switch.

This type of control switch may have

up to four different sets of contacts, all

of which are set to operate at different

temperatures and open and close the

various circuits as the gas-filled expan

sion system d ictates. One set of con tacts

would be for baking and broiling, while a

second set would be calibrated at the

factory to op erate th e oven at high tem

pera ture during the cleaning cycle.

Although oven temperatures are

high d uring t he cleaning cycle, only a lit

tle electricity is used. That is because

the elemen ts are conn ected in such a

manner that they operate at 120 V, pro

ducing less tha n the ir full wa ttage, b ut

staying on throu gho ut th e cycle. The ele

ments are not cycled on and off as fre

quently as they are during the cooking

operation, bu t are allowed to pro duc e

heat for a longer period of time. Extra

insulation is usually put into a self-clea

ing oven to a ssist th e elemen ts in

obtai

ing the proper temperature and preven

excessive heat from passing through to

the ou ter surfaces of the stove

itself.

A third set of contacts can be used

engage a latching mechanism in the

oven door. This prevents the door from

being open ed during the high tempera

tu re cleaning cycle. Th e oven do or latc

ing mechanism is set to keep the do or

closed whenever oven tem perature

ex cee ds 320°C for two safety rea son s.

First, burns to hands or face can be

severe when oven surface and air tern-

peratures reach this level. Second, a su

den inflow of oxygen from the air as the

oven doo r is open ed can cause food pa

tides

in the oven to burst into flames

when th e temp eratu re is in the high

range used for cleaning.

A

fourth set of co nta cts on th e

switch can be used to hold the food at

warm temperature, after the baking pro

cess,

until you are ready to eat the foo

This temp eratu re is approximately

80°C

Most modern ovens have useful

timer circu its built into their control

panels. Ovens can be set to come on at

predetermined hour of day or night, to

cook for a preset length of time, and to

sh ut off or keep food w arm un til need*

Elements, receptacles, and m inute mil

ers can all be timed and/or controlled.

Figure 10.13 illus trate s a circuit

dia

gram for a self-cleaning oven. All

switches co ntained within the do tted

lines are controlled by the gas-filled

expansion system . The door-lock switd

ope rates the door-lock solenoid, or

electrically powered, magnetic latch

assembly, once th e clean cycle has be

selected and preve nts the door from

being opened during the cleaning open

tion. The door's electrical interlock (5i

6) prevents the solenoid from releasin

132

Applications

ol




L

2

Q

240 V pow er s upply

Al l switches within dot ted

l ine are control led by

thermostat ,

(gas-f i l led bulb)

O L ,

-a-"

o-

door lock

switch

* "

O-

manual

door

interlock

^ C

5 6

door lock switch

electr ical interlock

keep warm switch

- /

8

main

cycl ing

contacts

3 4

hi temp,

clean -

switch

door lock

jy /solenoid

gr ound

broi l e lement

t her m al

relays

function selector

switch on control

panel

URE 10.13 A self-cleaning oven circuit

bake element

\door once the oven temperatu re

che s cleaning level.

The manual door interlock switch

asses

the norm al cycling con tacts,

i removing the expansion sy stem

xn the circuit for the cleaning o per-

kxi and allowing the oven to reach

D°C. A hi-temp clean switch preve nts

le oven from rising abo ve the desired

leaning tempe rature.

The function switch located on


the control panel of the stove/oven is

used by the owner to select bake, broil,

preh eat, etc ., functions for the oven .

Both bake and broil elements are further

controlled b y a therm al relay (part of th e

gas expansion system) which controls

their cycling to obtain p rope r oven tem

pera ture as selected by the o perator.

Figure 10.14 illustrates the internal lay

out of a self-cleaning oven switch, pyro-

lytic

type.

133



E xternal View

control knob shaft

insulat ing sleeve

Bourdon tube replaces diaphragm

(expanding spiral act ion)

Internal View

gas (heliurn)-f i l led bulb

FIGURE 10.14 A self-cleaning, pyrolytic oven control switch

Recent developm ents in suc h

switches ha ve brought ab out th e use of

a sodium/potassium-filled tube and bulb

expansion system . The sod ium/potas

sium m ixture turn s into a liquid

at

oven

operat ing tempe ratures, expanding to

operate

a

bellows dev ice in the switch.

A

higher degree

of

sensitivity is obtained

with the new expansion system, bu t th e

electr ical conta cts opera te in much the

same m anner as previous switch m echa

nisms.

Rotisserie.

Many mod ern ovens

are

equippe d with a motor driven u nit to

rotate foods w ithin the o ven while

cooking. Juices from th e food being

cooked fall from the rotating unit and

can often land on the lower bake

eleme nt. To preven t smoking of these

grease s, the broil element is used

by

many m anufacturers for the rotisseri

cooking cy cle. Its location in th e upp

par t of the oven p reven ts dripping pz

cles from landing on it, thu s red uc

ing the smo ke p roblem .

When selecting the cooking temp

ture for rotisserie cooking, the switch

kn ob is rotated clockw ise to th e broi

position, and then backed off to the

desired cooking tem peratu re. This

engages the broil element only, throu

a mechanical selection system built

i

th e front of th e switch, an d allows the

broil element to heat th e oven while

being controlled by the gas exp ansio

system.

134

Applications

oi




o r R e v i e w

List four appliances that use heat-

rol switches.

ain how three levels of heat

\»re obtained with the 3 heat

switch.

Of what use is the reference point

n the ba se of a 3 heat switch?

must

heat-control switches

opera ting on 240 V be c apa ble of

ipening

both live wires?

W hy has the 7 heat switch gradu-

replaced

the older 5 heat

i tch?

iy

is a pilot light an im por tan t

ure on heat-control switches?

two advantages the infinite-

at switch has over other heat-

ltrol switches,

lain in your own wo rds the

ration of the infinite-heat

tch.

ere is the oil bulb for an oven-

rol

switch located?

What precaution must be taken

when using the broil element?

itate

two advantages of the

self-

cleaning oven.

Which type of self-cleaning oven

cleans th e best? Explain why.

is the high tem peratu re

obtained for the cleaning cycle of

a self-cleaning oven?

Explain why extra insulation is

required around a self-cleaning

oven.

What are the advantages of an

electrically timed oven circuit?

Heat-Control Sw itches 135



A

rmoured cable (A/C) can be used

for both open and concealed wiring

sy ste m s. Unlike NMSC, it may be ru n on

the surface of walls and ceilings in build

ings of mason ry con struction .

Armoured cable is widely used as a

quick metho d for distributing power

throughout new industrial plants, adding

to existing plants, and relocating

machinery. It can also be used in public

and commercial buildings where the

possibility of physical damage to the

cable makes NMSC unsu itable .

Armoured cable is more flexible than

rigid conduit systems. It can be installed

in long continuou s run s without need for

joints and splices. Conduit system s,

however, require a box or fitting after

each 30 m of conduit and/or after an

accumulation of 360° of bend to ease the

pulling in of the con du ctor s.

Electrical Ratings

Unlike NMSC, A/C has a continuous

protective m etal covering, and so is

approv ed for use on circuits up to

600 V

maximum. It is available in 1,2,3, and 4

conductor combinations, ranging in size

from No. 14 t o No. 4/0. Larger co ndu c

tors may be made to order.

Individual cond ucto rs in the cable

used to be covered w ith a cotton-braid-

Armoured

Cable

over-rubber insulation which was

for use at a maximum temperature

60°C.

Chang es in th e C anadian

Ele

Code have resulted in improvem en

in the insulation on these conduc

Modern A/C cond uc tors are insula

with a durable material called

Cr

(X-Link). X-Link has a maximum

te

ature rating of 90°C.

Trade Names

Armoured cable was originally kn

armoured bushed cable (ABC),

bec

small, anti-short bushing w as inse

in to the end of each cable

termina

How ever, ins talle rs often refer to A

simply as

BX

or BXL.

BXL

refers t o

type that has an intern al lead shea

over the conductors.

Cable Construction

Figure

11.1

show s the materials us

the c onstru ction of the older style

A/C. Figure 11.2 shows modern ca

construction.

One type of armou red cable ha

lead she ath placed be tween th e co

ductors and the armour. This shea

prevents m oisture or chemicals fr

entering the conduc tor portion of

cable. Th e she ath makes the cable

136




able for outdoo r use or direct burial

ie ea rth . (See Fig. 11.3) The

utnum

arm our on m ost A/C, how-

t corrodes severely when placed

ler ground. Therefore, steel is used as

placement on the cable for outd oo r

(•nderground use (ACL).

Ie

T ermination

first step in fastening A/C to a box or

is to remove the armour with a

copper

black

cot ton braid

a lum inum s t r ip gr ound

Doe' insulat ion

paper

a l u m i n u m a r m o u r <S

11.1 O lder style 3 conductor

oured cable

RW-90

(X-link)

insulat ion

whi t e

.copper

g r ound w i r e

S

<

black paper

a lum inum ar m our

E

11.2

Mod ern flexible armo ured

RW-90 (X-link) insulat ion

fcned

copper

red

whi t e \

black

V

lead

/

\V^\

paper

\

kjlation

galvanized steel

ar m our

H E 11.3 A C L flexible armoured cable

c

3

33333)

S T E P

1.

Cut t h r ough

2 wrap s of armo ur

at appr ox im at e ly

45°

833333333*

paper wr app ing

mssssQ

S T E P 2. Rotate armour

and remove f rom cable.

Remove paper wrapping.

anti-short

bushing

STEP 3. Insert bu shing

between armour

and conductors.

grounding st r ip

T ighten locknut .

ant i -short bushing

(can be seen here)

Secure grounding st r ip

under connector c lamp.

STEP 4. T ighten conn ector on cable.

Install connector in box.

FIGURE 11.4 P rocedure for terminating

armoured cable in box

Armoured Cable

137



>•

outlet

box

ground screws

cable clamp

15

cm free conductor

7 X

X X X

XT -

anti-short bushing

swi tch mount ing

lug

ground str ip

armoured cable

cable strap within

30 cm of box

FIGURE

11.5

Old-style armoured cable secured to box by built-in clamp

hacksaw. (See Fig. 11.4) Take c are to

remove the correct amou nt of armour

the first time. It is often difficult to hold a

small length of cable for a second cut.

Take care, too,

to

protect the insulation

on the con duc tors from being damaged

by the saw du ring th e cutting. Trim the

paper wrapping around the conductors

as close to the arm our as p ossible.

After removing the armour and trim

ming the p ap er w rapping, fold b ack th e

aluminum grounding strip so that it is

out of the way beside th e cable. Insert a

fibre or plastic anti-short bushing

between the armour and the conduc

tors. This anti-short bushing prevents

the jagged edg es of th e arm our from cut

t ing into th e insulat ion aroun d th e con

duc tors. Once the anti-short bushing is

in place, insert the cable in to an

approved box connector. The box con-

138

nec tor h olds the anti-short bushing

place, secu res the cable to the box o

ting, and c lamp s on to the grounding

strip. Use of it ensures that the g ro u

circu it is co m ple te. (See Figs.

11.5

an

116)

Cables now being produced have

grounding conductor

instead

of an al

num grounding

str ip.

This feature e

inates the need for folding ba ck and

clamping a grounding strip.

Cable Supports

As does NMSC, arm oured cable mus

be suppo rted by an approve d strap

stap le within 30 cm

of

every box. A

maximum of 1.4 m be twee n th e

supp

on the cable run is allowed. If th e ca

is run through wood en joists , it mus

be kept back at least 3 cm from th e f

Applications

of

Electrical C onstruction



used

to

supply p ower to outd oor lights,

signs, and

related equipment. ACL can

also

be

used

for

underground supply

lines

to

electrical equipm ent. P um ps,

garden lighting, post lights, and supply

lines between buildings often require

ACL's water-resistant feature. (See Fig.

11.3)

Water-tight connectors must b e used

to sec ure this cable to a box or fitting in

a wet area. (See Fig. 11.7) There are sev

eral typ es

of

conn ecto rs, all of w hich

compress

a

moisture-proof lead sleev e

around the cable. Figure 8.10 shows this

method used

to

supply an outdoor post

light. Figure

11.8

shows

a

garden recep

tacle installation. Becau se it has steel

armour,

ACL

can be buried in masonry

or concrete where excessive moisture

is

present.

lea

FS weatherpr

(f it t ing)

wat

conp

FIGURE 11.7 ACL connected to mois

proof fitting

NMSC

w e a th e rp ro o f box and cover

octagon

box

water-t ight connector

w e a th e rp ro o f box

and receptacle cover

I

support

grade level

bolt and nut

house wal

protective board

preservative-treated)

1 m be low grade

L

7—i—in -i -ii i i i i i i r—i r r r r

r'-r

r-7—r

15 cmsand layer ACL

\

suppor

-steel po

FIGURE

11.8

Typical garden receptacle installation using ACL

140




A l u m i n u m

Sheathed

Cable

A

n aluminum-sheathed cable, which

is a

factory-assembled

wiring sys

tem, is a seam less m etal or welded

wrap

aroun d shea th enclosing a single or mul

tiple conductor assembly. The aluminum

sheath is both vapour- and liquid-tight,

and the condu ctors enclosed in the

sheath can be either copper or alumi

num. Co nduc tors w ere at one time insu

lated by rubber, but are now insulated

by

Cross-Link polyethlene,

rated at a max

imum tem pe ratu re of 90°C.

Smooth-Sheathed Cable

Aluminum -sheathed cable was basically

a

cable-in-a<onduit,

assembled and

tes ted at the factory. Using it

simplif

installation and saved considerable

and labour. While much smooth-shea

cable is still in u se (se e Fig. 12.1),

but man ufacturers are now producir

corrugated cable in all sizes, instead

Corrugated Cable

The conductors of this cable are

enclosed in an oversize aluminum

tu

The tube is then passed throug h a

revolving die

that compresses

two-t

of the tube on to the insulated condu

to rs . (See Fig. 12.2) Th e soft, m etal

arches

allow the cable to b e bent ea

while the w ork-hardened

flat spiral

FIGURE 12.1 O ld-style smooth-sheathed aluminum cable

FIGURE 12.2 C orrugated aluminum sheathed cable w ith a type " W " moisture-proof

connector

142




)port the co ndu ctors . Large cables

i

thus be bent without the us e of

spe-

I

tools such as tho se requ ired for a

Juit system.

leath Covering

vvinyl chloride (PVC)

jacket is

jded over the aluminum sheath. The

;t enables th e cable to resist corro-

i

chemicals and to b e used under-

ld.

Jackets are made in various

rs to aid identification of circuits

I

voltages.

itrical Ratings

inum-sheathed

cab le is made for

on any voltage require d. Most of th e

ion sizes of condu ctor units are

ily

available with a 600

V

rating. Part

[the

Canadian Electrical Co de lists

current-carrying capacity of the

in its ampacity tables,

rh e conductors of aluminum-

led cable car ry a maximum

tem-

lre

ratin g of

90°C.

igle

Versus

Iti-Conductor Cables

;onductor cables have a much

•current rating

than multi-conduc-

cables with th e sam e gauge of wire.

;fore, it is more econ om ical to us e

single-conductor cables, rather

one large multi-conductor cable, for

truction of heavy-current circuits.

leath Currents

lduc tor carrying electrical current

luces a ma gnetic field aro und

itself.

i

the cur ren t is alternating (AC), th e

gnetic field rises and falls in strength

th e current pulses through

the co nductor. This results in a moving

magnetic

field.

Any metal substa nce w ithin th e

range of this moving magnetic field will

have a curre nt induced into it by the

field. When both ends of the cable are

groun ded on a single-conductor unit, a

circuit is formed and th e shea th curr ents

circulate. The she ath c urre nts of cables

runn ing side by sid e will circulate

between them, if the cables are con

nected t o a comm on m etal box at each

end.

As the shea th curren ts increase in

volume, heat is generated in the she ath.

This heat can be severe enough to dam

age the insulation around the condu c

tor s within the cab le.

Single-conductor cables carrying

higher amounts of current, for example,

425 A and up, must receive special care

when run side by side. Copper cables of

250 MCM and a luminum cable s of 350 MC

and larger must hav e their shea ths insu

lated from one another at one end of the

cable run and be grounded at the oppo

site end. The se measures prevent she ath

currents from circulating within the

cab le sy stem . (See Figs. 12.3 and 12.4)

Note: Do not use m agnetic materials,

such as steel, for suppo rting

single-

condu ctor cables. These suppo rts can

become magnetized and have currents

circulating within them . The se ed dy

curr ents , as they are called, heat th e

supp ort and cause damage to the

cable insulation.

Con nectors used t o termina te single-

condu ctor cables mu st also be mad e

of

nonmagnetic

material. In a three co ndu c

tor system (3 ph ase system ), all three

cables mu st enter th e box or cab inet

through one, nonmagnetic plate. When

this plate is fastened to the bo x or cabi-

Aluminum-Sheathed Cable

143



nonmagnet ic box or p late

dry-type or

wet- type connector

a lum inum s heat hs

(smooth A/S or cor f lex)

insulat ing mater ia l

steel box

N O T E :

Gro undin g conductor is required with

insulat ing plate.

FIGURE 12.3 T ypical cable installation (no shea th currents)

^^ground ing

bushing

dry-type or

wet- type connector

supply

alternative method

(if cable no t grounded

on metal box or plate)

a lum inum s heat hs

(smooth A/S or cor f lex)

NO TE: Dry-type connectors prevent edges of

aluminum sheaths from damaging insulated conductors.

NOT E:

Grounding conductor may be required.

FIGURE 12.4 A lternative me thods for grounding cables at boxes (Sheath currents

prese

net where the cables terminate and

currents are in excess of 200 A, serious

eddy c urren ts will not occur at the box.

Multi<onductor cables are more

expensive than the single conductor

units required to replace them , but th ey

tend to eliminate the problem of sheath

curre nts. When two or more conduc

are enclosed by th e same sheath, th

magnetic fields around each condu

cancel one another. Multi-conducto

cables may be encircled or supporte

mag netic m aterials w ithout risk of e

current damage.

144




C able T erm ination

1

he old-style

smoo th-sheathed

c ables in

e smaller sizes made use of a connec-

r that was similar to an armoured

M e connector. Both dry-type and

aisture-proof

connectors were used.

P e e Figs.

12.5

and 12.6)

Modern

corrugated

cable requires

•sectors

of a design different from

kat used with smooth-sheathed cable.

loth dry-type and moisture-proof con-

Bctors are available. (See Figs. 12.7 and

US)

Corrugated

cable with a

PVC acket

be term inate d w ith a different typ e

trade size

threaded entrance

of co nn ec tor. (See Fig. 12.9 on page 147.)

P reparation of C able for

Termination

Removing the aluminum shea th from the

cable is easy to d o. Calculate how much

free conductor is required in the box,

mark the cable, then score the outer

sh ea th w ith a knife. Take care not to c ut

through the aluminum: just dent the sur

face. Bend the end of the shea th to be

removed u p and down by hand, cracking

the sh eath at the sco re line. Pull on the

sh ea th t o b e rem oved . It will slip off th e

conductors easily.

cable sheath stop

(shoulder)

seamless (smooth)

a luminum sheath

R-75 or R-90

rubber insulation

standard

locknut

t inned copper

conductors

•

5

•8

3

E X-link insulation is now being used

^Buminum-sheathed cables.

JRE 12.5 Dry-type conne ctors used on smo oth-shea thed cables (no longer produced)


145



N O T E :

Compresses clamping r ing

hexagon a luminum al loy or mal leable body

spl i t c lamping r ing

smo o th a lu m in u m sh e ath

(vapour- and liquid-t ig ht) pack nut

\

trade size

threaded

entrance

R-75 or R-90

rubber insulation

(braid overall)

gasket compressor

t inned

shoulder copper

neoprene or sil icone com pression gasket (sheath stop) conduc

I A c.

Alle n set-screw (3)

.

gasket rubber cla mp ing

p a c n u

com pressor gasket ring

body

outer standard

rubber gasket locknut

N O T E : X-link insulation is now being used in aluminum sheathed cables.

FIGURE 12.6 Moisture-proof connec tors used on smo oth-shea thed cables (no longer

produced)

N O T E :

X-link insulation is now being used in aluminum sheathed cables.

^n^^Ji

trade size threade d entrance standard locknut

WH»K?.9Pa

F

.tWJP

W

*-.

u

*

K

.

FIGURE 12.7 Type " D " dry location connector for corrugated cable (Suitable for cable w

sheath covering)

146




c X-link insulation is now being used in aluminum sheathed cables.

helically

corrugated

aluminum sheath

toapour- and

fcau id-tight)

arched helix

(for bendability)

hexagon

a l u m i n u m

alloy

gland nut

hexagon

a l u m i n u m

alloy body

neoprene

sealing

gasket

R-90

rubber

insulation

(braid

overall)

trade size

threaded entrance

RE 12.8 Ty pe " F M " mois t ure- proof or s ubm ers ib le c onnec t or f or c or rugat ed c able

only for cable wi th sheath cover ing)

rubber grommet

compression nut

2 / 0 C O R F L E X RA 9 0 X - L I N K

m m * * • « * • • « « < t • * > t u » « « • M * • • •

JRE 12.9 T y p e " W " s u b m e r s i b le c o n n e c t o r f o r c o r r u g a t e d c a b le with PVC jac k et

itable only for cable wi th sheath cover ing)


14



P O I N T M A R K E D

IN FIG 1 I

C O N N E C T O R A P P L I E D

T H I S E N D

STEP 1. Locate and mark end of a lum inum sheath

and temp orary end of jacket (sheath cove r ing) .

ST EP 2, S tr ip off sho rt leng th of jacket (sheath

cover ing) f rom point marked in Step 1 t owar ds end

of cable. Cut covering square (see Step 6).

REMOVE

THIS END

C O N N E C T O R A P P L I E D

T H I S E N D

STEP 3. Use f ine tooth hacksaw to cut fu l ly

through hel ix of a luminum sheath, us ing jacket

edge as guide. Score f lat por t ion of sheath to a bout

half of sheath thickness. Crack scored sheath by

bending cable gent ly back and for th.

STE P 4. P ull off left-hand end of cable sheath

(exposed sheath and jacket), leaving jacketed end

(at r ight) for app licat ion of connec tor. S mo oth o ff

burr on aluminum sheath th is end.

STE P 5. Use mark on hexagon of connector bo dy

to locate point for removal of jacket.

STEP 6. Wrap piece of paper around jacket as

guide to ensure jacket cut is square with axis of

cable.

148




R U BB E R G R O M M E T

Jacket removed and compon ents of con-

faced as show n. Wet rubber grom me t to

(turning it on jacket of sheath.

BODY OF CONNECTOR

STEP 8. Body of connector turned f i rm ly by hand

onto a lum inum sheath. Do not use wrench.

s

=8

9>

• Rubber grom me t turned f i rmly against STEP 1 0. Compressionnutthreaded onto body of

connector. connector. Use wrenche and compres s grom met

until it bulges slightly from under compression

nut.

12.10 P rocedure for terminating corrugated cable w ith moisture-proof connector

Corrugated cab le, with its PVC

t.

is a little m ore difficult to ha nd le.

12.10

shows how to prepare this

I

for a con necto r.

lie Supports

inum-sheathed

cable requires

non-

tetic aluminum

su pp ort s. (See Fig.

II)

The Canad ian E lectrical Code

?s a strap every 2 m, but som e sag

I cable may occur in the smaller

5.

One cable manufacturer recom-

O

XJT

Q

FIGURE 12.11 Aluminum clips for A /S

cable

Aluminum-Sh eathed Cable 149



m ot or w i r ing

mends a s t rap every 1 m to 2 m on

cables up to 3 cm in diameter. In m any

industrial installations, m ulti-conduc

cab les are laid in a trough or rack

designed

for

this purpose. Figure 12.1

show s typical cable installations.

pulp and paper mil

FIGURE 12.12 Cable applications

F o r R e v i e v

1.

What are th e two main typ es of

aluminum-sheathed cable?

2. Which aluminum-sheathed cable

is easier to bend

in

large sizes?

3. What jacket material is used for

corrosion-resistant cable?

4. What is the most common volta

rating for aluminum -sheathed

cable?

5. W hat is th e maximum temperatu

rating

for

the cond uctors

in alum

num-sheathed cable?

6. Why

is it

more econom ical to

run

single-conductor cab les, rather

than one multi-conductor cable'

1

7. Explain in your own words how

sheath currents are produced in

aluminum-sheathed cable install

tions.

8. Why are there no sheath curren

in multi-conductor cable syste

9. Magnetic materials must

not be

used to support or terminate sirv

gle-conductor

cables. Explain.

10. Describe briefly how to remove

the aluminum sheath from

a ca

that is to be terminated in a dis

bution panel.

11. W hat spacing is required by th e

Canadian Electrical Code for

straps supporting aluminum-

sheathed cable?

ISO

App lications of Electrical C onstruction



ineral-insulated (MI) cable was

developed to provide the electri-

tadustry with a fire-resistant wiring

:t. This cable cannot ca use or con-

l a t e to a fire bec aus e it contain s no

tamable

m ater ials. It was first intro-

d in th e 1930s. Since the n, it ha s

I

to be so versatile that new appli-

; are constantly being devised.

rturesof Ml Cable

[cable resists fire up to the point of

f copper melting in and aroun d th e

He. It is moisture-proof, corrosion

•stant, immune to oil product dam -

9? .

and not pron e to aging. It pro vide s a

mpact, neat, surface-wiring cable sys-

•L It doe s not sa g and is eas y to install.

be used indoors or out and is

long enough for direc t burial in th e

•rth. It will withstand an almo st u nbe

arable

amo unt of physical ab use before

i

electrical breakdow n o ccu rs.

D W

Ml C able Is M ade

1 to 7 high-conductivity

copper

9 m in length, are inserte d into a

i tube of seam less copper.

Mag-

<im

oxide, w hich is an excellent elec-

insulator and conductor of heat, is

eked under pressure around the rods.

Mineral-

Insulated

Cable

The end s of the tube are sealed, and the

9 m section is drawn throu gh a series of

reducing

dies. These dies decrease the

diameter of the cable and increase its

length.

The magnesium oxide insulation is

the sam e density as the coppe r used in

the tube and rods. This m eans that a s

the tube assem bly is pulled through the

reducing dies, the tube , insulation, and

rods are reduced in size simultaneously.

The relative spacing between t he con

ducto rs and th e tube is always main

tained, beca use the rods are reduced in

direct proportion to th e tube itself.

MI

cable can be produ ced in any con

duc tor size by continuing the drawing

process until the conductors have been

reduced to the desired w ire gauge num

ber. (See Fig. 13.1)

Cable Size and Voltage

Range

Mineral-insulated cables are produced in

the 300

V

and 600

V

ra ng es. Figure 13.2,

on pag e 153, illustrates the a ctual size of

each con ducto r in the cable, as well as

typical groupings for multi-conductor

cables , in the 300

V

range.

Figure 13.3, on page

154,

shows 600 V

cables and their conductor groupings.

Mineral-Insulated Cable

151



Th ese ca bles range in size from No. 16

AWG to 250 MCM. Single-conductor,

350 MCM and 500 MCM cables are also

available.

copper

tube

•

m agne s ium -ox ide

insulat ion

•

copper

rods

E

•J

FIGURE 13.1

insulated cable

Cutaway view of mineral-

Durabil ity

MI

cable can withstand severe

phys

abuse without electrical failure. Its a

ity to change the sh ap e of the outer

sheath, mineral insulation, and

in te

conductors at the same time makes

possible.

A

crushing blow from a h e

object will merely change the cable'

sh ap e. (See Fig. 13.4 on page 155.)

MI cable is as resistant to heat a

to mechanical injury. Figure 13.5

sh

how Pyrotenax MI cable compares w

other wiring systems under severe h

conditions.

The Underwriters' Laboratories

Canada tested th e cable's resistance

heat by mounting several 300 V and

600

V MI

cab les on the inside of a fu

nace. The cables w ere subjected to

furnace's fire for a two-hour period

carrying a full electrical load. Temp

tu re s re ac he d a level of 1010°C. As a

result of this test, Pyrotenax cables

given a two-hour fire rating under st

ard

S101.

Figure 13.6 illustrates a fire

rated cable and its attach ed label.

Fire E ndurance and

Comparison Test

Further testing of wiring products w

carried on at the Warnock Hersey

T

ing Labs in Vancouver, British Colum

Aluminum-sheathed cable, armoure

cable, 90°C X-link wire in cond uit, an

Pyrotenax cable were subjected t o

peratures reaching

939°C.

The wirin

produ cts were mounted on a double

layer of drywall m aterial and exp ose

an o pen furnace. All cables were

en

gized during the

one-hour

test perio

The conventional wiring produ c

failed within the first 3 min at

temp

tures n o higher than 316°C. The alu

num-sheathed cable failed to ground

152




I

rat ing

ims/1000ft

ohms/1000

m

i size

A W G

rat ing

nms/1000ft .

ohms/1000 m

i

size

A W G

[ ra t ing

hms/1000ft

Ohms/1000

m

i size

A W G

15

2.58

8.46

1/2 in.

0

240/2/D

15

2.58

8.46

1/2 in.

©

273/3/D

15

2.58

8.46

1/2 in.

©

344/4/LD

15

2.58

8 4 6

3/4 in.

/ • • \

1 " • • J

418/7/LD

20

1.62

5.31

1/2 in.

30

1

02

3 35

1/2 in.

©

273/2/D

20

1.62

5.31

1/2 in.

©

309/3/D

20

1.62

5.31

1/2 in.

©

319/2/D

3 0

1.02

3. 35

1/2 in.

. • •

355/3/D

3 9 3 / 4 / L D

1 3 . 2 T y p i c a l 30 0 V M l c a b l e c o n f i g u r a t i o n s and s i z e s

50 s; th e arm ou red cable failed

to

I in 3 m in; and t he X-Iink wire in

ait failed

to

ground

in

2 m in, 25

s.

j MI cab le, however, withsto od

the

:

temperatures for the entire one-

m

period and continued

to

operate

sfactorily after the test was com

pleted.

A major reason for the cable's fireproof

iarac teristic is that the magnesium oxide

•ulation

and the copper sheath tend to

•duct hea t away from t he cable. Fire

tern or pump circuits can use to advan

ce this cable's ability to op erate und er

Ji-temperature conditions.

reproof Applicat ions

idem,

complex smoke detection sys-

D S

and signalling methods no longer

iire a person to "pull-the-alarm" to

•e

warning of da ng er from fire. As well

as notifying

a

building's inh abita nts of

fire, ancillary system s such as smoke

control dampers, pressurization fans,

doo r closing, and elevator hom ing are

activated immediately. Many of these

systems are required by the Building

Code. Othe rs are installed by con cerned

building management companies.

Despite the progress m ade in alarm

and dete ction sy stem s, little or no prog

ress has been m ade in the way they are

interconnected. The Building Code

recognizes that fire protection and alarm

circuits require special treatm ent. If th e

conductors are installed

in a

service

space containing combustible materials,

they must

be

isolated from th es e ma teri

als by a one-hour, fire-rated sep aratio n.

Unfortunately, as mentioned previously,

raceways and other wiring products can

not withstand fire for more than a cou

ple of minutes.

MineraHnsulated Cable 15S



Resistance ohms/1000

ft

ohms/1000 m

Term ination size

16 AWG

Current rat ing

Resista nce ohms/1000 ft.

ohms/1000 m

Termination size

14 AWG

Current rating

Resistance

ohms/ioooft

ohms/1000

m

Termination size

12

AWG

Current rating

Resistance ohms/1000 ft.

ohms/1000 m

Termination size

10 AWG

Current rating

Resistance

ohms/ioooft

ohms/1000

m

Te rmination size

8

AWG

Current rating


ohms/1000 m

Termination size

6 AWG

Current rating

Resistance

ohms/i 000 ft

ohms/1000

m

Termination size

4

AWG

Current rat ing

Resistance

ohms/1000 ft

ohms/1000 m

Te rmination size

Current rat ing


ohms/1000 m

Te rmination size

4.094

13.43

1/2 in.

O

215/1

4.094

13.43

1/2 in.

©

340/2

4 094

13.43

1/2 in.

©

355/3

4.094

13.43

3/4 in.

©

387/4

4.094

13.43

3/4 in.

4

20

2.58 Q

8 4 6

1/2 in.

230/1

15

2.58 (77)

8.46

*—'

1/2 in.

371/2

15 ^

258 (£\

8.46

^zy

1/2 in.

387/3

15

III

(3

3/4 in.

418/4

12

2.58

(

8.46

/4 in.

4

25

1.62 0

5 31

1/2 in.

246/1

20

1.62

5.31

1/2

in

©

402/2

20

1.62

5.31

1/2

in

©

434/3

20 ^-~.

IS ©

3/4 in.

465/4

16

1.62

5 3 1

3/4 in.

®

5

4 0

1.02 (S)

3 3 5

W

1/2 in.

277/1

30 _^^

1.02 ( 1 )

3.35 \ L x

3/4 in.

449/2

3 0 _ ^

iS ©

3/4 in.

480/3

30

/

^ -

x

a ®

/4 in.

527/4

24

1.02

3.35

1 in.

^

(

6

70

0.641

2.1

1/2 in.

®

309/1

50

0.64

2

3/4 in.

641 f~»\

512/2

50

0.641

2 1

3/4 in.

543/3

40

0.641

2.1

3/4 in.

590/4

100

0 4 0 3

1.32

1/2 in.

®

340/1

70

0.403

1.32

3/4 in.

590/2

70

0.403

1.32

3/4 in.

• • ;

621/3

684/4

135

0.253

0,83

1/2 in.

®

402/1

684/2

90

/

—

N

0 253 I # \

0

83 \%%)

1 in.

V /

730/3

3

AWG

2

AWG

1

AWG 1/0 AWG 2/0

155

0.201

0.66

1/2 in.

< § >

434/1

180

0.159

0.52

3/4 in.

465/1

210

0.126

0 41

3/4 in.

®

496/1

245

0 100

0.33

3/4 in.

543/1

285

0.0795

0.26

3/4 in.

5

3 / 0 A W G

ir(§)

3/4 in. ^ - ^

637/1

4 / 0 A W G

385

/ ^ \

0.0500/^AA

016 \ W /

1 in.

v

—

'

699/1

2 5 0 M C M

425

/ ^ \

0 0431/ f lA)

0.14

^

746/1

FIGURE 13.3 Typical 600 V M l cable configurations and sizes

(The ratings shown for

sin

conductor cables are thos

design ated by the C anadia

E lectrical C ode, Pan 1, for

cables in free air.)

Screw-on seals for this

cable range.




RE 13.4 M l cable continues to func-

n flattened to one-third its original

iter.

O nly its shape changes.

tenax

cable (intact after 2 h)

sneathed rubber-insulated cable

foyed

after 25 s)

s

£

2

< 3

FIGURE 13.6 Fire-resistant

two-hour fire rating

cable w ith a

MI cables, tested and fire rated for

two hours, are invaluable in ensuring the

continuous operation of elevators,

pumps, emergency lighting, sprinkler

systems, smoke control systems, com

munication systems, and fire detection

systems. The additional operating time

guaranteed by

MI

cables enables people

to leave a building safely, while contrib

uting immensely to the control and even

tual put-out of the fire. As commercial

high-rise buildings continue to be built

in large cities, the ability to successfully

evacuate large buildings becom es

increasingly important. MI cable is one

way of providing the much needed time

to do so.

estos-insulated

wires in conduit

Minded after 6 mini

S

•r-insulated w i r es in c ond u i t

royed

after

2.5 min)

SURE 13.5 Fire test of960°C shows Ml

te durability under severe heat conditions

Special Applicat ions

Several special MI cables have been

developed for specific areas. For exam

ple, in keeping with the cable's fire pro

tection ability, a special instrumentcable containing a pair of twisted con

ducto rs inside a double sheath provides

single point grounding. It also provides a

shield from stray signals or electrical

interference. Figure 13.7 illustrates this

cable.

MlneraJ-lnsulated Cable 155



copper sheat

copper shield

twisted conductors

m agnes ium ox ide ins u la t ion

FIGURE 13.7 Twisted pair, shielded instrument cable

Both round and square cables having

solid or hollow conductors can be used

in high radiation environm ents. (See Fig.

13.8) The sturdiness and heat resistance

of the Ml cable make it most useful

around a space shu ttle's launch platform.

(See Fig. 13.9) Petrochemical plants

continue to develop automated circuit

and equipment where danger is

Applications

of




present from flash fire. Figure 13.10

:

a typical

MI

cable installation in

area.

Large-scale mining operations

•provide a challenge for this versa-

woduct. (See Fig. 13.11) Many oth er

PURE 13.10 M l cable is used in the petro-

^ B a l industry.

^ • R E 13.11 Ml was chosen for its dura-

id fire resistance in this large-scale

phg

ope ration.

industries such as breweries use MI

cab le for their c ontro l circ uits. (See Fig.

13.12) Also, a stainles s stee l MI cable can

be used near food and beverage products

or near chemicals that could dam age

the copp er sheath and its conduc tors.


FIGURE 13.12 This control panel for a

brewery bottling plant uses M l cable.

Cable Termination

Prepackaged termination kits are used

to connect

MI

cable to boxes, cabinets ,

and fittings. (See Fig. 13.13) Remove the

copper sheath with a stripping tool.

Place

a

gland connector on the cable just

before threading the self-tapping pot on

to the outer sheath. Press plastic sealing

com pound into the pot . Make sure yo ur

hands are clean so that no metal parti

cles are pressed in to th e sealing com

pound. A short circuit will likely occu r if

metal particles of any kind are allowed

to enter the pot.

Next, install the preasse m bled insu

lating

sleeves.

Use a crimping and

157



STEP

1.

Remove outer sheath with stripping

tool.

STE P 3. Force plastic sealing compoun d into po

by hand. Be sure hands are clean.

STEP

2.

A fter installing gland connector over

cable,

thread self-tapping pot onto copper sheath.

STEP 4 . C rimping and compression tool secure

sleeve sub-assembly to pot.

FIGURE 13 .13 P rocedure for typical Ml cable term inat io n

compression tool

to force the insulating

sleeves into place and lock them there.

Figure 13.14 show s a simple

screw

driver-operated tool and a m ore elabo

rate crimping tool tha t is also available.

Figure 13.15 shows a cutaway view of

the termination and an assembled unit.

These terminal fittings are designed for

use at temperatures up to 150°C. The

gland is equipped with a standard elec

trical conduit thread tha t will fasten to

electrical boxes with conduit

Iocknuts

or

thread into pretapped holes in moisture-

proof boxes and fittings.

Corrosive-resistant thermoplastic-

jacketed cab les and terminations are

available.

(See

Fig. 13.16)

158

hand-operated

crimping tool

screwdriver-operated

crimping tool

FIGURE 13 .14 C r i m p i n g a n d c o m p r e s s

tools




0)

c

c

o

o

"D

c

JO

brass

gland nut

brass

c om pr es s ion

r ing

brass

gland

body

tapered pipe

thread

brass pot cuts

own thread as

it screws onto

cable sheath

seal ing

c o m p o u n d

anchor ing

wedge

secur ing

sleeving

into cap

insulat ing cap

insulat ing

sleeve

JRE 13.15

A n Ml cable termination and

3d unit (cutaway v iew)

All cable terminations should be

Bcked with an insulation tester. This

^-resistance measuring instrument

I

apply approximately

500 V

to the

••ination and indicate whether or not

is safe for use.

o

a.

c

o

0)

o

CO

o

"5

o

FIGURE 13.16 A thermoplastic-jacketed

cable termination for corrosive areas

MI cable can be formed into a bend

having a radius no less than six times th

diameter of the cable being bent, with

out placing undue stre ss on it.

Multiple runs of Ml cable require

care and precision in planning. (See Figs

13.17 and 13.18)

ble

Installation

cable is supported by copper straps

ated every 1 m to 2 m throughout th e

i. A wooden block and hammer are

ed to straighten any irregularities in

3\e.

FIGURE 13.17 Ml cable mu ltiple runs

Mineral-Insulated Cable 159



Sheath Currents

Induced currents can flow in the outer

sheaths of single-conductor cables in

alternating current circuits. (See Chap

ter

12)

The electromagnetic fields sur

rounding nearby cables cause them.

Since heat generated by sheath currents

does not affect MI cables much, these

cables do not need to be spaced apart.

They can be grouped together under a

common strap. (See Fig. 13.18)

Cables carrying in excess of 200 A

must be fastened to a nonmagnetic plate

at both ends of the cable, prior to secur

ing to a box or panel. Doing so elim

inates heat induction which could dam

age the box and its contents.

General Purpose

Applicat ions

The versatile MI cable is used for many

purposes and in many situations besides

fire protection and warning systems.

Commercial buildings, factories, houses,

and apartments, as well as processing

plants, and railway and subway system s,

make use of this cable. It is used for elec

tric heating of driveways and ste ps to

aid in snow removal and of water p ipes

to provide protection from frost. It can

also eliminate solidification of waxes

FIGURE 13.18 S ingle-conductor M l ca

entering distribution panel

and other materials in oil refinery pir.

and systems.

In addition to these uses, MI cable

found in communication and transmis

sion systems and has particular applk

tion in all kinds of marine vessels and

hazardous areas that contain dust,

explosive vapours , or liquids. Figure

13.19 shows MI cable applications.

160




S

F o r R e v i e w

1. List three features of MI cable.

2. Make a neat sk etch of a piec e of MI

cable, and label its parts.

3.

D escribe how MI cable reacts to

crushing blows from blunt objects.

4. What special advantage has MI

cable when used for emergency

circuits, such as fire alarms and

pump sys tems?

5. List the steps for terminating an

MI

cable.

6. What is the high-temperature limi

tation of

MI

cable? its term inal fit

tings?

7. What type of MI cab le is used in

corrosive areas?

8. What precautions should be taken

to red uc e the po ssibility of dam

age from sheath currents when

fastening MI cab le to a box?

9. At wha t level do s hea th cu rren ts

beco m e a problem for MI cables?

10. List three typical electrical instal

lations where

MI

ca ble will have an

adv antage over othe r types of wir

ing systems.

ply electr icity to apartment building

JRE 13.19 Typical MI cable applications


161



A

conduit wiring system offers a

mechanical protection to electrical

circuits that is rare with other wiring

methods. Voltage in a conduit system is

limited only by the insulation on the

conduc tors within the system. Metallic

conduits provide a high degree of fire

protection, as well as the ability to safely

contain overloaded or short-circuited

conductors tha t could cause or contrib

ute to a fire.

Unlike any other wiring method, con

duit allows the conductors within the

system to be removed easily, without dis

mantling the system . A change in circuit

design or equipment will often require

conductors of a different

size,

colour,

material, or quantity to be installed in

the conduit. Consult the Canadian Elec

trical Code when changing the size or

quantity of conductors in a conduit.

Conduit Appl icat ions

Conduit wiring system s are used for sur

face wiring in apartm ents , factories,

garages, warehouses, and public build

ings and for service entrance equipment

for a house.

Conduit can be buried directly in

masonry construction. Commercial and

industrial buildings constructed of

poured concrete will often have a con-

Conduit

Wir ing

duit wiring system installed before the

concrete is poured. Conductors to be

installed under ground can be ade

quately p rotected by a conduit syste

When installed properly, conduit i

both water- and vapour-tight. Hazardc

areas , where explosive liquids, gases,

dusts are present, can be wired safely

with conduit and electrical fittings

approved for the purpose. Plastic-cc

conduits a re available for use in areas

where corrosive materials are presen

Motors and similar equipment subjec

vibration or movement can be con

nected with flexible conduit. Liquid-1

dust-tight varieties of flexible conduit

are also available.

Conduit Sizes

Conduit is usually produced in 3 m

lengths. This length, regardless of du

eter, provides an easy-to-estimate, pr

tical unit for installation and allows f

ease of bending and handling. Under

normal conditions, these lengths canl

quickly assembled into a continuous

run.

The second important dimension?

the conduit is internal diameter. This

measurement determines the quantity

and size of the conductors that can

safely installed in the conduit. Sectiod

162 Ap plications of Electrical Co nstru ction



I the C anadian E lectrical Cod e lists gen

ii installation ru les and allowab le con-

hit capacities.

Conduit is av ailable in th e following

fe sizes, as determined by the inter-

diameter, in millimetres: 13,20,25,

138,

51, 64,

76,89,102,127,

and 152.

ypes of Conduit

: are several typ es of condu it. This

lapter d iscu sses rigid (thickwall), EMT

binwall), rigid a lum inum , rigid PVC,

tarible, and PVC flexible (liquid-tigh t)

iduit.

d Conduit

1, or

thickwall,

conduit is produced

aluminum or steel. This thickwall type

ides th e greatest am oun t of

hanical

protection to co nd uc tors. It

ivailable

with a cho ice of e xterna l

Batings, such as electroplating, baked-

i enamel, or polyvinylchloride, to

jce th e damag ing effect of corro sive

licals in cer tain installation s. (See

14.1)

Rigid conduit must be supported by

)ved

strap s, cl ips, or hang ers at

lar

intervals . These sup po rts mu st

i located in acco rdan ce w ith Section 12

f the C anadian E lectrical Code, Pa rt 1.

tion 12 outlines interva ls as follows:

13 mm and 20 mm cond uit : Not

aceeding 1.5 m intervals;

25 mm and 32 mm c ond uit: Not

Breeding

2 m intervals;

38 mm a nd larger: Not exceeding 3 m

•terva l s .

Normal prac tice is to locate a sup

port within 75 cm of a box or ca bin et.

The inside of steel co ndu it is often

a>ated with an insulating paint or

mxrnish to ease the installation of con

ductors, insulate damaged conductors

r igid steel conduit (electroplated f inish)

RlSss

steel th inw al l (EMT) con duit

(elect roplated f in ish)

rigid steel conduit (baked enamel f inish)

r ig id aluminum conduit

r igid steel conduit (PVC-jacketed)

PVC -jacketed th inwal l (E MT) condu it

r ig id PVC c onduit

FIGURE 14.1 E lectrical cond uit raceways

Conduit Wiring

16



from the metal wall of the cond uit, a nd

prevent internal conduit rusting.

Lengths of rigid conduit mu st b e

threaded

at each end for connection to

coup lings, boxe s, or fittings.

Threading Rigid Conduit.

The best

method for holding conduit securely for

threadin g is in a pipe vise. (See Fig. 14.2)

For the best straight cut, hold th e

hacksaw at an angle of app roxim ately

45° to t h e ho rizontal. Figure 14.2 sho w s

the hacksaw being drawn back with one

hand, so that th e pipe vise would not be

hidden. In actual pra ctice, the second

hand should grip the front portion of the

saw. A more secure grip and a straighter

cut would result.

.cutting

wheels

. rollers

conduit

FIGURE 14.3 Pipe cutter

conduit

pipe

vise

hand reamer

FIGURE 14.4 Reaming conduit

FIGURE 14.2 C utting conduit w ith hacksaw

(Note: Hacksaw should have 24 teeth per

2.5cm.)

A pipe cutter is also e xcellent for p ro

ducing ne at cuts for thre adin g. (See Fig.

14.3) Using one , how ever, will neces si

tat e extensive reaming to the inside of

the conduit.

Whichever method is used to cut the

conduit, a sharp burr, cap able of damag

ing th e co nd ucto r insulation, will be pro

duced on the inside of the conduit. This

must be removed with a

round file

or

reamer. (See Fig. 14.4)

Reaming the pipe before threading is

best , because some conduit reamers

expand th e ends of newly thread ed cc

duits. An expa nd ed edge, flared like a

bugle, makes starting th e threade d

co»

duit fitting on t o th e new threa d difficu

The actual thread is cut into the

pi

pared end of the conduit by a

stock

ar

die set. (See Fig. 14.5) At one time,

elec

trical stocks and d ies cut parallel

thre ads . Modern threading tools pro

duce tapered threads similar to those

used with water pressure systems. (Se

Figs. 14.6 and 14.7) Th ese t oo ls allow

cond uit fittings to be installed secur

on the new thread.

Cut sufficient thread into the cor

to completely engage the threads a\

ble on the conduit fitting. Doing so

164

App lications of Electrical Construction



stock

ratchet

knob

squirt can for

cutting lubricant

IRE 14.5 C ut t ing thread on r ig id cond ui t

IE 14.6 P arallel thre ad

IRE 14.7 Tapered thread

provides the greatest mechanical secu

rity and ground continuity.

Application of a

cutting

liquid-

lubricant will ea se th e ph ysical effort

required to cut a threa d an d also extend

the life of the die's cutting edges. There

are severa l excellent thread ing lubri

cants , but oil or liquid soap can be used

when the proper lubricant is not at

han d. Th e simplest m etho d of applying

the cutting lubricant is with an oil squirt

can.

Bending Rigid Conduit. Installers nee d

many hours of practice to master the art

of bending and forming cond uit sy stem s.

Co nduits up to 25 mm internal diam

ete r are usually formed manually with

the h elp of a bending too l called a

hickey. (See Fig. 14.8) Hickeys a re av aila

ble in stand ard cond uit sizes; for b est

results, one of the p rop er size should be

used. Conduit of a larger trade size than

the hickey usually does not fit into the

bend ing tool. Smaller cond uit than the

tool is designed for often slips in th e

tool , producing kinks, inacc urate ben ds,

and /or bruises on the o perator .

Bends must be made without reduc

ing the internal diam eter of the cond uit.

A kink in th e b end will make installation

of conductors much more difficult and

1.2 m to 1.5 m handle

hickey

conduit

floor

4«

JJRE 14.8 Man ual con dui t bend er

Conduit Wiring



might even dam age th e insulation. (See

Fig. 14.9) Figure 14.10 shows tw o safe

methods for using the manually oper

ated hickey.

Conduit is bent to go aro und

corne rs, pass over obstacles, or enter a

box at the prop er ang le. Figure

14.11

shows five bends and their uses.

The

offset

ben ds are used to enter a

box or cabin et and can be also used to

bring the cond uit from one level to

ano ther on any surface, such as a wall or

ceiling.

The

square saddle

is used to by-pass

protrusion s in a wall or to p ass ov er sev

eral con du its located side by side.

The 90° bend is used to go aroun d

inside corners. (An outside corner

requires a conduit fitting of the type

sho wn in Figure 14.27.)

Note: The saddle bend s take the

time to form. Care and pra ctice,

h

ever, will result in smo oth , well-

aligned bends.

The 45° offset bends are often us

to overcome ob structions in the pat

the conduit.

The operator who uses body we

rather than arm strength can greatly

reduce th e strain of bending c on du i

25 mm d iameter con duit can b e ver

resilient at times—a challenge to th

operator . Good technique and prac

are esse ntial. Th e em pha sis is on ma

ing the ben der to the con duit . Inste

however, often have to use a buildin

su pp or t b eam , a hole in a wall, or sc

othe r means when a bend m ust be

i

and no h ickey is available. Take grea

smooth bend

kink

SS

^

F IG URE 14 .9 S moo th condu i t bend s a re i mpor tan t . C ondu i t bends w i th k inks a re no t

suil

for conductor insta l la t ion.

Pull on hickey.

Place foot

against hi

Lean on hickey using body

weight to bend conduit

conduit

conduit flat on floor

mmmmfr- '

floor

Support base of hickey with foot

F IG UR E 14 .10 M eth ods fo r bend i ng cond u i t manua l ly

166




offset

5

square saddle

^///////?////////M

pipe

^////////////////^////^//////////////////^

JURE 14.11 Types of conduit bends

Conduit Wiring

167



care not to kink the co ndu it in suc h con

ditions.

When bending conduit , the ope rator

should not try to make a full bend (90°)

with a single grip of the ben der. Th e

head of the hickey should be moved

away from or towards the operator

approxim ately 25 mm per grip.

Doing so makes the com pleted bend

a series of small, con tinuou s cu rve s (see

Fig. 14.12) and cre ate s a sym m etrical

bend with less chan ce of th e co ndu it

being kinked. The ac curac y of the ben d

can be easily checked by placing the ver

tical part of the co ndu it aga inst a wall.

Conduits larger than 25 mm in diam

eter are usually formed with a

hydraulic

conduit bender. Th ese units are available

with hand- or motor-driven pump

att ac hm en ts. (See Figs 14.13 and 14.14)

Take care to set th e cond uit in the

ben der carefully, bec aus e en orm ous

pre ssure is exerted by the hydrau lic sys

tem.

As in the case of the han d-op erated

hickey, bends sho uld be ma de u p of a

series of small cu rve s. When using th e

FIGURE 14.12 Typical 90°bend

[Note: Many small curves are required fo

a smooth bend.)

FIGURE 14.13 A hand-operated hydraulic bender simp lifies form ing large diame ter

condu

168

App lications of Electrical Construc tion



GURE 14.14 A motor-driven hydraulic bender speeds form ing large diameter conduits.

podi

ydraulic

bender, release the p ressu re

i reposition the conduit for each

te .

Place a serie s of equally spa ced

cil

marks on the conduit to as sist in

eating the pressure points needed to

luce a smo oth, symm etrical bend.

:e removing an exces s of ben d from

:

conduits is difficult, take care not

overbend.

It

is easier to place th e con-

back in the ben der and ad d a few

;s of bend than to take out bend. If,

>ever, a small amoun t of bend m ust

taken out, drop th e conduit onto the

[base of the ben d from abo ut 60 cm off

he

floor. The weight of the conduit and

he force of hitting the floor will

•raighten t he bend slightly. Take care

•ft to flatten the bottom of the bend or

Manage t he floor. (See Fig. 14.15)

Conduit system s are often installed

• large commercial buildings before the

concrete is po ure d. Figure 14.16 show s a

rtgid-steel cond uit sy stem for a high-rise

•nice building.

There are mechanical conduit

ben der s to help form medium size con

duits,

up to 38 mm in diame ter. (See Fig.

14.17)

Electric-powered benders, as shown i

Figure 14.18, can speed up conduit bend

ing. Th ese newly developed ben der s,

which can be equ ippe d with digital dis

play read-outs on their control boxes,

can be preset to quickly make several

identical be nd s or offsets with a mini

mum of set-up time. They are sold with

Shock will open bend.

. . .

N concrete floo

FIGURE 14.15 O pening a bend

Conduit Wiring

16



FIGURE 14.16 Installing condu it before

pouring concrete

FIGURE 14.18 A n electric bending mac

all

forms of roller support and shoe

attachments included. They control

accuracy and consistency of their I

electronically.

Thinwal l Condui t

iu

lis

E

o

O

FIGURE 14.17

bender

Typical mechanical conduit

The proper name for thinwall condi

electrical metallic tubing (EMT). T

conduit does not provide the same

degree of mechanical protection as

conduit, but it has several importan

advantages.

EMT is made of lightweight, s

tubing, and so does not require as m

physical strength on the part of the

installer as does rigid conduit, when

assembling the conduit system. (See

14.19)

Also,

because of its lightweig

construction it is not practical to th

EMT. This feature alone saves much

170




GURE 14.19 S teel thinwall conduit (EMT ).

;plated finish

nd

work w hen installing EMT. Because

IIT is not th rea de d into a fitting o r box,

fee job does not depend o n the

•Btaller's ability to r ota te a length of

conduit, which is full of bends and in an

wkward location, until the threa ded

n d is sec ure in the box or fitting.

Mechanical connectors eliminate this

bore .

Section 12 of the Ca nadian Electrical

ode lists the co ndition s und er wh ich

MT

can be substituted for rigid con-

r.:.t.

•Kings for EMT. Th ere ar e m echanical

Mings to co uple leng ths of

EMT

and /or

connect the conduit to boxes and

Bfoinets. These fittings are made of steel

r zinc alloy (d ie-ca st).

Note: Take care not to subject the die-

cast zinc fittings to great pressure or

stre ss, as the y break easily. Zinc alloy

is used be ca us e it is easily die-cast

and moderately priced, bu t a perso n

stepping on a run of conduit coupled

with die-cast fittings is likely to cra ck a

coupling. For this reaso n, die-cast zinc

fittings should not be used in poured

conc rete buildings wh ere they can b e

damaged (and go unnoticed) before

the pouring of co ncre te.

Th ere are tw o m ain typ es of EMT fit-

fcgs: the set-screw and the compression.

S e e Figs. 14.20 and 14.21) The set-screw

tope

is used in dry locations; only a

Krewdriver is needed to secure the con

nector to th e condu it . Glandular connec

tors are fastened to the cond uit by u sing

c om pr es s ion t y pe

set-screw type

FIGURE 14.20 EMT connectors

compression type set -screw type

FIGURE 14.21 EMT couplings

c

D

O

O

3

O

( J

FIGURE 14.22

conduit (EMT)

PVC-jacketed thinwal

>

t

3

O

adjustable p liers or a wrench . These

rain-tight connectors are used outdoo rs ,

in poured con crete installations, or in

other damp areas.

PVC-jacketed EMT. Some EMT is

jacketed with polyvinylchloride

(PVC),

which resists corrosive chemicals and

va po urs . (See Fig. 14.22) Take care not to

cut or damage this outer jacket when

forming bends.

Liquid

PVC is applied to

the con nec tors and couplings of such

installations to give com plete prote ction

in corrosive a reas.

Bending EMT. A special condu it

bender ( the hickey) is used to form

offsets and ben ds in EMT. (See Fig. 14.23

The hickey forms th e con duit with a

radius that will tend not to kink the

conduit where it has been bent. Also, it

su pp ort s the sides of the con duit as it

Conduit Wiring

171



FIGURE 14.23 An EMT bender (hickey)

I

.

4

rrm

bends , further reducing the possib

of kinking. The op era tor places a f

the hickey to make sure that th e co

rem ains within the hickey during b

ing. This action reduc es the tenden

the

EMT

to kink. Properly designe

dies permit the operator to bend t

con duit w ith a minimum of strain,

maintaining perfect balan ce for pe

safety. (See Fig. 14.24)

Because the ben der fits the co

closely, a sep ar ate hickey is nee de

each size of conduit from 13 mm t

32 mm .

EMT 32

mm in diam eter an

larger is usually formed in a hydr

bending unit. (See Fig. 14.25) The h

completely encloses the EMT at th

point of press ure , virtually elimina

kinks in the con duit.

Both manual and hy draulic

be

can form a 90° bend in one contin

movement of the bender. However

unlike rigid conduit, EMT does not

to b e ben t in a serie s of small curv

EMT ben der s can b e very accu rate

skilled operator, following the

me

ments provided on the unit, can p

a

90°

ben d th at is within 2 mm of

required d imension. Such accurac

necessary because

EMT

is difficul

straighten and rebend without kin

HEAT-TREATED

high strength

aluminum a lloy.

/

Square bottom hook

provides stability.

E

o

u

<3

S T

FIGURE 14.24 P roperly designed benders

and handles allow ease of bending and per

sonal safety.

FIGURE 14.25 A hydraulic E MT ben

172




i though EMT does not require as

i physical strength to bend as does

I conduit, considerable practice is

before truly professional results

I be obtained. Many people who

I conduit take great pride in their

Figure 14.26 illustrates a high-

ity installation in a com mercial/

strial area.

T hr eaded f or R ig id C ondu i t S e t -s c rew t y pe f o r E M T

«*9

typeC

typeLR

type LB

typeLL

t y pe LL

type LR

typeE

• m

/

typeT

typeT

o

typeX

t:

8

m£. 14.26 A cond uit installation requir-

|a high degree of skill and craftsmanship

FIGURE 14.27 C onduit fittings (condulets)

Conduit Wiring

173



Conduit Fitt ings

Often, during a cond uit installation, a

sha rpe r ben d tha n the co nduit will allow

must be made. A conduit fitting is th en

use d. (See Fig. 14.27 on pag e 173.) These

fittings, which are often called

condulets,

assist the c ondu it installer to go aroun d

corn ers and provide access to the con

duit for th e installation and remo val of

conductors.

Some fittings are designed to provide

a branch p ath from th e main condu it

run. (See Fig. 14.28)


requires that acc ess to the conduit be

provided every

30 m

of conduit o r ev ery

360° of accumu lated ben ds, wh ichever

occurs first. There are special fittings for

this purpose. (See Fig. 14.29)

Threadless, set-screw fittings a re avail

able for direct a pplication to EMT. The

standard fitting with its internal conduit

thre ad is suitable for use with rigid con

duit or connector-equipped EMT.

3

CD

CO

c

1

FIGURE 14.28 A

" T "

conduit fitting pro

vides a branch path from the main run.

There are many forms of

electri

boxes for conduit systems. Manufac

ers produce such a variety that com

plete catalogues a re nec essary to lis

them . Figure 14.30 sho ws a num ber o

them.

Some fittings are listed w ith th e p

fix

L

in com bination w ith ano ther

le

for example, LB,

LL,

or LR.

Th e first lette r of th e prefix indic

th e s ha pe of th e fitting. For exam ple

L of LB indica tes th at t he fitting is

sha ped like the capital letter

L.

(See

14.30:

FSC with switch; FSX with sw

FS with explosion-proof outlet and c

connector.)

<3 FIGURE 14.29 A

" C "

conduit fitting

vides access to a conduit for installing

removing conductors.

i




toswn-proof motor starting units

FS fitting w ith explosion-

proof outlet and cord

connector

FSX fitting with switch

(4 conduit openings)

JBfcL

&

j

r fitting w ith switch

onduit

openings)

FS fitting (single

conduit opening)

10

c m

diameter

round box

HIRE 14.30 Typical electrical boxes for

fittings

Conduit Wiring

FS fitting

with motor

starting

switch and

pilot light

(2

gang)

175



F I G U R E 1 4 .3 0 ( c o n t i n u e d )

explosion-pro

176

A pplications of E lectrical C onstruction



The secon d lette r of the prefix indi-

the location of th e conductor

opening in relation

to

the shorter

it opening; tha t is, th e d irection

short arm of the fitting is poin ting

the fitting is held with the conduc-

iccess opening facing th e viewer and

onger arm pointing up wa rds. For

le , when an

LR

fitting is he ld w ith

ronductor acce ss opening facing t he

and the longer arm is pointing

ards,

the short arm

of

the fitting will

pointing

to the right. An

LL

fitting

1 the sam e way will have its sh or t

I pointing to the left. An LB fitting will

e its short arm pointing backw ards.

Condulets can be cappe d with cov-

aade

from aluminum, steel, porce-

or

a

fibre com pos ition. When exc es-

moisture

is present, a

cork

or

rubber

must be used between cover and

(See Fig. 14.31)

FIGURE 14.32 Conduit connected to outlet

box

• MB*

N

raised blank cover

blank composit ion cover

V

a

5

u

I

gasket c

c

c

E 14.31 Condulet covers

rminating Conduit

en rigid cond uit is brou ght into

res through knockout holes,

locknuts

•d bushings are used to secure it to the

ax. (See Fig. 14.32) Th ese fasteners

st be installed tightly enough to pro-

I both mechanical security

(streng th) for the installation and

ground circuit continuity.

While it is always wise to u se a tool

for its intended purp ose, common prac

tice among electricians is to tighten the

locknut and bushing by placing the

blade of a screwdriver against the unit,

and then striking the ha ndle

of

the

scre wd river w ith th e flat side of a pair

of

pliers. (See Step 4, Fig. 11.4) A hammer

and cold chisel are often nee ded with

very large conduits.

Locknuts are usually made

of

steel

and have sharp teeth on one side to bite

in

to

the box and establish the ground

circuit.

Bushings, which provide

a

smooth

opening through which the conductors

can enter the box, are m ade of die-cast

aluminum, steel,

or

nylon. Steel bu sh

ings with a nylon inse rt are also availa

ble.

(See Fig. 14.33)

Conduit Wiring

177



locknut

- i

insulated bushing

F I G U R E 1 4 . 3 3

nat ing devices

bushing

L o c k n u t a n d b u s h in g t e r m i -

r

3

8

Figure 14.34 shows how conduits of

less than 32 mm in diameter are secured

to a

box.

When securing conduits of

32

mm

to

150 mm

in diameter, a system

of two locknuts and a plastic bushing is

used. This is because insulation on large

and heavy cables can be punctured or

NOTE: Tighten securely.

F IGU RE 14.35 Double

insta l la t ion

steel bushing

\

steel locknut

NOTE: Tighten securely.

F IG UR E 14 .34 S i ng l e l ocknut and bush i ng

instal lation

pierced by the weight of the cable pr

ing on a solid metal bushing. A meta

bushing with a plastic insert is also

available. This double-locknut meth

also used on conduit systems that I

an applied voltage of m ore than 250

(See Fig. 14.35)

Rigid A luminum Conduit

This lightweight, easily handled cond

is often used to enclose residential:

ice entrance conductors . Aluminum

rustproof and will not stain or streak

surface on which it is mounted. The

high-electrical conductivity of aim

provides a safe ground circuit for the

system.

As

a nonsparking m etal, it is

for use near explosive gases o r vap

It is also ideal for alternating-current

terns that require a nonmagnetic sub

stance to enclose the

conductors.

(S

Fig. 14.36)

178




Rigid aluminum conduit

FIGURE 14.37 Rigid PVC conduit

•ending Rigid Aluminum Conduit.

•ding aluminum conduit does not

lire much physical effort. It does

rever

require th e u se of a hickey o r

le other forming device that will not

t the bend. Standard rigid conduit

beys can be u sed if extrem e c are is

tn

not to flatten the bend with too

a radius. EMT be nd ers one size

er than the conduit are often used

:essfully. Hydraulic benders also

•ally produce satisfactory bends.

ding Rigid Aluminum Conduit.

t used for threading aluminum con-

should be sharp and well-lubricated

le cutting the thre ad . Chips of m etal

uld be cleared from the die occasion-

Otherwise, they will lodge between

die and the conduit and tea r the

rly cut thre ads. When reaming this

duit, take ca re no t to flare and

d the end because bugling makes

lifficult to attach conduit fittings.

ailing Rigid A lum inum

Conduit,

poid cross-threading aluminum conduit

ihen

attaching coup lings, locknu ts,

tashings, con dule ts, or similar devices.

»e soft aluminum will quickly lose its

be ad s if an attem pt is made to remov e

wross-threaded fitting. Putting lubricat-

l oil on the threa ds before assem bly

I

help eliminate this p roblem.

Aluminum cond uit should be sup

ported by

straps

placed at regular inter-

is.

as is rigid steel c ond uit. The m ate-

I*s

light weight is appreciated,

ticularly during conduit installations

nm a ladder or some oth er precarious

sition.

If aluminum co ndu it is to b e e mbe d

ded in conc rete below ground w here it

may be wetted every so often, a

bitumi

nous base paint

or

pitch

should be

applied to the conduit . This su bstanc e

will protect the conduit from any mois

ture in the concrete that may attack the

metal and corro de it .

Rigid PVC C onduit

Rigid PVC (Polyvinylchloride) conduit

protec ts cond uctors in the worst corro

sive locations. Moisture or cond ensation

has no effect on this durable product.

Since PVC will not co nd uc t electricity

and is non ma gne tic, it is not affected by

shea th cu rren ts. It has no voltage limita

tions. It resists aging, exposure to ozone,

sunlight, and undergrou nd environ

m en ts. It is imm une to electrolytic

action. Heavy blows d o not cau se per

manent damage to it. (See Fig. 14.37)

W eight Ad va nta ge of Rigid PVC

Co nduit. This con duit is

approximately

five times

lighter than

steel conduit and twice as light as

aluminum condu it of the sa me size. As a

result, the installer finds it mu ch easier

to handle, especially when working from

ladders or scaffolds.

Applications of Rigid P VC Conduit.

This conduit is used in areas w here

corro sion is a prob lem, for exam ple, in

paper mills, meat-packing plants,

chemical and electroplating p lants,

barns and animal shelters, hospitals,

and food prep aration pla nts. It is also

Conduit Wiring

179



being used more and more for residen

tial service entr anc e conduit, be cause it

is easily handled, nonrusting, and nons-

taining.

Joining and Terminating Rigid PVC

Conduit. A metal-cutting hacksaw or

carpenter's wood saw

can be used to cut

the conduit to length.

A pocketknife

will

quickly rem ove any bu rr on t he inside of

the cu t end. Leng ths of PVC and fittings

are assem bled by using a form of solvent

welding.

No thr ead s ar e required. Dirt

and grease from handling are removed

with a P VC cleaner. Solvent cement is

brush ed on to the prepared end of the

con duit and th e inside of the fitting to be

joined. The conduit is then pushed into

th e fitting, given a qu art er tu rn, and set

aside. After a few minutes the

con nec tion will w ithsta nd t he strain of

use. (See Fig. 14.38)

Bending Rigid PVC Conduit.

This

conduit is a thermop lastic m aterial that

will soften at temperatures between

115°C and 130°C. If proper care is taken,

the conduit will not flatten and/or kink

while being ben t. All be nd s should have

a rad ius of at least ten times t he

diameter of the conduit. Commercially

produ ced bend s are available from the

conduit's manufacturer.

There is an approv ed PVC heater that

directs a heated-air stream at the con

duit. This air stream is cap able of raising

the co nduit 's temp erature to the desired

level. Open flame will damage the con

duit and should not be used. Cold water

or natura l cooling will maintain th e

shap e of the bend. The conduit shou ld

be overbent slightly to allow for spring-

back as th e co ndu it is cooling. (See Figs.

14.39 and 14.40) Figures 14.41 and 14.42

illustrate several other forms of heating

equ ipm ent for bending rigid PVC con

duit. The heating blanket is used on

sizes of conduit and is

thermostatic

controlled for uniform bending . The

mo tor-driven elec tric PVC he ate r is

capable of automatically rotating th

conduit for even heating. Controls

include a heating chart and timer to

bring the PVC up to be nding tem per

ture.

Rigid P VC Conduit Expansion.

Whenever the temperature variation

excee ds a range of

15°C,

PVC condu

will expand and contract enough to

warra nt the u se of expansion joints.

expansion joint is simply one PVC tu

telescoping within another. A 30 m

length of conduit will expand

approx imately 9 cm . Expansion join

are available from th e man ufacturer

PVC con duit.

Rigid PVC Conductor Installation.

phys ical effort is need ed to pull

con duc tors into this condu it than in

other types. The conduit 's smooth,

friction-free inter ior is th e major rea

Rigid P VC Conduit Supports.

Supports for this conduit do not nee

be as sturdy as tho se for other form

condu it. They should be space d at

regular intervals and take into

accou

the possibility of snow, ice, and win

loads.

For example, ade qua te suppo

would be one s up po rt every 80 cm f

conduit

13

mm, 20 mm, and

25

mm

diameter.

Metallic Flexible Conduit

Flexible conduit (flex) combines

mechanical protection with maximi

flexibility for nonhazardous locatior

This versatile rac ewa y is made of an

interlocking steel or aluminum strip

180




100

JRE 14.38

A pply cement to pipe and f itt ing. Insert pipe into fitting and give it a quarter

E 14.39 Use a PVC heater to soften pipe for bending. Use guidelines to establish proper

wle.

o

U

£

FIGURE 14.40

Using a PVC heater before

bending rigid PVC cond uit

Conduit Wiring

181



full-length piano hinge

Heating chart and timer allow easy

accurate heating .

on/off switch

" o n "

pilot light

support and lifting

handle

F IG U RE 14 .42 A n e l ec tr ic P VC heater w i th a m otor i zed condu i t - ro ta t ion fea tu re




TABLE 14. 1 Me tallic Flexible C ondu it

Internal Diameter

8 mm

13 mm

32 mm

64 mm

9.5 mm

20 mm

38 mm

75 mm

11

mm

25 mm

51 mm

100 mm

Standard Length of Coil

7.5 m 30 m

75 m

«e Fig. 14.43) Flex is availab le in th e

tgths and internal diameters show n in

He 14.1.

illic

Flex Ap plications. Conduit

Krtection is sometimes needed in a

ration where rigid conduit cannot be

fcrmed to the con tours required

ecause

of close-working c on dition s. An

sample

is a wiring system tha t mu st

lass over and around steel girders,

Bsting mach inery and equipment, o r

- shed through ma sonry walls and

attngs. Using flex g reatly simplifies th e

Btallation work. Another exam ple is

tors and/or machines with vibrating

.ing

pa rts . The se parts must b e

•ovided with a supply syste m tha t will

Bt allow metal fatigue to set in and

tacture th e raceway . If th e m etallic

•ceway is broken or separa ted, ground

•tinuity can b e lost . To accom m odate

•und

mechanical and electrical

•tallation

methods, approved flex

••nectors must be used. (See

14.44)

Supports

for Metallic Flex. Appro ved

ex

sup ports are similar to thos e used

•th armoured cable. They must be

•tailed within 30 cm of each box or

binet and at regular intervals of not

•ore than 1.4 m throu gho ut th e run.

Pee

Fig.

14.45) Where flex is fished or

Bed in lengths of up to

1 m

requiring

Inability, su pp orts are not need ed.

a

O

FIGURE 14.43 Me tallic flexible cond uit

st raight conne ctors (squeeze type)

90° angle connector (squeeze type)

o

straight connector

90° angle c onne ctor (3 screw type)

FIGURE 14.44 Flexible conduit connectors

Nonmetall ic Flexible

Conduit

A

new form of extruded, flexible tubing,

which is non-corrosive, n on-condu ctive,

Cond uit Wiring 183



FIGURE 14.45

(2-hole)

f

Flexible condu it strap | g

and m oisture resistant, is now av ailable.

This lightweight tubing can be ob tained

in coils up to app roxim ately 100 m in

length.

Special connectors and couplings

exist for use w ith this p rod uc t only. With

their fast-acting,

snap-on

feature, the y

allow th e installer to inse rt th e flex into

the connector/coupling without the use

of any tool or piece of equipm ent. It

should be noted, however, tha t some

times the solvent-welding technique (as

used with PVC con duit) may be required

by local wiring co de s. Wh ichever

m eth od is used , the flex is not easily

removed from the connector/coupling

onc e installed. Figure 14.46 illustrate s

th e snap-on connector. Figure 14.47 illus

trates a snap-on coupling.

Nonm etal l ic Flex Appl icat ions.

Nonmetallic flexible conduit is often

used in metal-stud partitions (see Fig.

14.48) and poured con crete work. (See

Fig. 14.49) Care mu st b e taken not to use

this product in hazardous locations (as

des crib ed in th e Canadian Electrical

Code),

however. It shou ld a lso not be

buried in the earth , exposed to

mechanical injury, or enclosed in

thermal insulation materials.

Sup ports for Non metallic Flex. Fishing

of wires into the flex is ea sed by t he

corrugated design on the interior: the

corrugation results in less friction when

the co ndu ctors are pulled into the

tubing. (See Fig. 14.50) Flex should have

a sup po rt within

1

m of a junction box,

coupling, or fitting, plus supports no

184

more than 1 m ap art o n a ru n. It is a\

ble

in 13 mm , 20 mm , and 25 mm inte

diameters.

FIGURE 14.48 Typical use of PVC f

conduit in metal stud partitions




o

WE 14.49 This PVC flexible condu

prepared for use in a concre te slab.

tis

o

u

<

2

> t5

J 8 5

c

JRE 14.50 PVC flexible conduit

|uid-Tight Flexible

mduit

kcs PVC-jacketed flex

is excellent for

e in

damp locations, corrosive areas,

[around machines where coolants, cut-

tog. and/or lubricating liquids are likely

splash on to the flex. (See Fig. 14.51)

bisture-proofconnectors are used to ter-

taate

it. (See

Fig.

14.52 on page 186.)

tese

con nec tors make use of a

nylon

wipression

ring to grip the outer jacket;

fariar

flex con ne cto rs hav e a metallic

•raping

device.

•

nouio-riGm CONOU II IIOU'S«AI I*D{

U t t f f

IRE 14.51 L iquid-tight, flexible

v conduit w ith a PVC jacket

10 .Q

Take care no t to p unc ture th e PVC

jacket either during installation or later

when it is in use.


requires that this conduit not be u sed

where temperatures are higher than

60°C. These temperatures could dam age

the

PVC

jacket. Also, take ca re not to use

the condu it in tempe ratures that are low

enough to cau se injury to the jacket

when it flexes.


Code lists guidelines for the ty pe an d

size of con du cto rs allowed in liquid-tight

flexible conduit.

Condui t Grounding and

Terminat ion

Acc ording to th e Canadian Electrical

Code, neither metallic nor nonmetallic

conduit can be relied upon for ground

continuity.

A separate conductor (green

insulation) with the sole purpo se of

grounding the equipment must be

installed toge ther with the other cur

rent-carrying cond ucto rs in the system.

Cutting th e Flex.

Cut flex to leng th

with a hacksaw in the same m anner as

for arm oure d cab le. (See Fig. 11.4)

Terminating the Flex.

Flex con ne ctors

are used to secu re the flex to bo xes,

cabin ets, or condu lets, and to couple the

flex with oth er forms of con du it. (See

Fig. 14.44 on pag e 183.) An insulating

sleeve,

similar to the anti-short bushing

used with armo ured cab le, must b e

inserted between the cond uctors and

the armour to prevent chafing of the

con du ctors . Some mo dern flex

conne ctors have a plastic insert built

into th e thread ed end of th e unit.

Flex connectors should be fastened

Conduit Wiring 185



•

7.

straight connector

% * <

45°

connector

90°

connector

FIGURE 14.52

coupling

I

combination coupling

L iquid-tight con nectors and

securely to the box or cabinet w ith a

condu it locknut to provide m echanical

secu rity and assist in ground continuity.

Knockout Cutters

It is often nec essa ry to increa se the size

of an available knock out in a box or c abi

net. Using a ream er or file ten d s to be

clumsy, time-consuming, and damaging

to the wo rker 's hand s. Instead a knock

out cutter could be used.

These c utters are m ade in all s tand

ard c on duit sizes . Using, for exam ple, a

20 mm knocko ut c utter will produ ce an

ope ning that will acc ept a

20

mm con

duit or conn ector. The actual diam eter

of the h ole will be ap prox imately 27 mm.

The

hand-operated

cutter unit has a

hardene d-steel cutter, which is drawn

through the m etal box by a wrench-

tightened bolt. (See Fig. 14.53)

Once the knockout cutter has

removed a ring-shaped section of m etal

from th e box, th e installer may ha ve

som e difficulty in remo ving th e m etal

piece from th e cutter. He or s he can eas

ily w aste valu able time before making

the n ext hole in the box o r pan el. How

ever, a recently designe d typ e of c utte r

186

FIGURE 14.53 Hand-operated knock

punches




up to 10 gaug e mi ld

; s lug for easy rem oval

-

T

The punch

creasesthe

slug as it is

drawn into

th e die.

The slug is split

in hall as the

punching opera

tion is com

pleted.

/ J{

*-/\

t y ^ \ / i

Jto< /

^n2\v}

^ J / 7

C^

Sp lit slugs fall

free from the

die an d

stud.

. 14.54 N ew ly designed knockout punches require less time to

slugs than traditional c utte rs.

each metal slug into two s eparate

5.

The installer can there by remove

etal pieces quickly. This cu tter is

)le

in traditional kno ckout cutte r

(See Fig. 14.54)

Hydraulic-powered

units use the

I

type of hardened-steel cutter, but

:

much less physical effort on the

of th e op era tor. (See Fig. 14.55)

Smaller, compact, lightweight

hydrau-

ch drivers

are available to install-

These units can be stored and their

i

organized in custom-fitted ca ses .

i Figs. 14.56 and 14.57)

•-:,

FIGURE 14.56 C ompact hydraulic punch

systems ease hole-making operations in

metal boxes and cabinets.

•5URE

14.55

utpunch

nyOrau

r^C^TZM

liC-pOWGrGQ

o

Conduit W iring

FIGURE 14.57 Hydraulic punch driver set

187



Install ing the C onductors

The Canadian Electrical Code requires

that conductors be drawn into the con

duit system after the system h as been

completely assembled. Otherwise, con

ductors could be damaged while bend

ing, forming, or fastening th e cond uit to

boxes.

A

flattened,

tempered-steel

wire,

wh ich is prod uce d in 7.5 m, 15 m , 30 m,

and 60 m lengths, is pushed into the con

duit between boxes and fittings. This

steel wire, called a

fish tape,

is available

in 3 mm, 5 mm, and 6 mm widths to suit

light and heavy cond ucto r installations.

For ease of handling and storage , th e

tap e is wound onto a metal or plastic/

nylon reel. Figure

14.58

illustrates th e

older style metal reel. Figure 14.59 dis

plays the mo st comm on sizes of plastic/

nylon reels available to th e installer.

The tape is usually inserted into the

con duit b y mean s of a serie s of sho rt fre

quent p ush es. It is impo rtant to keep t he

5

FIGURE 14.58 Metal fish tape reel

188

tape in motion, because constant j

ing and vibration allow the tape to

eased arou nd b end s and offsets in

;

conduit. Figure

14.60

illustrate s a

I

us e of the fish tape /reel for the insc

of cond uct ors into conduit wiring

systems.

FIGURE 14.59 N umerous sizes of

nylon/plastic reels are available for use

\

fish tapes.




fish tape ree

end loop

URE

14.61 Conduit fishing (one loop)

end loops

conduit

fish tap

coupling

RE 14.6 2 C ondui t f i s h ing f rom bot h ends

of run (two

loops)

i

A loop that

is

almost closed helps

•de the tape around bend s, couplings,

fed fittings. (See Fig. 14.61) Often a sec-

Ad fish tape

is

push ed into the conduit

torn the oppos ite end. It is hooked on to

fee

first tap e by rotating th e first tap e

rveral

t imes

to

engage the en d loo ps,

feen

used

to

draw the first tape throug h

fee con duit. (See Fig. 14.62) This m eth od

s especially useful on conduit ru ns that

tave

a number

of

90° ben ds.

When pulling large conductors

or

•any condu ctors into

a

large conduit,

fee fish ape is

often

used to draw a

rope

t

cable into the con duit. The rope

is

fcen used

to

pull the con ducto rs

• rough .

Larger cables are extremely hard to

poQ into

a

conduit system when the con-

pit run

is

long

or

built with s eve ral

ends . For this reaso n, installers may

try

on heavy-duty electric w inch pull

ers.

(See Fig. 14.63) These units require

the use

of

special minimum-stretch rope

which rem oves som e of the dang er asso

ciated with this system . A t remendous

amount

of

energy can be store d in

a

tightly drawn rop e, and if th e rop e

breaks

or

releases, the installer can

be

seriously hurt by

it or

objects fastened

to i ts end s. Care mu st be taken to stand

clear and out of the way of the rope

wh ene ver pos sible. Figures 14.63 and

14.64 illustrate two w inch pullers.

Wire-pulling lubricants are available.

If a generous am ount of lubricant is

applied

to

the conductors ,

the

physical

strain

of

installation

is

greatly redu ced.

In fact, th ere a re many othe r ways

to

reduce the ph ysical strain. Every experi

enced electrician has devised some unu

sual apparatus

for

pulling co nd ucto rs

into

a

cond uit sys tem . (See Figs. 14.65,

14.66 and 14.67)

Conduit Wiring



FIGURE 14.63 Heavy-duty

electric winch pulling system

FIGURE 14.64

system

E lectric winch pulling FIGURE 14.65 Wire-pulling

luoncant is

available in

a

variety of easy-to-use conta




14.66 Wire-pu lling lubricant is

plied to condu ctors.

ing Conductors to Fish Tape,

n two or more conductors are to be

ed

through a conduit at the same

take care to fasten them securely to

Ksh

tape. Much time and effort will

wasted if any of the conduc tors break

y

from the tape. Figure

14.68

shows

i

methods for securing the

•luctors

to a tape.

FIGURE 14.67 T he pulling of conductors

is eased by the application of wire-pulling

lubricant.

end loop

Wrap one conductor

around other.

conductors

Remove insulation.

N O T E :

It is good practice to cover a connection wi th tape.

Tape over end loop.

wire rope strands

'W ^K*®*

tape \^

> i i i

^ *

c a b l e s o c k

N O T E :

The greater the pull on the fish tape, the tighter the sock grips.

IE 14.68 M e t h o d s f o r s e c u r i n g c o n d u c t o r s t o f i s h t a p e

Conduit Wiring

191



Compressed-Air Fishing

Compressed air can be used to force a

lightweight ball throug h

a

condu it. The

ball can be alm ost as large as the diame

ter

of

the inside

of

the conduit . A length

of strong string is attached to the ball.

Once the str ing reaches the opposite

end of th e run, it can b e used to draw in

a heavier fish tap e or rope. The com

pressed air can be obtained from

a

tank

or compressor. A hose and nozzle is

used

to

control the ra te

of

air flow. (See

Fig. 14.69) This m ethod is sim ple and

sav es much time and effort.

One manufacturer produces a series

of coiled-string, plastic<oated projectiles

that let out a fine, extremely strong

nylon string when forced through

the

conduit by compressed air.

A

heavier

string or line can th en be pulled into the

conduit by the nylon string. The se pro

jectiles are produced in sizes to match

the conduit being fished.

Vacuum/Blower Fishing

More recent developments in th e

duit tool and accessory industry h

made possible power fishing with

a blowing

or

vacuum/suction syste

series of solid foam pisto ns, sized

match th e conduit

in

use , are

con

t o a length of strong nylon line. Ai

sure

or

suction from a vacuum/blo

can then force or draw the pistons

th e condu it sy stem . Figure 14.70 i

tra tes a vacuum /blower in action.

lightweight ny lon string is inside t

conduit,

it

can pull

in

either a hea

stronge r line or a metal tape, then

conductors themselves. Figure 14

shows the components of a

vacuu

blower power fishing system.

Conduit Fill

As men tioned in Chapter 7, condu

requ ire air sp ace for cooling. For

control nozzle

ightweight ball

*C— ^^

compressed air

air hose

condu

FIGURE 14.69 Conduit fishing using compressed air

192




te

reason, the number of conductors

ny

given size of con duit or tubin g

be limited. The Canadian Electrical

le

specifies the num ber allowed. This

liber dep en ds on the con duc tor size

I

type of insulation. (See Table 14.2)

To determine th e num ber of conduc-

allowed, Table 14.2 is used with

: 5.1.

(See Ch apte r 5) For exam ple, a

14

gauge stranded conduc tor ha s a

-75 insulation thickness of 0.8 mm or

mm when you con sider b oth s ides of

condu ctor. When 1.6 mm is ad ded to

conductor 's approximate diam eter

L4

mm, a fairly a cc ura te dia m eter of

I mm

is estab lishe d. (See Table 5.1) To

FIGURE 14.71 C omponents of a

vacuum/blower power fishing system

determine how many of these conduc

tors are allowed in 13 mm tubing, look

for the dia m eter en try equ al to (and , if

necessary, larger than) 5.0 mm on Table

14.2. In this ca se, the no minal overall

diam eter is 5.1 mm , which allows th ree

con duc tors in the tube .

Since editions of the Code book con

tinue to be in th e imperial syste m of

m eas urem ent, t he following cond uit fill

me thod is included.

For simplified conduit fill calcula

tions, refer to Table

14.3

on p age 195.

This table lists the comm on tra de sizes

and ca pac ities of cond uit to be installed

with

RW-75

or R-90 insulated con du c

tor s. Its information is m ost useful w hen

the conductors to be installed in the

conduit are all of one type and gauge

size.

A

m ore detailed m ethod of arriving

at conduit fill is recommended when

con du ctors of various size and gauge

num ber are to be installed. (See Tables

14.4 and 14.5 on pages 196 and 197.)

Condu it Wiring

193



TABLE 14.2 M ax im um N umb er of C ondu c t ors o f O ne S iz e in T rade S iz es

Nominal *

Overall

Diameter

of

Condr.**

mil l imet res

2.5

2.8

3.0

3.3

3.6

3.8

4.1

4.3

4.6

4.8

5.1

5.7

6.4

7.0

7,6

8.3

8.9

9.5

10.0

10.8

11.0

12.0

13.0

14.0

15.0

16.5

18

0

19.0

20.0

22.0

23.0

24.0

25.0

28.0

30.0

33.0

36.0

38.0

41.0

43.0

46.0

48.0

50.0

64.0

***

* For intermediate si

• * For the purpose of

13

15

12

10

9

7

6

6

5

4

4

3

3

—

—

—

—

—

—

—

—

—

—

—

—

zes, use

conduit 1

20

27

22

18

15

13

11

10

9

8

7

6

5

4

3

3

1

—

—

—

—

—

—

—

—

the next

II, 'cond

of Condui t or Tub ing

Maximum Number of Conductors in Conduit or Tubing

Size of Conduit or Tubing—Mill imetre

25

4 4

36

30

26

22

19

17

15

13

12

10

8

7

5

4

4

3

3

2

—

—

—

—

—

—

30

76

63

53

45

39

33

29

26

23

21

19

15

12

10

8

7

6

5

4

4

3

3

3

—

40

101

85

72

61

53

46

40

35

32

28

26

20

16

13

11

9

8

7

6

5

5

4

4

3

2

1

50

171

141

119

105

87

76

67

59

53

47

42

33

27

22

19

16

13

12

10

9

8

7

6

5

4

4

3

3

2

1

65

—

169

143

124

108

95

84

75

67

60

48

38

32

27

23

19

17

15

13

12

10

9

8

6

5

4

4

3

3

3

2

1

1

1

1

1

1

1

1

1

75

—

—

—

192

163

146

130

116

104

94

74

60

49

41

35

30

26

23

20

18

16

15

12

10

8

7

6

5

5

4

4

3

3

2

90

—

—

—

197

174

155

139

126

99

80

66

56

47

41

35

31

27

24

22

20

16

14

11

10

8

7

6

6

5

5

4

3

2

1

arger dimension (e.g., for conductor with diameter 5.3 m m, u

jctor' means either insulated conductor, single or multiconduc

100

—

—

—

—

—

—

199

178

162

127

103

85

71

61

52

46

40

35

31

28

25

21

18

15

13

11

10

8

7

7

6

5

4

3

3

2

1

1

1

1

1

1

115

—

—

—

—

—

—

—

—

—

—

161

130

108

91

77

66

57

51

45

40

36

32

27

22

19

16

14

12

11

10

9

8

6

5

4

4

3

3

3

1

1

1

1

>e fill for 5 7 mm)

tor cable.

130

—

—

—

—

—

—

—

—

—

—

—

162

134

113

96

83

72

63

56

50

45

40

33

28

24

20

18

15

14

12

11

10

8

7

6

5

4

3

3

3

2

1

1




If, for example, a No. 8 gauge cond uc-

w

with R-90 insulation w as to be

stalled, you could refer to Table 14.4

id find tha t the co ndu ctor h as an area

f

0.076 0 in.

2

.

If 1

in. cond uit is to b e

stalled, you could refer to Table 14.5

tiich lists the c ross-sec tional are as of

te

conduits and their allowable percen-

ges of fill. From Table 14.6 you can find

lat three or m ore con du ctors in a given

conduit m ust not occu py m ore than 40%

of the available space in the conduit.

The

40%

column of Table 14.5 shows

that 1 in. conduit has a cross-sectional

area of 0.344 in.

2

. If yo u div ide 0.344 in.

2

by the conductor's area of

0.076

0, you

will arrive at an a nsw er of 4.52 cond uc

tors . Therefore, you can determ ine th at

four conductors could be installed in the

1 in. condu it, as s how n in Table 14.3.

6*

39

12:

10*

A

23

::

is

IE

•*

12

•:

;

5 i

L

L

T A BL E 14.3 Ma ximum N umber of Conductors of O ne Size in Trade Sizes

of Conduit or Tubing

HOTE:

For ampacity derating factors for more than three conductors in raceways, see Rule 4-004 in the

^^fnadian Electrical Code.

See of Conduit

or

lofting—Inches

Conductor

1 *"*

T

M C

Size

AWG.

MCM

14

12

10

8

6

4

3

2

1

0

00

000

0 000

250

300

350

400

500

600

700

750

800

900

1 000

1 250

1 500

1 750

2 000

Vt

3

3

2

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

%

6

5

4

2

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

10

9

7

4

2

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

I V .

18

15

13

8

5

3

3

3

1

0

0

0

0

0

0

0

0

0

0

0

0

V/z

25

21

17

10

6

5

4

4

3

2

1

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

2

41

35

29

17

11

8

7

6

5

4

3

3

2

1

0

0

0

0

2 V J

58

49

41

25

15

12

10

9

7

6

5

4

4

3

3

1

1

1

1

1

1

1

1

1

1

0

0

0

3

90

77

64

39

24

18

16

14

11

9

8

7

6

5

4

3

3

3

2

1

1

1

1

1

1

1

1

1

3'/2

121

103

86

52

32

24

21

19

14

12

11

9

8

6

5

5

4

4

3

3

3

2

2

4

155

132

110

67

41

31

28

24

18

16

14

12

10

8

7

6

6

5

4

4

3

3

3

2

1

1

1

1

4V2

195

166

138

84

51

39

35

31

23

20

18

15

13

10

9

8

7

6

5

4

4

4

4

3

3

2

1

1

5

200

200

174

105

64

50

44

38

29

25

22

19

16

13

11

10

9

8

6

6

5

5

6

A

3

3

2

2

6

200

200

200

152

93

72

63

56

42

37

32

28

24

19

17

15

14

11

9

8

8

8

7

6

5

4

4

3

Conduit Wiring 19



TA B LE 14 .4 D ime ns ions o f Ins u la t ed C ondu c t ors f or C a lc u la t ing Con dui t and Tubing F il

Size

AWG

M C M

14

14

14

12

12

12

10

10

10

8

6

4

3

2

1

0

00

000

0 000

250

300

350

400

500

600

700

750

800

900

1 000

1 250

1 500

1 750

2 000

"These ar

NO T E: To c

Rubber (ThermosetJ- and Thermoplastic-Insulated Conductors

(0 V—600 V I

Types

RW-75 end R-90

Diameter

Inches

(2/6410.171

(3/64)

0.204*

—

(2/64)0.188

(3/64)

0.221

*

—

0.242

—

—

0.311

0.397

0.452

0 481

0.513

0.588

0.629

0.675

0.727

0.785

0.868

0.933

0 9 8 5

1.032

1.119

1.233

1.304

1.339

1.372

1.435

1.494

1.676

1.801

1.916

2.021

B the dimensions fo

alculate conduit and

Area

Square

Inches

0.0230

0.032 7*

—

0.027 8

0. 0384*

—

0.0460

—

—

0.0760

0.123 8

0.160 5

0.181 7

0.206

7

0.271 5

0.310 7

0.357

8

0.4151

0.484 0

0.591 7

0.683 7

0.762

0

0.8365

0.983 4

1.1940

1.335 5

1.408 2

1.478 4

1.6173

1.753 1

2.206 2

2.547 5

2.889 5

3

207 9

types RW-75

tubing fill using

Types T . T W . T W H .

THHNJ, RW -76 (XLPE) i

RW-90 (XLPEIS

R-90 Silicone.

R-90

(XLPEI

i

Diameter

Inches

0 .131

0.166

—

0.148

0.183

—

0.168

0.204

—

0.248

0.323

0.372

0.401

0.433

0.508

0.549

0.595

0.647

0.705

0.788

0.843

0 8 9 5

0.942

1 029

1.143

1 214

1.249

1 282

1.345

1 404

1.577

1.702

1.817

1.922

Area

Square

Inches

0.013 5

0.021 6

—

0.017 2

0.0263

—

0.022 4

0.032 7

—

0.047

5

0

081

9

0.1087

0.1263

0.1473

0.202 7

0.2367

0.278 1

0.328

8

0.390 4

0.487 7

0.558 1

0.629

1

0.6969

0.8316

1.026 1

1.1575

1.225 2

1.290 8

1.420

8

1 548 2

1.9532

2.274 8

2.593 0

2.9013

ind R-90.

metric measu rements, refer t

Types

TWU,

RWU-75 (XLPEI i

RWU-90 (XLPEI

f

Diameter

Inches

—

0 193

—

0.209

—

—

0.230

0.324

0 3 6 3

0.412

0.440

0.473

0.544

0.585

0.632

0.684

0.744

0.822

0.878

0 9 3 0

0.978

1 064

1.180

1.252

1.287

1.321

1.385

1.444

1 616

1.741

1.858

1

966

Area

Square

Inches

—

—

0.029 3

—

0.034 3

—

—

0 041 5

0.082

4

0 1 0 3 5

0.1333

0 152 1

0.1757

0.232 4

0.2688

0.313 7

0.367

5

0.434 7

0.530 7

0.605 5

0 6 7 9 3

0.751 2

0.889 1

1.093 6

1.231 1

1.300 9

1.370 6

1.5066

1.637 7

2.051

0

2.380 6

2.7113

3.035

7

o page 193 of the text for gui

Types RW U-75 EP

RWU-90 EP

Diameter

Inches

—

—

0 2 3 1

—

0.247

—

—

0.268

0.345

0 456

0.505

0.533

0.566

0.649

0.690

0.737

0.789

0.849

0.977

1.033

1.085

1.133

1.218

1.301

1.373

1.408

1.442

1.506

1.565

1.809

1.934

2.051

2.159

lance.

Are

Sque

Inch

—

0.04

—

—

—

0.05

0.0

016

0.2

0.22

0.25

0 3

0.3

0.4

0.48

0.56

0.7

0 83

0 92

1.00

1 16

1 3 2

1.48

1.55

1.63

1.78

192

2.57

2

93

3 3

3.66

196 App lications of Electrical Construction



1

0

TABLE 14.5 C ros s -S ec t iona l A reas o f C ondui t and T ubing

Sam

1 metres

- *

*

:

2 -

3 :

1 :

£

s

Internal

Diameter

Inches

0.622

0.824

1.049

1.380

1.610

2.067

2.469

3.068

3.548

4.026

4.506

5.047

6.065

Per Cent C ross-Sectional Area of C onduit and Tubing—Square Inches

1 0 0 %

0.30

0.53

0.86

1.50

2.04

3.36

4.79

7.38

9.90

12.72

15.94

20.00

28.89

5 5 %

0.165

0.292

0.473

0.825

1.122

1.848

2.635

4.060

5.450

7.000

8.771

11.000

15.900

53%

0.159

0.281

0.456

0.795

1.081

1.780

2.540

3.910

5.250

6.745

8.452

10.600

15.320

4 0 %

0.120

0.212

0.344

0.600

0.816

1.344

1.916

2.952

3.960

5.088

6.378

8.000

11.556

38%

0.114

0.202

0.327

0.570

0.776

1.277

1.820

2.805

3.765

4.840

6.060

7.600

10.980

3 5 %

0.105

0.185

0.301

0.525

0.714

1.176

1.677

2.585

3.465

4.450

5.581

7.000

10.120

3 1 %

0.09

0.16

0.27

0.47

0.63

1.04

1.48

2.29

3.07

3.94

4.94

6.20

8.96

3 0 %

0.090

0.159

0.258

0.450

0.612

1.008

1.437

2.214

2.970

3.820

4.784

6.000

8.670

E Metric equ ivalents are not provided here , because they have no application in the electrical industry.

T

ABLE 14 .6 M a x i m u m A l l o w a b l e P e r C e n t C o n d u i t a n d T u b i n g F ill

iaro-clo's or multi-conductor cables

• c

sad-sheathed)

la«o-sreathed conductors or multi-conductor cables

Maxi mum Conduit and Tubing Rll

Par Cant

Numbar

o f

Conductor*

or Multi -conductor

Cablas

1

53

55

2

31

30

3

40

40

4

4 0

38

Ovar

4

40

35

Conduit Wiring

1«7



F o r R e v

i e w

1. List three main advantages that a

conduit wiring system has over

othe r wiring system s.

2.

List three a reas w here a conduit

wiring system is used to protect

the power supply.

3. In what length is conduit usually

produced? in what diameters?

4. How is conduit mea sured to deter

mine its trad e size?

5. List five main types of conduit.

6. Why is the inside of rigid con duit

coated with insulating paint or

varnish?

7. Explain in you r own w ords th e

steps for cutting and threading

rigid conduit.

8. What is the main disadvantage of

using a pipe cutter to prepare an

end of rigid conduit for threading?

9. What can be used a s a substitute

for thread-cutting lubricant?

10. What are the two type s of con duit

bender used for rigid conduit?

Which is used for the smaller sizes

of condu it? Which is used for

larger sizes?

11. Why must care be taken w hen

forming a bend in rigid conduit?

12. For what three purposes are

ben ds in rigid condu it m ade?

13. Explain in your own words how to

ma ke a 90° ben d in a length of

20 mm rigid con duit.

14. Why are EMT me chan ical fittings

m ade of zinc-alloy? W hat is the

main disadvantage of using zinc-

alloy?

15. What are the two main types of

EMT fittings? W here is each used?

16. What protection does a PVC jacket

give to EMT cond uit?

17. What is th e m ain difference

between a rigid conduit bend

and one used for thinwall

con

18.

List thre e u ses for con du lets.

19. List five different shapes of co

let fittings.

20.

Of wh at m ateria ls are condulc

covers made?

21. Describe two methods for se

ing rigid cond uit to box es,

plastic b ushings sometime s u

22. List four advantages of rigid

num conduit.

23. W hat is the main advantage o

ible condui t?

24. List three examples of how fl

useful.

25.

How is groun d c ontinu ity ma

tained in a flex system?

26. How is flex term inated ? How

PVC-jacketed flex terminated

27. Why mu st care be taken whe

installing PVC-jacketed flex?

28. W hat is a knockout cutter? He

and wh y is it used?

29. Why is it imp ortan t to keep t

fish tape in motion when ins

it into a run of conduit?

30 .

What meth od is used to help

a fish ta pe in to a run of

cond

with many bends?

31. W hat are the adv antage s of

c<

pressed-air fishing?

32 . Explain how power fishing is

33. Why is it ne ce ssa ry t o limit tl

num ber of conductors in con

or tubing?

34 . How many

No.

12 gauge cond

to rs w ith 1.2 mm RW-90 insula

can be placed in 20 mm cond

35. What precau tions should be

when using a pow er winch to

cond uctors into a conduit?

198




Residential

Service

Wiring

3 wire distribution s ystem is used

i

to supply re sidence s with

120 V

and

V.

The two main me thod s for bring-

the

3

wire system into a hous e are by

rhead

wiring from a pole transfo rm er

I

by

underground

wiring from a distri-

ion transformer mo unted below or

rve grade-level.

(See Cha pter 1) This

pter discusses both m ethods in

ater

detail.

ipply A uthor ity

I con duc tors carrying curre nt from

transformer—whether it is pole -

unted, at grade level, or below grade

i transformer vault—belong to the

a/

supply

authority (the hy dro u tility).

»the supply authority's responsibility

nstall, maintain, and service the con-

rtors, which are known as

service

sup-

conductors

(hy dro supply lines).

The cost of installing servic e supp ly

iductors is assum ed by the local sup-

authority, providing the residen ce is

hin

30 m of a distrib ution pole o r

asformer.

Home-ow ners beyond the

n distan ce often have to pay the co st

:.acing a pole or running cond uctors

ii

their hous es to the 30 m margin.

C onsumer's S ervice

The consu me r's service includes all

service boxes and related equipment, up

to and including the point at which the

supply authority m akes its conne ctions.

Figure 15.1 show s a typica l reside n

tial service w ith ov erhead supply lines.

Section 6 of the Canadian Electrical Code

provides up-to-date regulations for the

installation of a con sum er's service.

Service Size and Capacity

A residence use d to be considered well

equ ippe d if it had a 60 A main switch,

with an 8 circuit plus range (stove fuses)

distribution panel. Th e meter was usu

ally located inside the ho use between

th e se rvic e b ox es. (See Fig. 15.2)

As the demand for electrical appli

ances increased, the 60 A service instal

lation b ecam e in ade qua te. Also, local

hydro employees, who had to en ter

hom es to read meters so that custom ers

could be billed, often found no one there

to admit them.

The need for mo re circuits in the

hom e and, therefore, m ore fuses in the

distribution panel ma de the 100

A, 20

Residential Service Wiring

199



hydro supply lines

service entrance cap

(4 m to 9 m above grade)

mast support

(bolt, nut, and washer assembly)

2 cm w ood mounting board

(1 5.m above basement floor)

100 A, 24 circ

distribution pa

F I G U R E 15.1 A 100 A serv ice instal lat ion wi th overhead supply l ines

200




2 cm mounting board

URE 15.2 A 60 A serv ice instal lat ion w i th overhe ad sup ply l ines ( indoor me thod )


201



circuit panel a logical choic e. The extra

circuits (fuses) available allowed appli

ance receptacles in the kitchen and laun

dry are as to be fused separately. The

high current d em ands of mo dern appli

ances in thes e areas m ade this feature

necessary. At the sam e time, the me ters

were moved outdoors, eliminating the

access problem for meter readers.

The 100 A service can be installed

with a separate main switch and distri

bution panel or in the new com bination

un it. (See Figs. 15.1 and 15.3)

The switch and panel com bination

unit redu ces installation time and cos ts

by eliminating the n ipple, lockn uts, and

bushings required when the units are

installed separately. Since most combi

nation units are factory-prewired

(between m ain switch and distribution

panel) , even m ore time is saved. There

is , however, a metal

dividing wall

between th e two sections, so that a

short circuit in the distribution panel

cannot flash over to the main switch

(and vice versa) . This dividing wall also

isolates the non-fused service entrance

con duc tors. As a result, when a pe rson

attempts to change a circuit or fuse, the

o

U

E

CO

&

FIGURE 15.3 C ombination service entrance

panel with circuit breaker main disconnect and

pull-out units for branch circuit fuses

con duc tors are protected from dam

Despite the advantages of such a

c o

nation unit, before long manufactu

were encouraged to produce 24 ci

panels. The necessity of separate cir

cuits for clothes driers, electric wat

heaters and other modern appliance

led to this.

Many installers have discovered

versatility and convenience of circu

breaker combination panels for hou

Th ese p anels are available from sev

companies specializing in the manu

ture of service equipment. Figure

1

show s a typical 24 circuit combinat

panel.

Circuit Breakers

A more exten sive look will be taken

circuit breakers in Chapter 16. Ther

however, several basic features that

make a circuit breake r panel

attract

for residen tial installation. Such a p

is normally sm aller than a fuse pane

with th e sam e n um ber of circu its. It

th us ideal for installation in crowde

areas when upgrading the service

o

older house. Additional features su

tamper-proof current ratings, ease o

resetting (instead of replacing), and

abs ence of expose d live parts furth

en han ce this panel's practicality. (S

Figs.

15.5

and 15.6)

For a time , the 100 A service wa

considered the ultimate in residenti

equipment. But as larger, more

spac

houses were designed and often

equippe d with electric heating, the

service went the way of the 60

A

in

tion. Th e 200 A, 40 circuit se rvice tc

place. (See Figs. 15.5 and 15.7)

The 200 A unit is designed to pr

100 A and 20 circuits for heating, w

the other

100 A

and 20 circuits for

lighting, receptacles, and heavy

202




E

E

o

u

RES 15.4A and B C ombination service entrance load centre w ith 100 A main breaker

. sion for up to 24 individual circuit breakers. W ith the cover remo ved, the breaker con-

n points can be easily seen .

Upiiances.

With this sy stem, th e elec-

tkc

heating part of some serv ice b oxes

o n be turned off during the sum mer

k o n t h s .

As with

100 A

panels, circuit break-

HB

are pa rt of larger serv ice pa nel s. Fig-

are 15.5 illustrates a 200

A

circuit

beaker

panel.

Even 400

A,

600

A,

or 800

A

services

car. be found in some private resid enc es.

t a t is because larger modern hom es

demand

more circuits and have more

•rea

to heat. The installation of more

more electrical conveniences

•quires

a corresponding increase in

krvice

size.

Installation Techniques

Service entrance eq uipment m ust be

installed in a location suitable to both

the local supply authority and the

inspection department. Supply authori

ties a re usually qu ite willing to visit

homes on request and advise on the

location of service equ ipm ent. C onsulta

tion with them can preve nt installation

of servic e equipmen t in an unac ceptab le

manner; equipment installed contrary to

supply authority standard s must be

removed and reinstalled to their satis

faction. Mast height, meter height and

location, point of entry into the building,

and box location can be selected quickly

by an insp ector on a service location

visit.




bolt -on main

breakers

isolated main breaker

c om par t m ent

branch circuit neutral

t e r m ina l jum per

provis ion fo r 40 c ircui ts

in a com bina t ion of

s ingle- or double-pole

units , inc luding ground

fault protect ion breakers

wire direct ing posts

centre-l ine hole

(t

lower m ount ing s

cable entry locatio

f lat-rate water hea

wi r ing

ma in neutral b loc

easily accessible

bars on each side

panel

gr ound w i r e

conn

terminals on each

panel

branch circuit bre

single-

an d

doub

units f rom

15Ato

rat ings

t in-plated bus-ba

branch circuit bre

connect ion

FIGURE 15.5 Internal features of a comb ination service entrance load centre, 200 A rati

40 circu it capacity, in a total circuit breaker unit

204




f lush-surface style cover

bolt-on main breakers

branch circuit breaker

co mp a r tme n t

provision for mount ing

door kit

branch circuit breakers in

single-

and double-pole

units f rom 15 A to 60 A

ratings

circuit directory,

self-

adhesive type

isolated main breaker

co mp a r tme n t

i

RGURE15.6

•oughout

Features of a 200 A service entrar

permanent ly embossed

circuit numbers on cover

easily removed circuit

breaker twist-out

segments

manufacturer's name-

E

plate wit h user's

?

instruct ions

£

>ad centre, using circuit breakers

electric heating section

-nam switch

lighting and receptacles

cartridge fuses

plug fuses

ground wire (#2 bare copper)

IRE 15.7 A 200 A combination service entrance panel

Residential S ervice Wiring

20



Service Mast

Th e Canadian Electrical Code re quire s

that the service entrance cap be located

a minimum of 4.6 m abo ve gra de . Follow

ing this regulation helps ensu re h ydro

supp ly lines are not dam aged by large

vehicles and re du ces th e possibility of a

person moving a ladder, for example,

coming in con tact with the wires. Th e

entrance cap should not be located

more than 9 m above grade on high

bu ildings: th is wou ld m ake it difficult for

supply authority personn el to reach the

cap . Figure 15.8 show a typical ma st u nit

and its individual components, which

are available with 100 A and 200 A serv

ice fittings.

The service m ast, which is som e

times called th e standpipe, must be

securely fastened to the building to pre

vent hydro supply lines from pulling it

loose . Wind, rain, snow, ice, and co ntra c

tion of the wire in cold w eath er often

exert t remendous pressures on the

mast.

The re are several m etho ds for instal

ling th e m ast. (See Figs. 15.8,15.9,15.10;

see a lso Fig.

15.17)

One common method

for sec uring it is to u se long

bolts

that

pass completely through the wall and

fasten over a woo den mem ber on the

inside of the h ou se. Large squ are

washers and nuts are used to co mp lete

th e sys tem . (See Fig. 15.1 on page 200.)

The m ast is usually located abo ut

1 m from t he corn er of the building and

in suc h a way tha t n o supply lines will

pa ss within 1 m of a window o r any

other point that might provide access to

the w ires. Th us, if a pers on shook a m op

from a window, the re sho uld be n o likeli

hoo d of touc hing th e wires accidentally.

An 80 cm length of free co nd uc tor

mu st be left at the e ntra nc e ca p. Func

tioning as a drip loop, it ensu res tha t rain

J

1

will not run back in to the m ast. It al

gives the supp ly auth ority enough C

ductor for the connection.

Meter Socket

The local hydro autho rity determin

wh ere the m eter soc ket is installed,

usually at abou t

1.8

m abo ve grade

m eter socke t, a me tal enclosure wit

threa ded hu bs for conduit, is design

so that th e service cond uctors to b

metered are at tached to solderless

within the enc losure . (See Fig.

15.11

The

meter

is then plugged into th e

sure in much the sa m e way as a cor

is plugged into a rece ptacle .

In

fact.

is whe re the nam e meter socket cam

from. (See Fig. 15.13)

Meter sock ets , which are often

meter bases, a re available in seve ra

styles. (See Figs. 15.12,15.14,15.15,

15.16) T hreaded hubs are sized to a

the rigid conduit required for the s

installation, for example, 30 mm

100 A service and 50 mm for the 200

Some meter sock ets have hubs tha

on to the a ctual metal box of the soc

One type of me ter sock et is

equ

with a pa ir of special sold erless lug

the line side of the socket. These lu

allow a pair of No.

10

gauge,

red-in

lated

cond uc tors to be broug ht in t

main switch to supp ly th e flat-rate

heater . The smallest con du ctor allo

in a service conduit is a

No.

10 gau

wire. Since the se co ndu ctors are

attac he d t o the line side of the m e

any current passing through them

not register on the meter.

Flat-Rate Water Heater

System

Some local utilities op era te on a

fl

water heater supp ly system . The

C

sumer pays a set amount each

m o n




I

RE 15.8 S ervice mast and comp onents

Residential S ervice Wiring

207



insulator rack

grade level

jawnut

terminal screw

terminal

nut

pressure plate

terminal

FIGURE 15.11 S tandard terminal block

100 A and 200 A meter sockets

10 cmx 10 cm

angle

iron mast

(bolted to

house wa

strap

conduit standpipe

meter •

insulator rack

J

hydro

supply lines

I

grade level

FIGURE 15.10 Mast assembly on a 1-storey

house

FIGURE 15.12 A modern, 100 A meter

socket is rectangular in shape to provide

space inside the socket when connectin

service condu ctors.

208




2

URE 15.13 A plug-in style of residentia

•att hour me ter for use with

100

A and

A services

"

FIGURE 15.1 4

socket

A 200 A service m eter

and

may use as much power for heating

water as required. Large families, which

aeed

a lot of hot water, find this an eco

nomical system . Small families, however,

are usually be tter off if the water heater,

toge ther with the lights and other appli

ances, operate through the meter. With

•" • s

system, they pay only for the

amount

of power used.

The flat-rate water hea ter system is

food

for both the consumer and the

local utility. The demand for power is

neatest during the hours of 07:00 to

«:00 and 15:00 to

18:00.

During these

Wmes,

th e utility can turn off all the flat-

Bate

water heaters in the area . Power

irom the water heater units can then be

directed to industrial custom ers. A high

frequency signal is sent through the sup

ply lines, then picked up by the relay in

the basement of the house. The relay

then tu rns off the power to the heater.

The same process is used to restore the

power to the water heater.

Some communities require the two

red-insulated conductors to be enclosed

in the service conduit and m ast all the

way up to the weather head fitting. An

80 cm length of drip loop is left for con

nection to a fourth conductor, which is

brought to the home from the closest

hydro pole (on overhead service instal-

Resldentlal S ervice W iring

209



FIGURE 15.15 A meter socket assembly for use on a duplex or semi-detached house

lations). This fourth conductor a

the high-frequency signed to one red

wire,

while the second red conducto

connected to one of the incoming si

^ lines for the house . Underground se

installations normally use the meter

f socket with the special lugs.

c

I

{ S ervice E ntrance E lbows

| A 90° corner

is used to bring the

| standpipe from the m eter socket thi

the wall and into the serv ice boxes.

90° bend can be m ade in the service*

duit, but a groove must be chiselled

the wall for approximately

30

cm at

the hole to allow the conduit to fit I

FIGURE 15.16 A n old-style. 60

A /100

A

service meter socket in the original, round

configuration

210




meter

NO TE: Wal l must

be grooved.

meter

hole

grade

leve

main switch

RE 15.17 Me thod for driveway

instal

ls of standp ipe (90° bend)

against the wall. (See Fig. 15.17) Doing

his is worthwhile when th e serv ice con-

B at

is in a driveway or similar are a,

ibere the conduit may be abused by

[vehicles.

There is another way of handling the

f

b end . (See Fig. 15.18) It doe s awa y

•ith the need for grooving the wall, but

fee standpipe protrudes from the wall a

lew extra inches (several centimetres),

[his goose-neck

bend m ethod of enter-

kg the building was o nce u sed widely.

WUh the increase in condu it size and the

•welopment of condulet fittings, how-

• w , this difficult bend has become less

popular.

A condulet fitting, su ch a s th e LB, is

approved for use where there is little

iiance of mech anical injury crack ing

he

casting. (See Fig. 15.19)

The hole in the wall must be m ade

•ghtly

larger to allow the sh ort arm of

main switch

FIGURE 15.18 A lternative me thod for drive

wa y installation of standpipe (goose-neck

bend)

the cond ulet to ente r the wall. A weath

erproof

gasket

and

cover

fastened to the

LB seal out any mo isture. The LB fitting

provides access to the conduit and

mak es it easie r to pull in the large con

duc tors required for modern h ouse s.

A special fitting called the service ell

can a lso be used for ente ring a building.

(See Figs. 15.20 and 15.21) Its main

advantage is that the short arm does no

extend in to th e wall. Because the hole in

the wall does not need to b e made any

larger than th e conduit nipple, this ty pe

of installation is more weatherproof than

other types.

No m atter which metho d is used to

enter the building, the Canadian Electri

cal Code requires tha t all open ings

around the area where the conduit

en ter s th e wall be filled. Otherw ise,

there may be water damage to the h ouse

Residen tial Service Wiring

21



meter

meter

main sw itch

FIGU R E 15. 19 L B

condulet

met hod f or

enter ing bui ld ing

F I G U R E 1 5 . 2 0

and gasket

Serv ice el l f i t t ing wi th cover

and/or the service equipment.

Mortar,

or

a similar material, trowelled into place

will sto p m oisture o r cold air from com

ing in.

212

main switc

FIG URE 15.21 A serv ice el l instal lat ion

Underground Service

Most new subdivisions have under

ground service installations to help

stree ts look neat and uncluttered,

distribution transformer can be l

under ground in a transformer vault

on a conc rete p ad. The vault or pad

be out near the street o r behind the

house, with the supply lines coming

under the backyard. (See Fig. 15.22)

er-

elp

I.

T

oca

lul

L ocation o f S ervice Box

i

ection 6 of th e C anadian Electrical

lists the p laces where service boxes

must not be locate d. In general, serv

boxes shou ld be m ounted on a wall

abo ut 1.5 m above th e floor and as |

as possible to the point where the

I

ice cond uit en ter s t he building. If the

is any doub t ab out w here to install

box, the local inspection authority

should be asked for advice.




pA^ - j

Side View

Front View

doc

meter

socket

BGURE 15.22 Und erground service installation (front and side view s)

Residential Serv ice Wiring 213



S ervice M ou nting Board S ervice W iring

Service boxes must

be

suppo rted on

a

wooden mounting board approximately

2 cm thick. Plywood d oe s an exce llent

job,

but

regular

2

cm lumber can be used .

A 100 A service requires a i m

2

panel. A

200

A

serv ice w ill likely need

a 1.2

m

squ are board, and larger service s require

a full 120 cm x 240 cm plywood shee t.

The board should be fastened securely

to the w all with such devices as concrete

nails

or

ma sonry plugs and screw s.

The wood en panel allows bran ch cir

cuit con duc tors to be sup po rted close

to

the distribution p anel. Future equ ipmen t

can also easily be sec ured to it.

Service Boxes

Service boxes use d

to be

arranged

as

two sepa rate units. (See Figs. 15.1 and

15.2

on

pag es 200 and 201.) Modern

service equipment, in 100 A and 200 A

rang es, is usually arran ge d in th e form of

combination u nits. (See

Figs.

15.3,15.4,

and 15.5) Larger servic e boxe s are usu

ally arran ged as show n in Figure

15.23.

weatherhead

mast

n

LB

J

main

switch

Table 5.5,

on

page

61,

lists the size

copper conductors

to

be used wit

vario us a mp acities. Table 5.6, on p

62,

covers the requirements

of

alu

num condu ctors. Once condu ctor

has been determined, these tables

Tables 14.2,14.3,14.4,14.5 and 14

be used to establish c ond uit size

installation.

When an o utdoor meter is used

conductors must first pass throug

meter terminals (lugs). The neutra

m ust not be broken in the m eter

S

It must pa ss directly to the neutra

in the main switch. A neutral w ire

not m aking

a

good co ntac t will ca

uneven v oltage distribution

in an

anced system, which can be dang

The two live wires in the servi

duit are conn ected directly to the

terminals in the m ain switch. Thes

minals are nearly always located a

to p of th e switch and are designed

that when the switch

is

off, only th

two terminals are live. Some manu

ers design their equipm ent so tha

line terminals a re covered

by an

ing barrier

to

prevent

a

perso n fro

combinatio

sub-disconnec

distribution

pa

meter cabinet

splitter

F I G U R E 15.23 A l a r g e s e r v i c e l a y o u t

214




E

o

U

Q

RGURE 15.24 Typical main switch with line

nals at top and load terminals at bo ttom

accidentally touching them. (See Fig.

4) The load side of th e switch (b ot

tom terminals) is then connected to the

distribution panel.

Figure 15.25 sho w s th e wiring of a

Typical 100 A service. The 200 A service

•ses larger con du cto rs, but is wired in

the sam e way.

Figure 15.26, on pa ge 217, shows the

box arrangement and wiring for a semi-

ietached

house.

Figure 15.27, on p age 218, show s th e

»x arrang em ent and wiring for a

p p l e x .

Apartment buildings, where the

•>artments are metered separately,

•ust be handled differently. Figure 15.28

sho w s a typical servic e installation for a

bur-su ite apartm ent building. Large

Krvices of this type h ave indo or meter-

tag facilities.

When a

single-meter

system is

eded for a service with a ca pac ity

•rger

than 200

A,

th e curre nt flow m ust

be metered

without

actua lly pa ssing full

•oe

current through the m eter. Since

nost meters have a maximum current

cap acity of 200 A, a system of current-

reducing transformers is used. The se cur

rent t ransformers carry the full line cur

rent in a main (primary) winding, which

usually cons ists of a solid ba r of cop per.

They red uce th e line curren t to a safe

level through a secon dary winding. A 5 A

curren t is then p assed on to a specially

designed meter. (See Fig. 15.29)

The current t ransformers and me ter

are house d in a metal meter cabinet.

The re are several cabinet sizes: the

smallest mea sures about

1

m squa re and

is abo ut 30 cm d eep .

Figure 15.30, on pa ge

221,

shows an

indo or m eter for use in a m eter c abine t.

Figures

15.31,15.32

and

15.33Aand

B, on pag e 221, show current transform

ers.

Transfo rme rs are available in a vari

ety of sizes and a m pere capa cities.

Service Grounding

Electrical services m ust be groun ded for

two reasons. The first is that the steel

mast, which rises 4.6 m to 9 m, is an

attractive target for lightning. Grounding

the mast reduces the chance of lightning

striking the house.

If

lightning d oe s

strike, grounding provides a direct pa th

to the earth .

The seco nd reason is tha t grounding

of the boxes and cabinets gives another,

equally imp ortant, form of protection . If

on e of the live wires in the system

com es in con tact w ith any of the metal

enc losu res, the re will be a sho rt c ircuit.

The exc essive short-circuit curren t will

flow along the ground con du ctor and

pass harm lessly into the earth. The

usua l result is a blown fuse. On ce th e

fault has been located and repaired, the

fuse ca n b e repla ced easily. If the box es

were

not

gro und ed, all of the condu it,

boxes, and cabinets would beco me

alive

and dangerous.

A

person standing on


215



FIGURE 15.25 The once popular 100 A combination main switch and fuse panel, wi th w

round meter socket (covers removed) is used

216




•Based on copper conductor sizes

#3/0

RW-90*

mast

50

mm conduit

double meter base

#6 bare"

to ground clamp on water pipe

URE 15.26 Semi-detached house service installation

loist earth or a damp floor and touch-

tag

part

of

the metallic system would

Kceive

a

120 V

sho ck. In a large b uilding,

•ith no blown fuse on

an

ungrounded

Rrstem,

the fault m ay not sho w up for

m e time and then be almost impossi

ble to locate.

The most common method

for pro-

tatng a ground for a residential service

\

to connect

a

conductor

from

the

mitral block in the main switch

to

the

Bid-water supply pipe as it com es out

I fcom he basement floor. The neutral

[Mock is con necte d to the sw itch bo x by

a brass

bolt.

Thu s, both the box and neu

tral conductors are grounded. The

ground clamp must be fastened on to

the water pipe ahead

of

the meter,

because a leak-proof compound (a non

conductor

of

curren t) is applied to the

plumbing threads before assembly. (See

Fig. 15.34

on

page 222.) The groun d wire

from t he main switch b ox is usually b are

copper

or

covered with

a

white insula

tion. Table

16.1,

on page

231,

lists the

conduc tor size

to be

used.

When a house ha s

copper

plumbing,

which is properly soldered at the fit

tings,

the ground wire can

be

run from

the main switch to the closest cold-

water pipe. The hot-water tank interferes

with the electrical continuity of the hot-

Residential Service Wiring 217



#3/0 RW-90*

/

double meter base

'Based on copper conductor sizes

N O T E :

Boxes must

be labelled

combination

100 A

units

rVl

•

•

• • • • |i J pi

~

11,1 I*

b~

30 mm conduit and

#3 RW-90 conductor*

splitter box

50 mm conduit

double locknut and ground bushing

#2 bare wir e*

to ground clamp on water pipe

FIGURE 15.27 Duplex service installation (separate metering)

water pipe and should not be u sed.

Since the water meter with its water

proof connections

is

still

a

problem,

a

jumper

of the same gauge conductor as

the ground w ire must be installed to by

pass t he m eter. Then, if the water meter

is removed at any

time,

ground continu

ity is mainta ined. (See Fig. 15.35 on

pag e 222.)

In some areas, hou ses

do

not u se

a

water m eter. In the se ca ses, the ground

conductor should be connected by a

ground clamp to the cold-water pipe

where it first en ters th e basem ent. (See

Fig. 15.36 on page 222.)

Two precautions mu st be taken to

make sure tha t the m ast is grounded

effectively. First, two secu rely tight*

locknuts, one inside and one outside

box, are used. Second,

a

special groi

bushing

with provision for a

groundii

conduc tor is threaded on to the com

This conductor, which shou ld be

at

No.

6 gauge, joins the g round bushir

th e neutr al block. Figure 15.37, on

]

222,

shows a ground bushing.

Rural communities and cottage i

usually do not have the cold-water

su

ply pipe used for grounding services

urban comm unities. There are sever

different methods

for

grounding avai

ble

for these areas. The most

commo

218




a

re

3

3

00

a.

"

500

MCM

RW-90

w

00

>

" O

Co

3

3

C D

r-*

CO

CD

5

o

CD

5 '

en

o '

cT

CD

"a

cu

Q>

CD

3

CD

C D

5 '

CQ

Based on copper conductor sizes

T o A p t . 4

double locknut

a n d g r o u n d b u s h i n g

#2/0 bare

400 A spli t ter box

double locknut and bushing ( throughout )

to ground c lamp on water p ipe

NO TE: Boxes must be label led.



E

o

a

s

c

m

-»

>

CD

3

CD

« -

t t >

13-

Q)

3

CD

0 1

CD

<

o '

CD

3 '

en

3

5T

-*

o

3

100 A combinat ion pane

200 A combination panel

80 cm drip loop

500 MCM

RW-90

#3 RW-90 —

A — i

9 0 m m

mast conduit

400 A main switch

400 A splitter box

NOTE: Lighting panel wired similar to heating

panel. Use #3/0 RW-90*.

"Based

on copper conductor sizes

1m x 1 m meter cabinet

I

t l / ~

p r i m a r /

: rf ch_j

" " ; s e c o n d a r y ^ .

double locknut and ground bushing

# 2 / 0 b « r t "

double locknut and bushing (throughout)

ti i u

1

" ' ' IMUI|I ' in wii lni | i i | i i*

^—A

90 mm conduit nipple

500 MCM RW-90



.

l

FIGURE 15.31

transformer

A 200 A capacity current

£

o

U

FIGURE 15.30

^Her

cabinet

An indoor meter for use in a

FIGURE 15.32 Typical 800 A capacity cur

rent transformer designed to operate w ith

both live wires of the system

3

8

FIGURES

15.33A

A N D B Mod ern current transformers are more compact in size due to a

•designing

of the primary conductors' enclosure.

Residential S ervice W iring

22



2.5 cm

x 5.0 cm

wood

strap

\

«— ground wire

Romex

staple

water meter

waterproofing compound

ground clamp

>»

concrete floor

FIGURE 15.34

Ground clamp connected to

water pipe ahead of water meter

ground clam

conduct

FIGURE 15.35 A wate r meter by-pas

FIGURE 15.36 A water ground cla

use in a residential service

t in-p la ted, cold- formed

copper lug ( in variety

of ground wire capacit ies)

N O T E :

Insulator

swaged in

(resists pull out

at any one point)

f lat, r ibbed pads

(for contact wi th grounding lug)

posi t ioning and bonding screw

posit ive conduit s top

colour-coded insulator

cutaway v iew

ful l v iew

FIGURE 15.37 Full and cutaway views of a ground bushing

222




is to drive tw o 2 cm diam eter,

galva-

red steel rods (ground ele ctrode s) into

e earth . They must be sp aced approxi-

itely

2.5 m apa rt an d driven in a full

a.

The 3 m depth ensu res a high-qual-

ground contact with permanently

1st ea rth . (See Fig. 15.38)

Commercial

ground rod drivers

are

available, but most often a sledge

wnmer is used to drive rods into the

prth. Layers of clay and stones or rocky

rr ra in are problems to the installer.

Sometimes the rods , striking a layer of

lack, gradually turn and m ove back to

be surface, several metres from the

farting point. Inspection authorities

w rods to be driven in on an ang le If

the terrain is hard and the installation

difficult.

A grounding con ductor must run in a

continuous length

from th e neutral b lock

in the main switch to the first rod. Here

it passes unbroken through a clamp on

the rod, and then travels to the sec ond

ground electrod e som e 2.5 m away. Take

care to check with the inspection

authority for up-to-date information

about the typ e of clamp allowed on th e

ground rod. The clamping device m ust

make a secure electrical connection to

both rod and conductor. Once the rods

and ground conductor are covered with

earth, it may be many years before the y

are checked again.

HGURE 15.38 Ground rod installation




In rocky soil, it may be impossible to

drive in ground rods. In these cases, a

steel plate, 0.2 m

2

in area and

a

minimum

of 6 mm thick, can be buried

in the

earth . The plate should be installed as

deeply as possible to ensure a good

grou nd co nta ct. (See Fig. 15.39)

There are also other m ethod s

of

pro

viding a ground circuit under rugged ter

rain con ditions. A pair of ground rods

can be laid in a trench , dug as deeply as

the rocky terrain will permit, an d th en

cov ered w ith to p soil. Still an oth er

method requires a ground rod or copper

conductor to be buried or encased

within the concrete footings supporting

a bu ilding's walls. Sufficient co nd uc to r

size and length sho uld be provided to

make

a

con nection to the m ain n eutral

block within the m ain service discon

nect. Consult Section 10.700

of

the Elec

trical Code

for

co nfirmation

of

ground

ing technique s in difficult ar ea s. (Se

Fig. 15.40)

Often, when g roun d rod s (artific

grounding) are used, inspection

aut

ties require a grounding conductor o

least No. 8 gauge to be run from the

tral

block of the main switch to a

cl«

on the cop per p lumbing. This

happ

most often in rural com mu nities to

vent the chance of a voltage differer

existing between the earth and the

plumbing system in

the

ho use . If a

|

tic (PVC) w ater sy stem

is

used

thro

ou t the hou se, this extra ground cor

tor is not required.

Meters

The meter records the num ber

of

k

wa tt ho urs (1 kW is equal to 1000 V

power consumed. Modern meters

g

direct reading

the way odom eters do

»

."

0

ground w ire to service disconnect

6 m m

» »

rock layer

•^

o •

0-

NOTE:

Buried 25 cm below

permanent moisture level

O

F I G U R E 1 5 .3 9 P l a te e l e c t ro d e g r o u n d i n g m e t h o d

224

Applications

of




main service

equipment

ground cable sized to

match service requirements

1/2 in. /1.25 cm steel rod or 20 ft. / 6 m of copper cable

basement

wall

- > " ^

^ t o . L wall foot ing

5 cm poured concrete

clamp

1 0 f t . / 3

m

long

I

SURE 15.40 A rt if icial ground electrode system

» s . (See Fig. 15.30) Th ere a re still many

l*-fashioned me ters in use, however,

fcese

meters have

five small dials

to

tamcate the co nsu m ption . (See Fig.

141) Moving from right to left ac ro ss

e dials, the first dial shows single

• t s . the second tens, the third hun-

keds, the

fourth

thousa nds, and the

fifth

a s of tho us an ds . Figure 15.42 sho w s a

be-dial meter reading.

The consumer pays the local utility

W

power at a rate of so m any cen ts

per

btvatt hour. The num ber of kilowatt

•nrs

of power used during a given

period is read from th e m eter. The nu m-

s is

multiplied by th e ra te pe r kilowatt

•or. and the customer is billed.

Note: Many utilities have a rate

structure whereby th e price charged a

E

3

Q

o

E

£

2

FIGURE

15.41

Five-dial me ter




10 000

1 000

FIGURE 15.42 A five-dial meter reading (26 422

kW»h)

customer varies according to the

amount of power con sum ed. For exam

ple, the first 50 kW-h would be at a

base price, while the next 200 kWh

would be charged a t a lower rate pe r

kilowatt hour. This system rewards the

con sum er using a lot of electrical

energy, such as an electric heating cus

tomer. It makes electricity more com

petitive with other fuel ty pe s.

Temporary Service

On construc tion s ites power is needed

for portable drills, saws, concrete

mixers, and othe r equipm ent. A tempo

rary service is usually erected on a pole.

(See Fig. 15.43) Th is unit is desig ned

with a main switch, a small distribution

panel, several duplex receptac les, and a

weathe r-resistant cabinet to protec t it.

Mast height can b e as low as 4.6 m.

A

sin

gle ground rod is usually enough for th is

type of installation. Often, the local util

ity ch arg es a flat rat e or fee for serv ice,

and a meter is not installed.

Inspection Permit

An application for inspe ction must be

filed with th e local inspection auth ority

for a ll new installation s of electrica l

equipm ent. A residential serv ice is con

sidered an important installation and

receives careful attention from the

inspec tion authority. Power will not usu

ally be allowed o n until th e ins pec tor is

satisfied that every detail is comp

and safely installed. This inspectio

important, because it guarantees

owner and the insurance compan

every precaution h as been taken

sur e a safe and high-quality instal

F o r R e

v

i

e

m

ii

1. What are th e two main

meth

for bringing the 3 wire distrib

system to a house?

2. List the main pa rts of a con

sumer's service.

3.

Why did the 60 A service be

inadequate for modern hous

Give two reas on s.

4. W hy are combination servic

panels often used in modern

houses?

5. What are the minimum and

m

mum heights for service entr

fittings? Why?

6. Describe a

drip loop,

and

exp

its purpose.

7. What is the

m eter base?

How

above grade is it m ounted?

8. Why is the flat-rate water hea

system good for both the

ho

owner and the public utility?

9. Describe the two different

methods for supplying curren

flat-rate wa ter-hea ter system

226




25 mmconduit mast

f— NOTE:

Minimum height

4 m

#6 TW H copper conductor

-•—

conduit strap

2 pole, plug fuse units

"U '

ground duplex

receptacle .-

protect ive wood

'enclosure

fc5i« -~

hasp

- 60

A

main switch

max level

•*•-**••»••*•

5 cm x 10 cm

wood brace

#6 bare

or white

ground wire

ground rod

and clamp

NO TE : Suggested depth

1 m —*;

RGURE

15.43

T emporary service installation

Residential Service Wiring 227



10. Where are cast aluminum condu

cts a pproved for use? Why?

11. How is moisture stopped from

seeping in where a service conduit

ente rs a wall?

12. Whe re in th e Can adian Electrical

Code is information about the size

of service conductors and con

duit?

13.

What dang er exists if th e neutra l

wire of the 3 wire system is

accidentally broken or loosely

connected?

14. Explain why current transformers

are used with a service larger than

200 A.

15. List two rea son s for groun ding an

electrical service.

16. Why are services that have w ater

meters grounded ahead of the

water meter?

17. How is a servic e grou nded when a

house has copper plumbing

throughout?

18. Where in the Canadian Electrical

Code is information abo ut th e size

of ground w ire to be used on a res

idential service?

19.

What two precautions must be

taken when grounding a service

mast?

20. Describe in your own words two

different methods for grounding a

service in a rural community

where there is no municipal water

supply system.

21 .

Why are plastic bushings or metal

bushings with plastic liners used

on service conduits?

22.

Why is electrical inspection impor

tant to the home-owner?




S

mall factory and co mm ercial build

ings are sometim es equ ipped with

e 120 V/240 V service used in residen-

hfal installations. The larger capacity

fi V/240 V serv ices (400 A, 600 A, and

I A)

have more than enough circuits

the lights, receptac les, and m otors

hese

small, limited production facilities

Industrial

buildings usually have

ior-driven equipment. These m otors

Men need far more cu rrent than lighting

:uits. When being started, a mo tor

iws thr ee to five tim es' its norm al

crating

current, which places an even

^eater load on the service eq uipme nt. A

•otor

designed to oper ate on a higher

poltage will pro du ce th e sa m e am ount of

power but with a dec reas e in line cur

rent. For example, a 750 W motor opera

ting at 120 V will require approx imately

[K

A. The same m otor, internally con

nected to o pe rat e on 240 V, will re quire

about

8 A.

Motors and equipment designed to

•perate

on even higher voltages need

Mill less current. When the current is

•educed, the

w ire size

in th e motor

bin din gs can also be reduced. This

H o w s ,

for example, a 550 V motor to be

•uch sm aller in size tha n a 750 W, 120 V

Motor.

Special voltage systems are available

tor commercial and industrial use . Thes e

Industrial

Services

are known as polyphase (3 phase) sys

t ems . Three-phase motors and equip

ment are more efficient and smaller in

size and usually need less curre nt than

equivalent units designed for use with a

single-phase

supply system.

Three-phase voltages are produced

by the alternators (AC gene rators) at the

power station and can be transformed

by the consum er to any on e of thre e

comm on voltage levels. The m ost p opu

lar 3 ph as e voltage levels are

550 V,

440 V, and 208 V.

The 550 V and 440 V systems use 3

live wires without a neutral condu ctor.

The 208 V system is available in 3 wire

(3

live

con duc tors) and 4 wire (3 live and

1 neutral conducto r) com binations. The

adv anta ge of the 4 wire, 208

V

system is

that there are 120 V between the n eutral

con duc tor an d any one of the three live

con duc tors for lighting and receptac les.


Ano ther advantage of the 3 phase

system is that motors can be reversed

easily. A polyphase motor will rotate in

the opposite direction if any of the three

live wires are interch anged . To reve rse a

single-phase motor, the motor often has

to be dismantled and the internal con

nection of the windings changed.

When w orking on a 3 ph ase service,

take care not to interchange any of the

live

wires.

If the live wires are interchanged,

Industrial Services

229



Phase 1

11

00 0

V

11 000 V 11 000 V

Phase 2

11

000 V

11

000 V

I

3 phase alternator

(in power station)

Phase 3

11 000 V

a

0

D

3

0

3

I

1

J o

0

a

0

3

0

>

1

3 phase supply

t

550 V

* a

1

550 V

I

ratio 20:1

NOTE: Consumer's 3 phase transformer, connected with Delta primary, Delta secondary

FIGURE 16.1 Typical 3 phase 550 V or 440 V supply system

f

\ 2400 V

1 1 V v

3 phase alternator

(in power station)

r;

>

2400 V

t

2400 V

1

Phase

1 ^

2400 V

Phase 2

2400 V

Phase 3 ^

2400 V

»-a

I — _ s

« i

c

0

r

4

0

^ ^ » * p

o

0

0

o

o

o — 4

neu:r=

120V

•-4

120 V

_ i

120 V 20 8 V

ratio 20:1

NOTE: Consumer's 3 phase transformer, connected with Delta primary, Wye secondary

FIGURE 16.2 Typical 3 phase 120 V/208 V supply system

230




wry mo tor in the building will hav e its

Irection of rotation rever sed. For this

as on , high-voltage, 3 ph ase conduc-

JTS are often identified with red, white,

•d blue tags.

•0

V and 440 V S ystems

1550 V and 440 V 3 wire services are

Bed p rim arily

for

mo tors and their con-

pis . The meter is located within the

•Iding in a metal meter cabinet. These

ase services are available in sizes

•ging from 100 A up. The switch boxes

d distribution panels have terminals

^rthe

thre e live wires,

but not for a

neu-

•I

conductor, since the re

is

no neutral

Iductor.

Conductor and c onduit sizes are cho-

i in the sam e way as for the residen-

I

service. Also, ma st h eight, bo x

it, and location are the sam e as for

tsidential ser vice . Figure 16.3 show s a

:al 550

V

and /or 440

V

service instal

lation. The th ree live condu ctors are

often all the same colour, usually black,

red, or blue.

Grounding is limited to the boxes,

cabin ets, panels, and conduits of the sys

tem. A ground conductor is placed between

the ground ing lug in the main switch box

and th e cold-water supply pipe. Table

16.1 lists ground co nd uc tor sizes.

600 V/347 V S ystem

Fairly rece nt in origin, the 600 V/347 V

system is being use d increasingly in

comm ercial lighting and for mo tor and

equipm ent circuits. A Wye connected

secondary, formed by the joining of one

end

of

each

of

the thr ee seco nda ry coils

into

a

comm on point known

as

centre

tap,

provides 600 V betw een any two of

the three

live

wires. The com mon

or

cen

tre tap conductor provides a voltage of

approximately 347 V between itself and

any one

of

the thr ee live wires.

Figure 16.4 show s internal conn ec

tions

of

the m eter ca binet.

TABLE

16.1

Minimum Size of Grounding Conductor for AC

Systems or Common Grounding Conductor

A m p a c i t y of L argest

S ervice C onduc t or

or

Equivalent

f or Mul t ip le Conduc t ors

Size of

Copper Grounding

Conduc t or

AWG

100 or

less

101 to 125

126 to 165

166 to 200

201 to 260

261 to 355

356 to 475

Over 475

8

6

4

3

2

0

00

000

NOTE:

T he ampacity of the largest service conductor, or equivalent if multiple conductors are

used,

is

to be determined from the appropriate Code Table taking into consideration the number of con

ductors and the type of insulation.

Industrial S ervices

231



B

•o

E

o

o

§

I

n

o

3

c

30

m

—*

to

-<

-o

o'

9L

CO

"D

3 "

CO

CO

CD

Oi

CJ1

o

<

o

J

o

<

CO

CD

§

o

CD

5 '

CO

*»•

c o _

QT

r-*

o

3

drip loop

machine shop*

•Each switch must be labelled.

compressor*

sub-disconnect switch •—•

mast

from meter cabinet

2 locknuts and 1 bushing (throughout system)

1.2 m x 1.2 m meter cabinet

splitter box

NO TE : 1 wire to each terminal block

2 locknuts and

ground bushing

fuses •

ground wire for mast

Uttra

nipple

voltage coil

#10AWG

wire

V *WTTO» I

de

i * .

j _

current

coil

ground

\

X

. ?

X

?

I V c u r r e n t

I transform

ransformer

meter

teaser (to activate voltage coils)

i

*—

-jf

—

tospl

litter



Meter ing

fbe 3

pha se system nee ds a special

•eter,

containing two voltage and two

««rrent

co ils, for reco rding p ow er. This

•Dit

is like two m ete rs in one . Th e to tal

•nount

of power use d is equa l to the

mm

of both me ter section s. (This total

is

shown as a single reading on the

tastrument's dials.) (See Fig. 16.5)

Cur-

tent transformers are used with the 3

phase m eter. (See Figs. 16.6 and

16.7)

A

pec ial 3 phase "hybr id" meter combin-

g mechanical and electronic features is

, on occ asion , for multifunction

metering of large industrial loads. (See

Fig. 16.8)

M etho d of Distribution. As Figure 16.3

show s, the service con duc tors enter a

splitter box

after leaving th e m eter

cabinet.

Sub<lisconnect switches

are then

joined to th e splitter. Co ndu ctors of the

sam e ampacity rating as the disconnec t

switch the n distr ibute 3 phase supply to

various pa rts of the building. Each

sub-disconnect must b e labelled

correctly to show exactly which area or

what equipment it controls.

1.2

m

x 1.2 m meter cabinet

JURE 16.4 C urrent transformers and meter connections for a 3 phase, 600 V / 347 V

vice installation

Industrial Services



FIGURE 16.5

A 3 phase meter

o

u

FIGURE 16.7 C urrent transfo

r

mer

FIGURE 16. 6 A 3 phase kilowatt-hour

meter for use with current transformers

A second

disconnect switch is usu

ally mounted on or near the equipment.

Designed so that padlocks can be placed

on it, this switch serves as a safety meas

ure.

The padlocks keep the switch out of

service until personnel are clear of the

machine. Each padlock is removed as |

each person completes service. Whea

the last padlock has been removed,

ice may be restored safely.

Grounding. 550 V will both severely

shock a person and cause serious b

As a rule, none of the 3 phase 550 V a

440 V conductors are grounded. This

isolated system prevents a person in j

contact w ith grounded equipment frca

being injured if and when a live

conductor is also touched. Many

services are equipped with three

indicating lights

(ground detectors)

to

warn that a live conductor has

come •

con tact w ith a m etal box or associated

piece of equipm ent. All metal boxes,

panels, conduits, and fittings, howeve^

are grounded.

Take great care when working vtm

550 V or 440 V system, because all thn

conductors are alive and

dangerous

Sometimes current leaking from faultj

equipment establishes a partial gro

on one conductor. In these

cases,

any

protection given by the system being

isolated is gone.

234

Applications of Electrical Construc tion



E

o

u

31

a

S

iURE 16.8 A3 phase, mechanical/elec-

K mu ltifunction m eter for large industrial

L20 V/208 V S ystem

0

V

and 440

V

system s are excellent

purees of power for motors and related

pripment, but they are not ideal for

pieral

lighting and power requirem ents,

ften

the 550

V

system is reduced

rough a transformer to

120

V/240 V,

and then distributed to lighting and gen

eral power circuits. This can b e expen

sive, becau se of the c ost of the equ ip

ment required. The 3 ph ase, 4 wire,

120

V/208

V

supply system com bines the

best qualities of both 3 phase and single-

phase systems and is ideal for lighting

and gen eral power. (See Fig. 16.9)

The 3 phase , 208 V system can be

used for motor-driven equipm ent. The

fourth (neutral) cond uctor in the system

provides

120 V

between itself and any of

the three live conductors for lighting

and general power req uirem ents. Figure

16.2 show s how the two voltages are

obtained.

Service entrance equipment for the

120 V/ 208 V system looks very much

like th e eq uipm ent for 550 V/ 440

V

units

The difference is tha t a neu tral con duc

tor is used in the 120 V/ 208 V system,

and it is treated in much the sam e way

as the neutra l wire of a single-phase, res

idential sy stem .

Since

120 V

are available b etween

the neutral and live conductors, a group

of thr ee

current transformers

must be

used to record the power accurately. Fig

ure 16.10 sho w s a typical

120

V/208

V

servic e installation. Th ese services are

usually av ailable in sizes rang ing from

200 A up.

Figure 16.12 sho w s a 3 ph ase t ran s

former with the three sets of windings

for red ucing th e voltage in each ph ase of

the system .

Large industrial service

installations

often come in the form of a cabinet or

switchboard system and are ordered

from the manufacturer for each individ

ual job o r ins tallation. (See Fig.

16.11)

Figure

16.13,

on page 239, sho ws a small

unit. F igure

16.15,

on page 240, show s a

larger unit with room for

step-down

trans

formers in the screened cabinets (on the

right-hand side of the pho togra ph ).

Industrial Services



550 V m ain switch 550 V/208 V step-down t ransforme r

spl i tter t roug h

sub-disconnects

split ter trou gh circuit breaker panel

FIGURE 16.9 Typica 120 V/208 V, 3 phase,

*rvice

236




3

a.

c

^

c

33

m

—i

a>

o

-<

-g

o '

CO

" O

3 "

a>

0)

CD

r-o

o

<:

NJ

O

CO

<

w

CD

<

o

CD

5 '

en

i-+

9L

QT

o

3

machine shop

drip loop

L B

l o a d — Z

mast

from meter cabinet

2 locknuts and 1 bushing (throughout system)

splitter box

1.2

m

x 1.2 m meter cabinet

main switch

2 locknuts and

'

ground bushing

fuses •

ground wire for mast

neutral block

voltage coil

transformers • neutral

••

meter

ghting

-tease r (to activate voltage coils)

ground

r—A

Z : to splitter

• A

ground conductor to cold-water pipe



FIGURE 16.11 A main switchboard room installation

FIGURE 16.12 A dry-type, core and coil

assembly transformer used in a single-ended

unit sub-station

Co nduc tors are often run to these

switchboard systems from a

vault

or

tunnel

built under the unit. Instead

of

using one large, hard-to-handle conduc

tor, several smaller wires or cables

with

a combined am pacity to match the

larger cable are installed. Figure 16.16

shows this type of installation. Note

the

crimp-o,.

solderless lugs

being used to

terminate the cab les.

Grounding.

The

neutral

wire of the

120

V/208

V

system is

grounded

to the

water supply pipe in much the same

as the residential service. This connee

tion gives 120 V between any one of the

live con du cto rs and ground . Check T«

16.1 for sizes of the service ground

conductors.

C onductor and C onduit

Size

Table 5.5, on page 61, lists the current-

carrying capa city of the various

copr.

238




SURE 16 .13

A

C G L

fusioie-type

ion switchb oard . Rated 347 V/600 V,

ase, 4 wire, with a 1200 A main 3-pole

ble QMR switch feeding through the

Iro-metering compartment to the branch

fusible-type switches, all with provision

rHRC fusing

FIGURE 1 6.14

A 3 phase com bination

kilowatt-hour and demand m eter

Industrial Services 239



FIGURE 16.15 A C GE main switchboard, double-ended design. Rated 2 kA, for use on 575

3 phase, 3 wire service incoming. Reduced to operating s ystem of 120 V/208 V, 3 phase, 4

by internally mounted, dry-type core and coil transformer

FIGURE 16.16

A CGE "hydro collector bo x"

that feeds a main switchboard. Rated 12 kA

conductors, when no more than three

are enclosed in one conduit. The

120

V/208

V system requires four con

duc tors. Section 4 of the Canadian Elec

trical Code states that when four con

duc tors are used in a conduit, the

ampacity of the conductors listed in

Table 5.5 must be reduced to

80%

of the

current value listed in the

table. ConduMj

size

for this or any service is determined

by using Tables

5.1

and 14.2.

Demand Meters

Industrial users of electricity are

assessed for power used in two ways.

240 Applications of Electrical C onstruction



be first is the total power consumption,

Iculated

in much the s am e way as for

ential

customers.

le

second way is a charge bas ed on

r

demand factor,

the maximum amoun t

•power

drawn from the utility at any

lien time.

A

special indicator on the me ter

oords

the de ma nd factor by staying at

fc highest reading reached during a

pen

period of time. The meter reader

en takes the reading and tu rns the

fcator back to zero. The dem and fac-

charge

helps ensure that an industry

I

not place unreaso nab le loads on th e

Ity's

supply system for short periods

Ifene. Such load s force t he utility t o

call

large, expensive pieces of equip-

art just for that industry.

Figure 16.14 illustrates a typical 3

hose

com bination m eter which

du de s kilowatt-hours as well as a ther-

••t-type

demand measurement

system,

is me ter is designed to m onitor small

strial loads.

ireuit Breakers

tfh circuit breakers and fuses have

Vantages. This section c overs only the

hrantages

of circuit breaker protection.

One of the greatest adva ntages of th e

ruit breaker

is that it can be a

manu-

y operated

switch. If an ove r-curre nt

•dition

causes the breaker to open

tcircuit,

it can be reset by hand and

1

in opera tion again withou t replacing

• parts.

The built-in switch

mecha-

allows the breaker to b e used as a

itrol

switch for a circuit. Often these

sers

are used to control lighting or

tor circuits, as well as to p rovide

er-current protection . Circuit break ers

: more expensive, but sav e on mate-

l and labour that a re needed if sepa-

te control switches are installed.

l ine connect ion

FIGURE 16.17 O pen view of a circuit

breaker

Figure

16.17

shows a circuit breaker.

A

circuit breaker h as an advantage

when a

short circuit

occu rs. Since a s ho rt

circuit reduces the electrical resistance in

a circuit to a low value, the curr ent flow in

the circuit rises to a high level in

micro

seconds, that is, millionths of a second.

As the alternating cu rren t rises t o a maxi

mum value in its cycle (1/240 s), the cir

cuit breaker sens es this drastic increase

and op ens th e circuit safely.

The circuit is ope ned in two ways. A

heat-sensitive thermal element

(bimetal

strip) rises in temperature and triggers

the circuit break er when excessive cur

rent flows. Also, a prolonged overload

condition will heat u p and op era te th e

thermal elem ent. In the sud den overload

situation, however, a

latch-on,

magnetic

trip assembly quickly operates the cir

cuit breaker. Under short-circuit condi

tions, the sudd en excess in curren t flow

activates this magnetic trip assembly

Industrial Services 241



and open s the circuit in m icroseco nds.

Fuses do not have this m agnetic tripping

device.

A

third advantage of circuit breakers

is that th ey are m uch smaller in size

than fused disconnect switches. Figure

16.18 show s a 30 A, 2 pole fused discon

nec t. Figure 16.19 sho ws th e much

smaller 30 A, 2 pole circuit breake r,

which will be mou nted in the distribution

centre shown in the inset. The distribu

tion cen tre is then mo unte d in a wall and

fitted with a finishing cover once the

wall has been covered in. (See Figs. 16.20

and 16.21)

Large industrial load centres are

built with circuit breakers throughout,

and the breaker units are assembled

into sw itch bo ard s. (See Fig. 16.22)

Industrial circuit breakers are mi

in single-pole, double-p ole, and 3 pol

units, with voltage and c urrent

ratings

1

match the circuit conductors. Some

d

the larger units are tripped by com

pressed air to speed up tripping time <

help reduce arc damage to the

breaker

contacts.

Ground Fault Circuit

Interrupters

The ground fault circuit interrupter

(GFI) is a relatively new device

adapto

from the basic circuit breaker.

Provic

what one man ufacturer calls people

protection, it is designed both to pr

dang erous e lectrical shocks and pr

over-current

p rotection. (See Fig. 16J

FIGURE 16.18

switch

A 30 A fused disconnect

FIGURE 16.19

A compact circuit breal

a distribution centre installation

242




8

1

>-

c

B,

E

o

o

Q

T A B L E 1 6 . 2

0.001 A

.0.005 A

Up

to

0.010

A

0.010A-0.015A

0.015A-0.030A

0.050 A -0.100

A

0.100A-0.200A

Physiological Effects of Elec

trical Currents

Threshold of sensation

Discomfort and pain

Severe pain and shock

Local muscle contraction, possi

ble "freezing-to-the-circuit," or

being thrown back

Breathing becomes difficult, loss

of consciousness possibly result

ing

Possible rapid,

unco-ordinated

contractions of the heart, result

ing in loss of synchronism

between heart and pulse (ventric

ular

fibrillation)

Ventricular

fibrillation

of the heart

FIGURE 16.23 A ground fault circuit

interrupter

low that it will not trip the normal circuit

breaker (o r blow a fuse). But it is high

enough to electrocute, cause serious

harm, or give a painful shock to anyone

who comes in contact with th e faulty

equipment. Portable tools often have

ground faults and cause many electrical

shocks.

Body Resistance

The human body is not a good conduc

tor of electrical current under normal

conditions. The amount of moisture

present (sweat) on the skin and the mus

cle structure of the body help determine

the resistance to current flow at any

given time. Scientific tests have indi

cated body resistance to be between

1000 Q and 4000

Q.

The amount of volt

age present in the circuit will then deter

mine how well the curren t will penetra te

Over 0.200 A Severe burns and muscular con

tractions. Heart is more apt to

stop than fibrillate.

Over 1 A Irreparable damage to body tis

sues

the skin and flow through the

body.

The

higher the voltage present, th e greater

the current flow through the body and

the greater the effect on vital organs.

Table 16.2 indicates how various

amounts of current affect a human

bodd

Time/Current Factor

The age, general health, and amount of

current flow will have an effect on hoic

long a person can sustain a shock

with-

out serious or permanent damage to ti«

body. Figure 16.24 illustrates how mud

time and what current combinations

built into a modern GFI unit for the p

tection of persons using the circuit.

The GFl unit detects leakage curred

as low as 2 mA (0.002

A).

It then opens I

the circuit to protect the operator of tM

equipment.

The average person who receives a I

244




-

20 40

60

80 100 120 140 160 180 200 220 240 260

current in milliamperes

RGURE 16.24 T ime/C urrent C hart for Grou nd Faul t C i rcui t Interr upter Devices

shock of 20

mA

suffers great pain an d

loss of m uscu lar c ontro l. There is loss of

Ife at app roxim ately 300 mA.

Obviously, the current required to

trip a norm al 15 A circuit breaker can

seriously injure a person. The average

power tool equipped with a 3 prong plug

and operating on a 15 A circuit is poten

tially dan gero us if the grou nd pron g is

removed for any reason.

Operation of the

GFI.

The GF1 is a

self-contained unit that may fit directly

ID

to a distribution cen tre. (See Figs.

[16.21 and 16.23) Oth er typ es may

require special enclosures.

The

GFI

ope rates on the principle

that the current

leaving

a circuit is equa

to the current entering that circuit

(Kirchhoff's

Current Law).

Both supply con duc tors of the cir

cuit pass through a highly developed

transformer. W hen there is n o leakage

curren t, the m agnetic fields around the

supply conductors cancel one another.

No voltage is produ ced in the tran s

former. (See Fig. 16.25)

If a leakage cu rren t d evelo ps, more

current is entering the circuit on on e

supply con duc tor tha n is leaving on th e

other. This

ma gnetic imbalance

causes a

voltage to b e induced in to the tra ns

former coils. An amplifier incre ases the

strength of this voltage and uses it to

Industrial Service s 24



neutral wire

circuit ground

120 V

transformer

0.75

A

leakage c urrent

F I G U R E 1 6 . 2 5 S c h e m a t i c d i a g r a m f o r a g r o u n d f a u l t c i r c u i t i n t e r r u p t e r

trip the circuit breaker. Leakage currents

as low as 2

mA

will trip t he

GFI

breaker.

GFI units are made in a variety of cur

rent ratings to suit m ost circuits. They

are recommended for both home and

industrial protection.

A

special (and

mo re sens itive) unit is being m ade for

ho spita ls. The Canadian Electrical Cod

l ine

terminal

trip latch

surfaces

supervisory

test button

ground fault

calibration resistor

t r ip p in g

solenoid

overload d if ferent ia l

sensing to ro id t ra n sfo rme r

F I G U R E 1 6 . 2 6

I n t e r n a l c i r c u i t r y o f a m o d e r n G F I b r e a k e r u n i t

load lug

overload

calibration

resistor

neutral

toro id

panel

neutral lead

iL

<^g^




•quires

that swimming, deco rative, or

ler

pools with lighting units be pro-

ted with GFIs. Modern residential

stallations

mu st a lso u se GFIs on all

butdoor rec epta cles, as well as for per-

•onal protection in washroom /bathroom

| e a s .

The internal workings of a

GFI

breaker are not acce ssible to t he

hstaller

or breaker user. They are com

posed

of a sensitive elec tronic circuit

•hich

should not be tampered with or

adju sted in any way. Figure 16.26 illus

tra tes a typical GFI break er s ensing and

monito ring circuit. Figure 16.27 illus

tr at es t his GFI unit in th e form of a sin

gle-pole circuit breaker. Manufacturers

frequently te st their pro duc ts to main

tain qua lity and safety. Users of GFI-pro-

tected circuits should co ntinue to test

the ir GFI un its after ins tallatio n. Figure

16.28 illustrates a typical tes t pro ced ure

recording chart.

•ne terminal screws

•ocation

of labels to indicate

other than class "A "

Jest button

® class "A " ratin g label

©

factory installed permanent

handle t ie

© power wir ing terminals

terminal for " l o a d " neutral

white wire, if available

w h i te "p ig ta i l " mu st be con

nected to the panel neutral

BGURE 16.27 E xternal vie w of single- and double-pole GFI breakers

Industrial Services

247



TEST REMINDER

For maximum protection against electrical

shock hazard, test your ground fault circuit inter

rupter at least once a m onth.

TEST PROCEDURE

1. Push yel low TEST button. The red RESET

button will pop out exposing the word

TRIP.

Pow er is now o ff at all outlets protected by the

INTERRUPTER,

indicating that the device is

functioning properly.

2. If

TRIP

does not appear when testing, do not

use any outlets on this circuit. Protection is

lost. Call a qualified electrician.

3. To restore

power,

push

RESET

button. Enter

data on record below.

Marth

19

19

19

19

19

19

19

19

19

19

19

19

19

19

19

Jan

Feb

M r

%

May Jm

Jul Aug Sep Oct

Nov Dec

FIGU R E 16 .28 Typical GFI Tes t P roc edure

R ec ord ing Char t

F o r R e v

i

e w

1. What are three advantages of the

polyph ase, or 3 phase, voltage sys

tem in industrial or m anufacturing

buildings?

2.

How is a 3 pha se service

meteredl

3. W hat is the size of a grou nding

conductor for a 200

A

service'.' a

400

A

service? a 600

A

service?

4.

List the boxes or enclosures used

in a 3 pha se service.

5.

How is a 3 phase disconne ct

switch different from a single-

phase disconnect?

6. How is the gro unding of a 3 phasq

550

V

service different from

that

a single-phase service?

7.

Explain why current transformers

are used.

8. What advantage has the 4 wire,

120

V/208

V

service over the 3

wire, 550

V

or 440

V

installation?

9. When installing a 3 ph ase , 4 wire

service , how is the am pacity

of

conduc tors determined?

10.

What is a

demand

meter? Why

how is it used?

11.

List thre e m ain advan tages a cir

cuit break er h as over a fuse.

12.

List two types of circuit

protec

provided by circuit breakers.

13.

In which two ways d oe s a circuit

break er trip a circuit when under]

short-circuit conditions?

14.

Why is it im po rtant to trip a ci

breaker in microsecon ds w hen a

short circuit occurs?

15. What method is used to trip large

industrial circuit breakers? Whya

16.

What is aground fault?

17. List thre e ways in which ground

faults often occur.

18.

Why is a standard circuit breaker]

(or fuse) som etimes u seless when

a ground fault occurs in a circuit?

19.

What is the low est cur ren t level

which a

GFI

in th e circuit can o

ate?

20.

Explain in your own w ords how

GFI unit o pe ra tes .




Fuses

W

hen an electrical current passes

through a conductor, som e heat is

generated. The more current that passes

through a conductor, the m ore heat is

generated within the conductor.

The amount of heat pro duced is pro

portional to the squ are of the c urre nt.

That is, if the am oun t of curren t in a con

du cto r is dou bled, the h eat will be four

times as great. If th e am oun t of cur ren t

in the sam e con duc tor is tripled, the

heat will be nine times as great.

There are several othe r factors th at

affect the amount of heat produced in

any given cond ucto r. One is the ty pe of

metal used in the conductor. Copper is a

better conductor than aluminum, and so

will ca rry m ore cu rren t. Because it can

carry more current, a copp er condu ctor

of a given size and cu rrent load will gen

erate less heat than an aluminum con

ductor under the same conditions.

The physical

size—the gauge

number—of the conductor also helps

determine the current-carrying capacity

of the cond ucto r and, therefore, th e

amount of heat that will be generated

under certain loa ds. Small co ndu ctors

do not carry as much c urrent as large

cond uctors. Therefore, a small cond uc

tor trying to carry too large a cu rrent

load will generate more heat than a

conductor of the right size would.

A third factor is the air surrounding a

cond uctor. Air space h as a great deal to

do with the co ndu ctor's ability to cool or

give off its heat. The tem pe rat ur e of th e

air surroun ding th e condu ctor is called

th e ambient

temperature.

If con ductors

are crowded into a conduit or box wh ere

there is little air circulation, cooling will

be difficult, and a higher ambient tem

per atur e will result. This ambient tem

per atur e will therefore raise the tem per

ature of the cond ucto rs. Areas such as

boiler rooms and foundries often have

problems with conductors because of

high ambient temperatures.

A cond uctor 's insulation can also

affect a co nd uc to r's ability to give off

heat. Some modern plastic insulations

tend to retain the heat in the cond uctor

in the sa me way that insu lation in a

building's walls holds in heat. Therefore,

th e current ratings for these cond uctors

must not be exceeded. If they are, suffi

cient heat will be generated and retained

to melt or damage the insulation. Tables

5.5 and 5.6 list the curren t-carrying

capacities of copp er and aluminum con

du cto rs. Heat rises t o a significant level

in thes e cond uctors when about

80%

of

the listed current is passed through the

conductor.

Fuses

249



Note: Some electrical equipm ent,

such as special circuit breakers and

pressure-typ e switches designed for

use with HRC-L fuses, is rated for 100%

capacity.

Damage from Overheating

Overheating of condu ctors results in

several problem s. One is caused when

a conductor reaches a temperature

beyond its normal operating range.

There is a softening, called annealing, of

the con ducto r which rem oves any resili

ence (spring-like action) at the terminal

and may loosen th e connec tion. (This is

much like the cold flow of m etal exp eri

enced with aluminum conductors.)

An increase in tem per ature also

brings about a more rapid rate of

oxidation on a cond uctor. Copper is a

good conduc tor, but co pper oxide is not.

In fact, copper oxide tends to weaken

the electrical security of a terminal con

nection. Aluminum oxide causes an even

grea ter prob lem. Very close to be ing an

insulator, it will cause further heating at

the term inals. The oxide establishe s an

electrical resistance, which results in a

loss of voltage at the terminal. Often,

enough heat is generated to completely

destroy the terminal connection.

Overheating also causes

insulation

to

dry out and becom e hard and brittle. In

fact, movement of the conductor will

likely cause the insulation to crack and

fall off. The exposed conductors may

well sta rt a fire if they to uc h e ach oth er

or a groun ded box. Although it usually

takes m any months of circuit use to dry

out insulation, the problem can easily be

overlooked: conductors are seldom

checked after installation.

If th er e is an overload or short-cir

cuit current, conductors can heat up

until they actually glow red. When th is

overheating o ccurs , the insulation can

melt, causing arcing between conduc- |

tors or between the cond uctors and

ground. A fire can be ignited within the

cond uit, b ox, or b uilding w all. Even if I

actual damage from the fire is small,

tl

burning insulation gives off an offensn*

odour that will persist for a long time-

Obviously, the overh eating of con

du ctor s can have serious effects. The

Canadian Electrical Code recognizes I

by requiring over-current protection ti

be provid ed. One effective way to p r o -

tect a circuit is with a

fuse.

Weakest Thermal Link

A fuse

is a simple, current-sensitive

dev ice designed to limit curren t flow

pro tec t the co ndu ctors of a circuit.

P

tecting the co ndu ctors will prevent sd

ous dam age to equipmen t from overta(

and fire.

A fuse con tains a strip of

current-

sensitive metal that has been calibrated

to melt and restrict the amount of over

load and short-circuit currents for cop

per or aluminum circuit co ndu ctors,

metal used in a fuse can be zinc, cop

silver, or an alloy, depen ding on the

type and use. Industrial fuses have

co]

per or silver links to which a small

am oun t of tin or tin alloy has been

add ed to redu ce their melting tern

ture.

This principle is known as the

effect. Tin or tin alloy is deposited on

th e link, close to a restrictive segmenL

thus reduces the overload melting

tea

perature at that section of the link. Tta^

normal copper or silver used for the

links has a melting tem pe ratu re of

approximately 1000°C which will open

und er short-circuit cond itions, but not

at the lower, safer tem per ature range

required for protection from overload*

250




When

a tin alloy is ad ded to the notc hed

segment of a link, a mo lecular excha nge

takes place when tem pera tures nearing

the melting point of the tin (230°C) are

reached. The copper or silver link and

the tin alloy combine to pro duc e a com

mon melting point close to tha t of th e

tin. In this way, the fuse can provid e pro

tection from

both

short circuits and

overloa ds. Figure 17.1 illustrates a com

mon type of link.

element des ign incorporating

"W

effect

tin alloy

1 break

location

3 break

locations

E

x :

( / >

S

3

o

element functioning

on overload

element functioning

on short circuit

FIGURE 17.1 A mo de rn fuse l ink capable of

p-cviding protect ion f rom both short c i rcui ts

• n d ov er loads

Since the link has a higher electrical

resistance than the copper or aluminum

co nd uc tor s in the circuit, it will heat up

before they d o. The fuse will then auto

matically

open

at the restrictive segment

of the link (wh ere th e tin has been

added) when an overload current is

passed through th e conduc tors. Under

short-circuit conditions, the fuse link

can open (melt) at several notched seg

m en ts in just a fraction of a sec ond . (See

Fig.

17.1)

The fuse is designed to be a "weak

link in th e chain ." Its job is to brea k th e

circuit before any damage is done to the

circuit conductors. For this reason, it is

often called the w eakest thermal link in

the circuit. Although a fuse is current

sensitive, both ambient temperature and

the heat gene rated in the fuse determ ine

when the fuse link will melt. Some fuses

are designed to be m ore heat sensitive

than others . Type P (non-time-delay)

and type D (time-delay) fuses are used

frequently in residential circu its. (See

Fig. 17.2) Unlike the older fuses with zinc

links (se e Fig. 17.3), th es e fuses pro tec t

fuse panels and panel boards. In the

past, panels and boards tended to be

prone to overheating and possibly fire.

The older fuses were not designed to

react when excessive heat cond itions

deve loped in a panel b oard . Older zinc-

link fuses should be replaced by the

more protective, thermal-sensitive type

P and type

D

fuses. S ee Figure

17.4

for

examples of type D fuses.

Note: Remember that conductors of

electricity are often conductors of

heat, and so can transfer their heat on

to a fuse.

Time-Delay Fuses . Circuits containing

electric motors undergo a surge of

current during the motor's starting

Fuses

25



low melt ing

point,

solder-like

alloy

Type P Fuse

metal cap

glass body

element

(copper alloy)

screw shell

(copper alloy)

phenolic tip

solder connection

• centre contact

Type D Fuse

FIGURE 17.2 Type

P

and type

D

plug fuses. They provide protection from both short

circti

and overloads throug h the ir thermal sensitivity.

face

glass body

link

(conne

screw

she

colour-codec

ne

(with current

i

r

— zinc alloy fus e link

y

• central bushing

or

centre tip contact

FIGURE 17.3 A n older mod el, zinc type , screw-base plug fuse , available in 3 A, 6 A, and

sizes




SURE 17.4 Metal-capped type D plug

»es

period, and the surge co ntinues until th e

motor reaches operating speed. This

sudden increase of current frequently

exceeds th e curren t rating of th e circuit

and could ca use th e fuse to blow.

Air conditioners, fridges, freezers,

clothes driers, and other residential,

motor-driven equipment ca n be subject

to this condition.

Little danger to circuit conductors is

present when this overload lasts only

briefly (up to ten seconds). The develop

ment of a fuse that would not blow

under these temporary overloads but

would allow the m otor to sta rt u p and

reach normal running amperes made the

need for fuse oversizing in th es e c ircuits

unnece ssary. This fuse is the time-delay

fuse w hich provides a m uch be tter level

of protection for the circuit. Figures

17.2

and 17.4 illustrate this fuse typ e.

Fuse Ratings. Fuses are rated by th e

manufacturer in thr ee ways, with their

ratings expres sed in Root Mean Squ are

(RMS) va lue s.

RMS

values are those that

would be read on a stand ard voltme ter

or ammeter if placed into an alternating

current circuit.

The continuous current rating is the

amount of circuit current the fuse will

carry without blowing or interrupting

the circuit. For most pa nel-supply cir

cuits, this rating should b e matched to

the current rating of the circuit conduc

tors .

It mu st also com ply with Canadian

Electrical Code maximums for specific

loads, such as mo tors and transformers,

wh ere cur ren ts ar e likely to exceed cir

cuit ampacity.

Maximum AC rated voltage

indicates

to th e installer the typ e of circuit and

voltage conditions unde r which the fuse

can safely operate. In most cases, the

higher the voltage, the larger th e size

(length) of the fuse or distance between

the fuse's contact points. Figure 17.8

illustrates differences in physical size

between fuses of various voltage and

current ratings.

Due to the serious, sustained arcing

associated with

DC

circuits, special

designs have been developed for this cir

cuit t yp e. If the

DC

rating is not marked

on the fuse label, th e installer sho uld

contact the manufacturer about suitabil

ity of th e fuse on

DC

circuits.

Interrupting capacity is the am oun t of

current that the fuse can safely interrupt

in the circuit under short-circuit condi

t ions. The bo dy of the fuse m ust rem ain

intact, allowing for replacem ent. The

current flow can be very high when a

sho rt circuit occ urs, and so the inter

rupting capacity of the fuse used must

ma tch or exceed th e short-circuit cur

rent from the circuit's source.

Depending on their size, transform

ers supplying residential areas are capa

ble of delivering up to te n thou sand

amperes under short-circuit conditions.

In commercial and industrial applica

tions, they can deliver up to hundreds of

thou san ds of am peres. The Canadian

Electrical Code require s that fuses pro

tecting the se c ircuits must b e able to

safely open the circuits without fuse rup

ture or damage to their panels or the

equipment that contains them.

Fuses 253



S crew-Base, or P lug, Fuses

The m ost com mon type of fuse used in

residential buildings is the screw-base,

usually called the plug fuse. (See Figs.

17.2 and 17.3 on pag e 252.) Plug fuses

are used for all lighting and receptacle

circuits operating at a maximum voltage

of 125 V. Standard plug fuses are m ade in

current ratings of 3 A, 6 A, an d 10 A for

th e zinc-link type s and 15 A, 20 A, 25 A,

and 30 A for th e P and D types.

Time-delay plug fuses of less than

15 A

are available in fractional am pe re

rating s. Figure 17.2 show s a time-delay

fuse in th e plug-type configuration. (The

section on dual-element fuses in this

cha pter discu sses the cartridge type.)

Plug fuses a re all abo ut th e sam e

phy sical size. Older zinc-link typ es hav e

colour-coded inse rts. The ins erts are vis

ible through the transp aren t top s of the

fuses to aid in ea sy recogn ition of cur

rent ratings, even from a distanc e. In

the pa st, the current rating was often

stamped on the contact point at the fuse

base. Some manufacturers found that

stamping the base could distort the con

tac t point and lead to overheating in the

panel .

In

an effort t o preven t thes e p rob

lems,

they now take more care whe n

marking the se con tact p oints. Many

modern type P fuses still use colour-

code d inserts under their t ransparen t

faces,

though; mo dern type D fuses ha

colour-coded metal caps over their fa

and top s. Blue represen ts

15

A;

orangi

20 A; red, 25 A; and green , 30 A.

For a period of time, a

colour-cc

ba se was installed on th e fuse to mate

up with a fuse rejection system that

could be installed in a pan el's fuse

of

ing. Th ese sy stem s were designed to

pre ve nt th e placing of a fuse having to

large a current rating into the circ uit

(See Fig. 17.5) W hen this situation

occurred, the older zinc-link fuse wc

allow he at t o build up far bey ond sal

levels and not op en. Modern type P;

type

D

fuses, which have overload-sen

ing features built-in, will ope n the cird

when t he re is an overload he ating co«

tion. However, desp ite this additional

protect ion, their amp acity should not

exceed circuit conductor capacity.

Note: Some manufacturers of

paneM

built rejection features into their

panels and did not require the

coloured inserts to be installed at

a

later time.

20 A fuse

(central bushing

will not fit into

15 A rejection

washer)

contact

incomplete

rejector

washer

15 A fuse

fully installed

contact

complete

F I G U R E 1 7 . 5 A f u s e r e j e c t o r r i n g a p p l i c a t i o n u s i n g t y p e P o r t y p e D p l u g f u s e s

254

A ppl ications of E lectr ical C onstruct ion



RGURE 17.6 P lug fuse reject ion r ings

Fuse rejections rings, or washers, are

available for 15 A and 20 A plug fuses.

They are sometimes colour co ded and

are designed to be pu t into panel fuse

sock ets. (See Fig. 17.6) The colour c od e

helps a person to choose the right fuse

lor

the circuit, bec ause the fuse colour

code matches that of the rejection ring.

The ring itself makes it impossible to put

in a fuse of the wrong cu rrent rating,

because the higher the current rating

of

the fuse, th e larger the d iam eter of th e

base. For exam ple, using this sy stem

makes it impossible to insert a 25 A fuse

into a

15 A

circuit. In th e past, seri ou s

electrical problems w ere caused when

ever a perso n installed a fuse with too

large a current rating for the prote ction

of the circuit con du cto rs. Th e fuse rejec

tion ring helps to prev ent th is from hap

pening. Modern typ e P and typ e D fuses

have phenolic rejection tips or bases to

co-ordinate

with fuse rejection rings.


Circuit Fault Indications

The see-through glass body of th e plug

fuse is a great help for finding what

caused a fuse to blow. If an overloaded

circuit or a motor sta rting up ha s cause d

the fuse to open , the g lass face will still

be clear. Only a small part of the link will

have melted away and have cau sed a

Type P Plug Fuse Type D Plug Fuse

short circuit short circuit

overload

(or thermal condition)

overload

(or thermal condition)

FIG URE 17.7 C i rcui t faul t indicat ions on

s c rew - bas e p lug f us es

gap to appe ar. (See Fig. 17.7) If a sh or t

circuit has cau sed th e fuse to open, t he

inside of the fuse's glass face may

blacken. Seeing th e rem ains of th e fuse

link will be difficult, be cause m ost of the

link

will hav e melted from th e su dde n

heat. The cause of the problem should

be located and corrected before the fuse

is replaced.

When a fuse o per ates close to its

rated curre nt value for any length of

time, it sta rts to warm up. Th e circuits in

a distribution panel can be checked sim

ply by runn ing a finger over th e faces of

th e fuses. Any fuse th at feels warm is

carrying current close to its rated value.

On the older zinc-link fuses, the colour-

code d insert indicating the current value

would look brown or bu rned . A check to

see w heth er the correct size and typ e of

fuse have been installed and that the cir

cuit has not been overloaded for the size

Fuses

255



of the co ndu ctors w ould be in order.

Modern type P and typ e

D

fuses will not

brow n. Instead, the y will op en the cir

cuit: they are heat sensitive and respond

with this type of protection whe n t he

current and heat in the circuit go

beyond safe limits. Thus, the conductors

and the panel itself are protected. Stand

ard zinc-link fuses would not ope n th e

circuit unless the current exceeded the

fuse's amp rating. Considerable heat

damage could result from the heat

buildup being transferred to the panel

and the conductors themselves.

Ferrule-Contact Cartridge

Fuses

Residential equipmen t su ch as stoves,

clothes driers, water heaters, and

elee

trie

heaters operate at 240

V

and

oftea

need a different type of fuse, usually ta

250

V ferrule-contact

cartridge fuse.

A

600

V

unit is also available for

industry

use. (See

Fig. 17.9)

Within the two voltage ran ges

thea

are six physical sizes as determined

b

am pere rating group. The group s are a

follows: 1 A-30

A,

35 A-60

A,

70 A-100

A

o

FIGURE 17.8 Relative fuse sizes for standard code and HRCl-R fuses

256




RGURE

17.9

Ferrule-contact cart r idge

lower thermal

alloy

y

ferrule

contact

-/~V

•T>.

-lal/overload

mechanism

s v ,

\

s

\ vs

s

s

s

•, s V ^ - ^ m

fuse tube

short circuit g

element i

fuse opened on overload or high

temperature condition

11

t

;• •. -. -. '. '•

'. ',

'. s \ •. ', \ ^ ^

fuse opened on short circuit

FIGURE 17.10 Typical opera t ions of type P

ype D cart r idge fuses

110

A-200

A,

225

A-400 A,

450 A-600 A.

The larger the ampere rating of the

group, the larger the physical diameter

of

the fuse. (See Fig. 17.8)

The 600 V ferrule-contact code fuse

is much larger in physical size than the

250 V

unit. When originally d eve loped ,

standard code fuses at the 600 V level

required greater length and diameter to

cop e with th e high arcing e xperienced

during link openings. Standard code

fuses can interrupt a current of 10 kA

without rupturing. Modern fuse develop

me nts have resulted in mo re durab le

(fibreglass or porcelain) bodies and

improv ed fillers within fuses t o c ontain

and extinguish any arcs that form during

fuse openings. Figure 17.10 illustrates

the internal condition of a link after a

fuse has opened under short-circuit and

overload conditions.

Knife-Blade Cartridge Fuses

When cur ren ts in exc ess of 60 A are flow

ing in a circuit, t he larger

knife-blade

car

tridge fuse is used to protect the con

ductors. (See Figs. 17.11 and 17.12) The

250 V fuse is used for residential and

commercial purp oses, and the 600

V

knife-blade fuse is used for bo th in dus

trial and commercial applications.

As with the ferrule-contact cartri dge

fuse, the 600 V knife-blade fuse is muc h

larger in physical size th an the 250 V

knife-blade fuse. These fuses are made in

four current rating groups:

70A-100

A,

110 A-200 A, 225 A-400 A, and 450 A-600

The length and diam eter of the fuses

F I G U R E 1 7 . 1 1

f us es

Cart r idge and kni fe-blade

Fuses

25



FIGURE 17.12 C onstruction of ferrule-

contact and knife-blade fuses

in each group increase as the current

rating increa ses. For example, the fuses

in the 70 A-100 A group a re smaller in

length and diam eter than tho se in the

110A-200Agroup.

Arc-Quenching Mater ial

Many of the large cartrid ge fuses are

filled with an arc-quenching material.

This arc-extinguishing gypsum powd er

or silica sand is designed to quickly

extinguish an arc and to reduce the dam

aging short-circuit cu rrent to zero . Arc-

quenching material is therefore impor

tant. Figure

17.12

shows both the fuse

and the arc-quenching material con

tained within. The fuses in Figure 17.19

on page 262 also show arc-quench ing

material.

One-Time Fuses

The comm on one-time fuse h as for many

yea rs be en ma de with a zinc alloy link,

with an interrupting capacity of

10

kA

(stand ard cod e fuse). The zinc links in

some fuse applications suffered from

metal fatigue at the restrictive segments

(cutouts) due to the constant expansion

and con traction of the m etal in the link.

Loads that were constantly cycling on

and off, such as electric heaters,

freezers, fridges, etc., would

event

bring the link to a point w here it w

open the circuit for no apparen t re

The circuit had no fault o r problem

other than the metal fatigue in the

link. One rea son w hy co pp er is now

being used for the links in many m

fuses is that it is far less likely to

s

from metal fatigue.

If a one-tim e fuse is used and a

circuit or overload condition cause

fuse to blow, the entire fuse unit ha

be replaced. Special

one-time

fuses

available with an interru pting capa

of 50 kA. This fuse has a c op pe r al

link and provides much added prot

tion for a small incre ase in cost.

Th

fuses are available in th e 1 A-600 A

250

V/600 V, sta nd ard cod e sizes.

are available at 250

V,

from

15 A

to

Renewable-Link Cartrid

Fuses

In

specific industrial or training in

tions, fuses often need to be repla

Renewable link cartridge fuses acc

replace me nt links and can be insta

quickly. (See F igs. 17.13 and 17.14)

easily disassem bled units are know

th e ease and low cost with which t

links can be replac ed. The fuses th

selves do not need to be replaced .

Safety Note: Be sur e that th e lin

not oversized and do not double u

links (a practic e known as spiking)

oth er w ords, allow the fuse to prov

its intended level of protection. Sin

renewable-link cartrid ge fuses ha v

ther an interrupting capacity highe

tha n 10 000 A nor arc-quench ing m

rial, they should not be considered

use on circuits whe re higher cu rre

than that may be encountered.

258




=1GURE

17.13

-se

jyt .

FIGURE 17.14 A renewa ble-link knife-blade

High-Rupture Capacity

Fuses

Section 14 of the C anadian Electrical

Code states that standard code car

tridge fuses m ust no t be used in circuits

that have a curren t in exce ss of 600

A

and a voltage in ex cess of 600 V.

Another considera tion is that fuses

must have ratings app ropria te for th e

handling of anticip ated short-circu it

currents. High-rupture capacity (HRC)

fuses provide good protection from both

overloads and sho rt circuits; as noted

earlier in this chapter, mo dern distribu

tion systems often deliver short-circuit

currents far above the ability of stand

ard co de fuses to inter rup t safely.

HRC fuses can be used with m oto rs

when a time-delay feature is required, as

well as with other high current-consum

ing equipm ent, for exam ple, lighting

loads, transform ers, e tc. They provide

rapid protection from short circuits and

can also provide needed time delays

during the m oderate (tem porary) over

loads experienced when motors or

transformers are first turned on. HRC

fuses also do not deteriorate. Most have

moisture-proof fibreglass or ceramic bar

rels, filled with high -quality silica san d

for arc-quenching. Under heavy current,

short-circuit conditions, the silica sand

quickly tur ns into a glass-like m aterial,

blocking any ch an ce of an arc forming

between fuse ends. The copper links and

silver- or tin-plated, copper contact

blades add to th e

HRC

fuse's overall

quality. (See Fig. 17.15)

HRC fuses are designed to inter rup t

large short-circuit c urren ts without rup

turing and to pro tect ca bles and equip

men t w ell. They a re available in two

basic ty pes. The Form I and Form II fuse

are known as HRC-I and HRC-II, resp ec

tively. Electrical and physical differences

exist between the two types .

HRCI (Form I). The se fuses provide

protection from bo th overload s and

sho rt circuits. They hav e a high

interru pting capa city (200 kA) and are

made in a variety of types and classes

for use in protecting cables and

equipment.

HRCII (Form II). Th is kind of fuse

provides protection from sh ort circuits

Fuses 25



FIGURE 17.15 Typical HRCII-C fuses

only and m ust be used in conjunction

with som e other type of overload device

(most often an overload relay). Although

it ha s

a

200

kA

interrupting capacity,

it

mu st never be used to replace an HRCI

fuse. An

HRCI

fuse can, however,

be

used

to replace an HRCII fuse, sinc e it pro

vides both types

of

protection.

The common types of

HRC

fuses are

as follows.

HRCII-C This HRCII fuse is of British ori

gin, with

a

bolt-in design.

It is

availa

ble with electrical ra tings of

600 V

and 2 A-G00 A. It is generally used as

a backup, short circuit device for

motor circuits,

and

often u sed along

with combination motor starters

or

other o verload dev ices. (See Fig. 17.15)

Class H These fuses, of th e HRCI type,

had the same basic dimensions

as

standard code cartridge fuses of the

same current and voltage ratings.

The 1 A-60 A and 70 A-600 A types

had rejection tabs or notche s in thd

contact areas

to

prevent the insta ll

tion of 10 kA standard code fuses •

panels or equipment. They w ere pn

duced in bo th th e 250 V and 600 V

versions with current ratings from

1 A-600 A. Fast-acting and time-del^

units were also developed. Howewi

Class H fuses are now considered

obsolete and should

be

replaced

t l

HRCI-R fuses.

HRCI-J Th ese fuses are designed for us

in mod ern equipm ent and have sup

rior curr en t limiting ability. Their

specific compact dimensions pre- j

vent them from being intercha nge *

with any othe r type

of

fuse. T hese

fuses a re ma de in

the 1

A-60

A

fer

rule-contact type and the 70 A-600^

bolt-in/blade ty pe, all with voltage

ratings of 600 V. T he fast-acting typ

is used

for

the protection

of

feed-r-

circuits and for providing a needed

short-circuit protection for circuB

breakers. (See Fig. 17.16) HRCI-J

time-delay typ es a re available

for

both the NEMA and the sm aller 1EC

types

of

motor/control contactor;

They can also be used to protect

transformers.

HRCI-R T he HRCI-R fuse ha s overall

dimensions similar to those of the |

standard fuses covered earlier inl

chapter.

A

replacement

for

th e

CI

fuse, it has a special rejection feataj

—a groove on th e ferrule (1 A-60

or a "U" shap ed notch on the kni

blade contact

of

th e larger (70

A-l

type. The rejection feature

is

four

on one end of the fuse only.

The fuses are produced in

25C

and 600 V sizes with curr ent ratir

from 1 A-600 A, including fractional

260

Applications

of




FIGURE 17.16 Typical HRCI-J fuses

E

5

.c

to

2

O

o

>•

o

a

FIGURE 17.17 Typical HRCI-R fuses

ratings for time-delay fuses. The fast

act ing type serve s as a replacem ent

for the protection of feeder circuits

and as backup protection for circuit

break ers; the time-delay type is used

for motor circuit protection and for

circuits where a high mo men tary

inrush of current can be expected.

(See

Fig.

17.17)

HRC-L

These larger, specific dimension

fuses a re rated at

601

A-6000

A

at

600

They are specially designed t o pro

tect th e main pow er supplies to large

industrial complexes and apartm ent

buildings, wh ere serv ices larger than

600 A are required. Comm erce Cour

in To ronto, Ontario, is an exam ple.

(See Fig.

17.18)

HRC-L fuses, includ

ing time-delay on es, are used to p ro

tect circuits feeding large motors

such as chillers or air-conditioning

units in high-rise apartment or office

buildings. Since any loose con tact

with large, high ampere fuses will

soon cause tremendous heat to de

velo p at th e poin t of con tact, HRC-L

fuses are of the bolt-in type: firm,

positive connections with fuse

panels are thu s ensured and damage

to the fuses and panels avoided.

Dual-Element Fuses

Wh en referring to a fuse, "dual-elem ent"

is often confused with "time-delay."

Dual-element

is a ma nufacturer 's term

for describin g the con struction of the

fuse link or elem ent within th e fuse

body. Dual-element fuses can be made

in either time-delay or non-time-delay

types .

All dual-eleme nt fuses d o, how

ever, provide protec tion from both sho r

circuits and o verload s by the use of two

individual com pon ents on the sam e ele

ment (link). A cop per element is nor

mally us ed for th e link pa rt of th e fuse,

with restr ict ive notch es or segm ents

Fuses

26



e

i

2

providing pro tection from sh ort

circuM

(See Fig. 17.19) One end of the

element

attac he d to th e fuse c on tact by a low-

thermal alloy and a plunger

mechanisJ

(See Fig. 17.20) The m echanism provided

protection from overload by sensing aa

above normal temperature on the fuse

element, melting the low-thermal

allojt I

and allowing a spring within th e mecha-

nism to open the circuit. The time

required for this reaction se rves as the j

time-delay feature on type D fuses. The

thermal sensitivity of such fuses coven

th e requ irem ents of a residential code

ca rtridg e fuse. Dual-element fuses are

prod uce d in both ferrule-contact and

knife-blade contact types, in current

ranges from 1A - 600 A and in both 250

and 600

V

configurations.

FIGURE 17.18 Typical HRC-L fuses

arc-quenching m ater ia l

thermal cutout

lock-in device

arc-quenching mater ia l

FIGURE 17.19 O lder style, dual-element fuses, with therma l cutouts in centre sections

262

Applicat ions of Electr ical Construct ion



t her m al c u t out p lunger m ec han is m

short circuit l ink

knife blade

with reject ion

slot

f ibreglass barrel

end cap

RGURE 17.20 N ew

style,

dual-element fuse, with a plunger m echanism as a thermal cutou t

Time-Delay

The term time-delay is recognized by th e

Canadian Standards Association (CSA)

to refer to a specific time-current over

load blowing characteristic. It generally

mean s that a fuse, suc h a s an HRC or

standard code fuse, will carry up to

500% of its rate d am pe re cap acity for a

minimum of ten se co nd s. Th ese fuses

must then be marked by the manufac

turer as time-delay or type D. Plug fuses

designed as time-delay fuses must also

be marked type

D

and b e capab le of car

rying 200% of rated current for a period

of twelve se co nd s.

Such fuses are ideal for mo tor cir

cuits.

Unlike standard non-time-delay

fuses w hich often blow while mo tor s are

reaching their ope rating

rpm,

time-delay

fuses can accommodate high motor-

starting currents . These curre nts a re

three to five time s stronge r than a

motor's normal running current but last

only a few se co nd s. The time-delay char

acteristic allows motor-circuit fuses to

be sized lower, provid ing be tter circuit

protection, demanding less space within

a panel or fuse box, and permitting

lower equipm ent cos ts . The maximum

am pe re rating for th es e fuses, as pe rmit

ted by the CSA, is 175% of motor-runnin

current (full load); a non-time-delay fuse

may b e ra ted at 300% of the m oto r's full-

load running current.

Fuse-rating terminology found on

HRC

fuses can be seen in Figure

17.21.

Figure 17.22 illustrates the norm al sta rt

ing and running current for a 20 A mo tor

after approximately ten seconds the

current interrupting

rating = 200 000 A

standardized overload

blowing characteristics

at ten seconds

I - •

HR C :

I

protection from

overloads and

short circuits

rt

T i m e D e l a y

standardized current

limitation

standardized dimensions

FIGURE 17.21 Fuse-rating terminology

found on an HRC (high rupture capacity) fuse

Fuses

26



a

non-time-delay 60 A fuse

Non-time-delay 30 A fuse

will blow during start-up period

- - - . I of motor.

Time-delay 30 A fuse

/ allows motor to start.

motor starting amps

(locked-rotor current)

— 6X running amps

Fuse allows i

start but pro

poor circuit |

after start-up i

30 A

time-delay fuse;

proper circuit |

proper level of circuit

protection

normal running amps fo

.01 s time in seconds

10s

FIGURE 17.22 T ime-current characteristics for a 20 A mo tor using time-delay and/or nor

delay types of fuse protection

starting current drops to the much lower

running current. The graph also shows

that th e 30 A, time-delay fuse prov ides

the nec essary d elay in opening the cir

cuit. The fuse allows the motor to start

up while protect ing the con duc tors

under normal operat ing condit ions. The

60 A non-time-delay fuse h as th e sa m e

starting cha racteristics but, unlike

the 30 A time-delay fuse w hich would

require a 30 A switch, it would need a

larger, mo re costly 60 A switch.

F o r R e v

i

e

m

1. W hat i s th e effect of an electrical,

current on a conductor as the i

rent passes through?

2. Why is air circulation aroun d a

conductor impor tant?

3.

List and explain the types of da

age that the overheating of cor

ductors can cause.

4. W hat is th e pu rp os e of a fuse in 4

electrical circuit?

5. What is the "M" effect? How does

it affect the design of certain type

of fuse links?

6. Define weakest thermal link.

264




I

11.

12

13

14

15

16

17

18

19

20

21

List three different types (config

uratio ns) of fuses and give the ir

current and voltage limitations.

What is a fuse rejection ring? What

is its purp ose and how is it used?

List the circuit faults that can

cau se a fuse link to open . How

does each fault show on the ele

ment?

Describe a simple metho d for

deciding whether a fuse is opera

ting close to its rated current

value.

Why are som e cartridg e fuses

filled with a powder?

What is the main da nge r of using a

renewable-link cartridge fuse?

What is

spiking,

and why should it

be avoided wh en replacing a

renewable-link fuse element?

Describe the

HRC

fuse. Wha t is its

main advantage over the standard

cartridge fuse?

Explain what time-delay fuses are

and w hat kind of protec tion they

provide.

How many typ es o r clas ses of HRC

fuses are there? Name them .

What is the purpose of rejection

tabs or notches in the contact

ends of HRC fuses?

What protection beyond that pro

vided by HRC fuses do type P and

type D fuses offer?

Name the type of

HRC

fuse that

provides protec tion from s ho rt cir

cu its only.

Name the typ es of

HRC

fuse that

provide protection from both

overloads and short circuits.

Why are large (high) am pere fuses

bolted into the fuse panel rather

than held in place by spring clips?

Fuses



A

s energy costs rise, perso ns w ho

design and size electrical heating

syste m s are using more com plex

me thods to determ ine the pro per size of

hea t s ou rce for a given bu ilding. To pro

duce accurate heat loss and gain figures

for a variety of residential buildings

requires m any tables, charts, and formu

lae not suited to the purpose of this text.

Specialized heat loss/gain courses are

available throu gh local electrical leagues

and supply authorities, and successful

completion of such cou rses can lead to

certification as a heat loss designer/con

sultant. This chapter will introduce

som e of the p rinciples involved in hea t

loss calculation by pre senting a simpli

fied calculation method. It is not

intended to replace or meet the m ore

complex standards required by heating

industry professionals.

Electrical heating sy stem s for resi

dential buildings are discussed here.

They have several advantages over sys

tems using fossil fuels such as oil or nat

ural gas.

Advantages of Electr ical

Heating

Electrical heating sys tems are pro duced

in a varie ty of types t o m atch building

Residential

Electric

Heating

structure requirements. Central

heatiB,

system s, capable of replacing exis ting

gas or oil furnaces, are available in

forced air and hyd ronic (hot water) « •

figurations. They are especially useful

when a building is already equipped

with duct work or radiators. Central aar

conditioning is an option for an electric

furnace wh en a ducted , forced air sys

tem is selected for the building. (For

tl

unitary heating system described neitj

central air conditioning is not possible

unles s special d uct work is installed.)

A different and major type of electil

heating is the unitary or baseboard

he*

ing system which provides

independe«

tem pera ture co ntrol for each room or

I

area to be heated. A thermostat, whidJ

placed in th e room, perm its this sepa- |

rate control. In the eve nt of equipment

failure, heat from adjoining room s will

flow in to the one with the defective

heate r unit. Heating system s that use

furnaces as a heat sourc e, on the other

hand, let the entire building cool off

when equipment fails.

A

second major advantage of the

i

tary system is the saving of space in i

basem ent area. The area previously

required for th e furnace and associate*

duct work and plumbing can be put to

good use by the home-owner, and the

266




"finishing off" of a basement area can be

simplified. When converting from an oil

heating system, add itional sp ace saving

is achieved by the removal of th e oil

storage tank. Furtherm ore, the ho use

does not need a chimney for the removal

of fumes and hot gases because none are

created. All heat produ ced by the sys

tem is directed into the building itself,

providing 100% efficiency.

Electrical heating system s have

other advantages: they are noise-free,

odour-free, do n ot give off com bus tible

fumes, and are clean to operate.

Improvements in building stan dard s an d

construction materials should mean that

recently designed houses are well built,

making the installation of electrical heat

ing syste m s even m ore cost-effective.

Costs of Electrical Heating

Heat is often calc ulat ed in te rm s of

joules. One watt is one joule per sec on d

(1

W = 1

J/s).

Local utilities that supp ly e lectrical

energy usually agree that the electrically

produced heat unit is one of the more

expensive one s. When comparing the

cost of heating system s, however, other

tors must b e taken into accou nt. A

house designed with an electrical heat

ing system mu st b e of high-quality co n

struction. Windows, do ors , and oth er

places where air can ente r or leave m ust

be properly fitted, seale d w ith caulking

compound, and equipped with storm or

double glass window u nits.

In

some com

munities there are heating inspectors

who check all such installations. Their

inspections are in addition to th os e

made by the electrical inspection

authority.

The fact th at th e ow ner of an electri

cally heated hou se does not ha ve to pay

for a furnace and duct work and their

maintenance costs must also be consid

ere d. Capital is freed to be sp en t on t he

individual heating units required for

each area of the hom e. For hou ses tha t

already have duc t work, some heating

man ufacturers m ake electric furnaces

th at tak e adv antag e of it, which allows

the customer to convert to electrical

heating with a minimum of inconve

nience and expe nse. (In som e cases,

though, a customer m ay need to

increase the size of the main service

equipment to handle the increase in

electrical load.)

The average consum er wh o is using

electrical energy to heat a house uses

muc h m ore electricity than would othe r

wise be us ed. As a result, the

end rate

(lower cost to consu m er ) is reached

much sooner, and both h eating and

lighting energy is obta ined at th e

cheaper end rate. The end rate is also

applied to cooking and w ater-heating

units.

Electrical energy is in good supply,

which is not always the case with other

forms of energy. The advantage of availa

bility should be conside red.

When a cost analysis is prepared and

all factors are taken into a cco unt, a

properly installed electrical heating sys

tem is usually found to be com petitive in

terms of price with other forms of heatin

Insulation

The m ain function of insulation is to tra p

dead air

(air that is station ary) between

fibres or cells. Dead air retards heat from

escaping. Heat travels from hot to cold

(that is, from inside the house to out

side). Storm d oors and windows simply

trap dead air in the space between the

Residential Electric Heating

26



unheated

crawl space

or attic

vent

vent-

perimeter

inai

vapour barrier

(on ground)

FIGURE 18.1 Installing residential therm al insulation. {Note: All walls, ceilings, roofs, and

floors separating heated from unheated spaces should be insulated.)

layers of g lass. It is this

dead air layer

that is responsible for saving heat.

Insulation for the electrically heated

ho use must b e properly located (s ee Fig.

18.1),

be of high quality and be properly

installed. It m ust also con form to a mini

mum thermal resistance as shown in

Tables 18.1,18.2 and 18.3. Table 18.1 lists

the minimum insulation requirements

for vario us pa rts of a building.

The

R SI value *

of insulation is

assigned to a product by its manufac

turer. It refers to the product's heat-

retaining ability. The higher the RSI

*The insulation industry is adopting metric RSI

values; however, imperial R values are still evi

dent. To chang e RSI values to im perial R values,

multiply by 5.7. For exam ple, RSI-4.9 equals R-28.

TABLE 18.1 T he C anadian

Building J

Code's Minimum Insulation

Requirements for Buildings

Building Element Exposed

to the Exterior

or

to

Unheated Space

Ceiling below attic or roof

space

Roof assembly w ithou t attic or

roof space

Wall other than foundation wall

Masonry or concrete founda

tion wa ll

Frame foundation wall

Floor, other than slab-on-

ground

Slab-on-ground containing

pipes or heating ducts

Slab-on-ground not containing

pipes or heating ducts

RSI

Va

Requntf

: - .

2 '•

2 '•

4 - :

1.76 3




TABLE 18.2 T hermal RSI Values for Various Insulating Products

Description of Insulation

Mineral wool and glass fibre

C ellulose fibre

Vermiculite

Wood fibre

Wood shavings

Sprayed asbestos (health hazard)

• Expanded polystyrene complying with CGSB 51-GP-20M

(1978)

1

2 bead board

3

4 extruded

S emi-rigid glass fibre sheathing

Rigid glass fibre roof insulation

N atural cork

Rigid urethane or isocyanurate boa rd

Mineral aggregate board

Compressed straw board

Fibreboard

, Phenolic thermal insulation

Per m m

0.0208

0.0253

0.0144

0.0231

0.0169

0.0201

0.0257

0.0277

0.0298

0.0347

0.0305

0.0277

0.0257

0.0420

0.0182

0.0139

0.0194

0.0304

Pe r in .

2.99

3.65

2.08

3.33

2.44

2.90

3.71

3.99

4.30

5.00

4.40

3.99

3.71

6.06

2.62

2.00

2.80

4.38

value, the better the heat-retaining abil

ity of the prod uc t. Table 18.2 lists a vari

ety of insulating pro du cts and the ir RSI

values. Once a wall, ceiling, or othe r pa rt

of a building ha s been com pleted , all of

the prod ucts used in the building's con

struction add to that section's heat

retention. The C anadian Building Code

has set minimum stan dar ds for the vari

ous parts of a building, and these can be

seen in Table 18.3.

There are several forms of insulation:

batts , rolls, loose insulation which is

poured or blown, and rigid sheets

(slabs).

Batts.

Blanket insulation in th is form,

packaged for shipping in large p lastic

enclosures, can be seen in Figure 18.2. It

comes in a variety of lengths, widths,

and

RSI

values and is designed to form a

press ure fit betwe en st ud s and joists or

similar framing members. The

RSI

value

of a batt d epe nd s on its

thickness—the

thicker the b att, the higher the value. A

form of vapour barrier, for example,

polyethylene film, must be used on the

warm side of the batt to p revent mois

ture infiltration into the fibreglass and

the redu ction of the b att 's

RSI

value ove

a period of time. (See Fig.

18.5

on page

273.)

Rolls. Th is form of blanket insulation

can be see n in Figure 18.3. Produced in

long lengths , it is available in a variety of

thicknesses, widths and

RSI

va lue s. Like

th e batt, it relies on a friction fit. Th is

produ ct is used wherever unob structed

runs of insulation are possible: floors

and basem ent w alls are two exam ples.

(See Fig. 18.6 on page 273.)

Poured or Blown Insulation. This type

of insulation is made of loose, nodulated

wo od, verm iculite, o r c ellulose. Its RSI

value depends on its thickness, as


26



TABLE 18.3

Minim um RSI Values

for

Various Assemblies in a Building as Listed

by the Canadian Building Code (W/m

2

-°C)

Building

Assembly

Exposed walls

Exposed roof or

ceiling

—frame

—solid

Foundation

walls

—frame

—solid

E xposed floors

—frame

—solid

Slab-on-ground

at grade

—unheated

—heated

Maximum Number of

Celsius Degree Days

Up

to

5000

3.0

5.6

3.0

3.0

1.5

4.7

3.0

1.3

1.7

Above

5000

3.4

6.4

3.4

3.4

1.5

4.7

3.4

1.7

2.1

Notes on Table 18.3:

(1) "E xp os ed " means exposed to outdoor temperature or

unheated area.

(2) "S ol id " means brick concrete blocks or concrete.

(3) "Frame" means a wo od or steel stud frame to w hich

n

and exterior cladding is applied.

(4) The RS I value shown for slab-on-ground at grade is for

n

insulation.

15) Slab-on-ground at grade: "heated" means a concrete '<

containing heating ducts or pipes; "unh ea ted " means a

Crete

floor not containing heating ducts or

pipes

(a) Friction Fit Batts

(b)

Value

RSI R

1.4 8

1.7 10

2.1 12

2.4 14

3.5 20

4.9 28

5.4 31

6.1 35

7.0 40

Nominal Thickness

mm in.

65 2.5

89 3.5

89 3.5

89 3.5

152 6

202 8

222 8.75

251 9.87

265 10.37

Standard Widths

mm in.

381,584

15,23

381.584 15.23

381.584

15,23

381,584

15,23

381,584 15.23

406,610

16,24

406,610

16,24

406,610 16.24

406,610 16,™

Standard Lengths

mm in.

1219 48

1219 48

1219 48

1206 47.5

1219 48

1219 48

1219 48

1219 48

1219 48

FIGURE 18. 2

Batt insulation is available in a wi de variety

of

RSI values, thicknesses and

widths. (Note: Some dimensions appear in millimeters rather than in any larger metric unit

because the insulation industry uses millimetres.)

270




Friction Fit Rolls

Value

3SI R

1.4 8

1.7

10

2

1

12

Nominal Thickness

mm in.

70 2.75

89 3.5

89 3.5

Standard Widths

m m in .

381,584 15,23

381,584 15,23

381,584 15,23

Standard Lengths

m ft.

23 75.5

17 55.8

17 55.8

RGUR E 18.3 Roll insulation is we ll suited to areas whe re long open runs exist betwe en joists

j ds .

indicated in Figure 18.4, and it is sold by

the bag. Poured or blown insulation is

usually installed by an insulation con

trac tor using a fibre-blowing m ach ine. It

is mo st suited for horizontal spa ce s

such as attics or roof areas.

Hom e-owners often rely on this form

of insulation to boost the

RSI

value of

their existing insulation. To achieve this

end, they need to be sure to cho ose a

material that will maintain its RSI value

over the y ea rs. Cellulose insulation is a

form of paper product (similar to news

print) tha t is chem ically treate d (usually

with dry chem icals) to provide so me

mo isture- and fire-proofing. This typ e of

insulation, when dry, is a good insulating

material. Like ma ny oth er pap er pro

ducts,

however, the cellulose insulation

has a tend enc y to absor b m oisture after

it has been installed, thu s redu cing th e

RSI value drastically. Due to its compara

tively low initial cos t, m any h om e-insu

lating companies select this material for

residen tial u se. But if the moisture-proof

ing chemicals are not pro perly applied

and ad eq ua te ventilation in th e soffit

and peak a rea s allowed for, the installa

tion of this m aterial is virtually a w aste

of time and money. Figure 18.7, on page

273,

illustrates poured or blown insula

tion installed in an attic area.

Rigid. Th is typ e of insu lation is

produ ced in slab or sheet form and is

made from polystyrene or polyurethane

foam. Both foams are excellent

insulat ing prod ucts and v apou r ba rriers:

mo isture is unable to penetrate them.

Figures 18.8 and 18.9, both on page 274,

illustrate rigid glass fibre bo ard s, with

available thicknesses, widths, and RSI

values listed.

Residential Electric H eating

271



(b)

Value

RSI R

3.5 20

4.9 28

5.3 30

5.6 32

6.0 34

6.3 36

6.7 38

7.0 40

8.8 50

Min.

Thickness

mm in.

191 7.5

267 10.5

286 11.25

30 5 12

324 12.75

343 13.5

362 14.25

381 15

470 18.5

Max. Net Coverage

m

2

/bag ft.

2

/bag

5.9 63

4.2 45

3.9 42

3.7 39

3.4 37

3.3 35

3.1 33

2.9 31

2.4 26

Min.

Bags per

UtK

1 0 0 m

2

10001

17 16

24

22

25.5

24

27.5 25.5

29 27

31

28.5

32.5

30

34 32

42 39

FIGURE 18.4 A nodulated form of glass fibre insulation is frequen tly blown in attic

are;

upgrade the RSI value in older buildings.

These slabs are attached to masonry

walls by an adhesive. The adhesive is

necessary in commercial buildings

where no wood framing is presen t.

Installation of a protective surface

of

13 mm gypsum board or similar fire-

resistant product over the polystyrene

insulation is also necessary. Polystyrene

is combustible and gives off a dangerous

gas when ignited.

Vapour Retarders

Insulation traps dead air only when

dry and free from moisture. If the

tion is damp, it will conduct heat

the building

quickly.

The greatest

is from excess moisture inside the

ing trying to escape outside through

walls.

Moisture from cooking, bathin

(showers), and people must be remc

272




IGURE

18.5 A wall section show ing

iction-fit batt or roll insulation installed

Breath a vapour barrier and plaster board

FIGURE 18.6 Installation of friction fit rolls

- open run areas. [Note: Be sure to wear a

protective mask and protective clothing.)

u Step

1.

Place air-vapour barrier at bottom of space

jg between

joists.

Lap to ensure that there is a

good barr ier against t he f low of a i r and vapour.

S

S t ep 2. For requ i red t herm al res is t an ce va lue ,

a p o u r o r b l o w i n s u l a ti o n b e t w e e n

o j o i s t s t o d e p t h r e c o m m e n d e d b y m a n u f a c t u r e r .

IS

Take care insu la t ion doe s not cover sof f i t or

Jj

under-eave ventilators.

S tep 3. Rake or smooth insulation to ensure equal

thickness over entire area. To obtain proper

settled density and thickness, refer to CMHC

acceptance listing for manufacturer's product.

F I G U R E 1 8 . 7

insulation

P rocedure for installing loose

safely. Oth erw ise, it will co nd en se on th e

walls, form drops, and run down, which

often damages wall surfaces.

To keep insulation reason ably dry,

the vapour retarding barrier must be

installed on the warm side of the insula

tion, tha t is, between the

plaster

or pan

elling of the wall and the insulation

itself

A

continu ou s, 0.2 mm poly ethylen e film

is fastened over the insulation prior to

covering t he w all with

plaster

board or a

similar finish. Figure 18.10 illustrate s th e

pro per location of a vap our retarding

barrier.

When installing the film, do not

pu nctu re it in any way and b e sure to

secu re it properly with sta ples . In this

way you will prevent air flow th rou gh

tiny open ings o r crac ks. Air tend s to find

any weak spo t, such as the hole in a bal

loon, regardless of the sp ot's location.


27



(a)

(b)

Exterior Insulating Sheathing

Glass Fibre, Rigid Board on an Above-Ground

\

Value

RSI R

Nominal Thickness

mm in.

Standard W idths

mm in.

Standard Lengths

0.77

1.18

4.4

6.7

25

38

1

1.5

1219

1219

48

48

2438, 2743

2438, 2743

96,106

96,108

FIGURE 18.8 Glass f ibre, r ig id board used in con junc t ion wi th ba t t insulat ion to increase •

RSI value of wal ls

Air flow will be surprisingly high tht

and the air may be full of moisture .

Once the house is properly sealed

with vapour-retarding film, artificial j

tilation means, such as vents and fa

are needed to exhaust the moist air

I

accumulates in the home

daily.

These

measures are so important that some

localities will call for an insulation

inspection to ensure that the insulat

and vapour-retarding film have been

Value

RSI R

1.5 8.5

2.3 13

FIGU RE 18.S

w eeping t i le

N ominal T hickness

mm in.

50 2

75 3

Standard Widths

mm in.

1220 48

1220 48

Standard Lengths

mm in.

2440 96

2440 96

Rigid f ibreglass board for insulat ion on exter ior of basement wal ls , d o w n j H

evel

274




insulation

Air barrier/vapour

retarder prevents

moisture from

inside air coming

into contact with

concrete.




properly installed and not damaged by

other building trade areas.

Remember basement walls because

if they are insulated there will be a

higher degree of comfort in the hom e.

These walls must be pro tected from

moisture produced both inside and out

side the building, however. Figure

18.11

illustrates a basem ent wall section and

the methods used to prevent dam pness

from entering and spoiling the wall's

insulation.

Ventilating Devices

Ventilating fans are placed over stoves

and in bathroom s to remove excess

moisture. They also, however, remove

some of the heat from the house, and so

Methods of providing adequate air-flow

ventilation into attic areas

method A

o

i

8

gable end, ridge

or roof vents

NO TE : Under-eave vents should provide 50% venting area.

Gable end, ridge, or roof vents should provide other 50% venting area.

FIGURE 18.12 A t t ic v ent i la t ion. P rov ide a m in im um of 1 m

2

f ree (unobstructed) vent i la

tor each 300

m

?

insulated cei l ing area. Cathedral - type and low-pi tched roofs require

1

rr

t ion for each 150 m

2

insulated at t ic area. Dis t r ibut ion of vents must prov ide cross-

v ent i la t ion in a t t i c f rom end t o end and f rom t op t o bot t om.

276




should not be used continuously. These

tans are an important part of the heating

installation an d a re looked for by electri

cal heating in spec tors.

Attic insulation must a lso be k ept

moisture-free. Having a system of vents

placed in various pa rts of the attic will

achieve this. One sq uare m etre of vent is

required for each 150/300 m

2

of atti c

area . (See Fig. 18.12) Th e circu lation of

air tend s to keep the insulation d ry and

moisture-free. Remember that a cold

attic during the winter indicates that the

insulation is indeed w orking and keeping

beat in the h ou se.

Baseboard Heater

One of the m ost com mo n ty pes of elec

trical heating unit is the baseboard

heater. It co nsis ts of an enclosed heating

itlement, fitted with h eat-radiating metal

Mns

and su pp ort ed in a metal frame. It

ope rates on the principle that air heated

by the elem ent w ill rise and flow ou t of

th e top of the frame, w hile coole r air will

be drawn from the floor area into the

bottom of the heater. This process is

called convection of air. (See Fig. 18.13)

Baseboard heaters are rated in both

wattage and voltage. The m ost comm on

unit for residential use is the 240 V

heater, simply be cau se a 240 V he ate r of

a given wa ttage re quires half as m uch

current as a 120 V hea ter of the sam e

wattage. The need for extra large con

ducto rs in the heater circuits is reduced .

Baseboard heaters are made in low

and standard

wattage

densities. A

1000 W

hea ter in a low-watt density will be

approximately 1.8 m long and low

enough in surface temperature that it

may be installed safely under drapes

and other heat-sensitive m aterials. It is

suitable for use under heat-sensitive

synthetic fabrics, which shrink, lose

their shape, or discolour when exposed

to heat for a prolonged period of tim e.

A 1000 W heater in a standard w att

density will be approximately 1.2 m long

and reach a higher surface tem pera ture.

The heat is more concentrated, and so

this type of heater should

not

be used

und er o r nea r delicate fabrics. It is excel

lent, however, for use in are as w here

space is limited and higher surface tem

peratures are not a problem.

Draperies should be hung with th e

nearest fold at least 5 cm away from the

he ate r and 4 cm off th e floor. Prop er air

circulation through the heater is then

possible.

Baseboard heate rs are produced in a

variety of wattage ranges, star ting as low

as 250

W

and going as high as 3000

W.

Manufacturers provide specifications for

their own products.

Installation of Baseboard Heaters.

These heaters should be mounted at the

finished floor level to allow th e cool a ir

to enter the heater

easily.

Also, the y

must be mounted on a flat surface,

without bending or distorting the h eater

frame. If the frame is distorted in any

way, the heater

will

produce som e noise

as it expand s and con tracts during its

heat cy cles.

The hea ter is secure d to the wall

with several w ood screws. It needs

nearly no maintenan ce, except for an

occasional vacuum ing to remov e lint col

lected on the heater fins. Lint slows the

convection of air throug h the h eater and

low ers i ts efficiency. (See Figs. 18.14 and

18.15)

Radiant Heating for

Ceil ings

An other ty pe of electrical heating unit is

the radiant-heating ceiling cable. This


277



FIGURE 18.13 A ir convection in a baseboard heater

278




RGURE 18.14 A baseboard heater with a built-in thermos tat

RGURE 18.15 A baseboard heater w ith an air conditioner switch and receptacle attachment

slender, insulated w ire must b e carefully

installed on the ceiling before

plaster

is

applied.

It

is sold in calibrated leng ths,

with wattage and v oltage ratings

stamped on each cab le reel or container.

(See Fig. 18.16) A tag or label on the end s

of the cable further rem inds th e installer

of the wattage and voltage rating for tha t

cable length.

The cable mu st not be cut or sho rt

ened in any way, but used as it co m es

from the su pplier on th e voltage indi

cated on t he ca ble reel. Any installation-

site change in th e length of the heatin g

cable will alter th e wattag e ou tpu t and

current flow throu gh the ca ble. Any

attempt, to splice the cab le where it ha s

been shortened might establish a failure

point and cause considerable expense

and inconvenience after the cable has

been covered over with plaster.

Recent developments in the heating

industry hav e led to the introduction of

FIGURE 18.16 Reel of radiant-heating

ceiling cable

a new product, radiant-heating foil. This

con sists of thin metal heating elem ents

which are electrically insulated and

waterproof embedded in strong plastic

lamin ates. The pr od uct is available in a

variety of w idths, lengths, and wa ttages.

It is eas ier to install tha n th e ceiling


279



cable and requires no special tools or

equipment.

Any ceiling heating system radia tes

its heat energy into a room, warming any

heat-absorbing object present. The

entire ceiling, therefore, beco me s a hea t

sou rce. Objects in the room start to give

away their heat to the surroun ding air

and room tem perature becom es even

and comfortable.

Installation of a Ceiling Cable. If a

layer of drywall plaster has been

installed first, the ceiling cable can be

stapled d irectly to th e drywall with

special staple s. Take care not to staple

through the cable or dam age it in any

way. The cable should be kept a

minimum of 20 cm away from ceiling

light fixtures and about 15 cm from

walls. Taking thes e safety m eas ure s will

prevent driving a hook or fastener into

the cable when hanging dra pe s or new

light fixtures.

If a building has pou red co nc rete

walls and ceilings or a similar m aso nry

con struc tion , the ceiling cable will need

hanger strips. The se plastic strips are

run across the ceiling at each end of the

room, secured to the ceiling with ad he

sive, and then fitted with the heating

cable. The cable is looped from end to

end. The plastic supporting s trips pro

vide the proper spacing between the

cable run s. Cables should be kept a t

least 5 cm a part, depending on cable

spacing calculations. Manufacturers will

provide the p roper spacing require

ments for their cables. Often, adhesive

tape is needed at intervals in a long

room to prevent sagging of the cables

before plastering.

Each cable set c om es with a length

of heavily insulated con duc tor at each

end of the cable. Such a length is called a

cold

lead.

Cold leads are run from th e

ceiling down to an electrical box on

I

wall where the therm ostat and/or |

supp ly is located. The length of these |

leads should

not

be changed.

To ensu re tha t th e cable is not

nicked or damaged with a trowel,

based

gypsum plaster

must be

inste

in the ceiling carefully. The

plaster i

be allowed to dry fully before the

i

is energized. Take ca re to ch eck the

cable for continuity both before and

after plastering . Using the c able to

i

the plaster will only result in shrink

and /or cracking of the plaster aroi

the heating cable.

Once the plaster is dry (allow at

least a week), th e cab le can be ener

and allowed to heat the room . Inci

the tem pera ture setting of the ther

sta t slowly, and d o not pa ss the m id

point setting of the thermostat for at

least two we eks. Taking this safety |

caution is advisable beca use the

pla

may n ot be thoro ugh ly d ry in all ceili^

areas.

Installation of Radiant-Heating

Foil.

Th e foil is rolled ou t to th e p rop er

leoj

as supplied by the manufacturer,

without cuts or splices m ade to it. Th

unit is the n stapled to a joist, using

da

securing strips built into its edge.

Staples shou ld b e applied at 30 cm or

40 cm (12 in. or 16 in.) interv als.

Electrical connections are made in a

clear-cover connection box for easy

inspection prior to covering with the

ceiling mate rial. (See Fig. 18.17)

Specific Heat Loss A rea*

Windows are major heat loss areas,

ever, proper caulking around windc

frames will stop infiltration of cold I

and drafts and save heat over a per

time.

280




of

FIGURE 18.17 Installation of radiant-heating

For many years, it was com mon prac

tice to install wooden or aluminum

storm window s over existing window

openings in older homes. Aluminum-

framed windows were neat and easily

removed for cleaning and ma intenan ce.

They also did not require painting and

did not swell or jam from moisture

intake. The alum inum frame, however,

was a good cond uctor of heat and

passed this heat from the building's inte

rior to the o utsid e. Wood-framed win

dows required more maintenance, were

heavier to remove and install, and were

often difficult to open and close after a

few years. But th e wo oden frame did

retain heat much better than an alumi

num frame.

Now, with window deve lopm ents

keeping pace with other design improve

ments in the building industry, double

and triple

pane

window units are availa

ble. The herm etically sea led pa ne s of

glass create a dry air spa ce between the

panes.

They make heat retention possi

ble and the inconvenient removal, clean

ing and installation of stor m window

•nits unnecessary.

A further design improvement is spe

cially treated glass which can be pur

chased as part of dou ble and triple pane

window u nits. The glass limits ou tward

heat flow in th e winter and inward heat

flow during the sum mer even more th an

the stand ard d oub le or triple pane units.

Some window u nits have aluminum

frames designed to support the glass

without being in actual contact with it.

Th ese frames a re low in m aintenance

and can be obtained with section s that

open for cleaning or fresh air entry.

Modern window units may also have

wood en frames. In many case s, thes e

frames are covered with a plastic mate

rial to eliminate moisture intake and the

need for painting the wood.

Fireplaces

are attractive and give off

much heat when operating. When not

operating, however, they allow a great

deal of heat to be drawn out of the room,

up th e flue, and out th e chimney. A brisk

wind across th e chimney will speed heat

removal from the room. To prevent this,

the fireplace damper should always be

well-fitted and kept closed when the fire

place is not in us e. A se t of well-fitting

do ors to cover the fireplace's opening

will further aid heat retention when no

fire is burning in the unit. (See Fig. 18.18)

Many typ es of fuel-efficient fireplace

inse rts a re ava ilable for installation in

new or existing fireplaces. These mod

ern produc ts enhance a room's appear

ance and help heat the home when the y

are in use. They also provide sup erior

protection from heat loss when not in

use.

Another po ssible cause of heat loss

is carelessly installed insulation around

pipes and

electrical

boxes

within walls

and ceiling area s. Cold air will infiltrate

thes e weak spots; therefore, extra care

should be taken to ens ure a prop er fit

around boxes and plum bing pipes. As


281



FIGURE 18.18 A fireplace should have a

tight damper and a glass screen for effective

heat retention.

FIGURE 18.19 W hen installing plumbing

and wiring , particular attention should be

given to the installation of insulation. Insula

tion shou ld com pletely fi l l any cavities.

insulation —•

" S .

- a

founds:-

wall

— footing

insulation

FIGURE 18.20 Insulation on the outs

face of a slab on grade

mentioned in Chapter

7,

special pi

forms are available to prevent air I

age around wiring poxes. Figure 18.1

illustrates the insulation required

around such a box.

A house built on a concrete slab a

pad is vulnerable to heat loss, and

requires placement of a rigid exterior

type of insulation around various sec

tions of the slab and its footings. (See

Fig. 18.20) The insulation will prevenl

heat from radiating out of the slab I

into the cool earth.

282




Basement Heating

Residential basements are given special

treatment. For the purposes of heat loss

calculation, the basement is divided into

two par ts. (See

Fig.

18.21)

In a basement with a 2.4 m (8 ft.) ceil

ing, the area from the ceiling down to

grade level is called th e above grade por

tion. The rest of the basement is called

th e below grade portion.

Provincial building codes often

pargmg

I ' Moisture barrier

stops here.

insulation

air-vapour barrier

Air-vapour barrier

stops here.

moisture barrier

0.6 m above grade

dividing line

1.8 m below grade

waterproofing

to cover

parging

sleepers

membrane

air-vapour barrier

N O T E : The basement wall above grade must meet the same requirements as any other exterior wall exposed to

weather. The wall below grade should be moisture-proofed on the inside. Thermal insulation should be applied

on exposed wall to a distance of 610 m m below grade (w ith an air-vapour barrier). Vapour barriers and damp-

proofing must be in accordance with requirements detailed in Residental Standards Canada, sections

12E(3), 20E and2 0F.

FIGURE 18.21 Basement wall treatm ent


28



require bas em ent walls that are 50%

above grade to have a minimum of

RSI-2.1

value insulation installed over

the entire wall. Basement walls that

expo se less than

50%

of their surface to

above-grade temperatures must be insu

lated (RSI-2.1) to a de pth of 61 cm below

grade level.

Energy-conscious hom e-owners,

however, may wish to insulate the com

plete basem ent wall, thus reducing he at

loss and lowering energy costs for this

area of the hom e.

If

there is any c han ce

of water leaking into the basement area,

the insulation sho uld be kept approxi

mately 30 cm from th e floor to p reve nt

th e insulation from soaking (wicking) up

the water.

A

check of local building cod es is

advisable to determine the exact amount

of below-grade insulation required in a

given area of the country.

Often, rigid insulation is fastened to

the ab ove-grade walls with an a dhesive.

Wooden strapping and

RSI-1.4

value

batts can also be installed for heat reten

tion. Sometimes, small amo unts of h eat

ing cable a re placed in th e floor to help

the main heaters warm up the area.

Basic Heat Loss

Calculations

The First

Step: Heat-Retaining Walls

and

C eilings.

Walls and ceilings exp osed

to outdoor temperatures must be

examined to determ ine their ability to

resist the transmission of heat from

inside the building to the o utside. T he

ability of various building products and

their installation techn ique s to resist th e

flow of hea t will hav e a con side rab le

effect on the heat loss for a given wall or

ceiling. Figure 18.22 sh ow s a w all

cross-section and the

RSI

num bers

inside surface (still air)

gypsum wallboard - 13 m m

weatherproof sheathing - 11 m m

asbestos finishing felt

air space

backer board - 10 m m

clapboard

outside surface - 24 km/h wind

total resistance (exci. insulation)

FIGURE 18.22 Wa ll section RSI values

^

*— outside surface (ventilated attic)

—

gypsum wallboard -

13

m m

inside surface (still air)

total resistance (excl. insulation)

FIGURE 18.23 Ceiling section RSI vali

(res istan ce to heat flow) for each of

thi

materials used . Figure 18.23 shows a

ceiling installation and its RSI values.

The total RSI value in eac h figure

repre sents the heat-retaining ability

of

the ma terials used w ithout th e aid of

insulation.

Table

18.3,

on page

270,

lists the

i

imum

thermal resistance required for

the various building assem blies in a

hou se, regardless of the type of heat

system used. Table

18.1,

on page 268,

provid es the minimum therm al resist

anc e of insulation th at m ust be insta

in each building assembly. Table 18.2

lists a variety of insulation products i

can be used t o establish the minimum

284




TABLE

18.4

Resistance Values for Various Building Materials

;

Building Material

Insulating fibreboard

sheathing

Gypsum board

Plywood

Hardwoods (Maple, oak, etc.)

Softwoods (Pine, fir, spruce, etc.)

We stern cedar

(18% moisture content)

Loose fill insulation

Macerated paper

•(Cellulose fibre)

Mineral wools

(32 to 8 0 kg/m

3

den sity)

Vermiculite

(Expanded mica) 112 kg/m

3

density

A ir spaces (in walls)

Foamed styrene

(Density 26 kg/m

3

)

(See ma nufacturer's specifica

tions)

Polyurethane

Flooring (Hardwood)

Brick (C lay or shale)

Concrete block (Sand and gravel,

3 oval cores)

Cinder block

Thickness

(mm)

25

15

13

13

25

13

25

25

25

25

25

25

20 to 100

25

25

20

100

100

200

300

100

200

300

Resistance

Factor

0.419

0.262

0.209

0.056

0.220

0.110

0.160

0.220

0.274

0.628

to

0.704

0.586

0.366

0.171

0.608

to

0.704

1.04 to 1.06

0.120

0.060

0.125

0.195

0.225

0.195

0.303

0.333

Heat

Loss

Factor

(W/m

2

C)

2.38

3.82

4.78

17.85

4.54

9.09

6.25

4.54

3.64

1.59 to 1.42

1.71

2.73

5.85

1.64 to 1.42

0.96 to 0.94

8.33

16.66

8.00

5.13

4.44

5.13

3.30

3.00

Values shown above are taken from the Acceptable Building Material Systems & Equipment—Central Mortgage and Housing

Corporation.

'Illinois Institute of Technology




therm al resistan ce as listed in Table

18.1.

Additional information on the qual

ity and

RSI

value of the insulation ca n be

obtained from the manufacturers on

request.

For com parison pu rpos es, the RSI

value of variou s building pro duc ts can

be lo cated in Table 18.4. More c om plete

tables can usually be obtained from the

local hyd ro utility, electrical leag ue, or

building product supplier.

The Second Step: Heat Loss Through

Walls and C eilings. The second step in

determining the amount of heat needed

for a hou se is to calculate th e heat lost

thro ug h th e walls and ceilings. To do

this, the RSI total of the wall or ceiling

must be mathematically converted to a

U factor. The U factor (overall

co-efficient of heat transfer) is the

amount of heat transmitted through a

heat ba rrier in one hour per squ are

metre of surface for each 1°C of

temperature difference between the

inside and outside of the barrier.

Table 18.5 lists outside tem per ature s

experience d in selected Canadian loca

tions, along with the num ber of degree

day s below 18°C. Th ese figures are

based on

2.5%

of the Janu ary outd oor

tem peratu res recorded in thos e areas of

the country.

For example, an exposed wall listed

in Table 18.3 mu st h ave an

RSI

value of at

least 3.0 when its insulation an d all as

sembly produc ts are considered. The

U

factor eq uals one third, or 0.333 W/m

2

for

each

1°C

of

design temperature difference.

If

the hou se with this wall were in the

Toronto region of Ontario, the ou tdo or

design temp eratu re would be -18°C, and

the degree days would be 4082 (under

5000 as requ ired by Table 18.3). If th e

occupants want an indoor temperature

of

23°C,

the design tem per atur e differ-

286

ence would be

23°C

-

(-18°C) =

41°C.

If the

U

factor for a 1°C temperature)

difference is

0.333

W /m

2

, then the heat

loss for a 41°C tem pe rat ur e difference

will be

41

x

0.333

W/m

2

, which equals

13.65 W /m

2

or approximately 14

W

The h eat lost thro ugh the ceilings

i

calculated in much t he sam e way as

lost through the w alls.

To find th e total hea t loss through

walls of a roo m, t he tota l area of wall

exposed to cold air must be calculate*

To do so , multiply the h eight of the roa

by the length of the exposed wall.

(Remember that a corner room has tvd

exposed walls.) Figure 18.24, on page

290, sho w s a wall with a g ross area

high time s 4.6 m long, which is abo

11.04

m

2

. Since th e window occup ies

0.72 m

2

of spa ce, the ne t expo sed wal i

about 10.3

m

2

.

Th e amo unt of heat loa

through this wall in an hour is equr

lent to 14 W/m

2

x 10.3

m

2

,

which is

144.2 W

The Third

Step: Heat Loss Through

Doors and W indows.

Tab le 18.6, on

page

291,

lists the he at loss per

squaiej

m etre throu gh various typ es of door

tm

window installations for each degree •

design tem pe rat ur e difference. If the

room show n in Figure 18.24 ha s a

wood

framed window, that is,

single-glazed

with a storm , the he at loss will be

2.90 W /m

2

of window for e ach degre*

design tem per atur e difference. The

ti

heat loss throug h the g lass will be as

follows. Th e area of the window equa

0.6

m

x 1.2

m,

which is 0.72

m

2

.

Therefore, the heat loss per degree

Celsius will be 0.72

m

2

x 2.90 W/m

2

,

wh ich is 2.09 W /m

2

. W ith a

temperatu

difference of 41°C, th e h ea t lo ss will

t

41 x 2.09 W/m

2

, which is 85.7 W This

heat loss is added to the 144.2

W

lost

through the exposed wall.




TABLE 18.5 Design Data fo r Selected Locations in Canada

Province

and

Location

Design Degree

Temp-

Days

era-

Below

ture 18°C

2.5%

X

British Columbia

Abbotsford - 10

nftoassiz

- 13

Afcerni

- 5

| Ashcroft

- 2 5

Bearton River - 3 7

Burns Lake - 3 0

Cache Creek - 25

Campbell

River...

- 7

Carmi - 2 4

Castlegar

- 1 9

Chetwynd - 35

Chilhwack - 12

Ooverdale - 8

Comox

- 7

I Courtenay

- 7

Cranbrook - 2 7

Crescent Valley

. . -2 0

Crofton

- 6

Dawson

C reek. .. -3 6

Dog

Creek

- 2 8

Duncan

- 6

Elko

- 2 8

I Femie

-29

• j r t Nelson - 4 0

Port

S t.

John

- 3 6

3'acier - 27

MuMen -28

Grand Forks

- 2 0

Greenwood - 2 0

Haney - 9

Hope

- 1 6

Kamloops

- 2 5

Kaslo

- 23

Kelowna

- 17

Kimberley

- 2 6

Kitimat Plant

- 16

Kitimat

Townsite

- 16

Langley

- 8

Lillooet

- 2 3

Lytton

- 1 9

Mackenzie

- 3 5

McBride

- 3 4

McLeod Lake

- 35

Masset

- 7

Merritt - 2 6

Misson City

- 9

Montrose - 17

Nakusp - 24

Nanaimo - 7

Nelson - 20

New

Westminster

North

Vancouver - 7

Ocean Falls - 12

100 Mile House.. -2 8

Osoyoos

- 1 6

Penticton - 1 6

PortAlberni - 5

Port Hardy - 5

Port McNeill - 5

Powell River 9

Prince

George....

33

Prince Rupert

14

3150

296

3180

4 6

7010

572

4 8

32

5210

3747

589

297

3 3

32 3

325

4762

432

3140

589

5110

32

49

498

7 63

6119

573

495

4 5

452

328

3150

3756

4110

368

489

4110

4130

298

4130

322

595

572

572

372

4190

298

4 8

4130

3010

392

8 293

3 9

352

49

353

3514

3180

3661

348

29

5388

4117

Princeton

Oualicum Beach

Quesnel

Revelstoke

Richmond

Salmon

A rm

Sandspit

Sidney

Smithers

Smith River

Squamish....

Stewart

Taylor

Terrace

Totino

Trail

Ucluelet

Vancouver...

Vernon

Victoria

Williams

Lake.

Youbou

Alberta

Athabasca

Banff

Barrhead

Beaverlodge

Brooks

Calgary

Campsie

Camrose

Cardston

Claresholm

Cold Lake

Coleman

Coronation

Cowley

Drumheller

Edmonton

Edson

Embarras

Portage

Fairview

Fort

Saskatchewan

Fort

Vermilion..

Grande Prairie

Habay

Hardisty

High River

Jasper

Keg

River

Lac La Biche...

Lacombe

Lethbridge

McMurray

Manning

Medicine Hat .

Peace

River...

Penhold

Pincher Creek ....

Ranfurly

Red Deer

Rocky Mountain

House

Slave Lake

Stettler

Stony Plain

Suffield

- 27

- 7

- 3 3

-26

- 7

-23

- 6

- 6

- 2 9

- 4 6

-11

- 2 3

-36

-20

- 2

- 17

- 2

- 7

- 2 0

- 5

- 3 1

- 5

- 3 5

- 3 0

- 3 4

- 3 5

- 3 2

- 31

- 3 4

- 3 3

- 3 0

- 31

- 3 6

- 31

- 31

- 3 1

- 31

- 3 2

- 3 4

- 41

- 38

- 4 1

- 3 6

- 4 1

- 3 3

-31

-32

-40

-35

-33

-30

- 3 9

- 3 9

- 31

- 3 7

- 32

- 3 2

- 3 4

- 3 2

- 31

- 3 6

- 3 2

- 3 2

- 3 2

456

325

494

4 73

292

4 9

365

3 9

529

7610

3140

4710

589

443

325

365

325

3 7

4 4

3 76

5105

336

628

5719

6

582

529

5345

6010

572

483

5120

645

5120

59 6

5150

557

5589

5910

749

6170

32

589

7170

6145

7 5

595

532

5532

682

6140

574

4718

6778

66

4874

6424

5845

5010

598

57

555

622

5590

5780

5360

Taber

Turner

Valley...

Valleyview

Vegreville

Vermilion

Wagner

Wainwright . . . .

W et ask iw in. . .

Whitecourt

Wimborne

Saskatchewan

Assiniboia

Battrum

Biggar

Broadview

Dafoe

Dundurn

Estevan

Hudson Bay

Humbolt

Island Falls

Kamsack

Kindersley

Loydminster

Maple Creek

Meadow Lake ...

Melfort

Melville

Moose Jaw

Nipawin

North Battleford

Prince Albert

Qu'Appelle

Regina

Rosetown

Saskatoon

Scott

Strasbourg

Swift

C urrent .

Uranium

C i ty..

Weyburn

Yorkton

Manitoba

Beausejour

Boissevain

Brandon

Churchill

Dauphin

Flin Flon

Gimli

Island Lake

Lacdu

Bonnet.

Lynn Lake

Morden

Neepawa

Pine Falls

Portage

la

Prairie

Rivers

St. Boniface.

S t.

Vital

Sandi

lands...

Selkirk

Split Lake

Steinbach

Swan

Rver.

.

The Pas

Thompson....

- 31

- 3 1

-37

-34

-35

- 36

- 3 3

- 3 3

- 35

- 3 1

- 3 2

- 32

- 34

- 34

- 3 6

- 3 5

- 32

- 37

- 3 6

- 3 9

- 3 5

- 3 3

- 35

- 3 1

- 3 6

- 37

- 3 4

- 32

- 3 8

- 3 4

-37

-34

-34

-33

- 35

- 34

- 34

- 32

-44

- 33

- 3 3

- 32

- 3 3

- 3 9

- 3 3

- 3 8

- 34

- 3 6

- 34

-40

-31

- 3 2

- 34

- 31

- 3 4

- 33

- 33

- 32

- 33

- 38

- 33

- 36

- 36

- 42

4750

5700

6110

6000

6140

6180

6000

5670

6130

5620

5340

5400

5890

6080

6360

5840

5542

6470

6280

7100

6290

5710

6280

5180

6550

6390

6170

5400

6550

6050

6562

6060

5920

5860

6077

6260

5890

5482

8210

5720

- 3 4

6239

583

5610

6 37

9213

6150

678

6 3

7210

595

782

549

595

6

589

594

583

583

589

589

788

583

628

6852

793

287



Transcona

- 33

Virden - 3 3

Whiteshell - 3 4

Winnipeg - 3 3

Ontario

Ailsa Craig - 1 7

Ajax

- 2 0

Alexandria - 2 4

Alliston

- 2 3

Almonte - 2 6

Ansonville

- 33

Armstrong

- 39

Arnprior

- 27

Atikokan - 34

Aurora - 21

Bancroft - 27

Barrie

- 2 4

Barriefield -22

Beaverton - 24

Belleville

- 2 2

Belmont

- 17

Bowmanville - 20

Bracebridge - 26

Bradford

- 23

Brampton - 1 9

Brantford

- 1 7

Brighton - 21

Brockville

- 2 3

Brooklm - 20

Burks Falls - 26

Burlington - 17

Caledonia

- 17

Cambridge - 1 8

Campbellford

- 23

Camp Borden

- 23

Cannington

- 24

Carleton Place.... -25

Cavan - 22

Centralia

- 17

Chapleau - 35

Chatham - 1 6

Chelmsford - 28

Chesley

- 19

Clinton - 17

Coboconk

- 25

Cobourg -21

Cochrane - 34

Colborne - 21

Collingwood - 22

Cornwall

- 23

Corunna - 1 6

Deep River

- 2 9

Deseronto

- 22

Dorchester - 1 8

Dorion - 3 3

Dresden - 16

Dryden

- 3 4

Dunbarton - 1 9

Dunnville - 1 5

Durham

- 2 0

Dutton

- 1 6

Earlton - 3 3

Edison - 3 4

Elmvale - 24

Embro - 1 8

Englehart

- 33

Espanola - 2 5

Exeter

- 17

Fenelon Falls - 25

Fergus

- 2 0

Fonthill - 1 5

Forest

- 1 6

Fort Erie - 1 5

5830

5890

5950

5889

3980

4080

4580

4520

4740

6220

6892

4800

6040

4300

4960

4470

4240

4580

4190

3980

4130

4800

4410

4200

3920

4240

4300

4240

5070

3700

3920

4130

4410

4470

4580

4690

4470

3940

5950

3530

5290

4240

4130

4740

4190

6230

4190

4580

4470

3810

5180

4080

4030

5890

3700

6080

4030

3810

4620

3750

5866

6000

4580

4130

5950

5070

4080

4690

4610

3700

3830

3590

Fort Frances

- 33

Gananoque - 2 2

Georgetown

- 1 9

Geraldton - 35

Glencoe

- 16

Goderich - 16

Gore Bay -2 3

Graham - 3 7

Gravenhurst

- 26

Grimsby - 16

Guelph - 1 9

Guthrie

- 2 4

Hagersville

- 1 6

Haileybury

- 32

Haliburton - 27

Hamilton

- 17

Hanover - 1 9

Hastings

- 2 3

Hawkesbury - 2 5

Hearst

- 3 4

Honey Harbour... - 2 4

Hornepayne

- 3 7

Huntsville - 2 6

Ingersoll

- 18

Jarvis - 1 6

Jellicoe

- 36

Kapuskasing

- 33

Kempville

- 25

Kenora

- 33

Killaloe - 2 8

Kincardine

- 17

Kingston - 22

Kinmount - 2 6

KirklandLake - 33

Kitchener

- 1 9

Lakefield - 2 4

Lansdowne

House - 3 9

Leamington

- 1 5

Lindsay - 24

Lions Head

- 1 9

Listowel - 19

London - 18

Lucan - 17

Mailand

- 23

Markdale - 20

Martin - 3 6

Matheson

- 33

Mattawa

- 2 9

Midland - 2 3

Milton - 1 8

Milverton

- 1 9

Minden - 2 6

Mississauga - 1 8

Mitchell - 1 8

Moosonee

- 36

Morrisburg - 2 3

Mount Forest

- 21

Muskoka

Airport

- 26

Nakina - 35

Napanee

- 22

Newcastle - 2 0

NewLiskeard - 32

Newmarket - 22

Niagara Falls

- 1 6

North

Bay -2 8

Norwood - 2 4

Oakville

- 1 8

Orangeville

- 2 1

Orillia - 2 5

Oshawa - 19

Ottawa

- 2 5

Owen Sound - 19

5830

4240

4250

6550

3810

4190

4910

6470

4740

3580

4220

4520

3920

5830

4920

3710

4350

4470

4800

6500

4580

6580

4760

4030

3860

6450

6366

4540

5932

4940

4240

4266

4800

6150

4110

4630

7110

356

458

435

463

4 68

4 3

43

469

633

622

534

458

4 8

452

485

3810

44

6931

441

4755

4837

654

413

4130

583

4350

3740

5318

4520

3640

4650

4610

4130

4673

4220

Pagwa River - 3 *

Paris - 17

Parkhill - 16

Parry Sound

- 24

Pembroke - 28

Penetanguisbene

- 23

Perth - a

Petawawa

-29

Peterborough -23

Petrolia - * •

Picton - 21

Plattsville

- 18

Point

Alexander.. - 29

Porcupine - 34

PortBurwell

- 1 5

Port Colborne

- 15

Port Credit

- 18

Port Dover - 15

Port Elgin

- 17

Port Hope - 21

Port Perry -22

Port Stanley - 15

Prescott

- 23

Princeton - 17

Raith - 35

Re d Lake -34

Renfrew

- 27

Ridgeway -15

Rockland

- 26

S t.

Catharines....

- 16

S t.

Marys

-18

S t. Thomas - 16

Sarnia

- 16

Sault Ste. Marie

Schreiber -35

Seaforth - 17

Simcoe

Sioux

L o o k o u t . ..

- 34

Smiths Falls - 25

Smithville

- 16

Smooth Rock

Falls

- 34

Southampton -17

South

Porcupine -34

South River

-27

Stirling

-23

Stratford

- 18

Strathroy - 17

Streetsville

- 1 8

Sturgeon Fal ls. . . -27

Sudbury - 28

Sundridge - 27

Tavistock - 1 8

Thamesford

- 18

Thedford -16

Thunder

Bay -31

Tillsonburg -17

Timagami

-30

Timmins -34

Toronto

- 18

Trenton - 21

Trout Creek

- 27

Trout Lake -38

Uxbridge -22

Vanier

- 25

Vittoria - 15

Walkerton

-18

Wallaceburg - 16

Waterloo

- 19

Watford - 16

Wawa

- 35

Welland - 15

West Lome

- 16

Whitby - 20

288



o

-

:

-;•:

:•:

9::

C-J.:

5-5:

4 4 -

1 2 *

' r :

03C

»

57«

3 9 : :

6 5 " :

6181

4082

4 - - - :

5231

768C

4 4 b :

4 t : - .

386C

416C

362".

4 - - :

3 8 - :

564C

364:

3 7 b :

408C

White River - 3 9

Wiafton -18

Windsor

- 1 6

Wingham

- 1 8

Woodstock - 1 8

Wyoming - 1 6

Quebec

Acton Vale - 2 4

Alma - 30

Amos - 3 4

Ancienne

Lorette

- 2 5

Arvida

- 2 9

Asbestos - 29

Aytmer - 2 5

Bagotville

- 31

Baie Comeau

- 27

Beaconsfield

- 23

Beauport - 2 5

Bedford

- 23

Beioeil

- 24

Brossard

- 24

Buckingham - 2 6

Cacouna

- 25

Campbell's

Bay. . -2 8

Camp

Valcartier..

- 25

Chicoutimi - 30

Coaticook

- 24

Contrecoeur - 24

Cowansville

- 2 4

Dolbeau - 3 1

Dorval - 23

Drummondvi l le. . -25

Farnham

- 2 4

FortChimo - 3 9

Fort Coulonge. . . - 28

Gagnon

- 3 3

Gaspe - 23

Gatineau

- 2 5

Gentilly - 2 5

Gracefield - 2 8

Granby - 2 5

Great Whale

River

- 3 6

Harrington

Harbour - 2 5

Havre

St. Pierre.. -2 7

Hernmingford

- 2 3

Hull - 25

Iberville - 24

Joliette

- 25

Jonquiere

- 29

Kenogami

- 29

Knob Lake - 38

Knowlton - 24

KovikBay

- 3 8

Lachine

- 2 3

Lachute - 25

Lafleche - 2 4

La Malbaie - 2 6

La

Salle

- 23

La Tuque - 2 9

Laval

- 2 4

Lennoxville - 2 8

Lery - 23

LesSaules

- 2 5

Levis - 25

Lorettevilie - 25

Louiseville - 25

Magog

- 2 6

Malartic - 33

Maniwaki - 2 9

Masson - 2 6

6380

4412

3590

4240

4100

3810

4690

5830

6300

5110

5740

48

474

5776

5981

447

485

447

458

452

49

54

485

5120

5510

5010

48

458

595

447

474

459

846

485

749

534

474

485

5 7

458

8133

6110

6110

4580

4740

4630

4880

5720

5730

8229

4630

9550

4470

4850

4520

5340

4470

5350

4580

4850

4520

5010

4900

5120

5010

4730

6110

5319

4850

Matane - 2 4

Megantic

- 2 7

MontJoli - 24

Mont Laurier.... - 29

Montmagny - 25

Montreal

- 2 3

Montreal

N ord. .. . -2 3

Mount Royal - 23

Nitchequon - 3 8

Noranda

- 3 3

Outremont

- 2 3

Perce

- 22

Pierrefonds - 2 3

Pincourt - 2 3

Plessisville

- 2 6

Pointe Claire

- 23

Pointe Gatineau

- 2 5

Port Alfred - 2 9

PortCartier - 2 9

Port Harrison - 3 8

Preville

- 2 4

Quebec -25

Richmond - 2 5

Rimouski - 2 5

Riviere

du Loup. . -25

Roberval

- 3 0

Rock Island - 2 4

Rosemere - 2 4

Rouyn

- 3 3

Ste.

Agathe

des

Moms - 27

Ste.

Anne d e

Bellevue - 23

S t. Canut - 2 5

S t.

Felicien

- 31

Ste.

Foy -2 5

S t. Hubert - 2 4

S t. Hubert d e

Temiscouata... -26

S t.

Hyacinthe

- 2 4

S t. Jean - 24

S t. Jer6me - 2 5

S t.

Jovite

- 27

S t.

Lambert

- 2 3

S t. Laurent - 23

S t.

Nicholas

- 25

Schefferville

- 3 8

Senneterre

- 34

Seven Islands - 30

Shawinigan - 26

Shawville - 2 7

Sherbrooke - 28

Sillery

- 2 5

Sorel - 24

Sutton - 24

Tadoussac - 2 6

Temiskaming

- 3 0

Thetford

M ines. . - 26

Three Rivers

- 25

Thurso - 26

Vald'Or - 33

Valleyfield

- 2 3

Varennes

- 2 4

Vercheres - 2 4

Verdun - 2 3

Victoriaville

- 2 6

VilleD'Anjou

- 2 3

Ville Marie - 3 1

Waterloo - 2 4

Westmount - 2 3

Windsor Mills

. -25

N e w

runswick

Alma

Bathurst

21

23

54

528

5353

534

49

4471

447

447

788

622

447

529

447

452

5120

447

474

572

6

9 7

452

5 8

474

54

5533

574

49

458

622

538

452

49

6

49

454

578

465

463

5 6

529

447

447

485

8229

622

6135

5110

485

5242

49

484

469

538

522

535

5 7

485

6146

452

463

474

447

5 4

447

576

458

447

463

458

5160

Campbellton 26

Chatham 24

Edmundston

- 27

Fredericton - 24

Gagetown - 23

Grand Falls

-27

Moncton

- 22

Oromocto

- 23

Sackville - 2 1

Saint John

- 22

S t.

Stephen

- 22

Shippigan

- 22

Woodstock - 26

Nova Scotia

Amherst

- 2 1

Antigonish

- 2 0

Bridgewater

- 15

Canso - 1 7

Dartmouth - 1 6

Debert

- 2 2

Digby

- 1 5

Greenwood - 1 7

Halifax - 1 6

Kentville - 18

Liverpool

- 1 4

Lockeport - 1 4

Louisburg - 1 5

Lunenburg - 1 5

New Glasgow . . . - 21

Noah Sydney - 1 6

Pictou - 2 1

Port

Hawkesbury. . . -19

Springhill

- 2 0

Stewiacke

- 2 1

Sydney - 1 6

Tatamagouche.. . -21

Truro

- 21

Wolfville

- 1 9

Yarmouth - 1 3

Prince Edward Island

Char lo t t e t own. . . - 20

Souris

- 1 9

Summerside

- 2 0

Tignish

- 2 0

Newfoundland

Argentia

- 1 3

Bonavista

- 17

Buchans -21

Cape Harrison.... -2 9

Cape Race - 1 4

Cornerbrook

- 1 9

Gander

- 1 8

Goose Bay -3 1

Grand Bank - 14

Grand Falls

- 21

Labrador City - 35

Port aux

Basques

- 1 5

S t.

Anthony

- 2 4

S t.

John's

- 1 4

Stephenville - 17

Twin Falls

- 3 5

Wabana

- 1 5

WabushLake

- 3 5

Yukon Territory

Dawson - 5 0

Whitehorse - 41

Northwest Territories

FrobisherBay - 4 0

Yellowknife -43

5100

4884

534

4699

449

525

47 9

474

459

4771

458

5180

477

458

458

4190

4410

42

458

385

4130

4123

424

4010

398

4410

4190

458

4410

458

447

458

452

4459

458

47 4

43

4 24

4623

458

46

485

46

5010

553

688

5010

49

5 39

6522

456

5100

777

48

594

48 4

4783

782

485

777

8274

6879

9845

8593

289



61 cm x 122 cm window

rx

3 m

1000 W baseboard

heater

4.6 m-

ceiling height 2.4

m

N O T E :

Place thermostat

o n \

inside wal l approximately - s i y ^

1.5 m

above floor.

Cl)

-I *•

FIGURE 18.24 Heating a room electrically

The Fourth Step:

Infiltration Loss. Cold

air enters rooms through cracks around

doo rs and windows. Heat loss throu gh

such infiltration

is

calculated by th e air

change m etho d. Air in

a

room

or a

building changes constantly, entering

or

exiting throug h doo rs, windows, cracks,

etc.

The amount

of

the air change

is

influenced by the size of room, h eight of

ceiling, and ventilating devices, such as

fans.

Table 18.7 lists var ious room

conditions and the expected air change

over a period of one hour.

If, for example, the room shown in

Figure 18.24 is in a new house and h as no

doorway that is exposed

to

outside tem

peratures, then, according to Table 18.7,

0.75 air cha nge s per hour can be

expected.

Table 18.8 on pag e 293 lists th e hea t

loss factors (watts per square metre) for

various air changes and temp erature

differences. Under the 0.75 Air Change

heading, with a 2.4 m ceiling height i

a design temperature difference of 4V

the loss is 25 W/m

2

of floor sp ac e. The

floor area

of

th e room is 4.6 m

x

3 m,

which

is

13.8

m

2

.

The infiltration loss

a

13.8 m

2

x 25 W /m

2

, which is 345 W.

This heat loss

is

added

to

t he wai]

and window losses.

The Fifth Step:

Heat Loss Through d

Ceiling.

According

to

Tab le 18.3 on

page 270, an exposed roof or ceiling <

frame constru ction mu st have a the

resistance of 5.6

RSI

if it is in an area

ot

the cou ntry unde r 5000 degree days.

The

U

factor

for

the ceiling is 1/5.6 or

approximately 0.178 W /m

2

per degree

Celsius

of

tem pera ture difference. If tfcj

tem pe rat ure difference is 41°C, the

ha

loss is 41 x 0.178 W /m

2

, which is

7.30 W /m

2

for each hour of op eration.

290

Applications

of




TABLE 18.6 Heat Loss Factors for W indo ws and Doors

Heat load Factor per Degre e o f Tem peratu re D i f ference

W i n d o w s a n d D o o r s

Single glass—metal frame

Single glass—metal frame with storm

Double glass—metal frame (6 mm air space)

Double glass—metal frame (13 m m air space)

Triple

glass—metal

frame

(13

mm air space) + storm

Single glass—wood frame

Single glass—wood frame with storm

Double glass—wood frame (6 mm air space)

Double glass—wood frame (13 mm air space)

Triple glass—wood frame (13 mm air space) + storm

Skylight—metal frame—single glass

Skylight—metal frame—double glass (6 mm air space)

Skylight—wood frame—single glass

Skylight—wood frame—double glass (6 mm air space)

Doors

Patio

Doors—single glass—metal

frame

Patio Doors—double glass—wood frame

Solid wood—40 m m

Solid wood—40 mm (wood storm)

Solid wood—40 mm (metal storm)

Metal (Flat)

Metal (Corrugated)

Rt

0.16

0.32

0.23

0.25

0.41

0.17

0.35

0.28

0.30

0.52

0.14

0.21

0.16

0.27

0.16

0.20

0.36

0.65

0.53

0.16

0.13

W/m

2o

C

6.25

3.18

4.43

3.97

2.44

5.79

2.90

3.52

3.29

1.93

6.93

4.77

6.25

3.75

6.42

4.94

2.78

1.53

1.87

6.42

7.95

" : -neans

resistance total in RSI values.

The ceiling area of th e room shown

in Figure 18.24 is 13.8 m

2

. This is th e area

through which heat can p ass . The tota l

heat loss for the room over a pe riod of

one hour is 13.8 m

2

x 7.30 W/m

2

, which is

approximately 100.7 W.

The Sixth Step : Total

H eat Loss for the

Room. To calculate the total heat loss

for the roo m over a pe riod of on e hour,

the loss through eac h of the four a reas

must be added.

For example:

Heat Loss

Through the wall

Through the window

Infiltration

loss

Through the ceiling

Total

144.2 W

86.0 W

345.0

W

100.7 W

675.9 W

Determining Heater Size

Winter weather can be unpredictable

and h ave little in com mo n with carefully

recorded norm s. Care should be taken to

match the actual heater size (wattage)

with the calculated heat loss for the

room or area .

The sam ple room sh own in Figure

18.24 ha s a calc ulated hea t loss of

675.9 W. Table 18.9 lists low- and stan d

ard-watt density baseboard heater units

The closest heater unit in the standard-

watt density column to our calculated

heat loss is the 750

W

one. Our cho sen

hea ter unit has approximately

75 W

of

extr a heating ability: it can therefo re

provid e a margin of com fort if there is a

winter season that is colder than nor

mal. Care must be taken not to oversize


29



TABLE 18.7 A i r C hanges per H our f or Var ious R oom s a

Infiltration Factors

New Houses (Weatherstripped, storm doors and win dow s)

R o o m s w i t h o u t e x p o s e d d o o r s

R ooms w i t h ex pos ed door /s (E nt ranc e area)

B a s e m e n t s

W al ls les s t han 50% abov e grade

W al ls more t han 50% abov e grade or f u l l y ex pos ed

nd Condi t ions

Air Change Method

0.75 air

changes/hour

1.0 air

changes/hour

0.5 air

changes/hour

0.75 ai r changes/hour

Existing Houses (Not weatherstripped, but wi th storm doors and window s)

R o o m s w i t h o u t e x p o s e d d o o r s

R ooms w i t h ex pos ed door /s (E nt ranc e area)

B a s e m e n t s

W al ls les s t han 50% abov e grade

W al ls more t han 50% abov e grade or f u l l y ex pos ed

1.0 a ir

changes/hour

]

1.5

air changes/hour

j

0.75 ai r

changes/hour

]

1.0 a ir change s/hour

Coefficients

for

Infiltration per Square Me tre per Degree Celsius

Tempe rature Difference (2.4 m ceiling height

New Houses

A r e a s o t h e r th a n b a s e m e n t s

B a s e m e n t s

Ex is t ing /C onvers ion H ouses

A r e a s o t h e r t h a n b a s e m e n t s

B a s e m e n t s

No Exposed

Doors

(W/m

2o

C)

0.61

0.41

0.79

0.62

Wi th Exposed Doors

Entrance Area

(W/m

2o

C)

0.82

0.61

1.23

0.79

the heater units too much, though: extra

load will be placed on th e service e quip

ment if and w hen a sudd en d rop in tem

perature causes many of the heaters in

the bu ilding to come on at the sam e

time.

As a general rule, the selected

hea ter unit shou ld be within

10%

of the

calculated h eat loss for the room or a rea.

Ceiling cable or radian t-hea ting foil

of the sam e wattage rating could be

installed in the room as an alternate

heating source.

Heater Location

Heater units should always be located as

close as possible to the m ajor h eat loss

area of a room . Window areas a re usually

respo nsible for the greatest h eat

loss,

and so basebo ard he aters are

nor mal

located under them. Warm air rising a

of a he ate r te nd s to offset the cooling

effect of cold air entering th e room

th e w indow. (See Figs. 18.25 and 18.2

Thermostats and LocatioW

Thermostats are heat-sensitive switcha

designed to regulate the on/off cycles i

hea ter un its. They do not co ntrol the

amo unt of heat (wattage) p ut out by

I

hea ter unit. They m erely turn the h«

on

o r

off.

The length of tim e that the

heater rem ains on determines the tem

peratu re in the room . The therm ostat

cycles the hea ter unit to keep the roofl

292

Applications

of




TABLE 18.8 H eat L os s Fac t ors per Square Me t re F loor A rea and A i r C hange Values

(Inf i l t rat ion)

V alues for V arious Temperature

Differences

0. 5 A i r Change

0.75

A i r Change

1.0

Air C h a n g e

1.5

A i r C hange

Ceiling

Height

(m)

2.4

2.7

3.0

2.4

2.7

3.0

2.4

2.7

3.0

2.4

2.7

3.0

Heat Loss Factors P er Square M etre

(W/m

2

)

1°C

0.41

0.47

0.50

0.62

0.70

0.78

0.81

0. 93

1.0

1.2

1.4

1.5

38°C

15

18

19

24

27

29

31

35

39

46

52

58

41 °C

17

19

21

25

29

32

33

38

42

50

56

63

44°C

18

20

22

27

31

34

36

41

45

54

61

67

47°C

19

22

24

29

33

36

38

44

48

57

65

72

50°C

20

23

25

31

35

39

41

4 7

51

61

69

77

53°C

22

25

27

33

37

41

43

4 9

54

65

73

81

56°C

23

26

28

35

39

43

46

52

58

68

77

86

TABLE 18.9 L ow - and S t andard- W at t D ens i t y H eat er

Specifications

Specifications: Single P hase: Low -W att Density

Volts

(specify)

120 208 240

120 208 240

120 208 240

120 208 240

208 240

Watts

500

750

1000

1250

1500

Approximate

Length

(cm)

96

127

188

250

250

Approximate

Shipping Mass

(kg)

6

7

10

13

13

Specifications: Single Phase: Stan dard- Wa tt Density

120 208 240

120

2 0 8 2 4 0

120 208 240

120 208 240

120 208 240

2 0 8 2 4 0

208 2 4 0

208 240

500

750

1000

1250

1500

1 7 5 0

2 0 0 0

2250

66

96

127

188

188

250

250

250

4

6

7

10

10

13

13

13


293



FIGURE 18.25

installation

A residential baseboard

.e

i

c

O

&

O

FIGURE 18.26

installation

A baseboard heater corridor

at the tempera ture selected on th e

thermostat .

For many yea rs, conventional ther

mostats had basic mercury bulbs for

their sw itch co nta cts. The advent of cen

tral air conditioners meant that thermo

stats had to becom e more sophisti

cated—they had to be ab le to con trol

both heating and cooling cycles. Now

there are therm ostats that can sense

tem peratures accurately through elec

tronic circuitry.

An

electronic

thermostat smoo thes

out th e cycling proce ss of the hea ter

unit, providing a more con sistent

and

even temperature throughout the

rooa

As a result, th e

home-owner

can

oftea

choo se a lower therm ostat setting,

resulting in lower heating c os ts over a

perio d of time.

The rmo stats, as mentioned

earlieq

are highly tem per atur e sensitive and

should not be mounted on cold,

oi

walls. They should be located on

in

walls,

away from any draft or heat

source that might cause them to

op

and close the h eater circuit in an

i

mal

manner. They can be obtained

ii

both line and low voltage configura

to m atch th e type of heating system

use d. Figure 18.27 sho w s s evera l

of thermostat controls.

Tem perature regulation can be

I

died

differently in foyers and

entra

halls,

which are often s ubjec t to cold

blasts of air from door openings. If a

forced air unit

is installed in the wall

i

th e entra nc e, the effect of cold blasts

can b e counte racted . Cold air enter

the area will activate the

thermostat <

th e heater. The fan th en forces enc

warm air through the heater to

retur

the are a to inside design

temperati

Such a com pac t un it can also sc

times be used to adv antag e in

bath

rooms with limited wall space at

floo

level.

A forced air unit cons ists of a i

enclosure or tub with a detachable I

and heater unit. A grille placed over I

unit directs the air flow and protects I

heater coils. (See Figs 18.28 and 18.2

Heating Cost

Once the heat loss (heating load) has

been calculated for each area, the i

heat load

figure can be worked out.'

total hea t load is th e sum of the heat

losses calculated for each area. An

294




Low

voltage

thermostat

Line voltage thermostat

fan and heater unit

(fits

into

tub)

grillwork

(directs heated air

and protects heater element)

FIG URE 18.28 Forced air heater uni t

exam ple for calculating heatin g cos ts fol-

1 lows. It is based on estimated heat

| lo sse s (in roun d figures) for a five-room

I bunga low in Toro nto or a similar area.

Heating and co oling therm ostat

F I G U R E 1 8 .2 7 C o m m o n l y u s e d

t h e r m o s t a t s

c

o

I

1

8

Heated Area

Bedroom

#1:

Bedroom #2:

Kitchen:

Living and dining room :

Bathroom:

Basement:

Heat Loss

1000

w

1000 w

1000

w

2500 W

500 W

3000 W

9000 W

or9kW


295



FIGURE 18.29 Forced air heater unit applications (near cold air entry and where wall

limited)

296




Total heat load:

Annual kilowatt hour consumption •

HL x DD x C

DTD

Where:

HL

=

hea t loss in kilowatts

DD = annual deg ree days for the area

(See Table 18.5)

C

=

a consta nt (15.3 for the T oron to

area; consult local utility)

DTD = design tem pera ture difference

between indoors and ou tdoo rs

Therefore, kilowatt hour consumption is

9 x 4082 x 15.3

40

= 14 052kWh

Typical utility cha rges ar e as follows:

First 500 kW p er m onth

@ 7.9«/kW-h

Remaining kilowatt h ou rs

@

5.5<t/kW

h (end rate)

Electrical heating customers

approach the end rate with lighting and

cooking energy. The annu al heating cost,

therefore, is calculated by m ultiplying

the kilowatt hou r consum ption by t he

end rate.

Total annua l co st:

14052 kWhx5.5«/kW h = $772.86

Overheating Protection

Baseboard heaters are equipped with a

slender, liquid-filled or vapour-filled cop

per tube that trave ls the length of th e

heater. If for som e reaso n th e he ate r

reaches an abnormally high temp era

ture, the expa nding liquid or vap ou r will

cause a relay at one end of the tub e to

open th e circuit. This preven ts heat

damag e to the walls of the h om e. (See

Fig. 18.30)

Snow Melt ing Heaters

One type of radiant-h eating c able is

designed for use in drivewa ys to keep

th e wheel track areas clear of snow. It is

installed under the concrete pavement

and com es in

pre-assembled

lengths

from th e manufacturer. It is also used to

melt snow on ram ps and stairways . (See

Figs.

18.31 and 18.32)

Snow that has melted, run into

eaves, and refrozen also causes prob

lems. Eavestrough he aters are used to

keep th is pa rt of the roof clear. (See

Fig. 18.33)

Pipes can be kept from freezing by

wrapping them with pipe-heating cable.

A the rm os tat that fits along the side of

the pipe controls the heating p roce ss.

(See Fig. 18.34)


29



heat-radiat ing f ins

copper vapour t u n *

thermostat

heater element

FIGURE 18.30 S ection of

a

baseboard heater electrical con nection

FIGURE 18.31 Driveway sno w-m elting cable

298




conduit

heat mat

4 cm

1

asphalt or concrete

.•or.

'• .*.

0

.d.

•- . ^ . . ' 0 - . o '••

• . a •

a

• • . .c

•

•„ . . . .0

o

.

O:

O

o:

« O

. » • • •

C i .

•

o-. 0

<£?•.

• • . * " • • . * ? • • • ?

• ' • b - : .

9ravel base

0

. ; 0 - . ^ • ? • ' .*. ' ; 0 '• \ <b •. .«>.

N O T E :

For asphalt installations, place bituminous binder on base course both

under mat and over mat before placing final course.

FIGURE 18.32 A driveway installation of snow -me lting cable

FIGURE 18.33 A n eavestrough heating cable installation


29



FIGURE 18.34

thermostat

P ipe-heating cable wi th

F o r R e v

i

e w

1. List six advantages that electric

heating has over othe r heating

systems.

2. What is the main purpose of insu

lation?

3.

What are the minimum insulation

requirements for an electrically

heated house?

4. Explain what is meant by an insu

lation's RSI designation.

5. List the four types of insulation

tha t are su itable for electrically

heated houses.

6. What is a vapou r retard ing bar

rier? Explain its pu rpo se and

idea

tify w here it is installed .

7. Why is it imp ortan t to ventilate

m

attic?

8. Describe the general constructing

of a baseboard heater.

9. Why are baseboa rd heate rs made

in two wattage densities?

10. List three factors that must be

taken into account when installu^

baseboard heaters.

11. Describe briefly two typ es of

rati

ant heating systems.

12.

List three precautions that must

be taken w hen installing a

radiad

heating sy stem in the ceiling.

13. List four major residential heat I

loss areas.

14.

What tw o types of window

uni t s

should be used for an electrical^

heated home? Which type woukl

be the best?

15. Why are heaters usually placed

under windows?

16.

What is the a dva ntage of

pla

forced air heater unit in an

entrance hall or foyer?

17.

Why are base board heate rs

equipped with cutout relays?

18. What precaution should be t

when insulating basement w;

a hom e that is likely to hav e

entering in the basement?

19. Name one m ajor adv antag e of

using a forced air electric fur

to heat a house instead of

bas

board heaters.

20. Why must ou tside design tern;

ture be taken into consideratl

when calculating a heat loss?

\




F

luores cent lighting was first devel

oped during the 1930s. Its principle

is simple enough, b ut it took ye ars of

research before it was deve loped into

the highly developed tub e found in mod

ern lighting fixtures.

Advantages of

Fluorescent Lighting

Fluorescent lights have m any advan

tages over standard incandescent lamps.

Fluorescent lamps last approxi

mately

twenty times

as long as stan dard

incandesc ent lamps. The higher initial

cost of the fluorescent tube is more than

offset by it s long life.

As a result,

maintenance costs

are

much lower, bec aus e fluorescent lamps

do not need to be replaced as often as

standard incandescent lamps. Modern

40

W

fluorescent tu bes hav e an average

life exp ecta ncy of 20 000 h. The avera ge

incandesc ent bulb has a life exp ectancy

of 1000 h.

Fluorescent tubes p roduce more

than

five times

as m uch light per watt of

electricity consumed than the incandes

cent bulb . A 120 cm, 40

W

fluorescent

tube p rodu ces nearly as m uch light as a

150 W

incande scent bulb. The fluores-

Discharge

Light

Sources

cent tu be also keeps its brightoess for a

longer period of time.

Fluorescent tub es produ ce less hea

than incandescent bulbs of the same

size (wattage outp ut). Large incandes

cent bulbs will burn anyone trying to

remove them while they are still in oper

ation. In co ntra st, m ost fluorescent

tubes can be handled safely, regardless

of how long they have be en in o peration

Also, wh en a building is air cond itioned

fluorescent tubes provide adequate ligh

without placing as large a heat load on

the air conditioner as do incandescent

bulbs of the same light output.

Note: Tube life is greatly influenced

by the number of times the fixture is

turned on and off. The current that

surges throu gh th e lamp circuit when

the fixture is turned on tend s to

sho rten th e life of the lam p.

A

lamp

tha t is turn ed on and off frequently

will need to be replaced far sooner

than a lamp that is allowed to ope rate

for a num ber of hours betw een sta rts

As a result, lights in many indu strial

plants are left burning during lunch

ho urs , coffee break s, and shift

cha nge s. As the cost of electrical

energy continues to increase, a more

realistic compromise has been

Discharge Light Sources

3



reache d b etween tu be life and energy

cos ts. It is now considered more eco

nomical to turn th e lamps off when th e

off period is expected to be more than

20 min in duration.

Disadvantages of

Fluorescent Lighting

In some places, such as clothing, fabric,

and meat stores,

colour

is critical and

the de sign of the lighting system impor

tan t. Fluorescen t lights give off an abun

dan ce of blue and green ton es, but are

low in red s and yellows. The ir us e in, for

example, a clothing or m eat sto re, would

preven t a custom er from seeing the true

colour of the product. Walking outside to

natural light is not always practical, and

so in these cases both incandescent and

fluorescent lights are used to help bring

out true colours. However, fluorescent

tub es for "colour critical" areas have

now been developed.

Using discharge lamps over rotating

machinery can sometimes be danger

ous . The 60

Hz AC

supply system of fluo

rescent fixtures makes the light flicker at

a very high speed. This flickering is

almost invisible to the naked eye, except

whe n t he light falls directly on ro tating

m achine ry. If th e m achin e is rotating at a

speed close to the speed at which the

light is flickering, th e m ach ine will

app ear to b e standing still. This strobo-

scopic effect deceives the human eye.

The re have been cases where an opera

tor has absent-mindedly reached in to

touch a rotating part, thinking that the

mach ine has com e to a standstill.

Fortunately, this problem can be

remedied by installing a small incandes

cent lamp over the moving part or

assembly. This filament type of lamp will

cancel out any strobe effect produced by

the fluorescent tube fixture.

Fluorescent Tube Parts

T he he art of th e fluorescent fixture

t

the tube

itself.

The tub e ha s several

components . (See Fig. 19.1)

Glass Tube. The tub e provides an

airtight enclosure in which the

mer

gas, and pho sph or can function.

Base. As the end of the tube , the

bai

con nec ts the lamp to the electrical

circuit. Several pin configurations are

available.

Ca thod e. Th ese small, oxide-coated

filaments heat up and emit electrons

•

to the tube.

Mercury. Drop lets of m ercu ry are

placed in the tub e. They vapourize

during the o peration of the lamp and

emit (give off) ultrav iolet energy.

Filling Gas.

A

small am oun t of high

purified argo n gas is also placed in tbi

tube. This gas ionizes (producing

electrical conductivity in gases) wha

sufficient voltage is applied. Current i

then flow readily through the tube.

Ph osp ho r Co ating . All of th e light

energy produ ced by the m ercury is

ultraviolet and invisible to the naked

eye. The pho sph or coating reacts to I

ultraviolet rays and turns this energy

into visible light.

The Starter

Some fluorescent fixtures (preheat

i

need a small starting mechanism to

establish an electron emission from

I

cathode (filament). (See Fig. 19.2)

Current enters the starter through

one of the contact pins. T he neon gas a

302




triple coil

£ &

? J ^ coiled coil

Types of cathode

cathode

exhaust tube

phosphor coating

lead-in wires

stem press

high output and

1500 mA

recessed

double-contact

base

T-12

med.

bi-pin

T-12 single pin

T-17

mogu l bi-pin

T -5 min. bi-pin

Types of base

FIGURE 19.1 Fluorescent tube and com pone nts

8

v


303



electrolytic capacitor

glass tube

aluminum can

contacts

bimetal strip

neon gas

insulating

sleeve

fibre base

contact

pin

F I G U R E

19.2

F l u o r e s c e n t s t a r t e r

the glass bottle provides a high-resist

ance path from one conta ct

to

the other

for a small amo unt of curre nt. T his

cause s the gas to glow. Heat from the

glowing gas warms the bimetal strip,

which then bends and closes the

contacts.

This action cre ates

a

low-resist

ance path through the

starter.

Once the

contac ts have closed, the gas ceases

to

glow, th e bim etal strip co ols, and the

con tacts open . All this takes abo ut tw o

or three seco nds.

The capacitor in the st art er contro ls

the amount of arcing between th e con

tacts when they open and close. It thus

prolongs the life

of

the starter.

The Ballast

Mercury droplets in the tube vapourize

during th e oper ation of the lamp. Cur

rent then flows through the tub e m ore

and m ore easily. This ionization process

could allow the current flow to incr

to the p oint were the tub e would d«

itself. The ballast controls and regulal

this cu rren t flow in much th e same

*w\

that ballast

in a

ship con trols the staU

ity

of

the ves sel. It is

a

coil

of

wire wc

on a laminated steel core.

Operation

of

the Fixture

When a fluorescent lamp is switche

current flows through the ballast,

ments, and starter. (See Fig. 19.3) Th

high-resistance neon gas in th e starta

glows (heats up) and bends the bimtM

contacts until they touc h. This closh^B

the c ontacts provides

a

low-resista

path, and the filaments heat up quickl

as

a

result

of

the extra current flow.

Heating

of

the filaments ca use s elec

to be emitted in to the tu be. The neon

gas in the sta rter stop s glowing, and

bimetal contacts cool and open the I

resistance path.

Th e increa se in cu rren t flow throi

automatic starter

w

ballast

1

f

FIGURE 19.3

A

circuit

for

the operation

lamp

304




the filaments also caus es a stron g

mag

netic field around the ballast. When the

bimetal contacts open, the high-resist

ance path is re-established. This ca uses

the strong magnetic field a rou nd the bal

last coils to co llapse. As the mag netic

field collapses, it induces a high-voltage

kick

in to the ballast coils. This voltage

is high enough t o strike an arc acr oss

the tube, using the emitted electrons,

argon gas, and m ercury vapo ur as a cur

rent path.

Once an arc is established acro ss the

tube, m ost of the circuit current flows

through the tub e. Not enough curre nt

flows to the starter to re-establish a

starting cycle in the neo n gas.

As men tioned before, curren t flow in

the tube tend s to increase. When t he

current flow increases, a stronger mag

netic field is estab lished aroun d th e bal

last. This magn etic field pro du ces

(induces) a voltage in the ballast, which

flows in th e opposite direction to the

applied voltage from t he so urc e. The

more the current tries to increase in the

tube,

the more the ballast tries to hold

back the applied voltage and current.

The current flow in the fixture quickly

stabilizes

itself.

When the ultraviolet light energy from

the mercury vapour strikes the phosphor

coating

on th e inside of the tu be , a cool,

comfortable, visible light is pro duc ed.

As the tu be n ears the end of its life

expectancy, an

oxide coating

from the

filaments gradually ap pe ars on th e en ds

of the tub e. Such a dark ened area indi

cates that the tu be is abou t ready to be

replaced.

A

tube th at is flickering bu t not star t

ing should be replaced before the star ter

and/o r ballast are damaged by the con

tinuous starting currents.

Rapid-Start Fixtures

This fluorescent fixture does

not

need a

sep arate starting device. Approximately

4 V is continu ously supplied to th e fila

me nts of the tub e by special heater

windings in the ballast while th e tub e is

in operation. The constantly heated fila

me nts emit a steady stream of electrons

thereby allowing the ballast voltage to

easily strike an arc acro ss th e tub e.

Rapid-start fixtures, which w ere

developed after the pre-heat and instan

start types, take advantage of the volt

age that exists between the cathodes

and the metal frame of the fixture. For

this reason,

all

rapid -start fixtures

mus

be grounded. Otherwise, in cool wea the

the y will often fail to st ar t.

As a result of th e con tinuo us heating

of th e ca tho de s (filaments), a lower open

circuit voltage can be used and t he ph ysi

cal size and weight of th e ballast red uce d

Figure 19.4 shows a single-tube, rapi

star t circuit. The se po pular fixtures are

availab le in two-lamp u nit s. (See Fig. 19.5

The two-lamp fixture st ar ts one tu be

slightly ahead of the other, with the help

of a capacitor in the ballast.

Many industrial plants with a large

number of electrical motors have a poo

power

factor.

They receive large quanti

ties of electrical ene rgy and require larg

conductors and control equipment, but

waste much of the power. (This situatio

is like paying for only two flavours of ic

cream from a 3-flavour brick, because

you w ant only two of the flavours. The

cos t of the wasted third flavour would

then have to be covered by the sup

plier.) The capacitor in fluorescent fix

ture b allasts helps to overcome th is

problem. That is why industries with a

poor power factor often switch to fluo

rescent fixtures. They can then reduce

their electrical bills.

Discharge Light Sou rces

3



da

•JLSAZJLA

heater extension

winding winding

:

iS-B-MJ

primary

line

w i n d i n g

line

winding

heater

FIGURE 19.4 A single-tube, rapid-start cir

cuit. (The rapid-start b allast supplies a sm all

amo unt of voltage co ntinuously to the

cathodes.)

lamp

£

series

start

capacitor

" /

H(

heater

winding

=3

J

lamp

yellow

' leads

— |

TBfwi

pnnrp-

power factor |_l 1

capacitor

blue leads

—*i

- heater

winding

ballast

FIGURE 19.5 A 2 lamp rapid-start circuit

Ballast O verheating

In the pro cess of limiting tub e cu rren ts

and p roviding starting voltages, th e bal

last tend s to warm up. As a ballast ages,

the laminated steel core of the tran s

former often loo sens, vib rates (produ c

ing a humming sound ), and pen etrates

the insulation on th e windings. At times,

this will sh or t circuit som e of th e wind

ings, cau sing an e xce ss cu rren t flow in

th e remaining windings. As a result of

this breakd ow n in insulation, a damag

ing amount of heat is produced in the

ballast. Today, manufacturers are

eqi

ping ballasts w ith a

therm al protector

(cutout) to open th e ballast circuit

ai

matically when the heat reaches a dan

gerous level.

Ambient temperature ( the temper*-]

ture of the surrounding air) also playsi

im po rtan t role in th e life span of the

I

last. Figure 19.6 shows the life expect

ancy of a ballast und er various t em |

ture con dition s. Figure 19.7 shows a

rapid-start ballast and its constructed

Th e Canadian Electrical cod e

requ ires that all fixtures m ounted on

<

combustible surface be equipped wi

thermally protected ballast. Ballasts aie

rated by the m anufacturer to operate a

tem pera tures up to 90°C.

Instant-Start

Fixtures

The tubes for this fixture are

generalh

th e single-pin type and cannot be

,

110°C

100°C

life vs. temperature

lost

life

lost

•

90°C

0

FIGURE 19.6 L ife versus tempe rature

generally accepted "lost l ife rule" is

every 10°C increase in tem perature,

life is cut in half." |

306




FIGURE 19.7 Rapid-start ballast

Discharge Ught Sources

307



substituted for by any other type of

tub e. At on e time, a bi-pin tub e was

m ade an d is still found in som e lighting

installations.

This fixture does not require

preheating. It is started by creating a

higher ballast output voltage with a

s tep-

up transformer in the larger ballast. The

lamp cathodes must be strong enough to

withstand this sudden and forceful start

ing techniq ue.

Instant-start fixtures start their

lamps

in sequence,

much like that of the

rapid-start unit. (See Fig. 19.8) Because

of this higher starting voltage, many of

the tub e sockets are built so that th ey

open the ballast circuit when a tube is

removed from the fixture.

Instant-start lamps are ma de in

lengths ranging from 60 cm (2 ft.) to

240 cm (8 ft.).

I

\

E

r C "

Lb ™

primary

winding

lamp

2

U*a

econdary—.8>

winding N^

auxiliary win ding ra_/

lamp 1

FIGURE 19.8 A 2 lamp rapid-start circuit.

Series operation reduces size, weight, watt

age loss, and cost.

Metric Lamps

A

m etric lam p in a 166 cm length

operates satisfactorily with the F40

(40 W lamp) ba llasts ava ilable. Light out

pu t and lam p life are the sam e as for a

40 W

lam p. This lamp can fit into a previ-

308

ously

dim ension ed 48 in. fixture

becaad

of a small ad ap ter at one end of the

lai^

which m akes up the difference in lengn

Fixtures specifically produced for use

with such lamps are referred to as

1200 m m units.

L ow W attage Biaxial

Fluorescent Lights

In recent ye ars, a newly designed, mini

ture,

twin-tube-and-globe typ e of fluosB

cent lamp has been increasingly in

deman d. These new lamps have

inca*-

descent-like

colour and m ay be used

•

areas previously illuminated by incan- I

des cen t lam ps. With an estimate d usdU

life span of 10 000 h, they last from

fow

to thirteen times longer than normal

incandescent lamps.

Biaxial fluorescent lamps are pro

duce d in a num ber of sizes, for

exampii

7

W,

9

W,

and 13

W.

While the ra ted Ian

wa ttage is low, rem em ber tha t fluores

cent lamps put out approximately four

times as much light per watt as a

normt

incand escent lamp of the same size.

N ^

only do th es e lam ps co m bine high effi

ciency, long life, and warm, incandes

cent-like colour, they also save energy:

Figure 19.9 sho ws t he se new lamps,

which are produced with a bi-pin pi

conn ect ion . (See Fig. 19.10)

A specially designed screw-in

adapter allows the 7 W and 9 W biaxial |

lamps to be installed in almost any

incan desce nt sock et having a medium-

sized lamp ba se. The adapt er contain*

small ballast an d can be fitted with a

retaining collar and scre ws . It can thu s

be used in areas subjected to

vibratk»

and should be able to prevent a lamp

from falling out of its mount when

installed in a base up configuration. Fig

ure 19.11 shows this mounting kit. To

accom mo date th e various s hape s of




FIGURE 19.9 Biaxial fluores cen t lamps in

7 W , 9 Wand 13 Wsizes

FIGURE 19.10 A bi-pin mo unting cap for

a

low wattage biaxial fluorescent lamp

lighting fixtures, a more co m pac t ver

sion of the 13 W lamp is now being pro

duced. Figure 19.12 shows the standard

size and co mpac t 13 W biaxial lamp

units.

An equally new and clever lamp

design further simplifies the replace

ment of incandescent lamps with low

wattage fluorescent units. These energy-

efficient, long-life (9000 h), one-piece

lamp-and-ballast

combination lamps

screw in to most incande scent sockets

without further adjustment to the socke

or the circuit wiring. (See

Fig.

19.13)

They use

15

W, and if installed in place o

a 60 W lamp of the sam e light outpu t, a

savings of $24.30 will be made over the

lamp 's life when calculating energy co sts

at 6<t/kWh. The warm colour of th ese

FIGURE 19.11 Biaxial lamp and screwbase

adapter with built-in ballast for use in medium

.-• '•' base lainpholders

FIGURE 19.12 A standard 13 W double biaxial lamp com pared w ith an ultra com pact 13 W

amp of the sam e type . A screw-in adapter base allows either lamp to be used in an incandescen

socket.

Discharge Light Sources 30



FIGURE 19.13 A combination lamp and

ballast, globe typ e, for use in a m edium-base

lampholder

lamps will blend well with oth er incan

descent lamps that may be installed

nearby. Figure 19.14 shows typical use

these units.

The lamps do have som e limitation

though . Some manufacturers recom

mend that they not be used with dimna

switches, be allowed to come in

contad

with m oisture, or be used outdoors or I

enclosed fixtures where temperature

changes may be too extreme for safe

proper lamp use.

Power Groove Lamps

| During the late 1950s, a fluorescent rd

3 that used indentations, or grooves, on

f one side of the glass tube to increase

§

light output was developed. Later

g research showed that grooving both

| sides of the tube produced an even

I higher light output. (See Figs. 19.15 ani

8

19.16)

The grooves in the tube bring the

phosphor-coated glass closer to the

stream . This squeezing of the arc read

in more v isible light energy. In the pooa

groove tube, the arc stream must

folk*

a

wavy

path as it travels th e length

of

th e tube. (If the arc is straightened

ou

the re is approximately

2.7

m of arc

tained in the 2.4 m tube. This increase

and concentration of the arc length

allows the tub e to produce more light

than a conventional fluorescent tube.

g

The name

power

groove was

give*

this tube by one manufacturer. Power

groove lamps are useful light sources

I industrial applications. (See Fig. 19.11

3

C3

FIGURE 19 .14 T ypical application of a globe

type fluorescent lamp

| High-Intensity Discharge

E

Lamps

The term high-intensity discharge (HIL

describes a wide variety of lam ps. Be

310




I P O W E R G R O O V E

1 '

A

m***^^

• r

o

FIGURE 19.15 P ower groove fluorescent tubes and sockets


311



FIGURE 19.16 A power groove fluorescent

fixture for industrial applications

FIGURE 19.17 P ower groove lighting

installation

HID lamp s are alike in one way: they pro

duce light from a gaseous discharge arc

tub e and operate at a pressure above

that found in regular fluorescent lamps.

HID lamps were first introduced in

1934. They can be divided in to thre e

major categories: the mercury vapour

lamp, the m etal halide lamp, and the

high-pressure sodium lamp.

Mercury Vapour Lamps

In a sta nd ard , low-pressure fluorescen

tube,

most of the light energy is in the

ultraviolet range.

Phosphor-coated

tubes m ust be used to produce visibta

light. The higher-pressure mercury

vapour tube produces visible light

directly.

(See F igs. 19.18 and 19.19)

Some mercu ry vapour lamps have

phospho r coating on the inside of the

outer

bulb. This coating reacts to the

i

violet energy p rodu ced by the lamp

j

modifies th e colou r of the light outpi* .

The m ercury vap our lamp is pro

duced in sizes ranging from 50

W

to

1000

W

outp ut. Average life exp ectan t

is m ore tha n 24 000 h, which makes I

an ideal light so urc e w here re-lamp

both costly and time-consuming. The

me rcury vapo ur lamp is used for

strei

and road lighting, area lighting (for

exam ple, parking lots), and industrial

lighting in factories and

warehouses.

It

has several compon ents.

Base. The mogul screw-base found

most mercury vapour lamps connect

the lamp to the ballast and external

circuits. Letters (matching the

mondi

of the yea r) and nu m bers are imprinl^

in th e b ase . They he lp in keeping a

record of lamp life.

Sta rting Resistor. This tiny,

heat-withstanding resistor limits ci

in th e s tartin g circuit to a safe value.

Sta rting Electro des. The arc is

established between the main and

starting electrodes, ionizing the

argoi

gas and helping to strik e th e m ain arc

Main Electro des. Made of a double

layer of tungsten wire and coated w*

rare earth oxides, they ac t as termini

points for the main arc.

312




arc tube

arc tube s upport

base

pinch seal

start ing electrode

FIGURE 19.18 A clear mercu ry vapour lamp (400 W)

outer bulb

ma in elect rodes

<

FIGURE 19.19 A phosphor-coated mercury vapour lamp (1000 W)

o

Arc Tube Support. This polished metal

frame supports the arc tube and

conducts current to the upper main

electrode.

Arc Tube. This pure quartz tube is

called the heart of the mercury lamp. It

contains a precise quantity of mercury

and a small amount of argon gas. Some

manufacturers coat the ends of this tube

(around the electrodes) with platinum.

Doing so ensures that the tube will start

in cold weather.

Pinch

Seal.

It seals the ends of the arc

tube and prevents both the escape of

Discharge Ught Sources

31



argon and th e entry of nitrogen. (Nitro

gen is used between the arc tube and the

outer tube.)

Outer Bulb. Heat- and

wea ther-resistant glass is used to

protect the internal parts and maintain a

nearly constant arc-tube temperature.

Maintaining a high arc-tube temperature

is important if the lamp is to operate

efficiently. T hes e bulbs are som etim es

pho spho r-coated , and they filter

ultraviolet light energy.

How a Mercury Vapour Lamp Produces

Light. The operation of the me rcury

lamp begins with the arc tube. Th ere is a

starting electrode beside the main

electrode

at one end of the tube.

Increased starting voltage from the

ballast (approximately do uble the line

voltage) strikes an a rc between th ese

two electrodes , using the argon gas as a

current path. The argon ionizes (breaks

up) and spreads rapidly throughout the

tube . As the ionized argon reac hes the

main electrode at th e op posite end of

the tube, the light-producing arc is

formed.

The small

starting resistor

(approxi

ma tely 40 k

Q)

limits th e arc curr ent dur

ing start ing . As a d irect re sult of its high

resista nce , curre nt flow quickly shifts to

the lower resistance, main arc stream.

Once the main arc has been established ,

cu rren t flow along its path is approxi

mately 1000 tim es grea ter tha n th e flow

between the starting electrodes.

Heat from th e main arc continue s to

vapourize the mercury in the a rc tub e for

several minutes after starting. As more

and more m ercury is vapourized, cur

rent flow in crea ses. Only the stabilizing,

current-limiting feature of the ballast

(similar to a fluorescent ballast)

preve nts th e lamp from d estroying itself.

Light energy is pro du ced by the

ic

ized argon gas pa rticle s colliding with

the mercury ato m s. As electro ns in the

mercury atom are jarred out of orbit |

replaced by electrons from a nearby

atom, radiation is given off. The coloirt

light (wave length) produced depends

on which ring of the o rbiting electro ns

ha s bee n hit by th e colliding particles*

argon. High pres sures in the arc tube ;

responsible for deeper penetration

in th e fluorescent tub e. This results

ii

more visible and less ultraviolet light

energy.

Horizontal Operation of Mercury'

Lamps.

The se lam ps are slightly i

efficient when operated while in a

vertical

position. Horizontal

operation

reduces the lamp's efficiency slightly

bec aus e th e arc will float u pw ards in 1

arc tube.

Restarting Mercury V apour Lamps.

the pow er supply to a mercu ry

vap

lamp is inte rrup ted, th e arc will

extinguish and not restart for several

m inute s. This is beca us e sufficient

pre ssu re will have built up in the tube

during operation to preven t the arc

]

re-establishing

itself

immediately, i

the tub e has cooled and the pressure

lowered, th e arc will re start

autom atically as usu al. Th ere is not

enough ballast voltage to restart the

lamp until it cools and the pressu re

i

the arc tube decreases.

Lamp life is sho rten ed by

contini

startin g. If a m ercu ry vap ou r lamp is

allowed t o o pe rat e for long period s of

time , its life sp an w ill be m uch long

Mercury Vapour Ballast.

Although

bulbs able to operate without

balla

have been designed, most mercury

vap our lamps need a ballast. The bz

314




does for

HID

lam ps w hat it doe s for fluo

rescent lamps. Line voltage is boosted

slightly, lamp current is stead ied, a nd

the power factor is corrected.

Figures

19.20,19.21,

and 19.22 show

a ballast circuit, a cutaway view of an

outdoo r weatherproof unit, and an

indoor model with the sam e circuitry as

the outdoor unit.

Mercury V apour Applications. For

many years m ercury vapo ur lighting was

used to replace incande scent lighting

system s over roadways. Although m ore

recent lamp developmen ts are now

replacing mercury vapour in these

areas ,

shopping malls, commercial build

ings, and safety and security systems—

plac es wh ere dusk to dawn lighting is

required—still

make use of mercury

vapour lighting.

Figure

19.23

show s the difference in

street light output.

Figures

19.24,19.25,

and 19.26 show

mercury vapour lighting used for area

ballast -

voltage taps

power factor correction

capacitor

O O

live

120 V

neutral

O--

FIGURE 19.20 A me rcury vapour ballast circuit


31



waterproof adhesives

waterproof ro l led seal

smooth drawn case

low temperature

dielectr ic capacitor

stainless steel band

colour-coded neoprene leads

(moulded in waterproof p lug)

removable handle

precis ion wound

coils

welded core

thermal barrier

FIGURE 19.21 A wea therproof me rcury vapour ballast

FIGURE 19.22 A n indoor mercury vapour ballast

316




N O T E :

500 W incandescent luminaires.

Mo unt in g height 7.5 m; poles 24 m s taggered.

N O T E :

400 W L ucalox luminaires.

M ount ing he ight

11

m; poles 15

m

s taggered.

FIGURE 19.23 A difference in light output on a 12.8 m roadway width

FIGURE 19.24 A lighting fixture suitable for use with mercury vapour and other high intensity

discharge light sources

Discharge Lig ht Sources 31



o

0 1

8 FIGURE 19.26 Mercury vapour and

FIGURE 19.25 Me rcury vapour lighting for descent lighting used in com bination f

outdoor decorative use outdo or area lighting

lighting (for example, in parking lots)

and decorative lighting.

Figures 19.27 and 19.28 show a 250 W

lamp used for area lighting around a

swimming pool.

Figures 19.29 and 19.30 show 1000 W

lamps and fixtures used for a large park

ing lot.

Figure 19.31 shows this lamp used as

a decorative, residential, street lighting

unit to brighten the area around a

drive

way.

HID Lamp Sizes and

Shapes

HID lamps are made in many shapes |

sizes.

(See Fig. 19.32)

Metal Halide Lamps

During the early 1960s, experim ents'

other metals produced a lamp with I

ter light radiation characteristics

the m ercury vapour lamp. The prot

FIGURE 19.27 A 250 W me rcury vapour, metal halide, and high-pressure sodium light f

(luminaire)

318

Applications of Electrical

Construction



FIGURE 19.28 A n outdoor area lit by a 250 W lamp unit

FIGURE 19.29 Typical 400 W or 1000 W high intensity discharge fixture for use in roadway

• h t i n g .

This "C obra he ad " unit is equipped with a photo-electric control

unit.


31



FIGURE 19.30 A n outdoor area

lit

by

1000 W mercury vapour lamps

FIGURE 19.31 A decorative street

IN

unit

arbitrary (A) parabolic

aluminized

reflector (PAR)

elliptical (E)

reflector (R)

FIGURE 19.32 HID lamp shapes

bulged-tubular (BT) refle ctor (R)




was to find m etals that could b e easily

vapourized bu t would remain chemically

stable. It was finally solved wh en me tals

in the form of thei r halide salts (usually

iodides) were adde d t o the basic m er

cury arc tube .

Today, lam ps u se iodid es of sodium,

thallium,

and

indium

along with the mer

cury in th e arc tub e. The result is a

metal halide lamp that can prod uce

50%

more light than a mercury lamp, with

greatly improved colour. (See

Figs. 19.33

19.34, and 19.35)

How a Metal Halide Lamp Produces

Light.

The ope ration of this lamp is

similar to that of the m ercury lamp, and

mo st m ercu ry lamp fixtures will readily

accept the halide lamps. A metal halide

ballast

must be used, however, becau se

\\*t\

4i<«r

FIGURE 19.33 A 400 W metal halide lamp

FIGURE 19.34 A 1000 W metal halide lamp


321



quartz arc tub e

white reflective coating

electric discharge

through mercury plus

metallic iodide additives

bimetal switch

FIGURE 19.35 Internal com pone nts of a metal halide lamp

the lamp requires a higher voltage. The

fused quartz arc tube of a metal halide

lam p is slightly sm aller than t ha t of th e

me rcury lamp and h as a special coating

on the ends to m aintain proper elec

trode temp erature during operation. A

small bimetal switch is built in to the

lamp to short out the starting contacts

during operation . It helps to prolong

electrode life.

Metal halide lamps

will

maintain

about

40%

more light throughout their

useful life. This average s ou t to 15 000 h,

rated at 10 h operation pe r s tart.

Me tal Halide Lamp Applications. The

clear, heat-resistant glass bulbs need no

pho sph or coating, provide a better

colour than mercury vapour lamps, and

are used extensively to light sports

stadium s wh ere their colour and light

outpu t is com patible with the

requirem ents of colour TV cam eras .

Made in 175

W

to 1500

W

sizes, the se

lamps are also used for stores and other

comm ercial ap plications. Due to their

higher efficiency, they are gradually

replacing mercury va pour lamps as a

light source.

Figure 19.36 sh ow s a typical fixture.

It is used for ball park lighting and other

area lighting system s with many of the

FIGURE 19.36 A

P-1000

floodlight *

trunnion-type mount. For use with nert

vapour and me tal halide lamps.

HID lam ps. There mu st b e a ballast

th e circuit supplying th is fixture.

Figure 19.37 sho w s a m odern

ii

trial fixture design. The ballast is b

directly over the reflector on this 4

322




FIGURE 19.37 A metal

ballast and reflector unit

door

Figure 19.38 show s a double-lamp

un it. It is useful for indu strial lighting

applications.

High-Pressure Sodium

Lamps

The high-p ressure sodium lam p is quite

different from other HID la m ps . It is

much simpler in design, beca use of the

t remendo us research and development

tha t went in to the prod uction of materi

als used in its construction. (See Fig.

19.39) It is reg ard ed as th e mo st efficient

source of white light artificially pro

duced. The 35 W, 50 W, 70 W, 100 W,

150 W 200 W 250 W 400 W and 1000 W

lamps put out approximately 50% more

light than either mercury vapour or

metal halide lamps of the same wa ttage

rating s. (See Figs. 19.40,19.41, and 19.42)

One reason for th e succe ss of th e

high-pressure sodium lamp is the

FIGURE 19.38

al halide lamp indoor ballast and double reflector unit

Discharge Light Sou rces

323



arc tube support

exhaust tube (with amalgam

re

electric discharge

through sodium vapour coated tungsten electrodes

ceramic end cap

\

ceramic arc tube

FIGURE 19.39 Construction of a high-pressure sodium lamp

50Wto100W

^^ •PB^^

250 W

400

W

1000 W

FIGURE 19.40 High-pressure sodium lamps

324




FIGURE 19.41 Deluxe Lucalox high-pressure sodium lamps

FIGURE 19.42 A n outdoor floodlight appli

cation of a high-pressure sodium lamp

ceramic

m aterial used for the

arc tube.

A

special method for sealing off the tube,

which allows it to contain the high-pres

sure sodium discharges, was also devel

oped.

The ceramic is made of translucent

aluminum oxide and was developed spe

cially for this lamp. One trade name is

Lucalox.

Like many ceram ics, Lucalox can

withstand operating temperatures as

high as 1300°C. Unlike many othe r

ceram ics, it is virtually free of tiny pores

so a high percentage (92%) of visible

light can pass through. Lucalox contains

few if any

im purities,

which makes it

highly resistant t o the corrosive effects

of hot sodium. Q uartz, on the other

hand, deteriora tes rapidly when

exposed to sodium.


325



The ceramic end caps are joined to

the a rc tu be in such a way that the y will

maintain the seal during the expansion

and contraction (heating and cooling)

cycles of the tu be . The oxide-embedded

electrodes and the end caps are also

designed to withstand the corrosive

effects of hot sodium.

Th e tub e is filled w ith a m ixture of

xenon and mercury as well as sodium.

A

special c ircuit consisting of a small elec

tronic board pro duc es a high voltage

pulse (2500 V) for about 1

u.

s during

each half of the alternatin g c urre nt

cycle. This voltage p ulse is stron g

enough to ionize the xenon acros s t he

main electrode gap, making starting

electrodes unnecessary. Once the arc

has been estab lished, th e high voltage

pulsing is discontinued and n ormal bal

last voltage m aintains the a rc.

Th ese lam ps reac h full brilliancy in a

sho rter period of time than me rcury or

metal halide lam ps. Also, they may b e

resta rted without waiting for the tub e

pressure to drop.

Colour changes in the lamp can be

seen as the sodium becomes fully

vapourized. A dim, bluish white light is

given off as the xenon ionizes. This

chan ges quickly to a brighter

mercury-

blue glow as tem pera ture rises in the

tube . A

yellow

shade takes over

from

the

blue, showing that the sodium has

reached low-pressure temperature. As

temp erature and pressu re in the tub e

reach norm al operating levels, the

colour changes to the white light seen

during operation. The arc temperature is

over 2000°C when t he lam p is at norm al

operating tem perature.

Lucalox lamps were m ade at one

time in tw o different m odels for base up

or

base down

o peration. Each could

op erate in a near horizontal position.

The reason for this wa s tha t the ex cess

LUCALOX LAMP CONSTRUCTION

E N D C L A M P

O U T E R B U L B

V A C U U M

L U C A L O X C E R A M I C

A R C T U B E

A R C T U B E

S T R U C T U R E

A M A L G A M

l i C R E l - r i A T E D

1 Q C 0 L

B A S E

FIGURE 19.43 A ne w h igh- pres s ure si

l a m p ,

sui table for use in any burning posh

sodium mixture collected at the cook

point in the a rc tub e. A special reser

was fitted to the arc tub e at th e cook

end of the lamp to collect it. In base

i

lamp s, the reservoir was p laced at the

end farthest from th e ba se. In bas e i

units, the reservo ir was placed near

I

bas e of the lam p.

Mo dern Lucalox lam ps are univer

burning, th at is, they bu rn in any posi

tion, and they have an external

amah

reservoir located a t one end of the arc

tube . This special rese rvoir contains

I

excess sodium amalgam, keeping it;

from th e arc stream, and thereb y

ext«

ing the life spa n of the lam p. The se

lam ps are available in both clear and i

fused coated versio ns to accommc

the v arious light distribution and li

naire requ irem ents. The clear lamps |

vide the best optical control of the I

energy, while th e difuse-coated lamps

provide a smoother, but lower bright

ne ss light in low-m ounted, decora tive

applications. Figure 19.43 illustrates

new lamp.

Deluxe Colour High-Pressure Sodium

Lamps.

The most recent lamps

provide a major improvement in the

app ear anc e of people, foliage, and

326

Applications

ol

Electrical C onstruction



FIGURE 19.48

lighting system

jrehouse

storage area

sourc es as w ell. The trem end ous light

output of this form of lighting makes it

suitab le for roadway lighting installa

tions as seen in Figure 19.49.

Mult i-Vapour Lamps

New high efficiency, multi-vapour lamps

provide use rs with

50%

more light o ver

th e life of the lam p than t he older mer

cury vapou r lam ps. The se lamps will

opera te with

80%

of the m ercury v apour

ballasts now in use, indoo rs or ou tdo ors,

and function in all burnin g pos itions.

The lamps, rated at 400 W, are pr

in clear and phosphored glass units,

clear lamp provides good colour

and|

useful where good light control and

"cut off" are important considera

lighting. The phosphor coated lamp

vides even better colour when a

diffused light source is needed.

These lamps, which operate on =

mixture of metal halides rather than

one,

such as the mercury or sodium

lam ps, are suita ble for use in all wi

cond itions where the tem peratu re is

-18°C or ab ove. The lamps require

between two to four minutes to read

full brilliancy and will res tar t after s i

off in 10 t o 15 min. This ty pe of lamp

recom me nded for use by energy c

scious users of lighting systems

funds are not available for complet

tern

change-over

to ne we r light fo

The lamps h ave an average rated

span of

15

000 h b ased on 10 h o

per start.

As well as being used to m od

the less efficient mercury vapour

system s, multi-vapour lamps are

ble for new system installations,

sal (any position) burning, greatly

increased light output, and lower

i

co st ar e just a few of the re aso ns for

selecting this ty pe of lam p. It is

higH

FIGURE 19.49 Highway 400 lighting syste m w ith Lucalox lamps

328




acceptable for use in floodlighting build

ings,

merchandise displays, and sports-

playing fields.

Standard multi-vapour lamps are

used for new equipment installations,

while Mine (Interchangeable) lamps are

used as replacements for mercury

vapour lamp u nits.

The most recent development in the

multi-vapour lamp family is tha t of a

metal halide lamp containing a unique

blend of ph os ph ors . The lamp prov ides

a warm, rich colour which add s to th e

appeal of the prod ucts and are as it

illuminates. It wa s designed to co mp le

ment other light sources, such as fluo

rescent, incandescent and halogen

lamps, while providing uniform colo ur

on the areas it illuminates.

Metal halide lamps can be installed

in existing socke ts, ope rat e in any posi

tion, and provide the advan tages associ

ated w ith long life. Th ey are p rod uce d in

three sizes—175 W, 250 W, and 400 W.

(See Fig. 19.50)

FIGURE 19.50

lamps

Multi-vapour metal halide

Tungsten-Halogen Lamps

The tungsten-halogen lamp is not a

member of the metallic vapour/arc fam

ily, but it is often co nfused with th e

vapou r/arc lamps.

Like oth er incand escent lamps, the

tungsten-halogen lamp has a

tungsten

filament. It produces light energy by

passing current through this filament,

causing it to glow brightly.

Argon

and a

small amount of halogen gas are com

bined under relatively high pressure

within the quartz filament tube to pro

duc e a brighter, whiter light.

A unique cleaning cycle is responsi

ble for the long life and continued high

outp ut of this

lamp.

As th e tu ng sten fila

ment reaches operating tempe rature,

small particles a re boiled off (em itted)

into the tube . The halogen gas picks up

these particles and returns them to the

filament. This circulating process keeps

the tu be wall clear, preve nts deteriora

tion of th e filament, and ma intains high

outpu t and colour rendition during the

life span of the lamp.

Tungsten-halogen lamps are availa

ble in standard, screw-base sizes and in

a linear arrange m ent of tube and fila

ment. (See Figs. 19.51 and 19.53) The

screw-base lamps can replace standard

incandescent lamps without changing

either the fixture o r th e wiring. Take care

when handling lamps with an exposed

filament tube. Perspiration from the

han ds will ero de the quartz tu be.

A

pair

of cloth gloves will preven t dam age to

the tu be during installation.

Most tungsten-halogen lam ps are

m ade for specific u ses, suc h as for stage ,

stud io, and pho tograp hic lighting wh ere

control of colour and direction are

required. They are also used for decora

tive lighting around buildings. Figure

19.52 shows a floodlight fixture.


329



" ^ ^ V I E nergy S aving

fc— '

.

fn iKPrvatinn

r-nncr-in

FIGURE 19.53

lamps

Single-ended quartz halogen f

In recent yea rs, the use of halogen

light sou rces for merch andise display

and residential area lighting and

highlighting has increased. T his is du e to

som e extent to the developm ent of

smaller, more comp act light sourc es,

such as the

PAR

20 and PAR 30 lam ps .

Lamp Siz in g. P arabolic -shaped lamps

as sho w n in Figures 19.32 and 19.54 are

sized according to the diam eter of th e

lamp 's lens face, in eigh ths of an inch.

The PAR 20 size lamp unit would the n be

20

-=-

or 2.5 in. in d iam eter. T he PAR 30

o

30

lamp would then be

-=-

o r 3.75 in. in

diameter.

Conservation conscious manufacturers

are now producing a range of fluorescent

tubes that provide nearly as much light

output as conventional tubes but reduce

power consu mp tion between 14 and

20%. Use of these lamps can add u p t o

cons iderable savings over th e period of

a year. Th ese new lam ps are ab le to fit

into existing fixtures, providing com

plete interchangeability with existing

tub e sizes and wattage rating s. There is

no loss in averag e lam p life when using

these tub es .

Many comm ercial u se rs of lighting,

wh ere large num bers of units are opera

ting for exten ded per iod s of time, are

updating their systems to the newer,

more efficient forms of lighting such as

the High Intensity Discharge lamps.

Some companies have claimed complete

coverage of their change-over cos ts

within severa l year s. The m ore efficient

the light sourc e, the m ore energy (and

mo ney) ca n b e save d. Figure 19.55

* Lumens per watt

140

120

100

so

60

40

20

n

67-100

17 22

S&63

80-116

83-140

ncandescent Mercu ry Fluorescent

•lamp source efficiency

M u l t -

Vapour

FIGURE 19.54 A quartz halogen flood lamp

FIGURE 19.55 N ewer, more efficient light

sources provide more light at a lower rate of

power consumption and costs.


331



$z:

•

$•:

S:

U 2« 3«

P ow er ra t e per

kW-h

8C

FIGU R E 19. 56 A c ompa r is on o f t he c os t t o i ll uminat e 2000 m

?

t o 540

Ix

for a year by

I

t y pe. (The s y m bol " I x " i s t he s ho r t f orm f or " lu x , " t he m et r ic un i t f or mea s ur ing i llumine

source of l ight per unit area on a surface.)

illustrates the differences in lamp effi

ciency for the vario us t yp es of light

sou rce s available. The co st of lighting

can be comp ared for the various forms

of lighting in Figure 19.56.

Lamp Maintenance

Lamps are rated by the man ufacturers to

give the user an idea of the expec ted

average life from the lamp installed. Flu

ores cen t lamp s, for instance , are rated at

20 000 h average life. If the lamps were to

bur n 20 h a day for 6 d a week, it would

take over three y ears for the lamps to

burn out. In large industrial or commer

cial lighting layouts, the co st of labou r

for lamp replacement often outweighs

the cost of the actual lamp. It is recom

mended by manufacturers that the

lamps be replaced when they have

I

burning for

75%

of their rated life s |

On the average, only

15%

of the

lamps will have actually burned out

i

the 0.75 life span level, and so

repl

ment

c os ts will not be to o high. Or

lamps reach

75%

of their life span .

rJ

remaining lamps

(85%

of them ) can

I

exp ecte d to bu rn o ut in fairly rapid

i

cession. The labour co st from there

in can be quite heavy.

If all the lam ps are replac ed at tl

rat ed 75% life span level and thi

tures cleaned and washed to

increaa

reflection, the amount of light will be

increased considerably and mainte

nance costs kept within reasonable

limits.

332

\ppl\cat\ons of Electrical Construction

http://ppl/cat/ons

http://ppl/cat/ons

http://ppl/cat/ons



F o r R e v i e w

1. List thr ee main adv anta ges that

fluorescent lighting has over

incandescent lighting.

2.

List the disadvantages of fluores

cent lighting.

3.

List and explain th e us e of th e

parts of the fluorescent tube.

4. Explain how a sta rter ope rates in a

preheat lamp.

5. W hat are the two functions of the

ballast? How does it work?

6. Why must rapid-start fixtures be

grounded?

7. What effect does fluorescent light

ing have on pow er factor in indus

trial plants?

8. What are man ufacturers now

doing to prevent damage from bal

last overheating?

9. What change has been made in the

design of tube so cke ts for instant-

start fixtures? Why?

10.

List and explain the use of the

par ts of a me rcury vapo ur lamp .

11. Explain briefly in your own words

how a me rcury vapo ur lamp pro

duces light.

12.

W hat are the disadv antages of

me rcury vapou r lighting?

13. List four areas of use for mercury

vapour lighting.

14. How does a m etal halide lamp

differ from a mercury vapour

lamp?

15. What are the ad vantages of metal

halide lamps?

16. What special material was devel

oped for use with the high-pres

sure sodium lamp?

17. What are the advantages of high-

pressure sodium lamps?

18.

Describe the colour sequ enc e of a

high-pressure sodium lamp during

its warm-up period.

19. To what family of lamps does the

tungsten-halogen lamp belong?

20.

Explain briefly how a tun gste n-

halogen lamp works.

21 . What are the advan tages of the

tungsten-halogen lamp?

22 . What type and size of metric lam p

is available?

23. What two me thod s can be used to

con serve energy when using a

lighting system?

24.

At what point in a fluorescent

lamp's rated life span should it be

replaced ? Explain why.

25.

What type of light sourc e can be

used to replace mercury vapou r

lamps for improved lighting co sts

and energy conservation?


333



E

lectrical motors are used for a wide

variety of residential, commercial,

and industrial ope ration s. Because of

this, guidelines are necessary. This

ch apte r deais with the need for motor

control and some of the more common

control systems.

T he N eed for S pecial

Contro l Equipment

Electrical m otors op erate on magnetism.

The amou nt of current n eeded to crea te

the magnetism depends on the size and

design of the motor.

Nearly all m otors tend to d raw muc h

more current during the starting period

(starting curre nt) than w hen rotating at

operating speed (running current).

Motors are rated in horsepower or

wa tts. The higher th e rating of th e

motor, the higher the starting and run

ning curre nts will be.

Every motor tends to produce a

counter voltage and current within its

winding s. This generator action pro

duces a voltage and current that flows

opposite to the applied current; in fact,

the g enerated current flow he lps to con

trol the flow of incoming curre nt throu gh

the motor. Manufacturers design motors

with this current in mind. Prope r co ntrol

Motor

Control

of incoming cu rren t ex tend s th e life I

of the motor. Excessive input c urrent

will severely damage or burn the moti

windings.

One main factor in determ ining

thi

amoun t of generated v oltage and

ci

in the m otor is its

speed.

If th e load

placed on a motor reduces the speed,

less gene rated curr ent will be develc

and more applied current will flow,

is ,

t he greater the load on th e m otor, I

slower it will rotat e and t he more

applied cu rren t will flow throu gh its

windings. This is why a m otor req uire

more cu rrent du ring the starting per

most electrical mo tors hav e a starting

current that is three to five times' the

normal running current.

As the speed picks up, the gener

voltage within the motor gradually

increa ses. However, the instant the I

ing switch is closed, no generated vol

age exists and the applied current

becom es very high.

If

the motor is

jammed or prevented from rotating ii

any way, a locked rotor condition

is'

ated. The part of the motor that rota

is often called the

rotor.

When the:

fails to tu rn, th e exc essive app lied i

rent is called th e locked rotor

current.

This high current will cause the

mote

burn out quickly.

334




Motor Control Switches

There are two basic meth od s for starting

motors : across-the-line starting, in which

full-line voltage is applied to the motor,

an d reduced voltage starting. This sec

tion will discu ss only the across-the-line

starting method.

Any switch or con trol device used to

start (and stop) a motor must be able to

withstand a higher inrush of curre nt dur

ing the starting period. Switch con tacts

must close rapidly, make a sure co nnec

tion, and prevent arc damage to the

switch. Since anothe r im portant func

tion of the switch is to open the circuit,

allowing the motor to stop, any switch

or control device must a lso be able to

open the circuit un der locked rotor con

ditions . (See Section 28, Canadian Elec

trical Code.) The switch or control

device must have a strong

spring action

to open th e con tacts quickly. Otherw ise,

there may be considerable arc damage

to the sw itch.

A

control switch without the appro

priate design features cannot safely con

trol the m otor's starting or running cur

rent. It also cannot provide safe stopping

under abnormal overcurrent co nditions

caused by locked rotors o r sho rt cir

cuits. All these conditions can lead to

serious arc dam age within the switch,

resulting in the destruction of the switch

contacts and their control mechanism.

Safety Note:

For this reas on , experi

enced electricians usually do

not

stand

in front of a switch when it is being oper

ated. The

safest

way is to ke ep th e face

and b ody off to on e side and us e the left

hand to operate the switch. Although

severe arcing doe s not happen often, th e

danger of serious damag e to the sw itch

and injury to the ope rato r

is

always the re.

Motor starting current and running

curren t vary with the mo tor's power. As

the power increases, the starting and

running curre nts also increase . Any

switch used to control a motor, wh ether

in a basem ent wo rkshop or for industrial

duty, should h ave a

power rating

marked

on it. This rating will indicate w he ther

the switch can start and stop the motor

safely. (See Section 28 , Can adian Electri

cal Code.)

Location of Control Devices


Code recommends that a control switch

be located within sight of the motor. The

operator can then check that there is no

danger to equipment or persons before

starting the motor.

Overcurrent Protection

Like any other electrical circuit, motor

circuits

must

be protected from

over-

curre nt cond itions. Otherwise, a locked

rotor condition or a short circuit will

damag e both th e wiring and control

devices. The Canadian Electrical Code

lists the fuse or circuit breaker devices

tha t can be use d. (See Table 20.1)

As a general rule, overcu rrent pro

tection should not exceed 300% of the

m otor's runn ing curren t, which is listed

as the full load current on the namep late

of the motor. High starting currents are

responsible for fusing the motor at a

value above its rated curre nt. The Cana

dian Electrical Code gives more detailed

figures for the va rious typ es of moto rs.

(See Table 20.2)

Motor Conductor Sizes

The Canadian Electrical Code lists ampa

city ratings for cond ucto rs supplying

cu rren t to a single motor. (See Table

20.1) Motors with larger current ratings

than those l isted require cond uctors

Motor Control 33



TABLE 20. 1

Full-

Load

Current

Rating

of

Motor

Amperes

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1 5

1 6

17

18

19

2 0

22

2 4

2 6

2 8

3 0

3 2

3 4

3 6

3 8

4 0

4 2

4 4

4 6

4 8

5 0

52

54

56

58

6 0

C ol .

1

Minimum

Allowable

Ampacity

of

Conductor

15

15

15

15

15

15

15

15

15

1 5

15. 00

15. 00

1 6 . 2 5

17.50

1 8 . 7 5

2 0 . 0 0

2 1 . 2 5

2 2 . 5 0

2 3 . 7 5

2 5 . 0 0

27. 5

3 0 . 0

3 2 . 5

3 5 . 0

3 7 . 5

4 0 . 0

4 2 . 5

4 5 . 0

4 7 . 5

50. 0

52. 5

5 5 . 0

57. 5

60. 0

62. 5

65. 0

67. 5

70. 0

7 2 . 5

75. 0

Col. 2

Overload P rotection

for Running

Protection of Motors

Maxi

mum

Rating of

Type D

Fuses

Amperes

1.125

2.225

3. 5

4. 5

5.6

7

8

9

10

12

12

1 5

1 5

17. 5

17. 5

17. 5

2 0

2 0

2 0

2 5

2 5

3 0

3 0

3 5

3 5

4 0

4 0

4 5

4 5

5 0

5 0

5 0

5 0

6 0

6 0

6 0

6 0

7 0

7 0

7 0

C ol .

3

Maxi

mum

Setting of

Overload

Devices

Amperes

1.25

2. 50

3. 75

5. 00

6. 25

7. 50

8. 75

10. 00

11.25

12. 50

13. 75

15. 00

16. 25

17. 50

18. 75

2 0 . 0 0

2 1 . 2 5

2 2 . 5 0

2 3 . 7 5

2 5 . 0 0

2 7 . 5

3 0 . 0

3 2 . 5

3 5 . 0

3 7 . 5

4 0 . 0

4 2 . 5

4 5 . 0

4 7 . 5

50. 0

52. 5

5 5 . 0

57. 5

6 0 . 0

62. 5

6 5 . 0

6 7 . 5

70. 0

72. 5

75. 0

Col.

4

Overcurrent P rotection Maxim um Allowable

Rat ing

i

Fuses and M a x i m u m A l l o w a b l e S e t t in g of Circuit

Breakers of the

Time-Limit

Type for Motor Circuits

Single P hase

All Types

and

Squirrel Cage

and

Synchronous

(Full V oltage,

Resistor and

Reactor Starting)

Fuse

Amperes

1 5

1 5

1 5

15

1 5

2 0

2 5

2 5

3 0

3 0

3 0

4 0

4 0

4 5

4 5

5 0

6 0

6 0

6 0

6 0

6 0

8 0

8 0

9 0

9 0

1 0 0

1 1 0

1 1 0

1 2 5

1 2 5

1 2 5

1 2 5

150

1 5 0

150

175

175

1 7 5

175

2 0 0

C ol .

5

Circuit

Breaker

Amperes

15

15

1 5

1 5

1 5

1 5

15

2 0

2 0

2 0

3 0

3 0

3 0

3 0

3 0

4 0

4 0

4 0

4 0

5 0

5 0

50

7 0

7 0

7 0

7 0

7 0

100

100

100

1 0 0

100

100

100

1 2 5

1 2 5

1 2 5

1 2 5

125

150

C ol .

6

Squirrel Cage

and

Synchronous

(Auto-transformer

and

Star-Delta

Starting)

Fuse

Amperes

15

15

1 5

1 5

1 5

1 5

15

2 0

2 5

2 5

3 0

3 0

3 5

35

4 0

4 0

4 5

4 5

5 0

5 0

6 0

6 0

7 0

7 0

7 0

7 0

7 0

80

80

8 0

90

9 0

100

100

100

1 1 0

110

125

125

125

C o l .

7

Circuit

Breaker

Amperes

15

15

15

15

1 5

15

1 5

1 5

1 5

2 0

2 0

2 0

3 0

3 0

3 0

3 0

30

3 0

4 0

4 0

4 0

4 0

5 0

5 0

5 0

7 0

7 0

7 0

7 0

7 0

7 0

1 0 0

100

100

100

1 0 0

100

100

100

100

Col. 8

DCorV

Roto

Fuse

Amperes

15

15

15

1 5

1 5

1 5

15

15

15

15

2 0

2 0

2 0

2 5

2 5

2 5

3 0

3 0

3 0

3 0

3 5

4 0

4 0

4 5

4 5

5 0

6 0

6 0

6 0

6 0

7 0

7 0

7 0

8 0

8 0

8 0

9 0

9 0

9 0

90

Col. 9

if

Voatf

rAC

c» a

For full information of conditions that may change the values in this

table,

see the corresponding table in the Canadian Electrical (

336




TABLE 20.2 R at ing or S et t ing o f O v erc urrent D ev ic es f or t he P rot ec t ion o f

Motor Branch Circui ts

Type of Mo tor

A l ternat ing C urrent

Single-phase al l types

Squi r re l - c age and Sy nc hronous :

Ful l -vol tage Start ing

Resis tor and Reactor Start ing

A u t o - t ra n s f o r m e r S t a r ti n g :

N o t m o r e t h a n 3 0 A

M o r e t h a n 3 0 A

W o u n d R o t o r

Direct Current

N o t m o r e t h a n 4 0 kW

M o r e t h a n 4 0 k W

P er Cent of Full Load Current

Fuse

Rating

300

3 0 0

300

250

200

150

150

150

Max imum

Circuit-Breaker

Setting

Instan

taneous

Type

—

7 0 0

—

—

—

—

250

175

Time-

Limit

Type

250

250

250

200

200

150

150

150

For full information of conditions that may change the values in this table, see the corresponding table in the Canadian Electrical Code.

(Note that the 40 kW m otors were form erly rated as 50 horsepower motors.)

with ratings equal to 125% of the

motor's full load current.

Motors that are operated for short

periods can be supplied with conduc

tors that have a somewhat lower current

rating. The C anadian Electrical Code

shows how to determine condu ctor

am pacities. (See Table 20.3)

When conduc tors are used to supply

two or more m otors on th e same circuit,

conductor ampacity can be determined

by adding th e full load c ur ren ts of all the

mo tors in the circuit; then 25 % of the

largest m otor 's full load cu rren t is add ed

to th e total. (See Section 28, Canadian

Electrical Code.)

Thermal Overload Relay

Protection

Often a moto r is loaded beyond its

designed capacity. Motors in wood- and

metal-cutting machines, pumps, hoists,

and fans are examples of where over

loading can occur. Overloading slows

down the m otor, which results in less

genera ted voltage and an increase of

input cu rrent. For example, when using a

saw, if th e bo ard is da m p or the cu t is

too deep, the motor

will

be overloaded

and slow down. The current flow in the

windings will increase and heat the

motor beyond i ts design tem perature.

A

jamm ed pu m p or an extra-heavy load on

a hoist will have the sam e effect on a

motor. Most electrical motors have

cooling fans or b lades built in, but su ch

cooling system becomes less and less

effective as the motor's speed is

reduced.

If

nothing is done, the re may b

permanent damage to the motor's wind

ings and expensive repairs will be

needed.

It is hum an n atu re to try for "one

Motor Control 33



TABLE 20.3 Data for Determining Conductor Sizes for Motors of Different Duty Types

Classif icat ion of Service

Short-t im e Duty.

Operating valves, raising or lowering

rolls, etc.

Intermittent Duty.

Freight and passenger elevators, tool

heads, pumps, drawbridges,

turntables, etc.

Periodic Duty. Rolls, ore- and

coal-handling machines, etc.

V arying Duty.

P ercentage of N ameplat e

Current Rat ing of Motor

5

Min

Rat ing

110

8 5

85

110

15 30 and 60

Min Min

Rat ing Rat ing

120 150

85 90

90 95

120 150

Continues 1

Rating

140

140

2c:

more cut" or "one last load." Knowing

this, manufacturers have designed a

heat-sensitive mechanical device. When

a mo tor has been overload ed for a cer

tain length of time, this device , called a

thermal overload relay, opens the circuit.

(See Fig. 20.1) It doe s no t c au se " nui

san ce tripping," however, by opening

th e circuit every time the re is a brief o r

minor overload. The relay open s the cir

cuit only when the re is a prolonged over

load condition.

Modern 3 phase motor control units

require three overload relays to provide

full pro tectio n for the m otor. On so m e

manu facturers ' motor controllers, there

are three h eater un its with a m echanical

linkage. These relays operate a single set

of overlo ad co nt ac ts . (See Fig. 20.26 on

page 354.) Other manufacturers prod uce

motor controllers with bimetallic relays,

each having individual conta cts. Th ese

con tacts are connec ted in a series cir

cuit: any on e set of con tac ts o pen ing will

shu t down the mo tor sta rter if an over

load condition exists on the motor.

Relay Class Designations. There are

heater wir

solder pot

N O T E :

The solder pot is heat sensit ive. The

Ihetn

unit p rovides an accurate response to

ttie

overload current .

N O T E :

The heater winding is heat producing

manent ly jo ine d to the solder pot to ensui

proper heat transfer.

FIGURE 20. 1 Front and cutaway view s]

thermal overload relay unit

338




three class designations for overload

relays—Class

10, Class 20, and Class 30.

These class sizes are based on th e

amount of time required to trip the relay

or current element. The most common

of the se is th e Class

20,

which refers to a

relay that trips within twenty seconds of

the mo tor curr ent being at 600% of its

rating. Similarly, a Class 10 relay m us t

trip within ten sec on ds , and a Class 30

relay must trip within thirty seco nds

under 600% current conditions.

Operation of the Thermal O verload

Relay. The relay has several pa rts .

Each part passes its energy on to the

next.

The heater part is connected to the

motor

in series

with the

supply

conductor. Under normal load condi

tions,

the heater remains at a mode rate

tem pera ture. As the load increases

beyond the m otor's designed capacity,

more current flows and the temperature

of th e hea ter ris es. Within a sh or t period

of time, the h eate r m elts the solder in

the so lder pot. The small ratchet wheel

can then rotate, triggering th e

mechanical part of the relay. These

eutectic alloy relays

are designed with

precision heater elements which raise

the solder alloy's tem pera ture until th e

alloy liquefies at a predetermined tem

pe ratu re. (A eutec tic alloy is a mix ture of

several metals that will consistently turn

from a solid to a liquid upon reaching

the lowest pos sible m elting poin t for

that pa rticular mixture.)

A

variety

of

interchangeable heater elements can be

used, there by p roviding a choice of trip

times for the motor controller. In this

manner, the overload relay's trip chara c

teristics can be tailored to specific

motor requirements. Figures 20.2 and

20.3 illustrate the operation of this relay

type. Motors requiring a longer start-u p

time should have a relay unit that

accom mo dates the starting process and

provides overload protection to the

motor under running conditions. The

mo vem ent of the spring-loaded m echani

cal section cuts off current to the motor

in one of two w ays.

In th e

manual

motor starter, the

action is a simple m echanical o peration .

The main switching mechan ism of the

sta rter is released and allowed to spring

or trip to an open position by the opera

tion of th e ove rload relay. The circuit

delivering current to the motor then

opens,

preventing further operation of

the motor. The manual motor starter

must be reset by the operator once the

motor and

OL

relay have cooled down.

The magnetic motor starter u ses th e

OL relay ac tion in a slightly different

manner. The relay's m echanical a ction,

set in motion by the heating of the

relay's solder pot, opens a set of con

tacts w hich are connected in series with

the s tart er's con trol circuit. When thes e

con tacts op en, they cut off th e cu rrent

flow to th e m agnetic coil of the starter.

As th e coil lose s its magn etism, it in turn

releases the main con tacts from th eir

closed position. Current flow to the

thermal relay unit

to motor

to magnet coi

The operation of a melting alloy overload relay is shown

As heat melts the alloy, the ratchet wheel is free to

turn -

a

spring then pushes the contacts open.

F IGU R E 20. 2 A n ov er load relay me c han is m

Motor Control



Eutectic Alloy Overload Relay

reset position tripped position

power

circuit

ratchet

eutectic alloy

, heater

power

circuit

heater coil

FIGURES 20.3A AND B A eutectic alloy

solder-pot relay with a ratchet-wheel trip

mechanism

motor is cut off. These

OL

relay un its

must be reset by the op erator once they

and the motor have cooled down, but

only the control circuit is re-established

by the resetting action.

A

separate start

button must

be

operated

to

get th e

m oto r run ning again. Figure 20.2

illustrates an o verload (OL) relay

mechanism.

Many manufacturers produce

a

sol

der-pot type

of OL

relay

for

use in their

motor control equipment, but two other

types of relay can be found in various

motor control units.

Bimetallic

thermal overload relays

contact

FIGURE 20.4 A bimetallic overload'

make use

of a

simp le, U-shaped

strip*

metal (fabricated from two different

types of metal) which ben ds or defied

when h eated by the heater portion

a

th e relay. This ben ding action will opfl

set

of

con tacts and prevent further o

ation

of

the m otor.

In

many cases tha

relays are adjustable o ver a range oil

to 115% of nominal heate r ratings. (See

Fig. 20.4)

Unlike eu tectic alloy relays,

bimetallic

un its are often sensitive

to

shock and vibration, tripping n eedles

The two different m etals tha t make

9

the bending strip m ove gradually to

release the trip mechanism. This gra*

movement means that the electrical

a

tacts open slowly. Con tacts opened

slowly are pron e

to

arc damage

from 1

current in th e circuit. They can

flutten

fluctuate open and close, causing ev

more arc damage.

Some manufacturers produ ce,

pie

heater units that monitor each

of

three phases in

a

polyp hase system.

1

differential m echanism is used to pro

vide phase-loss

sen sitivity.

This, simf

stated, means that the motor

w ill:

340




allowed to run c ontinuo usly if on e of th e

three phases is opened or disconnected.

Three pha se m otors will run on any two

of the three phases, but at approxi

mately half their horsepower. They are

likely to heat up and burn out if not pre

vented from running.

The differential me chanism is nec es

sary on bimetallic 3 ph ase relays

because they lose some of their force on

the trip bar when one of the sections has

actuated . The mechanism uses the cool

ing action of the tripp ed relay section to

help initiate a tripping action o n on e

of

the remaining two section s. The m otor

can therefore be stopped at or below the

normal 3 phase tripping current level.

See Figures 20.5 and 20 .6.

Some manufacturers produce a

bimetallic relay that make s use of a

replaceable

hea ter elem ent, similar to

that used with the solder-pot relay type.

In the manual position, this relay

behaves much like the relays discussed

previously. Once set in the automatic

position, the relay will res tor e pow er to

the circuit as soon a s it cools dow n to

the pro pe r level. This ability is quite

convenient if the relay is installed in an

inaccessible place but can also ca use

several problems.

If the c aus e of the overlo ad ha s not

been removed from the motor, the relay

will allow th e moto r to re start e ach time

it cools down, and th e m otor will eventu

ally be damaged as a result of the co ntin

uous inrush cu rrents from the m any

restarts.

A second and more serious problem

for the operator is the fact the relay will

allow the mo tor to resta rt as so on as it

cools dow n, even if th e ope rato r is work

ing on the m achine at th e time.

Safety Note:

Great care m ust be

taken, when using the automa tic setting,

to open the main switch for the motor.

heater

bimetal

strip

control

circuit

to

starter

coil

contact

actuator

1

F I G U R E 2 0 . 5

m e c h a n i s m

A 3 phas e, bime tal l ic relay

power

circuit

Balanced Overload

\

\ \

/

[

r % — c * — L W _*.? »

heater and bimetal strip

differential mechanism

~f

•Both trip bars move.

to

starter

coil

I

power

circuit

control circuit

Unbalanced Overload

~ \

moving trip bar

differential mechanism

T

to

starter

coil

I

control circuit

F IGUR E 20.6 A d i f ferent ia l over load re lay

me cha nism for use on 3 phase m otor contro l

sys t e m s

To prevent injury to the op erator, the

motor must not be allowed to restart

while investigation or repa irs are in

pro gre ss. Figures 20.4, 20.5, and 20.6

illustrate this type of relay.

Motor Control

341



FIGURE 20.7 Ma gnetic overload relay units

Magnetic

overload relays have a

mo veable, magnetic co re inside a coil

which is con nected in series with th e

mo tor supply leads that c arry current to

the motor. Normal operation of the

motor will allow the core to rest in such

a position that th e con tacts of the relay

are closed. When an overload condition

is experience d by the m otor, more cur

rent will be drawn by the m otor and the

coil. Th e magne tic attrac tion of the coil

will becom e stronge r than norm al, and it

will dra w th e core further into the relay.

As th e co re is pulled in to th e relay, it

ope ns th e conta cts in the relay that are

used to turn the motor starter off. To

prevent nuisance tripping, a piston-in-oil

or piston-in-air unit attached to the core

slows the movem ent of the co re. This

dash pot,

as it is called, wo rks like an

automobile shock absorber and prevents

rapid cor e mo vem ent. The time taken for

the core to open the contacts depe nds

on the adjustmen t of a screw that op ens

or close s an oil or air by-p ass. The

amount of current required to draw the

core into th e coil (tripping cu rrent) is

adjusted by a threa ded rod, which

pod

t ions the core inside the magnetic c o i.

This typ e of relay is often used to

protect motors that have unusual duty

cycles or require longer than normal

perio ds of time to reach o perating

sp ee d. Figure 20.7 illustra tes magnetic

OL

relays.

Determining Overload Relay Size.

size of thermal overload relay used is

determined by th e current requ irem e*

of the m otor. The time it tak es to o pea

the circuit is determ ined by the extent'

the overload condition.

M ethod 1. Under norm al operating

conditions, m otors can han dle

125%

of

their rated full load amperes

(namepM

current).

C urrents larger than this are

likely to d am age th e m otor if allowed

M

continue for more than a few minutes.

The overload relay should be

capable 4

opening the circuit when curren t

exceeds

125%

of the full load amperes

342




For exam ple, if a moto r n eed s 8 A to

opera te, the overload relay should be

capable of handling

10

A

(125%

x 8

A).

This slight, extra allowance prevents

nuisance tripping during minor ov erloads.

Method 2. M anufacturers usually

place an overload relay

selection chart

inside th e covers of control s witche s.

(See Fig. 20.8) The m anu facturer's nam e-

plate on th e m otor will show th e full

load amperes.

For examp le, if the full load am per es

is 8

A,

look for the value th at is

mathematically closest under the Motor

Amps column in Figure

20.8.

In this case ,

th e value 8.23 is close st. Now find th e

heater num ber for this manu facturer's

model und er the H eater Element head

ing. The hea ter num ber is opp osite the

cur rent value, 8.23. It is W50 and is th e

man ufacturer's catalogue num ber. Use it

when placing an order, but rem em ber

that although it may b e quite close to

the 125% calculation, the he ater num ber

is not a curre nt rating.

Restarting After an Overload. To

restart a manual motor starter equipped

with a thermal o verload device, move

the operating handle (toggle') from the

central trip to the reset position. (The

overload condition will have moved the

toggle hand le from th e o n to the central

trip position.) The toggle handle must be

moved to the

off

position to reset the

spring-loaded mechanical section of the

relay. The control switch can then be

turned on.

The solder po t in the thermal relay

will

require sev eral m inutes to cool off

before the solder solidifies and grips the

ratche t wheel. As a result, the m otor has

a cooling out pe riod before it is placed

back in service.

The mechanical section of the relay

O verload Heater E lem ent

M o t o r

A m p s

0.19

0.21

0.23

0.25

0.28

0.30

0.33

0.36

0.39

0.43

0.48

0.52

0.57

0.62

0.69

0.76

0.83

0.91

1.01

1.12

1.22

1.34

1.47

1.62

1.78

1.96

2. 15

2.36

Select ion

Heater

E lement

W 1 0

W11

W12

W13

W14

W15

W16

W17

W18

W19

W 2 0

W 2 1

W 2 2

W 2 3

W 2 4

W 2 5

W 2 6

W 2 7

W 2 8

W 2 9

W 3 0

W 3 1

W 3 2

W 3 3

W 3 4

W 3 5

W 3 6

W 3 7

M o t o r

A m p s

2.60

2.86

3.16

3.48

3.84

4.22

4.65

5.12

5.63

6.20

6.82

7.51

8. 23

9.07

9.95

10.8

11.9

13.3

14.6

16.0

17.4

19.0

20. 7

22.7

24.7

27. 0

Heater

E lement

W 3 8

W 3 9

W 4 0

W41

W 4 2

W 4 3

W 4 4

W 4 5

W 4 6

W 4 7

W 4 8

W 4 9

W 5 0

W 5 1

W 5 2

W 5 3

W 5 4

W 5 5

W 5 6

W 5 7

W 5 8

W 5 9

W 6 0

W 6 1

W 6 2

W 6 3

FIGURE 20.8 O verload relay selection chart

for fractional horsepower motors

on som e older m odels of m otor controll

ers would not reset fully until the solder

had c ooled com pletely. If th e resettin g

mech anism was pre ssed while the sol

de r was cooling and only in a semi-

hardened state, the solder would not

grip the ratche t wheel. The relay had to

be removed from the controller,

reheated with a match, allowed to cool

properly before resetting, and then rein

stalled in th e controller.

Motor Control

343



Relays on modern motor controllers

do not have to be removed and

rehea ted. They use a solder that will

only reset when the relay has cooled

properly. The sold er will even rese t

when there have been prem ature

attempts at resetting during the cooling

process.

Manual Motor Control

Switches

Figure 20.9 show s a com pac t,

manual

motor control

switch, which is an

across-

the-Iine

type of starter. The overload

relay is on th e left-hand side (mark ed

A2.57). Th is unit fits into a s pec ial en clo

sure and can control most fractional

kilowatt, single-phase m oto rs. (See Fig.

20.10) It is ideal for use in home

workshops and in industry.

Three-phase systems require

3 pole

switches

cap ab le of opening all th re e live

con du ctors of the circuit.

Figure

20.11

shows the more com

plex manual typ e 3 ph ase switch with

thermal overload protection. There are

two relays visible on this switch. In some

provinces (for example, Ontario), how

ever, an ov erload relay is required for

each

p ha se (that is, three relays). The

unit shown in Figure

20.11

can control

600

V

m oto rs with ra tings up to 7.5 kW.

Magnetic Motor Control

A secon d type of

across-the-line

motor

starte r is th e

magnetic controller

which

uses an

electromagnet

to activate the

motor control switch.

This typ e of motor con trol has three

main advantages. The first is low-voltage-

protection.

W ith this pro tection, th e elec

troma gnet will disengage and open th e

m oto r circuit wh en the re is a significant

redu ction , o r loss, of line voltage .

FIGURE 20.9

switch

-

A m anual motor control

FIGURE 20.10 A single-phase fractional

kilowatt motor control switch with therr

overload relay and locking cover

344




u

a

o

FIGURE 20.11 A 3 phase manual control

switch with thermal overload protection

Motors that continue to ope rate when

there has been a reduction in line volt

age often o verheat, causing dam age t o

the m otor's w indings. Once the line volt

age is returne d t o full value, the m ag

netic motor controller will

not

reactivate

on its own. An op erato r mu st pres s t he

start

button to

re-energize

the electro

magn et. The nece ssity of doing this

prevents accidents (when using machin

ery such as saws, presses, and con

veyo rs). Th ere is no way of accurately

pred icting whe n line voltage will be

restored . If the m achine can sta rt up

without

the starter being reset, opera

tors working on or near the machine

could be seriously injured.

The second advantage of magnetic

motor control is that a great variety of

activating devices are available. Activat

ing device styles include push butto ns,

limit switches, float switches, pressure

switche s, and foot con trols.

Magnetic motor control is extremely

versatile

and can perform many opera

tions . Also, it can be loc ated anyw here

required for convenience or safety, and

it can have any n um ber of smaller con

trol stations in the circuit to activate the

starter. In con trast, a man ual m otor

starter must be placed within easy reach

of the operator. If the starter is bulky, if

damaging liquids or vapo urs are pres

ent, or if multiple control points are

required, placing the starter near the

operato r m ay present a problem.

A

third major advantage of magnetic

mo tor con trol is the use of

low voltage

in

the co ntrol circuits. Service and m ainte

nan ce to th e control circuit is less dan

gerous if 120

V

is used to co ntrol a 600

V

motor circuit. Controllers with this fea

ture use a

step-down transformer

in th e

controller to arrive at the prop er voltage

for the control circuit. Figure 20.12

show s a circuit b reaker-comb ination

starter,

step-down

transformer, and mag

netic start er in one cabinet.

Magnetic Motor Starters. Magnetic

motor starters sized in accordance with

the Electrical and Electronic

Manufacturers' Association of Canada

(EEMAC) or t he National Electrical

M anufactu rers' A ssociation (NEMA) are

available in eleven siz es. Each size

is

limited to the am ount of horse pow er it

can be exp ected to han dle safely. See

Table 20.4. Sta rter s tha t d o not ha ve a

class size assigned to them are simply

rated in horsepower and volts.

Motor Control

34



FIGURE 20.12 Typical breaker-combination

starter, type 1, in a size 2 en closu re. (Door

removed for photograph.)

P rotection by Disconnecting Uni ts.

Each mo tor must be protected by an

overcurrent device such as a fuse or cir

cuit breaker. The disconnecting switch,

with or witho ut fuses, or a circuit

breaker, must be sized in accordance

with Section 28 of th e Canad ian Electi

cal Code. The disconn ecting unit for a

single mo tor m ust have a current rati

of not les s than

115%

of the full-load c

rent rating of the motor it controls.'

disconnecting unit must be able to

i

and close the circuit safely, without

exposing the o pera tor or surrounc

equipment to danger from arcing or

flashing. C hapter 17 explains this i

more fully.

Operation of the Magnetic Motor

Starter. There are three basic

i

for opening and closing the contac

ma gnetic m oto r starte r. (See Fig.

When current is passe d through thi

the

magnet

attracts the

armature

the moveable contacts are brought

connection with the stationary cc

The pulsating effect of alternat

current causes several problems,

armature and magnet assemblies ti

heat up as a re sult of the pulsati

netic field aro und th e m ain coil. To

red uce th is h eating effect, called I

teresis loss, the a rma ture and ma

m ade of many thin lay ers of steel

(laminations}.

The coil loses its strength for;

instant each time the alternating <

falls to zero (120 time s pe r sec ond i

60 Hz syste m ). Damage results:

the

con stant, high-speed attraction and

release of the a rm atur e by th e ma

which can be h eard a s an annoying

or hum from the controller.

Extensive wear and heat on tl

net 's

pole faces

can also be

exp

Small co pp er rings, called

shading

are embedded in the face of the:

to coun teract a nd red uce this unc

able effect. The pulsating magnetic I

around the main coil induces (gen

erates ) a voltage and curre nt in the




TABLE 20.4 E E M A C ( N E M A ) S ize s and Rat ings of Ma gnet ic Mot o r S t ar ters

Size

00

0

1

2

3

4

5

6

7

8

9

Ampere

Rating

9

18

27

45

90

135

270

540

810

1 215

2 250

115V

HP

3

A

2

3

Th

15

25

50

kW

0.6

1.5

2.2

5.6

11.2

18.7

37.3

200 V

HP

Vh

3

Th

10

25

40

75

150

kW

I.'

2.2

5.6

7.5

18.7

29.8

56.0

112.0

230 V

HP

Vh

3

Th

15

30

50

100

200

300

450

800

kW

1.1

2.2

5.6

11.2

22.4

37.3

74.6

149.2

224.0

335.7

596.8

460 V /575 V

HP

2

5

10

25

50

100

200

400

600

900

1

600

kW

1.5

3.7

7.5

18.7

37.3

74.6

149.2

298.4

447.6

671.4

1

193.6

NOTE:

All kilowatt figures are

approximate.

moveable contacts

magnet

•

1 1

•

;

1

s

j r ^

.J

v

coil

armature

stationary contacts

Bell-Crank Type Clapper Type Solenoid or Vertical A ction Typ

FIGURE 20.13 Three basic methods for operating magnetic motor starter contacts

shading coils. This induced current

allows the shading coils to produce their

own magnetic field, which helps to

attract and hold the armature during the

times that the main coil is weakened.

(See Fig. 20.14)

A

magnetic star ter is made up of two

electrical circuits. The main, or power,

circuit, which has line terminals, main

contacts, overload heaters, and motor

terminals, is used to supply current to

the

motor.

The control circuit, which has

FIGURE 20.14

a s s e m b l y

Magnet and armat ure

Motor C ontrol

34



switches

disconnect

circuit

interrupter

i i i

> • > • )

circuit breaker

w A h e r m a l OL

V - V - )

circuit breaker

w / m a g n e t i c OL

V ) - - )

circuit breaker

w A h e r m a l

and

magnet ic

OL

}-})

l imi t swi tches

normally

open (NO)

°^

°==r°

held closed

normally

closed (NCI

O^CTtJ

o

held open

pen

loot

s-. • •

N O

cvCjo

pressure

&

vacuum swi tches

l iquid level switch

temperature

actuated swi tch

f low swi tch

lair, water, etc.)

N O

N C

N O

NC

N O

N C

N O

N C

Y T

Y T

•> • °-p

T

^

speed plugging

anti-plug selector

*F 2 position

A '

A 2

X

low

X

high

nr

0 _ * A 1 ^

o o A2

3 position

A1

A 2

X

hand

off

X

auto

o o A1 t

o o A2

2 pos. sel . push but ton

Al

A 2

X

free

X

depres ' d

log

X

free

X

3 e : ; :

run

_D A1

o A2

push buttons

pilot lights

mom entary contact main ta in contact

indicate colour by i

single circuit

N O

N C

double circuit

N O

N C

contacts

m u s h r o o m

head

two s ing le

circuit

.-T

one double

circuit

non push-to-test

o | o T

-®-

Qj$- : - s

* &

instant operating

w i t h b l o w o u t

N O

i f

T

N C

wi thout b lowout

N O

1

T

N C

t imed contacts - contact

act ion re tarded whe n coil is

energized

N O

N C

T

de-energized

N O N C

Q—r—O

shunt

o

overload relays

thermal

*

magnetic

transformers

AC motors

DC motors

LE u

n

u

n

m

dual

voltage

single

phase

LxJ

n

6

3 phase

squirrel

cage

2 phase

4 wire

0

w o u n d

rotor

o

shunt

field

( s h o w 4

loops)

series

field

( s h o w 3

loops)

s-r

FIGURE 20.15 Standard elementary diagram symbols




an electromagnet, overload contacts,

auxiliary (or maintain) conta cts, and an

asso rtm ent of control station s, is used

to activate the mo tor star ter and en sure

its safe o pera tion.

Both of the se circuits can b e repre

sented in the form of schematic wiring

diagram s. Special sym bols are used to

represent eac h com pone nt in th e circuit .

(See Fig. 20.15)

Figure 20.16 shows a 3 ph ase mag

netic motor starter. Figure 20.17 shows

the wiring diagram for this con troller.

The main power circuit is outlined in

black and th e control circuit in red . This

type of diagram, which show s each pa rt

in its correct location, is used when wir

ing or trouble sho oting a controller.

start

T

h

top

-

1

-

1

-

|

-

1

-

J

-

MC

i

Lm.

V

I

Ls

i

N O T E :

3 overload

heater units

9T2

9 T3

I

j 3 phase

V J motor

FIGURE 20.17 Wiring diagram for a 3 phase

magnetic motor starter

FIGURE 20.16 A self-contained, 3 phase magne tic mo tor starter (with pilot l ight)

Motor Control

349



start

M

L i -

L 2 -

L 3-

stop

O L

3 Wire Control (momentary contact)

r,

C

MC

R X ,

l i 5 ^ _ j f 3 phase

. M C *

RXy

F I G U R E 2 0 . 1 8

S c h e m a t i c ( e l e m e n t a r y ) d i a

g r a m f o r a 3 p h a s e m a g n e t i c m o t o r s t a r t e r

Figure

20.18

shows an elementary

(schematic) diagram of the same con

troller. Although the parts are not in

their true locations, this type of diagram

gives an easily understood picture of the

circuit and is most helpful when trouble

shooting more complicated controller

types. When a complex control system is

to be developed, electricians often make

a schem atic diagram of the control

cir

cuit only. Figure 20.19 shows a variety of

the se diagrams.

Holding,

or M aintain,

Contacts

Magnetic motor s tarte rs must be able to

open the power circuit to a motor when

ever an overload relay indicates a dan

gerous condition, an under-voltage con

dition develops, or any form of control

switch indicates that operation of the

motor should be stopped .

To

do this,

most control stations use a set of start

con tacts that remain closed only as long

as the operator keeps a finger on th e

star t button. The moment the button is

released, a spring forces the contac ts

3 Wire Control (with pilot light)

stop

2 1 L '

3

® -

N O TE : Pilot light can be wired in parallel

wrtl

to show when starter energized ana

running.

3 Wire C ontrol (momentary contact

multiple push button station)

L i

start

1 stop stop stop

start

M O

"~20*

start

•MC

NO TE : Wh ere a motor must be started

and

from more than one location, any

i

start and stop push buttons may be i

together. Also, it is possible to

start/stop

station in combination w *

stop buttons at different locations

*

emergencies.

F I G U R E 2 0 . 1 9

S c h e m a t i c diagr

m o t o r c o n t r o l c i r c u i t s

350




open again. This de-energizes th e coil in

the s tarter and al lows the m otor to stop.

A set of holding, or maintain, con

tacts are ei ther mounted on the same

contact carr ier bar as th e main po wer

circuit co nta cts or are activated by the

con tact carrier bar. Therefore, the main

tain contac ts open and close toge ther

with the main power circuit co nta cts.

They are electrically con nec ted in

parallel with the start button con tacts

and keep the coil energized on ce th e

start button has been released. Maintain

con tacts are represented by a normally

open contact (NO) sym bol in both sche

matic and wiring diagram s. Often, t he

letters MC will ap pe ar b eside the con

tacts to show that they are the maintain

contacts. (See Figs.

20.17

and 20.18)

Control Stat ions

Figure 20.16 show s a self-contained

mo tor controller with the sta rt /s top con

trol station m oun ted on the front of th e

unit. When there is to be mu ltiple-point

control, a remote push-button station is

used. Other types of control stations are

available, such as limit sw itches to con

trol the up and dow n m ovem ent of an

electric door, float switches to control

th e level of liquid in a tank, and dual-

action pu mp control sw itches. (See Figs.

20.20,

20.21, 20.22 and 20.23)

Sometimes it is nec essa ry to by-pass

the automatic control device and oper

ate th e con troller m anu ally to fill a tan k

or start a pump .

A

push button stat ion

with a selecto r switch is used with th e

controller to provide both manual and

automatic

co ntro l func tions. (See Fig.

20.24)

Occasionally, an ope rato r wishes to

control th e length of time a m otor

op era tes or th e length of time before a

seco nd control circuit is energized. A

FIGURE 20.20 A remote push button start/

stop control station

timing controller

is used for this p urp ose

(See Fig. 20.25) To calibr ate th e time

cycle, an a djusting screw at the top of the

unit regulates air (or oil) flow in and out

of a compression chamber. T his typ e of

con trol de vice is useful in redu ced volt

age starting un its for large m oto rs.

As me ntioned earlier, regulations

require three overload relays (one per

ph ase ) on a 3 ph ase m otor controller.

(See Fig. 20.26, page 354.) The reaso n

why is tha t a 3 ph ase m otor will con

t inue to ope rate o n any two of i ts th ree

phases if one should fail. It will not res

tart on two p has es, but if one p ha se is

disconnected, it can handle approxi

ma tely half of its rate d power.

A

motor

tha t is putting ou t less than its rated

pow er will soon hea t up from t he over

load, and its windings will be d am aged if

it is not d isco nn ec ted from th e line. An

overload relay on each ph ase ensures

Motor

Control

35



FIGURE 20.21 Limit switch

o

a

that two or more phases will indicate

overload conditions and remove the

motor from the line.

Overload relays on a magnetic

star ter function much like those on

manual motor starters. The usual

thermal element, solder pot, and ratd

wheel are used. The spring-loaded

mechanical section of the relay, how

ever, does not open the power circuit <

the controller directly. Instead, when

ratchet wheel is allowed to rotate, a sa

of normally closed contacts (NC) are

forced open by the mechanical sea

These contac ts are connected in sene

with the control circuit. Once they ha

been opened, th e magnetic holding a

is de-energized, and the armature fa

back to open the main power circuit

<

tacts.

As

in the case of the manual

starter, a reset button in the contr

must be pressed to reactivate the

FIGURE 20.22 A f loat-operated switch

352 Applications of Electrical Cons truction



FIGURE 20.23 A dual-action pum p control sw itch

**

I «®

* f t

o

a

1

s

O

U

FIGURE 20.24 A push button control

station for manual/automatic control

FIGURE 20.25

trol circuits

A pneumatic t imer for con-

Motor Control

35



ger to slide off. Th e spring in th e jog bu t

ton might close the upp er con tacts

quickly, before the arm atu re and pow er

contac ts have had a chan ce to open th e

pow er circuit. If this h app en s, th e main

tain contacts will still be closed and the

coil will rem ain energ ized, keep ing t h e

mo tor operating. To stop th e motor, the

stop button

must

be pressed. Although

this situation doe s not hap pen often,

when i t do es, the ope rator can be

injured if the m oto r fails to st op wh en

the jog button is released.

Selector Jog . A safer form of jogging

circuit is th e se lec tor jog. (See Fig. 20.28)

The selector switch jog circuit elim

inates the dan ger of an op erato r releas

ing the jog bu tton to o quickly. This cir

cuit places a single-pole selector switch

in series with the maintain contacts.

When th e switch is closed (run position)

th e circuit opera tes normally. When t he

switch is open

(jog position),

the main

tain co ntac ts cann ot k eep the coil circuit

energized. The pow er circuit opens as

soo n as th e opera tor releases the start

button.

As well, the re are m ore specialized

jogging circuits tha t m ake use of a con

tro l relay. (See Fig. 20.29)

If a motor circuit is to be jogged

L 2

O L

-M -

FIGURE 20.28 S tart/stop/selector jog con trol circuit

N O T E :

Pressing the start button energizes the control relay (CR), which in turn energizes the starter coil. The

normally open starter interlock and relay contact then form a holding circuit around the start button.

Pressing the jog button energizes the starter coil independently of the relay. No holding circuit forms, and

so jogging can be obtained.

FIGURE 20.29 Jog circuit with control relay

Motor Control 355



continuously (m ore than five time s p er

minute), controllers must be de-rated,

that is, either moto rs smaller than th e

nam eplate rating of the controller mu st

be used or a larger controller must be

installed. The cons tant expo sure to high

inrush currents (motor starting current)

will soon d am age the con tac ts of th e

controller if jogging opera tion s are car

ried on continuously.

Reduced Voltage Control

Many

3

phase m otors ope rate on 480

V

and 600 V (CSA stan dar d C-235-83, pre

ferred voltage levels for AC system s).

Voltage at this level can cause painful

injury to an opera tor or service

m echa nic if con tact is m ade with live

equipm ent. It is not uncom mon to con

trol the m otor-starting equipm ent, at

this voltage level, with a redu ced voltage

control system. Such a system makes

th e contro l circuit safer for installers

and service person nel to work on and

simplifies the actual equipment in the

control circuit: less danger of a flashover

or arc exists. There are tw o basic

me thods of connecting this type of

reduced voltage control circuit. Figures

20.30 and

20.31

illustrate the se tw o

methods.

Figure 20.30 makes u se of a control

circuit transformer

to red uce th e line

voltage down to a safer level (120 V).

With this method , both motor and con

trol voltage can be cut off by the same

disconnect sw itch used to supply the

motor circuit.

Figure 20.31 use s a sep ara te s ou rce

of supply for the control vo ltage. This

system is useful when direct current

(battery) or other separate source is

needed to control the motor starter. In

some work areas, windows or na tural

light sources are not available. If the

FIGURE 20.30 A reduced voltage com

circuit using a source com mo n to the i

and control circuit

to separate

control voltage source

FIGURE 20.31 A reduced voltage

circuit using a separate voltage source

lighting system should fail, machine

op era tor s are left in a darken ed room

with all the machines running, a pote

tially dangerous situation. By conn

the control circuit sourc e to the

li

panel in such an area, a loss of ligh

voltage will also can cel o pera tion of

ma chines. O perato rs will be able to

356 Applications of Electrical Con struction



abou t in the da rkened area m ore safely.

While only 480

V

and 600

V

were

men tioned at the star t of this se ction,

supply vo ltages of many levels can be

controlled by a reduced voltage system.

The higher the supp ly voltage, th e m ore

likely a control circuit using reduced

voltage will be requ ired.

Reversing Controllers

Interchanging an y two of the lea ds to a 3

ph ase m otor will cau se it to run in the

reverse direction. Single-phase m oto rs

tend to be mo re complicated and often

need connection changes within the

motor itself. For this rea son , only 3

phase controllers will be discussed in

this section.

A 3 ph ase reversing starte r consists

of

two contactors

enclosed in the same

cab inet. Only one set of overload relays

is used , however, since bo th forward

and reve rse control circuits are intercon

nected.

W hen rev ersing a motor, it is vital

that both contactors

not

b e energized at

the same time. Activating both co ntac tors

would ca use a sho rt circuit since two of

th e

line

condu ctors are reversed on one

con tactor. Preventing a sho rt circuit

from this ca us e is called interlocking.

Mechanical and electrical interlocking

sys tem s are available in m ost reversing

controllers.

The

mechanical

interlock u ses a sys

tem of levers to prevent the armature

of

th e reversing co ntac tor from engaging

when the forward con tactor 's arm ature

is in opera tion . Figure 20.32 sho ws a

schem atic diagram of the control circuit

for this type of unit.

The

electrical

interlock makes use of

two double-contact (4 terminal) push

bu ttons . When the forward bu tton is

pressed, the upper contacts open the

rev erse coil circuit. Even if the rev erse

coil is energized, th e c ontro l circuit will

be broken. The pow er circuit is opened

as soon as the forward button is

pre sse d. (See Fig. 20.33)

The electrical interlock circuit allows

the mo tor to be reversed simply by

pressing the reverse button. The

mechanical interlock system requires

that th e stop button be pressed. When it

Li

forward

stop

-0 I

Q-

reverse

< = >

O L

MC

1.2

FIGURE 20.32 Mechanical interlock forward/reve rse/stop control circuit

Motor Control 35



Li

stop I forward

-Q-J D -&

OL

FIGU RE 20.33 E lectr ical inter lock forw ard /rev erse /s top contro l c i rcui t

Li

stop

jrward

J

^Hvic

•everse I

-o I o—I

xr

electricalt interlock

R 6

•it 1 •-

F

-Vh

f o r . k -

7

-• »-

O L

Yr

mit

switches (if used delete jumpers 6

and

i

F IGU R E 20. 34 S c hemat ic d iagram s ho w ing a rev ers ing c ont ro l c i rcu i t w i t h lim i t s w i t c h es

<

separate elect r ical inter lock contacts

is , th e forward co nta cto r will be disen

gaged before the reversing c on tacto r

can be brought into service.

Figure 20.34 shows a sche m atic dia

gram for a reversing con trol circuit util

izing limit switch es a nd electrical inter

lock contacts. Operation of either the

forward or reverse co ntac tors will open

the matching interlocking contac t. This

makes it unnecessary to press the stop

button before changing the motor's

direction of rotation.

Safety Note: Take care when revers

ing large mo tors . The s ud de n jar of

direct reversal can damage the machine

or equipm ent the m otor is driving. High

inrush currents can cause damage to

both the motor and the controller if

tt*

motor is reversed without allowing

enough time for the speed of the motor

to decrease.

Figure 20.35 shows a complete wir

diagram for a reversing controller.

Figure 20.36 show s an altern ate

con

trol circuit for such a controller sche

matically.

Multiple push-button stations can

1

used with the reversing controller. Fig

ure 20.37 shows a schematic diagram a

two forward/reverse/stop stations.

358




push button stations

forward

(for.)

reverse

(rev.)

* <S

r-

#

V

stop

i -

M C

L i

La

O L

contacts

f or )

coil

• r

L 3

1 .. ..

43<

O L heater

T3

N O TE : Power circuit in

black,

control circuit in red

maintain

contacts (MC)

J

FIGURE 20.35 C om plete wiring diagram of a 3 phase reversing controller

limit switches (if used)

N O TE : 3 wire control of a reversing starter is possible

with this forward/reverse/stop push button station.

Limit switches can be added to stop the motor at

a certain point in either direction. Jumpers from

terminal 6 and terminal 7 to the forward and reverse

coils must then be removed.

FIGURE 20.36 A lternate diagram of a

reversing control circuit (with limit switches)

stop stop I rev. rev for. for.

— o l n — o l r > — k i l o - o l n - , h l n - n l r^

maintain-

contacts

*8w

OL contacts '

FIGURE 20.37 S chematic diagram showing

multiple push button control for a reversing

starter

Motor Control

35



Mult i -Speed Motor Control

Some 3 ph ase m oto rs, referred to as

multi-speed

moto rs, are designed to

pro

vide two sepa rate speed ranges. There

are two main types of multi-speed

motors, the

separate winding

and

conse

quent pole

motors.

The separate winding motor, as the

nam e implies, uses two or m ore wind

ings which are electrically separate from

eac h o ther. Each winding is cap able of

delivering the motor's rated horsepower

(wattage) at the rated speed. The

mechanical arrangem ent of the windings

determines the number of magnetic

poles per p hase built into the motor, and

thu s the different sp eed s. The m ore

poles per phase, the slower the opera

ting

rpm

of the motor when that set of

poles is being used. Since the windings

are indepen dent of one another, th e

speeds designed into the motor can be

quite varied, such a s 3600 rpm/600 rpm

or 900 rpm/700 rpm . Figures 20.38 and

Li

La

stop

slow

raBki—rhMo—i _QMQ:

fast

ru ftJl

OL contacts

FIGURE 20.38 S chematic diagram show ing

a control circuit for a 2 speed (dual winding)

motor

20.39 illu strate

two-speed

motor control

circuits for use with separate winding

motors.

The conseq uent pole motor uses a

special winding which can be recon

nected, using contac tors, to obtain dif

ferent speeds.

Two-speed

consequent

pole m otors always have a speed ra

2:1.

Th ree types of conseq uen t pole

motors are

available—constant

horsepower, con stant torque,

and

varia

ble torque.

The nam es of the th ree types

indicate the outp ut ch aracteris tics of

the m otors .

A two-speed

consequent pole

mo*

starter consists of two contactors,

mechanically and electrically designed

not to be activated at th e same time

(interlocking). One con tacto r ha s thre e

poles, or contacts; the other has

fivi

For one sp eed, the 3 pole

contacts

sup plies full-line v oltage to th e m otoc

For the sec ond spee d, th e 5 pole cor

tor is activa ted, and th e 3 pole conta

is automatically disconne cted by the

interlocking sy stem . Three of the five

poles provide full-line voltage to the

motor through a separate set of

mote

leads.

The remaining two poles recon

nect the motor leads used by the

31

contactor, there by creating a conse

quent pole configuration. This allows

the motor to operate at a different

speed.

With constant horsepo wer

motors,

the 5 pole con tactor is energized on

tta

lowest of the two speeds available.

Vfc^

constant and variable torque motors

the 5 pole conta cto r is utilized during

the

high

speed operation of the motoc

Wiring diagrams for the starters of the*

m oto rs can be seen in Figures 20.40 and

20.41.

With all multi-speed con trollers,

overload relays are provided for both

the high- and low-speed circuits to

360




fast

slow

_4_MC

L i

I ?

La

1

In

\

MC

OL OL

stop

I

Ti

^-ESS-i

T2 T3 T* Ts T

3 phase 2 speed motor

F I G U R E 2 0 . 3 9 A d u a l - s p e e d , 3 p h a s e m o t o r c o n t r o l c i r c u i t ( d u al w i n d i n g m o t o r )

ensure that there is adeq uate protect ion

on each spee d rang e (set of m otor

windings).

Reduced Voltage Starters

W hen mo tors a re start ed with full-line

voltage, high {locked rotor) curren ts and

maximum torque can be exp ected . Under

full-line v oltage co nd itions, large m oto rs

often develop enough torque to damage

belts, gears, and o the r drive line com

ponents. Starting current is often high

enough to endanger the controller con

tacts, as w ell as to c rea te a voltage dis

turban ce on the l ine that can bothe r

other motors or electrical equipment.

For these reasons, a starting system

with

less

than line voltage is used.

Th ese sta rte rs are ma de in Size 2 and

larger. Th ey are of two typ es: the pri

mary resistor and the auto transformer.

Primary Res istor Starter. This older

starting method is not in common use

today, but can be m ade available

through many m otor control

ma nufacturers. M otor controllers of this

type c onn ect a set of resistors in series

with the line which red uce s line voltage

for a pre de term ined length of time (3 s

to 15 s) . A timing relay activates the

Motor Control

36



:jf^F:^

i

hjgh _

rs

ow

Q_1_0

stop

0_i_J

I O W X N J

T I

T2 T 3

connections made by starter

speed

low

high

supply lines

L i L2 L3

T I

T2 T3

T e T 4 T s

open

none

T i

2 3

together

T l 6 6

none

Motor

Terminal

Markings

constant horsepower

stop

- Q _ | _ S -

L i

high

—o.

low

1_0 • 0 o — •

L

H

~s

H

2 i , 3

J

4K5^

OL

OL

L 2

5

—

FIGURE 20.40 Connection diagrams for a consequent pole motor starter, constant

horsepower type

3 62 Applications

of




I

high

9

o.

low

l_l_0<

•-o o-

slop

I I I I

high

« >

T s

J 5 J

m

:2_

1-

L

low

X>n

T2A T

3

i

connections made by starter

speed

low

high

supply lines

L i

L 2

L s

T . T 2 T 3

Te

T*

Ts

open

T 4 5 6

none

together

none

T i

2 3

T2 Te

FIGURE 20.41 C onnection diagrams for a consequent pole motor starter, constant

torque or variable torque type

Motor Control

36



controller automatically for the second

stage . (See Fig. 20.25) The m otor- starting

proc ess begins with the pressing of th e

start push button. This pressing

activates the line contacts coil, allowing

current to flow through the primary

starting resistors, and into the m otor.

The primary starting resistors reduce

the line voltage to a level that allows th e

mo tor to start, but not draw an exces

sive amo unt of starting c urrent.

A

timing relay is activated at t he

sam e time as th e line con tacts coil. This

relay can be preset by the opera tor to

close its contacts at a predetermined

time.

When the con tacts of the timing

relay close, the y activate the by-pass

con tacts coil. This in turn close s the

resistor by-pass contacts, and current

now flows around the prim ary resistors

to th e m otor. No voltage is lost or

reduced by this path to the motor

and

full speed is soon reached by the

moti

The m otor can b e stopped simply by

pressing th e stop push button.

This type of starting gives smooth

acceleration to full operating speed

without loss of speed during the

cr

over cycle.

Figure 20.42 show s a wiring di<

for this type of motor starter.

Au to Transformer Starter. The ai

transformer starter, which is often

i

a

compensator,

uses a set of

single-winding (auto transformer),

step-down transformers to reduce th

line voltage. As with th e p rima ry

i

starter,

partial voltage

is supplied to

mo tor on starting, with a timer relay

regulated timing

relay contacts

(TR)

line contact

resistor by-pass

contacts (BO

by-pass contacts coi

OL contact

3 phase motor

F IGU R E 20. 42 W i r ing d iagram of a pr imary res is tor , reduc ed v o l t age mot or s t ar t er

364




calibrated to activate the start er's sec

ond stage.

The starting seq uen ce of this unit is

set in motion by the press ing of the start

push button. The pressing ac tivates

three electromechanical devices at the

sam e time:

a) The timing relay is set for its pred e

termined time and begins its count

down. The maintain contacts in thi s

controller are activated by the timing

relay and keep the control circuit

energized once the start button has

been released.

b) The

start contacts coil

is activated

and in turn clo ses the starting contacts

c) The transformer contacts coil is also

energized and closes th e transformer

contacts, allowing curent to flow into

the 3 pha se transforme r circuit (Wye

connected).

As can be see n in the wiring diagram,

Figure

20.43,

the starting contacts

receive their voltage and current from

approximately midpoint on the tran s

former. This starting vo ltage is about

65% of the full-line voltage available. It

can thus start the motor with a moder

ate am ount of starting current, while

preventing dangerous current surges.

stop

start

maintain contacts -

controlled by

timing relay

contacts

t imed

to open

contacts

t imed

to close

timing \

relay coil

=*—Q4

transformer \

contacts coil

_ H L

tart

contacts coil

run

^

contacts coil

L i

I?

L 3

IT

-run

contacts

"C

1.

,

IrM

i I I

Hi -

transformer

contacts

(T)

transforme

auto transformer

Wye connected

starting contacts

F I G U R E 2 0 . 4 3 T y p i c al a u t o t r a n s f o r m e r , r e d u c e d v o l t a g e m o t o r s t a r t e r d i a g r a m

Motor Control 365



When the timing relay reach es the

end of its coun tdow n (5 s to 15 s), it

automatically opens the starting and

transformer con tac ts by de-energizing

the coils controlling th ose con tacts . At

the sam e time, the

run contacts coil

is

activated and the run contacts are

closed. Current is now allowed to travel

straight throu gh to the m otor instead of

detouring through th e transformer cir

cuit. Full-line volta ge is now applied to

the motor which soon reaches its full

operating speed. Operation can be

brought to a halt by pressing the stop

push button.

More starting torque is available with

this type of controller than with the pri

mary resistor type of unit. Starting

torque under reduced voltage condi

tions, however, is never eq ual to that

obtained when using full-line voltage.

When the commonly used 65% voltage

tap is connected for start-up of the

motor, the torqu e outpu t is reduced to

approximately

50%

of the tor qu e that

would be available if full-line voltage w as

used . This may be qu ite sufficient for

many applications, but high-inertia

loads,

such as large b all mills, may not

be able to use the reduc ed voltage,

starting-controllers due to the loss of

torque during the starting sequence. Use

of the

80%

tap on th e transform er will

provide about 75% torqu e, w hile th e 50%

transformer tap will reduce torque level

to approximately 30%.

Figure 20.43 show s this typ e of con

troller circu it.

To prevent th e current surge nor

mally occ urring as the co ntroller shifts

from partial to full-line voltage, some

manufacturers have produced a unit

with a different type of control circuit.

Operating Sequence for a Reduced

Voltage

Starter,

Closed Circuit Transition

(Fig. 20.44):

oil

rrr.iii«

to

a) Pressing the start button activates

the

IS

coil circuit. T his

IS

coil, in

turn, closes th e group of three IS

co nta cts located at the right-hand

side of the auto transformers in

tin

circuit diagram. This completes a

W ye connection in the transforraen

them selves. At the sam e time, the

I

(normally op en) co nta ct in the 2S

coil circuit is clo sed.

b) Closing th e 2S coil circuit a ctiv ate

the 2S (normally open ) contac ts

a

the left-hand side of the auto

transformers, feeding line voltage

into the transformers. The 2S coi

also closes the 2S con tacts

(no

open ) in the R coil circuit an d si

pair of

timed,

TR2S cont act s into

their timed sequence operation.

At this

point,

the motor starts on 65

of the full-line voltage.

c) After 5 s to 15 s, pr eset b y

either d

manufacturer or the installer, the

"timed-to-open" TR2S co ntacts

ope

the IS coil circuit, there by causing

the transformers '

IS

contacts to

drop open and deactivate the Wjn

connection.

d) Simultaneously, th e "timed-tc

TR2S conta cts ac tivate the

R

co

cuit. This in turn closes t he m ain

(Run) con tacts in the starter, si

ing full-line v oltage to th e m oto r i

perm itting it to reach ope rating

i

and torque .

e) The R coil also closes the R cor

circuit contact (which acts as a

i

tain contact) and opens the nor

closed R contacts in both the ISi

2S coil circuits . This cu ts power t

the transform ers while they are

•

the ru n mod e.

f) Pressing th e stop button will opee

Line 1 to the entire control circu

and allow the m otor to stop .

366




t imin g relay for IM

TO means contacts

are timed to open;

TC means contacts

are timed to close.

• T C "

Open Circuit Transition

FIGURE 20.45 A Wye-D elta, reduced voltage mo tor starter using open circuit transition

switch the m otor windings from the

W ye/star configuration t o the de lta con

nec tion. Th is supp lies full-line vo ltage to

the mo tor, allowing it to com e u p to full-

rated speed. During operation in the

delta configuration, the contacts supply

ing current to the m otor and th e over

load relays are subjected to

57.7%

of t h e

line cu rrent. As a result, the controller

will carry a lower curren t to th e m otor

and have a higher horsepower rating.

Wye-Delta con trollers, like the auta

transformer type of unit, take advant

of the

closed-circuit

transitio n princ

whereby the mo tor can start up

witr

any large curre nt surg es on the supply

lines to t he motor. F igure 20.46 illus

tra tes th is type of circuit.

368




mechanical

interlock

timed controls (TC)

"timing

relay for 1M

Closed Circuit Transition

FIGURE 20.46 A Wye -Delta, reduced voltage motor starter using closed circuit transition

Motor Control



Solid-State S tarter

Solid-state starters use microprocessor-

based circuitry to control silicon control

rectifiers (power SCRs), providing

smooth, stepless, torque-controlled

acceleration. This acceleration, known

in the indu stry as

soft

start,

can provide

a curre nt limit to th e motor. On som e

mo tor applications, it is nec essa ry t o

limit the maximum starting current, and

with this type of unit, the current can be

adjusted from 50% to 500% of th e full

load am peres. Programmed time and

current levels can be selected throug h

various sw itch settings {DIP) located on

the microprocessor's printed circuit

board.

Note:

DIP sw itche s, known as

dual-in

line-package switches, frequently have

moulded plastic bodies and are

always small and thumbnail sized.

Placed into an open or closed position

by a small pointer o r ballpoint pen ,

they are soldered into the controller's

printed circuit board where they

remain for the life of the circuit board.

(See Fig. 20.47)

Pressing the

start

push button sig

nals the

solid-state

starter t o begin oper

ating. Internal hold-in circuit la tche s an d

auxiliary co ntac ts ch ange sta te. At this

point, an initial voltage is d elivered,to

th e m oto r windings. In the soft-start

mod e, this voltage continu es to rise until

the motor receives full-line voltage over

a preprogram med period of time and

rea ch es full-rated rpm . Figure 20.48 illus

tra tes a circuit for this controller.

The solid-state m otor star ter p ro

vides several useful, additional features.

Visual indication of fault conditions, for

example, stalled m otor, phase loss, too

high temperature, etc., can be built into

the unit. An energy-saving feature for

lightly loaded m oto rs, along with con-

u u u u u

FIGURE 20.47

A dual-in-line-package

switch,

also kno wn as a DIP switch

trolled stopp ing times (braking or

extend ed sto p time) further ad ds to

th

convenience and usefulness of these

mod ern units.

Reversing Single-Phase

Motors

Single-phase motors (split-phase ty

are usually used in hom e workshops a

light industry. They have two indepen

de nt w indings, called start a nd run.

The fine-wire start winding is con

nected to the circuit during the

startup

period only. It determines the directia

of the motor's rotation and provides

some starting torque.

The larger, heavier gauge

run

wind

ing is conn ecte d t o th e line at all times

that t he motor is operating. It keeps tin

motor running.

To reverse the split-phase motor,

start winding or run winding leads

be interchanged. A m echanical reve

unit, called a

drum switch,

can be

usee

do this. (See Fig. 20.49)

Figure 20.50 shows th e internal co«

nections of this

three-position

switch,

and Figure 20.51 sho w s a wiring diagn

for th e split-p hase mo tor. If a drum

switch is used for reversing the mot

may be nece ssary to take the motor

apa rt to gain access to the s tart win

leads.

370

App lications of Electrical Construction



3 phase

disconnect

power

input

3-phase

SMC controller

fuse

H

primary

H J

control circuit

transformer

stop

- Q j _ 0 -

x?r~yv~Y-'i

* secondary

start

X .

OL contacts

—Nr-

solid-state starter

(soft start)

microprocessor

> 11

ground

FIGURE 20.48 A solid-state motor control circuit

Direct-Current Motor

Control

Direct-current mo tors a re used far less

often than alternating-current units, and

they need special starting equipment.

As with large AC m otors, high starting

currents

are a prob lem with large DC

mo tors. The start ing controllers used

have a tapped resistor to raise the

motor's speed gradually without exces

sive starting curren t.

DC motors of the compo und type

hav e tw o field winding s, called series

and shu nt (parallel) fields.

To provide starting torque , the shunt

field rece ives line voltage a t all time s.

The armature and series field, however,

have a va riable resistor connected in

series. Figure 20.52 show s a 3 point

( three connections to the starte r)

reduced-voltage starter.

As the startin g arm is moved gradu

ally across the face of the starter, series

field and armature circuit, resistance is

decreased gradually. As a result, th es e

Motor Control

371



F I G U R E 2 0 . 4 9 A 3 position—reversing, c

a nd forward—drum s w i t c h , w i t h t he c ov er

r e m o v e d

starting

resistance

starting arm

L i -

reverse

3 C - ^ 4

50 0 6

handle end

of*

1 0

3 0

5 0

0 2

0 4

0 6

for.-.

36

6 4

5 0 — O i l

FIGU R E 20. 50 In t erna l c onne c t ions f or

pos i t ion rev ers ing drum s w i t c h

motor

F IGU R E 20. 51 W i r ing d iagram s how i r

a spl i t -phase motor (wi th drum swi tch)

revers ing

holding coil

to disconnect

L 2 *

FIGU RE 20.52 Typical 3 point man ual DC mo tor s tarter

372




windings are exposed to m ore and more

voltage, until full op eratin g spe ed is

reached. A holding coil keep s the start

ing arm in the ru n position until the

ope rator re turns it to the off position.

If the shunt field circuit is opened or

dam aged in any way, th e h olding coil,

which is conn ected in series with the

shunt field, releases the spring-loaded

startin g arm and th e m otor s hu ts off.

This no-field-release protection is very

imp ortant for DC m oto rs. Without it, an

extremely dangerou s spe ed will be

reached quickly if the shunt field is

disconnec ted. Large

DC

motors can

speed up to the point at which the arma

ture windings are thrown out of their

retainers (by centrifugal force) and the

motor destroyed. The direct-current

controller can be used to regulate the

starting of a shunt motor, which has no

series field, by placing the A2 side of the

arma ture directly on the arm ature termi

nal of the controller.

Figure 20.53 shows the wiring for a

second type of manual motor starter, th e

4 point (four connections to the starter)

motor starter. These controllers provide

no-voltage-protection , which prevents th

motor from restarting by itself if a power

failure has caused the holding coil to

release the starting arm.

Successful sta rting of th e m otor w ith

a manual starter depends entirely on the

operator. If th e starting arm is moved

too quickly, strong inru sh cu rren ts will

damage the controller and/or th e motor.

An automatic m otor starter to prevent

such hum an erro r is available. The oper

ator simply press es a start button,

which in turn activates a solenoid

(electromagnet). The solenoid is anoth er

form of timer relay, which controls th e

speed at which th e conta cts of the con

troller close . Closing of th e co nta cts grad

ually eliminates the starting resistance

and the motor accelerates smoothly.

Figure 20.54 show s a w iring diagram

for an automatic DC motor starter.

FIGURE 20.53 Typical 4 point manual DC motor starter

Motor Control

37



arc-reducing blowo ut coil

start stop

starting resistor

R.

R R,

0

6

6

moveable contact

/

to disconnect

adjustment

screw

armature

— solenoid

series

field

dash pot (timer)

quid level

F I G U R E 2 0 . 5 4 W i r i n g d i a g r a m s h o w i n g a n a u t o m a t i c D C m o t o r s ta r te r

F o r R e v

i

e w

1. Why do motors need special con

trol switches?

2.

How does the voltage generated in

a motor affect the input current?

3. Define locked rotor current.

4.

W hat are the two basic m ethod s

for starting motors? What are the

advantages of each method?

5.

Why are motor-starting switches

rated in kilowatts or ho rsepow er?

6. According to the Canadian Electri

cal Code, where should control

switches be located?

7. How is the fuse size for a motor

determined? What effect has the

fuse size on the ty pe of d iscon nect

switch installed?

8. Explain how motor conductor

sizes are determ ined.

9. What are the three types of relay

used to give thermal overload pro

tection? Explain briefly how each

works.

10. What two factors determ ine the

size of the overload relay?

Explain

in your own words two method s

for determining relay size for a

motor.

11. When restarting a motor after an

overload has tripped the relay,

wh at p recau tion m ust be taken'.

1

12.

List the thre e m ain advan tages of

magnetic motor co ntrol.

13. List the eleven sizes of magnetic

motor starters and the motors

each can control safely.

14. What is the pu rpo se of the sh adi

coil in a sta rter ?

15. What are the two circuits that

make up a magnetic m otor stc

16. Draw a sche m atic diagram of |

control circuit used when four

start /sto p stations are to be

con-J

nec ted to the magnetic starter.

17. What is the purpose of the

holdi

(maintain) contacts? How do th<

work?

374




18. List three types of control stations

that may be used with magnetic

motor star ters .

19. Why is more than one o verload

relay required in a 3 ph ase starter?

20 . How do es an overload relay used

with a magnetic motor sta rter

differ from a relay used on a man

ual starter.

21.

W hat is the pu rpo se of the jogging

circuit?

22. What is the danger when using a

push button jog circuit?

23 . Explain how a 3 ph ase m oto r is

reversed.

24.

What is the purpose of the inter

lock on a reversing controller?

25 .

W hat might hap pe n if a large

mo tor is reversed too quickly?

26. What is the difference betw een a

dual-speed motor controller and a

standard reversing controller?

27. What is the p urp ose of the timer

relay in a reduce d v oltage starter?

28.

Explain briefly how th e a uto tra ns

former starter operates.

29.

What are the advantages of using

the two types of reduced voltage

s tar ters?

30. Explain briefly how a single-phase

motor can be reversed.

31. What problem do both DC and AC

mo tors have when starting?

32. Define no-field

release.

33.

Why is no-field-release protection

important when using a DC motor?

34 . Define no-voltage-protection.

35.

W hy is an autom atic star ter safer

than a manual motor starter when

controlling

DC

motors?

36. What special features d oe s a solid-

state motor starter provide that

other types of starters do not?

Motor Control

375



A

s in most building construction

areas, th e electrical trade relies

heavily on fastening devices to mount

boxes and panels, to support conduits

and cables, and to secure the many fit

tings associated with the trad e. Fasten

ing devic es are available in many forms

for the s up po rt of electrical equip me nt

on wood, steel, and all types of masonry

surface s. Due to th e variety of m aterials

that the fasteners must penetrate, they

are designed to accommodate either a

wood- or mac hine-type screw . To make

the best use of the fastening systems

available, an un derstand ing of wood

screw and m achine screw features is

desirable.

round

binding

Fastening I

Devices

Screw Fasteners

The following parts of a screw fastener

are im por tant to the installer and will b

discu ssed: head, driving configuration,

neck and/or shoulder, shank and body

thread, and point.

Head Des ign. The enlarged,

preforna

shape on one end of the screw is know

as the he ad. Heads are shaped to meet

the many requirements of the electria

and other industries. (See Fig. 21.1) Tk

oval and flat-undercut heads are

design ed to allow a semi-flush o r flust

with the surface of th e object being

(e.g., switch or receptacle cover plat

1

/2£k

f

-*^

u

>

rjZD £±

im

O

hex flange round flange flat undercut fillister

(hex washer) (round washer)

F I G U R E 2 1 . 1 C o m m o n h e a d d e s ig n s for s c rew f as t eners

376




The other types of head are for use

where it is desirable to h ave the entire

head of the screw on the surface being

held (e.g., the cover on an octagon or

squ are box). The head of any threa ded

fastener is the bearing surface which

suppo rts the load.

Driving Configuration. To meet the

many installation problem s that are

enco untered , a variety of tools and /or

drivers are available for the screw

fasteners. Figure 21.2 illustrates th e

various driving configurations produced

in the heads of screws.

The slotted typ e is an old stan dard,

designed for the comm on screwdriver

found in most h om e or sh op a rea s. It is

produced in many sizes to meet the

requirem ents of the various screw sizes.

square

recess

hexagon

"Phillips"

Allen head

F I G U R E 2 1 . 2 C o m m o n h e a d c o n f ig u r a t io n s

f or s c rew f as t eners

The ele ctrician's tool kit would n ot

be com plete without a set of square

recess

(commonly known as Robertson

he ad) sc rew driv ers. This form of driving

configuration is patented under the

trade name of Scrulox. It is produ ced in

six sizes ranging from No. 4 (largest) to

No. 00 (smallest).

A colour-coded handle indicates th e

size of the dr iver as follows. No. 4 black

is for

No.

16 screw s and larger.

No.

3

black, which is som ewhat mo re com

mo n, is used for No. 12 and No. 14 gauge

screw s. No. 2 red drive rs install No. 8,

No.

9, and No. 10 gauge screw s. No. 1

green is for th e No. 5, No. 6, and No. 7

gauge s crew s. No. 0 yellow installs gauge

No. 3 and No. 4. The No. 00 o range-han

dled d river is for the tiny N o.

1

and No. 2

gauge screws.

The Scrulox design ha s two highly

desirable features. The squa re reces s for

the driver is tapered slightly and causes

the screw to "cling" once it has been

placed on the tip of the driver. This

allows the installer to use one hand on

the driver/screw combination and the

other hand to supp ort the equipment

being installed. Heat treating (harden

ing) along with proper recess design pro

duces an excellent driving configuration,

thus reducing the frequency of "cam-

out." Cam-out is the action between

driver and rec ess that cau ses the driver

to disengage from the recess in the head.

Scrulox units are ideal for use with

mechanical or power-operated

screwdrivers.

Phillips-type screws and drivers are

used extensively for appliance assembly.

This ty pe of driving configuration per

mits th e use of air- or electric-powered

driving tools, thus speed ing up assem

bly-line procedures. Screwdrivers are

available in sizes similar to th os e of th e

square recess driver, but are seldom

Fastening Devices

377



colour coded. The Pozidriv unit is

designed primarily

for

use w ith power-

driven tools.

//exagon-shaped he ads a re found on

most

of

the larger machine screw s. They

require a wrench to tighten the m

securely without damage to the head.

Socket wrenches

or

specially de signed

nutdrivers (screwdriver handle and

shaft with

a

socket

at

th e tip) a re useful

in hard-to-get-at are as.

Hexagon recess screws, frequently

referred

to

as Allen head screw s, make

use of an L-shaped wre nch or key to

tighten them . They are frequently used

as "grub screw s"

to

hold motor pulleys

to shafts. They are also often u sed in the

assembly of mechanical devices or

frameworks. The fastening tools, known

as Allen keys, are available in sets of dif

ferent sizes, cove ring the br oad rang e of

screws equipped with this type of driv

ing configuration (See Fig. 22.14).

Torx

fasteners pro vide ano ther fas

tening alternative. They have bee n u sed

in th e construction of automobiles and

trucks for several yea rs. Headlight

m ounts, interior bod y trim, and mould

ing,

to

name

a

few specific applications,

have been sec ured by the se efficient,

slip-reducing fasteners, available in a

number

of

sizes. M anufacturers

of

elec

trical and electronic equipm ent have

also used the Torx fastener to assemble

their p rod ucts . Figure 21.3 shows a Torx

driver an d its tip configuration.

Some manufacturers prod uce a

screw-type fastener that can

be

installed

or removed w ith either of two driver

configurations. Th is concep t of th e dual-

drive

fastener has two advan tages.

Manufacturers of electrical equipm ent

are able

to

use both po wer screw and

nut drivers in the assembly of their prod

ucts . Doing so speed s up the production

process

and

helps

to

keep equipment

screw

head

c onf igur a t ion

driver

dr iver tip conf igurat ion

FIGURE 21.3 An efficient Torx screwdrnj

manufacturing costs down. Secondly,

installers and se rvice perso nnel can no

choose w hich

of

the two drivers they

prefer to use when servicing this equip

ment. Figure 21.4 illustrates thre e of

the se dual-drive fasteners.

Ne ck/Sh oulde r. The area directly

under the head of a screw is

frequently

given a special design treatme nt. Figim

21.5 illustrates several designs intende

to prevent rotation

of

the screw while

*

nut

is

being tightene d

on

the bolt.

A

screw t ha t relies on th e tightening of a

nut to secure

it

is mo re likely to have

this feature than one with some form a

driver configuration in the he ad. Such i

unit is ideal for u se in areas wh ere

access to both ends of the screw is

impo ssible or (for security reaso ns)

t<

prevent removal of the sc rew from the

outside (e.g., on the hinges of a supply

box).

Sha nk and Body. Th e length of sen

from u nde r the head

to

the t ip

is kne

as the

shank.

Any unth reade d portion

the shank is called the body of the

i

Long screw fasteners will often have

JIOWB

tioiU

scnJ

378

Applications

of




p

a

combination hex and slot driver configuration

combination square recess and slot driver configuration

with square

recess drivers

with

Phillips drivers

corner clearance

for positive

sidewall engagement

acceptable for 2

driving or removing

5

wi th P hillips driver

o

no corner

engagement

positive engagement

even at slight angle

new Quadrex configuration using

square recess and Phillips drivers

FIGURE 21.4 Dual-drive fasteners

thre ad only at the tip are a, leaving a long

body. Shorter screws are frequently

threa ded over the entire length of the

shank, leaving no bo dy at all. When o nly

the necessary amount of thread is

formed on the shank, screw produ ction

time and costs are reduced and the

upp er portion of the screw is stronger.

rC7>

oval shoulder

fin neck

square (carriage) neck

F I G U R E 21 .5 C o m m o n n e c k a n d s h o u l d e r

d e s i g n s

8 F I G U R E 2 1 . 6 S m a l l d i a m e t e r ( G a u g e N o .)

a m a c h i n e s c r e w s

Thread Types. Many threa d types are

available, each designed to fasten

securely in a particu lar building

material. Some of the m ore co mm on

types are as follows.

Machine screws. These

bolt-and-nut

units w ere designed primarily to join

metal to a variety of othe r ma terials.

They are produced in many thicknesses

and thread pitches, depending on the

amount of support strength and/o r

compression between surfaces required.

The smaller diameter machine screws

(having a gauge num ber) are available

with a variety of head s hap es and

designs as seen in Figure 21.6. Larger

Fastening Devices

379



I

carriage

bolts

hexagon

head cap

screws

machine

bolts

FIGURE 21.7 La rge d ia meter machine bolts

diameter units, frequently called

bolts.

are produ ced in three basic head shapes

as seen

in

Figure

21.7.

Most machine screw and /or bolt

sizes are produced with either coarse a

fine threa ds . The coarse-thread bolt

installs faster, since the nut advances

along the bolt

(thread pitch) a

greater

distance

for

each com plete turn . Fine-

threa d u nits require more turns of the

nut to tighten them, but excellent com

pression is obtained betw een the sur

faces joined. Table

21.1

compares com

mon coarse- and fine-thread screw sizes

with their m etric equivalen ts.

Instead a

producing metric screws that exactly

match their imperial measure (inches)

counterparts, manufacturers have

estal

lished

a

new set of popu lar m etric sizes

They have thu s avoided p roducing

TABLE

21.1 C omparing C ommon Coarse-and Fine-Thread Machine S crew S izes

Figures in this table are based on Unified scre w thread sizes as established by the A merican N ational Standards In stitute. The

tpi,

signify threads per

inch.

Unified Screw Threads

Coarse

no.

2

3

4

5

6

8

10

12

diam.

1/4

5/16

3/8

7/16

1/2

9/16

5/8

tp i

56

48

40

40

32

32

24

24

tp i

20

18

16

14

13

12

11

Fine

no.

2

3

4

5

6

8

10

12

diam.

1/4

5/16

3/8

7/16

1/2

9/16

5/8

tp i

64

56

48

44

40

36

32

28

tp i

28

24

24

20

20

18

18

Metric Screw Threads

Screw Thread

M2.2x0.45

M2.5x0.45

M3x0.5

M3.5x0.6

M4x0.7

M4.5x0.75

M5x0.8

M6x1

M7x1

M8x1.25

M 1 0 x 1 . 5

M 1 2 x 1 . 7 5

M 1 4 x 2

M 1 6 x 2

Example: To convert a 10-24 machine screw to metric, select M5

x

0.8.

Caution: Never mismatch m etric screws w ith imperial (inches) nuts or tapped

holes

380




screw s in awkward dimension s

(decim als). The new screw sizes h ave

simplified metric dimensions that are

reasonab ly close to the inch units they

repla ce. Table 21.2 offers a co m paris on

between th e old and new fastener

dimensions.

For prope r installation, m achine

screws req uire a clearan ce hole to be

drilled or a pre-threaded hole in the

ma terials being joined. The internal

thre ads of the h ole or nut being used to

secure the assembly must match the

external threa ds of the b olt or mach ine

screw to prevent damage to either part.

Machine screw nu ts are shown in

Figure 21.8.

win g hex square

FIGURE 21.8 Machine screw nuts

TABLE 21.2 C omparison Guide for P opular Me tric and Imperial Fastener S crew S izes

Diameters

The range of diameters listed in metric standards is

from

M l

.6 to

M l 0 0 .

Wherever possible designers are

asked to use the stock and preferred sizes listed here.

Metric

Diameter

M2

M2.5

M 3

M3.5

M 4

M 5

M 6

M 8

M1 0

M12

M14

M16

M20

M2 4

M3 0

M3 6

M42

M48

M56

M64

M72

M80

M90

M100

Imperial Diameter

(Gauge/Inches)

#2

#3

#5

#6

#8

3/16

1/4

5/16

3/8

7/16

1/2

9/16

5/8

3/4

1

1 1/8

1 1/4

13/8

1 1/2

13/4

2

2 1/4

2 1/2

2 3/4

3

31/2

4

Lengths

The metric lengths given are the preferred lengths,

and these should be used wherever possible. Some

of the sho rter len gths wi ll not b e available in larger

diameters.

If lengths over 200 mm are required, then incre

me nts of 20 m m should be used, and for lengths over

300 mm, increments of 25 mm should be used.

Metric Length

(mm)

10

12

16

20

25

30

35

40

45

50

55

60

65

70

75

80

90

100

110

120

130

140

150

160

170

180

190

200

Imperial Length

(Inches approx.)

3/8

1/2

5/8

3/4

1

1 1/4

13/8

1 1/2

1 3/4

2

2 1/4

2 1/2

2 3/4

3

3 1/4

3 1/2

4

41/2

4 3/4

5

51/2

6

6 1/4

61/2

7

7 1/2

8

Fastening Devices

381



Self-tapping screws. Self-tapping screws

are made of low-carbon, heat-treated

(hardened) steel and are available in five

basic types.

(1 )

Thread-forming

screws, as seen

in Figure

21.9,

reshap e the m aterial in

the pilot ho le and do not rem ove any of

the surrounding material. They provide

an excellent fit and fast assembly when

joining metal to metal.

(2 )

Thread<utting

screws are

designed w ith cutting edges and ch ip

cavities to remo ve material as they are

being installed. They are used in thick,

brittle, or granular materials w here

thread-forming screws are not suitable.

(See

Fig. 21.10)

(3) High-performance

thread-*

screws, shown in Figure

21.11,

en;

approximately

30%

more efficiently

ordinary self-tapping screws and 60%

more efficiently than machine screws

tapp ed hole s. Figure 21.12 illustrates

how the tight-fitting thread-forming

screw fits the material much more

securely than the tappe d hole and

mac hine screw with its thread

cle

Thread stripping and screw

breakage

virtually eliminated by the well-desipi

projections (spaced 120° apa rt at th e

tip) which form an accurate, mating

threa d in the screw-su pporting materi

These screws are ideal for

assembly-

production.

FIGURE 21.9 T hread-forming screws

8

CO

| FIGURE 21.11 High-performance tt

55 forming screws

FIGURE 21. 10 T hread-cutting screws

(4 )

High-performance thread<uttwg

1

screws are particularly suited for use

with brittle materials. Chips are quicttj

removed, reducing stripping or

cractti

hazards. These screws permit

quick,

easy assem bly and can be seen in

Figure

21.13.

(5 )

Metallic-drive

screws are

designed for perm anen t fastenings. T

are pressure driven by punch press or

ham me r into the holding material and

ar e well sui ted for attachi ng

nameplam

and covers, for example. Figure 21.14

illustrates this type of screw.

Wood

screws.

Wood screw s are used

it

man y different are as of the construct*

field and are available in four basic

thread configurations.

(1 ) Single lead (thread) tapered

wood screws have been in use for

mam

382




S3

FIGURE 21. 12 Machine screw installation

(top) and thread-forming screw installation

(bottom)

~^ &

in

FIGURE 21. 13

cutting screws

High-performance thread-

ye ars . (See Fig. 21.15) The tapered neck

and shank design, however, caused fre

quent splitting problems w hen installed

in wood. The amou nt of torq ue required

to install the screw increases greatly as

it pe ne trate s de eper into the wood. As a

direct result of this increase in torque,

more stre ss is placed both on the screw

driver and on the installer.

a

w»

FIGURE

21.15

screw

A tapered thread woo d

(2) A more recent developm ent is

the

double lead

(thread) and fast-spiral-

thread screw. Produced under different

t rade names (Kwixin and Twin-fast), this

type of screw has a neck and body thick

ness that is less than th e thread diam e

ter. Splitting is virtually eliminated and

driver/installer stress reduced signifi

cantly due to this d esign. In addition, the

sides of the dou ble-threaded shank are

parallel, providing greater holding

power and faster penetration.

Figure 21.16 offers a comparison

between single- and double-lead wood

screws. The sharp point on the do uble

lead screw red uce s the need for pre-

5

single

thread

d o u b le

thread

FIGURE 21.14 A metallic-drive screw

FIGURE 21. 16

C omparison betw een single

and double thread screws

Fastening Devices

383



drilling and permits easier starting of the

screw.

(3) Fastening to par ticle board, plas

tic, and similar materials often presents

a powd ering or stripping problem in th e

material being fastened to. A specially

designed screw, with wider thread spac

ing, sharper and deeper threads, and a

well-designed self-starting point, is avail

able. One manufacturer h as named this

product the

Lo-root

screw. The screw

provides approximately

70%

greater

thread engagement with the material.

Figure 21.17 illustrate s this thre ad typ e

and the eight-point driver configuration

that makes this screw convenient for u se

with power screwdrivers.

(4)

A

wood screw for use in hard

an d

kiln-dried

woods is available.

It

has

a special augered flute in the tip that

I for

cu ts and clears th e wood fibres di

installation, eliminating the need

drilled holes and speeding up installa

tion co nsid erab ly. Figure 21.18 illus

trates this type of screw and its driver

configuration. It is a fast-starting ser e*

suitable for use with power drivers. |

is produced by one manufacturer

<•

the trade name Candril screw.

sere-

Length of Sc rew s. Th e length of a

wood screw is determ ined by the

distan ce betw een the he ad and tip of i

screw . (See Fig. 21.19) M achine and

sheet metal (self-tapping) screws are

sized in a like manner. Screw s of each

thread type are produced in various

lengths to meet construction needs

are available in both imperial and

measurement.

2

FIGURE 21.17

configuration

Lo-root screw and driver

FIGURE 21.18 An augered-flute

t ip

and driver configuration




length

length

length

FIGURE 21.19 Method of determining

screw length

Screw Diameter. Th e thickne ss, or

diameter, of a screw is indicated by a

gauge num ber ranging from 0 to 24. Th e

higher the gauge num ber, the thicker the

screw. Large, heavy-du ty screw -thread

units are available as illustrated in

Figure

21.20.

These lag bolts, as they are

called, find extensive use in

expansion-type masonry fasteners and

are available in standard machine bolt

diam eters and lengths.

Point Design. The tip or poin t of a

screw is designed to perform a variety

of

operations. Figure 21.21 illustrate s a

selection of point designs. Gimlet and

pinch points are for the penetration of

material.

Conical,

pilot (dog), and flat

(plain) points are to assist in the

alignment of the part s being sec ured .

Spherical, header,

and

chamfer

points

ease the insertion and starting of the

screw thread.

Screw Construction Materials.

Many

typ es of metal and alloy are used to

produ ce the many types of screws

available. Some of the more common

metals used are as follows.

Aluminum is used to prod uce a

s

I

FIGURE 21.20 Lag bolt

gimlet

conical

pinch

flat (plain)

header

spherical

FIGURE 21.21

screws

pilot (dog)

chamfer

Common point designs for

screw suitable for use with other alumi

num pro du cts where chem ical (gal

vanic) action between screw and mate

rial could take place. If other than

aluminum screw s were to be us ed,

severe damag e could result to the mate

rial.

Aluminum screw s ha ve less

strength than steel and brass screws,

and care must be taken during installa

tion not to twist them off.

Brass is used a great deal where cor

rosion from th e elem ents (rain, snow, air,

etc.) cou ld be a pro blem . It is easily

Fastening Devices



plated (chrome, etc.) by the manufac

turer for further corrosion resistance

and improved appearance. Silicone

bronz e is similar to b rass in strength and

corrosion resistance.

Monel, a nickel alloy, and stain less

steel are used where strength and extra

corrosion resistanc e are required. Steel

is by far the most com mon me tal used in

the manufacture of screws. It is stron g

and ea sily worked, and can be p lated for

resistance to corrosion.

Zinc or cadmium plating is applied

over the steel to pro tect it from corro

sion. Cadmium is the be tter of the tw o

coatings.

Bolt Strength. Steel hex-head m achine

bolts, or

ca p

screw s as they are often

called, are prod uce d in a num ber of

different tensile strengths, or SAE

(Society of Automotive Engineers)

grade s. The grade s rang e from 1 through

8 and the u ser is advised of the potential

holding power of each grade of bolt. A

simple pattern of ridges on the head

forms a grad e identification ma rk,

indicating the SAE rating. Table 21.3

illustrates typical markings, along with

size, load, strength, and hardness ratings.

Grade

1

and g rade 2 bolts can b e

used for the simple moun ting or fasten

ing of equipm ent w here strain and load

are not sev ere. The mid- and high-grade

units are used for heavy loads wh ere

stress and strain are greater, thus

preventing bolt or thread failure. As the

grade num ber increases, the carbon

steel of the bolt is subjected to a more

intensive heat/quench (hardening)

process .

Masonry Fasteners

Due to th e extensive use of m aso nry

m aterials (con crete, brick, etc.) in bo th

old and new buildings, a greater v ariety

of fastening devices ha s been develope d

for use by the construction trades. Much

of the electrical equipm ent installed

must be fastened to or sup po rted on

m ason ry surfaces, with one o r mo re of

the following fastening systems.

Screw A nchors.

Screw anc ho rs are

available in jute fibre, lead, n ylon, and

plastic. This comm on fastening dev ice is

inserted into a

pre-drilled

hole in the

ma sonry surface. A screw is then used

to com plete th e fastening system . Figure

21.22 illustrates lead and jute screw

anchors suitable for use with wood

scre w s. Figure

21.23

show s a well-

engineered plastic screw anchor which

can be used effectively with either a

wood or sheet metal screw. Whatever

anc hor is used should be as long as th e

threade d shank of the screw

(approximately of screw len gth).

Screw anc ho rs are also ma de in a variety

FIGURE 21.22 Screw anchors—lead (top)

and jute fibre (bottom)

FIGURE 21.23 A well-engineered plastic

scre w anchor for use in masonry materials

Fastening D evices

387



of wid ths, app ropr iate to the gauge

diam eters of screws. For example, th e

newer plastic screw anchors can accom

modate

No.

6 t o

No. 16

gauge screws.

Figure 21.24 show s a handy plastic

anch or kit with a num ber of anc ho rs,

matching screws and a drill bit.

Figure 21.25 m atche s up app rop riate

anchor and screw sizes.

Figures

21.26

and 21.27 illustrate

fibre and lead anchor installations.

FIGU R E

21.24

A versat i le plast ic anch or k i t

wi th anchors, screws and a masonry dr i l l b i t

Length of

Anchor

(inches)

3/4

7/8

1

1-3/8

Screw

Size

6-8

8-10

10-12

14-16

Size of

Drill

(inches)

3/16

3/16

1/4

5/16

FIGURE

21.25

P lastic anch ors are pro duc ed

in a range of s izes so that they can be used

w i t h t h e m o s t c o m m o n l y u s e d w o o d o r s h e e t

m e t a l s c r e w s . (Note: S peci f icat ions appear in

imper ia l meas ure on ly bec aus e t he equipment

is sold in that measuring system.)

For a stur die r installation, a metal

alloy ex pansion (lag) sh ield is available.

(See Fig. 21.28) Such a un it h as been

designed t o acce pt lag bolts and is use

ful where a larger su pp or t d evice is

required for heavy loads.

cutaway

outlet box

i«£«» ;;

:

:

;

i;":'

masonry

material

«•'

••"';

fibre plus

FIGU R E 21 .26 Insta l lat ion of a f ibre

anchor

wood

screw

1

..-':

expanded lead anchor

81

<7> F IGURE

21.27

A lead anch or instal lat ion"

^ jrmji ;? -.

FIGURE

21.28

Lag bol t expa nsion sh

388




Expansion Shields.

Expansion shields

are primarily designed for use with

ma chine o r lag bo lts. The se zinc alloy

units are produc ed in various lengths

and diam eters, with internal threa ds in

common machine screw/bolt sizes. A

hole of the correct diameter, as

indicated on the expansion shield, m ust

be drilled into th e m aso nr y for th e full

depth of the shield. The shield is then

inserted and the m achine or lag bolt

threade d into position. As the bolt is

tightened, the threaded section of the

shield is drawn tow ards the mo unting

surface, expanding th e bod y of th e

shield against the sides of the

pre-drilled

hole. Since the shield can exert great

pres sure on the sides of the hole as it

expa nds, care m ust be taken to use it in

solid or firm m aso nry m aterial. If not,

cracking of the m ason ry and releas e of

the shield can result. Figure 21.29

illustrates two types of the se s hields.

2

to

FIGU RE 21.29 Z inc al loy expa nsion shields

Self-Drilling Shield. A hardened steel

expansion shield has been produced. It

is capa ble of drilling its own hole . (See

Fig.

21.30)

The bo dy of the shield h as a

break-off,

tapered end which is held in a

power hammering device during

installation. Once the harden ed teeth at

the tip of the shield have drilled the

hole, a tapered steel plug is inserted into

F I G U R E 21.30 A harde ned stee l , sel f-

dr i l l ing, expansion shield and plug

th e

t ip.

The shield assem bly is then

placed back in the m ason ry ho le. Fur

ther pressure from the power hammer

drives the tapered

steel

plug up into the

shield, expanding the cutting tips and

widening the bottom of the hole. This

typ e of shield ha s extraordina ry holding

power du e to the increased hole and

shield diameter at the base of the hole.

Th e taper ed knock-off neck of the sh ield

can be rem oved easily onc e the shield

has been fully installed. A bolt of higher

SAE grade can be used with these

shields, since the internal thre ads of the

shield are also formed of hardened steel

Figures

21.31

and 21.32 illustrate th e u se

of expansion and self-drilling shields.

Lead Sle eve Anchor. A

simplified form

of expan sion sh ield is illustrated in

Figure

21.33.

These u nits are placed in a

pre-drilled h ole and set in to their final

machine

bolt

steel

bracket

FIGURE 21.31

installation

Shield expands against sides

of hole.

v - - .

J

. : - . : -

ole in

•

masonry

A z inc al loy expansion shield

Fastening Devices 38



removable tapered neck ,_ . ....

••';.;.'•.-vA.••'.", '•.•.'.'. tapered steel plug

.'-"..'.

J

' '' cutting teeth ..-.

•

•" '• • .•

' internal threads ' • " ••^

,

~I

£c£

:

;-.

,'.".;-. body :_;.:•. .'•;.•; ;..••• •>• ' . .• . :• . '

-'.'•'.'.. Hole and shield widens at base.

F I G U R E 2 1 . 3 2 A h a r d e n e d s t e e l, self-

dri l l ing, expansion shield instal lat ion

expanded position by a setting tool. (See

Fig.

21.34) Blows from a hammer provide

the necessary force to expand the lead

anchor into irregularities in the sides of

the hole. Figure 21.35 illustrates this

process.

An

internally threaded,

zinc-alloy cone assists in the expansion

and accepts standard machine

screws/bolts in

a

variety of

sizes.

Sleeve

anchors do not provide as m uch holding

power as o ther types of fasteners, but

are widely accepted for use in position

ing

machinery on a concrete floor. The

unit illustrated in Figure 21.35 uses a

machine bolt instead of a

FIGURE 21.33

FIGURE 21.34

Lead sleeve anchors

•^TipTiMPIM -

Lead sleeve setting tool

threaded cone. The bolt is left protrud

ing from the floor; the m achine is then

put into position and a standard

FIGU RE 21.35 Instal lat ion of a lead s leeve anchor and bol t

390 A pplications of E lectrical C onstruction



nut placed on the threaded end of the

bolt to tighten it in place.

Drive-in Anchors. Drive-in an ch ors are

basic expansion shields that a re secured

in masonry material by driven nails or

pins.

A

hole must b e

pre-drilled

in th e

mounting surface; an anchor is then

placed through the device being

supported and inserted into the

masonry hole.

A

series of blows from a

hammer will drive th e nail or pin into t he

shield, thus expanding the back po rtion

of th e shield against th e sides of the

hole. The shield itself supports the load

with this type of fastener, sinc e it pa sse s

through the device being supported.

One example of this type of unit is

illustrated in Figure 21.36. These u nits

are normally produced in sm aller

diam eters (5 mm to 13 mm for light-duty ]

applications. j

FIGURE 21.36 Drive-in anchor

i

Drilling Devices

Hammer-Driven Units.

In th e past,

holes in masonry surfaces w ere made

with the use of a hand-held,

hammer-driven, masonry drill. This

manual drill is still used by installers,

especially in areas w here electric or air

pow er is not readily available. It com es

in two parts as shown in Figures 21.37A

and B. The drill holder ha s a rubb er grip

assem bly to lessen the hamm ering

vibrations during drilling and to protect

the user's hand. The drill bits are formed

of high-quality carbon steel. They are

hardened, temp ered, and sharpen ed at

the tip to produce a relatively quick hole

in concrete, brick, or stone surfaces. The

shan k is tap ere d at the end to fit easily

into the drill holder. It is rec om m ende d

that the drill unit be rotated by the oper

ator during the drilling process to pre

vent binding and even tual breakage of

th e drill bit in the ho le. Drill bits ar e pro

duce d in sizes up to 15 mm diam eter for

use with th e smaller expansion type

shields.

Larger holes can be produced with a

four-point d rill, available in diam eters up

to 40 m m. Four-point drills are also

m ade in leng ths of 380 mm and 460 mm

whe re a dee p hole must be made, or

access to the work surface is awkward.

Figure 21.38 illustrat es this ty pe of dril

ling device. This hard ened -steel drill is

for use on all m aso nry su rfaces and

should be rotated d uring use to prevent

binding and/or jamming in the hole.

Power-Driven Units. Due to th e

pop ularity and availability of good

quality electric drills, a m aso nry drill bit

FIGURE 21.37A A manual, rubber grip,

masonry drill holder

FIGURE 21 37B Drill bit for a ma sonry drill

holder

FIGURE 21.38 A four-point masonry dril

Fastening Devices 391



has been produced for use with these

tools.

Air-powered drills can also u se

this type of bit for work on masonry sur

faces.

Th e shap e of the bit closely

resem bles that of a stand ard steel drill

bit. Th e cutting tip, however, is mad e

from a small piece of carbide brazed

(welded) into position. The carbide is an

extremely hard metal, capa ble of cutting

clean, fast, and a ccu rate ho les in most

masonry surfaces. The hardness of the

carbide tip makes it necessary to

re -

sharp en s uch a bit on a grinding wheel

specially compounded for the purpose.

Attempts to sharpen the bits on a stand

ard grinding wheel usually result in the

wearing dow n o r forming of grooves in

the grinding wheel itself. The bits are

prod uced in a variety of sizes, and sam

ples of the se are sh ow n in Figure 21.39.

The carbide bit is excellent for use with

most of the smaller fastening devices.

Figure 21.40 illustrate s t he us e of car

bide bits.

Larger holes can be prod uced in

m ason ry surfaces w ith a "multi" car

bide-tipped, spiral flute drill. This unit

ha s a hollow co re, allowing clearanc e i

chi ps and remo val of larger piec es of tf

m ason ry m aterial. Figure

21.41

illus

tr at es this form of drill bit. Drill bits

ate

available in assorte d d iam eters and

lengths to meet the needs of most large-

hole installations. Due to th e cos t

of

the se drill units, care should be taken

during the drilling not to damage or

remove the carbide cutting tips.

Removal of the drill bit from the hole

several times during the drilling

opera

tion will aid in chip cle aran ce and pro

long the life spa n of the bit.

Hollow-Wall

Fasteners

Many fastening op eration s are per

formed in residential or other buildings

where plaster materials are applied

to the wall and ceiling areas. These

surfaces are generally too thin and low

in density to accom mo date other thaa

the small screw-type anchors. There B

depth

of hole

to match

fastener

masonry

wall ,

M

carbide tip:.- '••.'. '•; .'•'.

F I G U R E 2 1 . 4 0

3

surfaces

Dri l l ing a hole in

masor

2

2

F I G U R E 21.39 C arb ide- t ipped, pow e r-

dr iven masonry dr i l l b i ts

F IG U RE 2 1 .4 1 A " m u l t i " carbide-tippt

masonry dr i l l

bit

392




however

a

series

of

mechan ical

fasteners designed

to

make use

of

the

space behind these

plaster or

similar

surfaces. Figure 21.42 illustrates

a

spring-wing, toggle-bolt fastener. The

tem pered steel wings are installed

on

the standard thread machine screw after

it has been passed through

the

device

being m oun ted. The wings are then

inserted into

a

pre-drilled hole in the

mo unting surface. Once clear

of

the back

of th e hole, the wings spring

to

an open

position. Tightening

of

the machine

screw draw s the wings

up

against

the

inside surface

of

the m ounting area, thus

securing the m ounted device. Figure

21.43 illus trates a toggle-bolt installa

tion. This typ e of fastener ca nnot be

reused, since

it

is virtually im possible

to

remove th e open, spring-wing portion

from th e sp ace beh ind th e wall. Th ese

units are available

in a

number

of

sizes

and types

for

the m ounting

of

equipment

on hollow-wall surfa ces.

Where

it is

necessa ry to remove and

replace equipm ent on the mounting sur

face, a type of fastener that rem ains in

place is us ed. Figure 21.44 illustrates this

type

of

fastener. The fastener unit fits

into

a

pre-drilled hole

in

the surface,

expands, and grips the back

of

the

mounting surface when the machine

screw is tightened. The machine screw

can be removed and the complete fas

ten er will remain

in

position

for

reuse.

These units are produced

in

several

sizes

for

use where th e load

to

be sup

ported

is

light. Figure

21.45

illustrates

the installation

of

this fastening device.

hollow

plaster

wall

spring wing

Tighten

machine screw

to secure

bracket

clearance hole

for toggle section

FIGURE 21.43

A

s pr ing- w ing t ogg le b o l t

instal lat ion

F I G U R E 2 1 . 4 4

A

ho l low - w al l s c rew anc hor

fastener

in

process of expanding

machine

screw

/

threaded body

mounting surface

machi

screw

head

FIGURE 21.42 A spring-wing toggle bolt

FIGURE 21.45

installation

A hollow-wall screw anchor

Fastening Devices

3



Powder-Actuated Fasteners

The drilling

of

holes

in

masonry

or

steel

surfaces is

a

tedio us and often time-con

suming operation. L abour versus fas

tener costs must be considered when

choosing

a

fastening system. Powder-

actuated fastening s ystem s speed u p fas

tening time and greatly redu ce the physi

cal strain on the installer. These systems

release much energy at the time

of

firing,

making it necess ary

to

fully tra in com pe

tent o per ato rs. Manufacturers of

powder-actuated tools and acce ssories

are m ost willing to train and advise

installers

in

the use

of

their e quipm ent.

In accorda nce w ith th e

CSA

standard for

powder-actuated tools (CSA, CAN 3-

Z166-M85), man ufacture rs

of

thes e tools

must train tool u ser s. After training,

the

potential tool user is tes ted through a

written examination and actual use of

appro priate fasteners in the tool. When

she

or

he has successfully com pleted

the test, an ope rato r's licence is issued.

(See Fig. 21.46) Powder-actuated tools

are divided into two main categories:

low- and high-velocity s yst em s.

Low-Velocity E quipment.

Low-

velocity tools ope rate at 90 m/s or less

and are suitable

for

fastening to most

masonry

or

steel surfaces. They are the

safest form of pow der-actuated tool

available, partly bec au se both piston

and fastener m ust be accelerated by the

powder charge. If

at

any time t he

fastener should pass through the

receiving surface, its speed and energy

will not

be

sufficient

to

endanger human

life. These tools have

a

somew hat higher

recoil than the high-velocity tools but

are quieter in operation. Due to the low

velocity

of

th e fastener, the tool do es n ot

have

a

controlled fire angle. This feature

is most necessary, however, on the

NOT TRANSFERABLE

®

Ramset

FASTENING SYSTEMS

QUALIFIED OPERATOR OF

EXPLOSIVE ACTUATED TOOLS

This Cer t i f ies that

has received training

in the

operation

of

the Ramset explosive actuated tool speci

fied herein,

has

passed

the

examination,

and

is

deemed com petent to operate such

a

tool.

Daiecf Issue

NO.

Manufacturer's Certified Agent

IN

ACCORDANCE WITH

CSA STANDARD Z166

FIGURE

21.46

A licence for operating

explosive-actuated tools

high-velocity to ols. A levelling device is

available as an option with the low-

velocity too ls an d will provide fire angle

control

if

desired.

The low-velocity tools are designed

and manufactured

in

accordance with

the CSA standard and must incorporate

several safety features: air-fire safety

to

prevent the tool from being discharged

into the air like a regular gun, a

safety

trigger lock to prevent accidental firing

when the tool is not

in

use , and drop-fire

prevention

to

prevent accidental firing if

th e tool is dro pp ed on the floor.

A

well-

designed buffer system prevents over-

travel

of

the d rive mechanism

if

and

when improper charges are inserted.

Figures

21.47

and

21.48

illustrate th e

mechanisms of low-velocity t oo ls.

Operation. Th e low-velocity tool

discharges a powder cartridge inside the

394

App l i ca t i ons of El ec tr i ca l C ons t ruc t i on



Piston hammers fastener.

f i r ing p in

Special piston-set

power load

•;i austempered

fastener

FIGURE 21.47 A low-ve locity, .22 calibre, piston-set tool and mec hanism used for many years

m the fastening industry

charge disc

austempered fastener

FIGURE 21.48 A m odern, low-velocity, .25 calibre, piston-type tool and mechanism

breach of the tool. This energy is the n

transferred to a special drive piston,

which in turn forces the harde ned steel

fastener into the mounting surface. Since

the fastener is nearly in contact with the

receiving surface prior to firing, it

canno t reach a high spee d. The energy

from the piston is then used to force the

fastener into the m ounting surface.

Approximately

5%

of th e driving

pow er in a low-velocity tool a cts on th e

fasteners. The remaining

95%

moves the

Fastening Devices

395



piston, which is designed in such a way

that it cann ot leave the tool.

Powder-Charge Cartridges.

The

explosive u sed in low-velocity tools

com es in the form of a brass and/o r

nickel rim fire cartrid ge. T hese

cartridg es are factory-loaded to prec ise

power levels and are given both a

number and a colour code to indicate

the se levels. Both cartridge and bo x or

container are equipped with the code

markings. Figure 21.49 show s som e

cartridges.

To speed up fastener op eration s,

some tools have been designed to

accep t groups of loads assembled onto

strips or discs. Figures 21.50 and 21.51

illustrate this method of load handling.

FIGURE 21.50

loading system

A multiple cartridge disc

M M * * * "

a

«*- *

V ,

FIGURE 21.51

ing cartridges

A lternative method of

FIGURE 21.43 A .22 calibre, rim fire, low-

velocity cartridge (left); .22 calibre, rim fire,

high-velocity c artridges (centre); a .38 calibre,

centre fire, high-velocity cartridge (right)

The Canadian Standards Association

has regulated that all manufacturers fol

low a common coding system for car

tridge pow er levels. Cartridges supplied

by a manufacturer should, however, be

used only in tha t manufacturer's tools

and not in tools from a different source.

The cartridg e coding system is outlined

in Table 21.4.

Fasteners. Four basic typ es of

fasteners are available. Drive pins are

used to nail materials directly to

TA BLE 21.4 P ower Loads (In Accoraa

with the CSA

Z166

Standard)

Low-

Velocity

Tools

High-

Velocity

Tools

Load

No.

1

2

3

4

5

6

7

8

9

10

11

:2

Case

Brass

Brass

Brass

Brass

Brass

Brass

Nickel

Nickel

Nickel

Nickel

Nickel

Nickel

L c s :

Cotow

B--

S M

v

e " I

~-z

P. . -

£ . . .

G - ~ -

v^ -

-~-

"-•; =

concrete, steel, and

horizontal

mortar

joints. They are perm anent fasteners,

intended for use with equipmen t that

doe s not need to be removed and

396




rem ounted . They are available in

asso rted lengths and d iame ters to fit the

tool system.

Threaded studs

are for use where

washer-and-threaded-nut mounting is

desire d, e.g., to facilitate removal and

remoun ting of equipm ent. They are also

ideal wh ere adjustment or repositioning

of the equipment is sometimes neces

sary. Care should be taken not to

over

tighten the nut; otherw ise, the stud will

be loosened in the mou nting surface

material. These versatile fasteners are

produced in

4

in. (6 m m) and

%

in.

(10 mm) threa d d iame ters, with various

thread and shank lengths to suit many

applications.

Eye pins find considerable use in

suspended ceiling installations, hanging

lighting fixtures, and attaching veneers

or wire mesh to co ncre te. They are

available in several sizes and lengths

for use in both high- and low-velocity

tools.

Light fixtures an d su spe nd ed ceil

ings often require the extra holding

strength achieved with the high-velocity

tool.

A

specially designed

clip-and-fasten

is available for use with the low-velocity

tool when fastening conduit or other fix

tures.

Fastening Surfaces. Figure 21.52

illustrates a few combinations of mat

erials that can be secured or sup

ported by powder-actuated fasteners.

W hen a stud or pin is fired in to con

crete (or similar, non-brittle masonry), a

compressive bond or ball is formed

around the point of the fastener. This

studs into steel

3 E

wood or non-metals

to steel

steel to

steel

•f'.'.'.'si

o • •

•

o:

O .

• • • 0 V

r> -

studs into concrete

wood or non-metals

to concrete

steel to concrete

conduit clips

under floor

electrical duct

= &

J

signs

panel boards

and junction

boxes

light

fixtures

timber framework

FIGURE 21.52 C ombinations of material to be secured by powder-actuated fasteners

suspended

ceilings

Fastening Devices

397



area acco unts for much of the holding

power, and so the fastener sho uld be

driven into the co ncre te to a dep th of

approximately

3

A

in. (20 mm ) when

securing to high strength con crete or at

least l'/4 in. (32 mm ) when fastening into

low strength con crete . Maximum hold

ing power is achieved when the strength

of the c onc rete in area

X

of F igure

21.53A

is greater than the bond at the point. If

penetration is not sufficient, the fastener

may pull out under load, removing a

cone-shaped section of the con crete as

indicated by the d otted lines in the

figure.

Con crete requires abo ut twenty-eight

days to reach its full compressive

strength. Any fastener set in "green"

concrete (less than four days old) will

only deve lop low holding power, but will

improve slightly as the concrete ages. It

is not recommended that fasteners be

driven into any concre te that is

less

than

four days old.

The small chips of con crete (known

as

spa/0

that break away from around

the pin area do not lessen th e holding

pow er of the fastener.

A

spall guard o n

the fastening tool will help eliminate

this, however, and improve the appear

an ce of the finished job . (See Fig.

21.53B)

Any fastener driven into a hollow

block must not be allowed to protru de

through the block. The compressive

bond at the point is lost com pletely

und er the se cond itions and little or no

holding pow er will be th e result.

Fasteners sh ould no t be driven into ver

tical mo rtar se am s on any brick or block

wall. M ortar in these seam s tend s to be

less in quantity and definitely lacking in

com pressive s trength. Only horizontal

mortar seams provide sufficient quantity

of material and adequate compressive

strength for holding power.

Care shou ld b e taken to drive sev eral

spall area

— stud

pull-out cone area

t

.' •'• • ;•': •'•''; v? ," *> compressive baJ

" ; i ;

;

. •. section of concrete ':

.].

'.•; A

FIGURE 21 53A A threaded stud in

concrete

FIGURE

21.53B

T hreaded studs driven in

concrete without a spall guard (left) and .

spall guard (right)

test

pins into an out-of-the-way area

of

the mounting surface to determine

proper cartridge strength and fastener

size.

Use great care to ensure th at the

fastener does not pass completely

through the receiving surface and

endanger som eone on the other side.

Always start with the weakest charge

and progress u p in strength until the

CM

rect combination is determined.

The use r of a pow der-actuated tool

sho uld be familiar with th e minimum da

tance recommended between fasteners.

398




T A B L E 2 1 . 5

L imi tat ion of Use When Fastening to Concrete

Shank

Diameter

(mm)

3.8

4.3

5.5

Spac ing

(mm)

75

75

100

Min imum D is t anc e

Edge to Fastener

(mm)

50

7 5

150

M i n i m u m

Thickness

(mm)

65

100

100

L imi tat io n of Use Wh en Fastening to S teel

3.8

4.3

5.5

50

50

50

2 5

2 5

25

5

10

10

T A B L E 2 1 . 6

Holding Power in Average Concrete

(3000 psi)

S hank

Diamet er

(mm)

3.8

4.3

5.5

5.5

P enet rat ion

(mm)

25

32

38

50

P ul l - out Load

w i t h

Safety

Factor

Inc luded

(kN)

1.2

1.9

3.4

3.9

Holding Power in Steel

S hank

Diameter

(mm)

3.8

3.8

3.8

Steel

Thickness

(mm)

5

6

8

P ul l - out

Load

w i t h Safety Factor

Included

(kN)

1.6

2.8

3.4

the minimum distance from the edge,

and the minimum thickn ess of the con

crete to provide safe installation and

adequate holding power. Table 21.5 lists

the important distances to be observed

with various fasteners.

Fasteners of different shank diame

ter s have different holding pow ers in

con crete . Table 21.6 lists the holding

power of pins or stu ds in averag e

concrete.

When driving a fastener into steel,

metal is displaced towards the surface of

the steel by the p enetrating fastener.

If

the steel is thin ner tha n the d epth of

threaded stud

steel

Point must pass

completely through.

FIGURE 21.54 A threaded stud in steel

penetration required, a mound forms

around the fastener's point of entry and

around its protruding point. Owing to

friction between the fastener and the

steel, so much energy is conv erted to

heat that both the surface and the fas

tener heat up to approximately 900°C.

The fastener and th e base steel then

weld and fuse together. The holding

pow er is a comb ination of fusion, braz

ing, keying action, a nd friction hold. (See

Fig. 21.54) On ce th e pro per am ount of

penetration has been achieved, the hold

ing pow er is determ ined by steel thick

ness and fastener diameter. The thicker

the steel and/or the larger the fastener,

the m ore holding pow er is realized. For

optimum holding power, fasteners

should completely penetrate the steel.

Fastening Devices



TABLE

21.7

Holding P ower in Steel Using High-V elocity

Fastening Tools

Shank

Diameter

(mm)

3.8

4 .3

5.5

Steel

Thickness

(mm)

10

10

12

Pull -out

Load w ith

Safety Fac

tor Included

(kN)

2.8

3.1

6.7

The ho lding pow er figures listed in Table

21.7 represe nt safe working loads for

steel applications.

On occasion , fasteners must b e

driven into thick steel where com plete

pen etration is impo ssible. In such a

case, a redu ced holding pow er is

achiev ed, but it is still enough for m ost

application s. Loads can be safely s up

ported on these fasteners, because 50%

of the fastener's potential holding power

can be achieved without full penetra

tion. When in dou bt abo ut the fastener's

ability to sup po rt a load, consult th e

manufacturer.

A

straight

spline-knurl

on the fas

tener's shank increases the holding

power and preve nts the threaded-stud

typ e of fastener from tu rning w hile the

i n

fasteners for use in

masonry materials

fasteners for use in steel

FIGU R E

21.55

Fas t eners f or ma s onry

steel

nut is being tightene d. Care should be

taken not to overtighten the nu t,

because tremendous pressure can be

exerted b y the turning

effort—even w *

a short w rench.

Fasteners for steel can b e easily

recof-

nized by the knurled sections on their

shanks and should not be used in

mason

surfaces or materials. Figure

21.55

com

pares concrete and steel fasteners.

threaded stud

Most of tip

guide is visible

'on surface.

Tip guide

is

badly

'shredded.

Upper end of tip guide is

i

. /

. steel beam

too little

FIGU R E 21 .56 T he plast ic t ip guide gives proo f of proper pen etra t ion.




Many fasteners com e equipped with

coloured plastic tip guides and plastic

washers. The plastic

tip-and-washer

guides t he fastene r while it is in th e bar

rel of the tool and ensures a straight

entry into the receiving surface. Another

im por tant function of the plastic tip is to

act as a pe net ratio n gu ide. If mo st of the

plastic tip is visible at th e po int of pene

tration after firing, penetration is insuffi

cient. W hen no plastic is visible, too

strong a charge has been used . Correct

pe netra tion will leave a small ring or

flange of plastic whe re the fastener

en ters th e ste el. (See Fig. 21.56) Once

again, sta rt w ith a light charg e, and

increase the ch arge strength until

proper penetration is achieved. Pins

should not be driven closer than 1.3 cm

from th e edge of steel. Fastening clo ser

to the edge could caus e a dangero us ric

oche t. When steel has been w elded,

the re is frequently an increase in the

hardness of the steel surrounding the

weld. For this reason, fasteners should

not be driven any closer than 5 cm from

a welded area.

High-Velocity Equipment.

High-

velocity tools (ab ove 90 m/s) a re

suitable for use in denser materials

wh ere pene tration is m ore difficult

and /or increased holding power is

requ ired. Th e high-velocity tool is

similar to a gun, in that th e fastener

accelerates down th e length of the

barrel, striking the receiving surface

with considerab le force. The tools are

designed in such a way that they canno t

be fired unless pressed firmly against

th e receiving surface. In this way th e

tool canno t be misused or accidentally

discharged. The firing mechanism of the

tool is also designed so tha t it will not

function whe n the too l is held at an

angle of

8°

off the perpendicular to the

<sv

shield

cartridge

pin fastener

barrel

"receiving surface

FIGURE 21.57 A high-velocity, .22 calibre

tool and mechanism

receiving surface . As a d irect result of

the fastener's speed and striking energy,

care must be taken to use manufacturer-

recommended procedures, safety guards

and equipm ent, as well as com mon

sense.

The se tools, when used by trained,

com petent operators, perform many

oth erw ise ted iou s task s in a fraction of

the time required by oth er fastening

m etho ds. Danger exists only when th e

tool or its related equipment is used

improperly. Figure 21.57 illustrates a

high-velocity tool mechanism.

Powder charges used with high-

velocity tools often exceed the strength

of tho se used in low-velocity un its. The

powerful .38 calibre fastener, as sho wn

in Figure 21.58, is restricted to the su s

pension of heavy loads. A special appli

catio ns tool is available for fastening

dev ices und erw ater. (See Fig. 21.59)

Figures 21.60 and 21.62 show a variety

of

powder-actuated fastening tools.

Fastening Devices

401



FIGURE 21.58

tool

A .38 calibre high-velocity

Safety Equipment. As pe r CSA

standards, personal protective

equipm ent should be worn by the tool

opera tor and any helpers or ob servers

in hazardo us proximity to the operation

FIGURE 21.59

underwater use

A high-velocity too l for

of the too l.

It

should include protective

headgear (hard hat) along with safety

gla sses or goggles. (See Fig. 21.61) Noise

levels from the more powerful tools

(especially in confined are as) make ear

pro tection well wo rth co nsidering. Com

mon sen se and consideration of others

working near by will greatly add to th e

safe use of these versatile

.22 ca libre

high-veloci ty

mult i -shot

low-veloci ty

s ingle-shot

low-veloci ty

FIGURE 21.60 P owder-actuated fastening tools that have been chosen by many installers

the years

402




FIGURE 21.61 P rotective headgear and

safety glasses must be worn by an operator

and observers in hazardous p roximity to any

fastening ope ration.

fastening systems. Manufacturers of the

tools pro duc e a variety of special g uards

and fastening aids to speed up the safe

operation of their equipment. The fol

lowing is a list of safety recom m enda

tions well wo rth rem emb ering.

Never use a pow der-actu ated tool

without having its op eration

and limitations explained to

you.

Always use the proper recomm ended

safety shield on the tool.

Never attem pt to set a fastener

through a pre-drilled hole in

steel .

Always try the wea kest cartridge on

the first shot. Progress to the

next heaviest load only when

necessary.

Never fire a fastener into th e immedi

ate area w here a previous fas

tener has just failed.

RGURE 21.62 Mod em powder-actuated fastening tools designed for single- and disc-loading

operations

Fastening Devices

403



Always check the receiving surface to

make sure it will safely accept

the intended fastener.

Never attem pt to fasten into hard

steel or near welds.

Always maintain prop er, safe firing dis

tances between fasteners and

the edge of mounting surfaces.

Never atte m pt to modify any tool or

to ada pt piec es of one manu

facturer's tool for use in

another 's .

Always check to see wh ether the bar

rel is clear before inserting a

fresh cartridge or fastener.

Never car ry fasteners or metal

objects in the s am e pocket as

the pow der cartridges.

Always wea r pro tectiv e safety equ ip

ment when using these tools .

Never load a tool until you are ready

to fire; never pu t a loaded tool

away: an untrained pers on

could fire it.

Always keep th e tool in good sh ap e.

Clean it regularly, and have it

checked by a manufacturer's

representative periodically.

Never point th e tool, loaded or

unloaded, at yourself or

another person.

Always keep the tool against the

receiving surface for at least

15 s to 20 s, if it should fail to

fire when triggered.

F o r R e v

i e w

1. List four pieces of electrical

eqi

ment that m ay require the use <

fastening devices to assist in

mounting them to masonry or

ilar

surfaces.

2. What are the three main type s i

screw fasteners?

3.

Name five driver configurations

for screw fasteners.

4.

List the different head types

ust

for screw fasteners.

5. State three advantages of using

square-recess (Robertson head)

screw fasteners.

6. Where are hexagon (Allen)

re«

type machine screws used?

7. What are th e adv antag es of using

self-tapping screws?

8. What is the difference between a

standard single lead and a Kwixin

wood screw?

9. How is the length of a wood screw

determined?

10.

What are the phy sical differences

between a wood screw and a lag

bolt?

11.

Name thr ee different ma terials

used for wood-screw construction

and state one use for each.

12.

Why is "bolt strength" imports

when using a machine bolt?

13.

Nam e four different ma terials

in the construction of m asonry

fasteners.

14.

Outline the procedure for fasten

ing an electrical box to a mas or

wall with a m aso nry fastener i

wood screw.

15. Describe four different methods"

creating a hole in a ma sonry v.

for an expansion-type fastening

device.

•101




16. Name two types of hollow-wall

fasteners an d give one app lication

of each.

17. State three adva ntages of a power-

actuated fastening system.

18.

Why is a licence ne ces sar y for

operating powder-actuated fasten

ing systems?

19. List th e cartridg e and c harg e iden

tifications for low-velocity fasten

ing system s.

20. Explain why a threaded stud is

used to mount equipment, rather

than a d rive pin.

21.

How does a threaded stud for steel

differ from a masonry stud?

22. List three precautions to be taken

when driving fasteners into steel

surfaces.

23. What is the main difference

between the gun mechanisms of a

low-velocity and a high-velocity

tool?

24. What safety equipment is needed

by the operator of a pow der-

actuated tool?

25.

What is the calibre of the powder

cartrid ges used in high- and low-

velocity tools?

Fastening Devices

405



Tools of the

Electrical

Trade

E

ach t rad e or skill area h as sp ecial

ized tools designed for safety and

eas e of use, and the electrical trade is no

exception. Over many years, the tool

manufacturing industry has provided a

wide variety of both hand and power

tools to help both amateur and skilled

professional electricians perform their

tasks effectively.

Tool Quality

In

toda y's m arketplace, tools are availa

ble in many p rice ra nge s. As a g eneral

rule, higher quality tools tend to be in

the higher price ranges. Their cost is

often the result of extensive research by

the manufacturer, higher quality materi

als used, more elabora te manufacturing

processe s, and unique or patented

design features.

Many professionals have listened to

part-time tool us ers explain why they

refuse to buy th e more expensive but

highe r quality too ls. All to o frequently,

inexperienced part-time tool users

abuse , overwork, or prematurely wear

out th e lower quality tools they have

cho sen. They have practised false econ

omy, because now they hav e to pur

cha se tools again to complete what they

have started.

Consider, too, that low-quality

tool

material and poor design features oftea

put great stres s on the tool and the oper

ator. Even the experie nced professional

will notice an increa se in physical stress

frustration, a nd wo rk time when using

equipment not designed for the job at

han d. This fact alone would suggest

that

quality tools are essential to both the

training and continuing development of

apprentices and professionals

alike.

High-quality, well-designed too ls

hav e a well-balanced, easy-to-use "feel'

when handled. Tools with comfortable

grips designed to fit the human hand

with minimal discomfort indicate care

and attention to detail on the part of tta

manufacturer. Improperly designed t<

can not only tire out the operator pr

turely, but place him or her in physica

danger.

Tool users vary in height, weight

and arm and h and size, so the tools tta

select should take their physical diffe

ences into account, as well as the

requirem ents of the task at hand. Ha

-

.

pro per too l size will prevent many

accidents caused by exposure to a

tc

that is simply too powerful for a pera

to control safely.

406




The Driver Family of

Hand T ools

The electrician relies heavily on a vari

ety of tools designed to sec ure equip

ment in place and /or install co ndu ctors

into terminal points or connections.

Drivers in a nu m be r of different ty pe s

and sizes are available. Chapter

21

of

this text illustrates many of the driver

configurations encountered by the

installer (See Fig. 21.2)

Standard Slot Screwdriver. This

versatile driver is used primarily for the

installation of woo d and metal screw s

having a slotted head . Many sizes are

produc ed for the electrician.

An electrician's screwdriver should

have a strong plastic han dle ca pable of

handling the physical stress associated

with normal u se.

A

plastic hand le is also

desirable because it is safe for operation

on or around live equip m ent. Some

man ufacturers provide cushion grips of

rubber on th e handles of their

screwdrivers, thereby preventing the

buildup of blisters and callouses on th e

hand, as well.

Large diam eter ha ndles are normally

indications of high-quality steel in the

blade and sh ank. Steel quality is impor

tant because hand torque is transferred

directly to the blade. (See Fig. 22.1)

Blades should be specially heat tre ated

to the proper hardness and temper to

ensure that they have maximum

strength and useful life span.

For bo th t he safety of th e installer

and pro per screw tension, the screw

driver's blad e should fit th e slot of t he

fastener. (See Fig. 22.3) This pr ev en ts

damage to the fastener's slot as well as

possible injury to th e user's hand or sur

rounding equipm ent sho uld th e tip slip

out of th e slo t.

F I G U R E 2 2 . 1

blade

heavy-duty

square blade

Slot screwdr iver wi th a round

C omfort grip of rubber is locked

around a slotted plastic handle.

specially

heat-treated

tip

Bolster provides

reinforcement

for hard use.

impact-

resistant

plastic handle

F IG U RE 22 .2 Heavy-du ty s l o t screwdr i ver

wi th a square b lade

F IG URE 22 .3

safety.

Blades must

fit—and fill—

the screw

slot.

Proper t ip size is a must for

Blades are produce d in bo th round

and square sha pes to provide the

required strength for

heavy-duty

opera

tions.

(See Fig. 22.2)

Slot Screwdriver Maintenance. Even

top quality drivers will eventually wear

or chip at th e corn ers. This condition

frequently causes damage to the screw

slot, needless slip-out of the screwd river

from th e slot, and personal injury to th e

user. For the m ost efficient use of th e

driver, be sure to keep tip edges straight

Tools of th e Electrical Trad e

407



Tip edges should

be sharp and complete.

Broken or worn edges

should be reground or

filed

to a new -like shape.

FIGURE 22.4 P roper care of the tip

improves driver efficiency and the personal

safety of the user.

FIGURE 22.5 P roper tip thickness and

shape are most important for safe and

efficient driver use.

and crisp . (See Fig. 22.4) Reshaping the

tip with a sm oo th hand file or a grinding

wheel will achieve t his.

Great ca re mus t b e taken if a po wer

grinder is used. Overhea ting th e tip will

destroy its hard nes s/tem per ratio, allow

ing the blade to bend each time high

torq ue is applied to th e screwdriver. A

clear indication of heat damage is tip

Phillips

o

o

orx

Square-tip

FIGURE 22.6 The four most comm on

tip configurations

discolouration. T he tip will change to a

straw colour to brown and to b lue.

When resha ping the tip, cold water

for the tip 's rapid cooling should be kept

in a container close to the grinding

wheel. The tip can be dipped in the

wa ter every few sec on ds to help control

tem pera ture rises while grinding.

In addition to sharp, crisp tip edges,

thickness is essential for safe and effi

cient screwdriver performance. A prop

erly ground tip will have a gradual tape r |

when viewed from the side. (See Fig.

22.5) Excessive tip thickn ess preve nts

th e tip from fully e ntering t he fastener

slot and can result in dam age to the fas

tener and poo r torq ue application. Ove»-

grinding and thinning of the tip will

weaken the blade and can lead to break

age of the d river's tip, as well as dam age

to the fastener and /or the surrounding

material.

Screwdrivers are produ ced in a

4 0 8




number of configurations (at the tip)

and the more common sha pes can be

seen in Figure 22.6. Pro ced ure s for main

taining screwdrivers in good co ndition

apply only to th e slot.

Square-tip Screwdriver.

Many

installers prefer squ are-tip screw drivers

when installing equipment because of

the unique "cling" feature of the square

recess screws used with

them—the

screw will remain on th e tip of the driv er

while being installed. This feature ha s

saved many hands from injury and

permitted one-handed driver operation,

an advantage because the second hand

is free to sup po rt th e equipment being

installed. The square-tip driver is

commonly known as a

Robertson

driver.

Robertson drivers (See

Fig.

22.7)

are

colour coded by som e manufacturers for

ease of recognition. A yellow ha nd le indi

cates sizing for No. 3 and No. 4 gauge

screws. The three most comm on colours

of handles are green, for No. 5, No. 6, and

No.

7

gauge sc rew s; red, for N o. 8, No. 9,

and

N o.

10; and black, for th e larg er

No.

12

and N o. 14 gauge scr ew s.

FIGURE 22.8 A P hillips screwdriver, availa

ble in tip sizes of N os. 1 ,2,3 and 4

(B

e

3

FIGURE 22. 9 A Torx screwdriver, produced £

in tip sizes of

T8, T10, T15,

T 20, T25, T27 and §

T 30 8

ma tches the fastener. If not, the screw

driver

will

cam-out of the ind enta tion in

the fastener, causing possible eq uipm ent

dam age o r per son al injury. See Figures

22.8

and

22.9

for th es e two drivers .

Safety Note: In area s near

live

con

ductors , an insulated screw driver blade

is desira ble. U sing a driver w ith one will

prevent sho rt circuits and dangerou s

flashes due to accidental c ontact

between live and grounded pa rts. (See

Fig. 22.10)

URE 22.7 A square-tip or Robertson

ewd river for use w ith square recess

ews. Robertson driver handles are colour

d to indicate tip sizes.

P hillips and Torx Screwdrivers. The

autom otive and electrical appliance

industries use two oth er typ es of

screw drivers, the Phillips and the Torx,

for product assembly, and in recent

years the Torx has become particularly

popular. Care m ust b e taken with a

Phillips driver to ensure that the tip

tr

'ML

FIGURE 22. 10 A n insulated-blade screw

driver for use near live equipment

Multi-Purpose Driver. This clever type

of driver stores several tip configura

tions in a hollowed-out handle. A

mag netic tube or chuck firmly ho lds th e

steel tips in place while th e drive r is

being used. Th e mu lti-purpose driver

replaces many individual drivers and is

an ideal tool for service and repair

pe rso ns w ho are unable to carry large

tool kits to the jo b. (See Fig. 22.11) The

Tools of the E lectrical Tra de

409



FIGURE 22.11

screwdriver

A multi-purpose magnetic

tips are made of high-quality steel and

will withstand consid erable torqu e from

th e user. However, du e to its hollow h an

dle and screw-on cap , this d river will not

stand up to as much impact abuse as

some of the other drivers.

Hollow-Shaft Nutdriver.

Many

electrical installations require the use of

a driver cap able of turning a hex he ad

bolt or nut. On occasion, the threa ded

bolt may be lengthy and require a driver

capa ble of fitting o ver t he extr a length of

the bolt. These unique drivers are

available in both metric and imperial

sizes,

and may be obtained with an

insulated shaft for protection near live

circuits.

Nutdrivers are usually purch ased in

sets of approximately seven. Figures

22.12 and 22.13 illustrate th is d river typ e.

Hex Key Driver. An othe r form of

driver, not usually found with a

FIGURE 22.12

a cushion grip

A h ollow-shaft nutdriver w ith §

FIGURE 22.1 3 A n insulated-shaft nutdriver

FIGURE 22.14 A versatile A llen key driv

set

FIGURE 22.15 A set of

" T "

handle, long

reach Allen key drivers

screw-d river h and le, is the hex key,

monly

known am ong installers as an

Allen key.

Hex key drivers are frequently

used to secu re pulleys to motor shafts,

as well as terminal scre w s in large main

service panels and equipment.

A

conve

nient set of nine can be seen in Figure

22.14. These drivers are produced in

both metric and

imperial

sizes.

410




Large handles, as on the "T " handle

un its in Figure 22.15, can b e mo st useful

when w orking on large service panels.

Having your han ds o utside of the box

and clear of sharp metal edges can be a

genuine safety feature. "T" handle units

can be purchased individually or in sets,

with a large plastic grip hand le ava ilable

for hand comfort and extra torq ue when

tightening.

T he Plier Family of

Hand T ools

The cutting and shaping of c ond ucto rs

when securing them to electrical equip

ment terminals has caused many types

of pliers to be dev elop ed. Each type is

uniq ue in its design features and is pro

duced to perform specific operations.

Installers usually have a variety of typ es

and sizes in their tool kits, their choice

based on personal preference and the

type of work they expect to perform.

Several manufacturers produce high-

quality pliers, and m any installers have a

nam e brand they like more than th e oth

ers. Pliers, after all, are an ex tens ion of

the hum an hand, and installers want

tools that will fit their hands and feel

right when being used.

Side Cutting Pliers.

Side cutters, as

they are commonly known, are one of

the most common types of pliers. They

are so named because their cutting

edges a re located on one side of th e

plier. Side cu tter s g rip fish ta pe s, tw ist

con duc tors to form splices, cut and trim

con duc tors to length, and hold nut an d

bolt fasteners while being tightened.

They are produ ced in a variety of

sizes, ran ging from 6 4 in. to 9'/4 in.

(15.9 cm to 23.5 cm ). The larger mo dels

are frequently referred to as "lineman's

pliers"

bec ause of their popularity with

wire cutter-

__ ,

cen tre of pivot pin

Standard side cutters have the pivot pin

located approximately twice as far from

the cutter (dimension A) as the high

leverage models, providing less

cutting pressure.

wire

cutter

, , — centre of pivot pin

Distance "A " on high leverage models is

less,

providing twice the cutting pressure.

FIGURE 22.16 C omparison of standard and

high leverage side cutters

the installers of pole and line equipment.

High-leverage m odels are available in

certain larger sizes. In the se pliers, the

pivot point is located closer to the tool's

cutting edge. This feature nearly doubles

the ease of cutting large diameter con

duc tors in the No. 3 or No. 2

AWG

range

of sizes. (See Fig. 22.16)

High-quality pliers a re forged, pro

portioned, shaped, hardened and tem

pered so that the handles have a certain

amount of

flex

or bend. This characteris

tic prev ents excessive hand strain to the

operator. (See Fig. 22.17) Modern cutting

edges are specially tough and hard, with

som e com panies using laser technology

in hardening to provide the user with

yea rs of reliable servic e from the tool.

Tools of the Electrical Trade

411



FIGURE 22.17 High leverage side cutting

pliers with comfort-grip handles

FIGURE 22.18 C hoosing pliers based on the

size of the user's hand ensures safe and effi

cient operation.

Pliers, like many other tools, should

be purchased to fit the hand size of the

owner, as well as to me et job req uire

ments. Figure 22.18 illustrates a pair of

high leverage side cutte rs well m atched

to the hand of the user.

Plastic comfort-grips are fitted to the

handles of many pliers to p rovide a

higher degree of user comfort. T hese

handles can lessen hand strain but often

lower the degree of cutting/gripping

power th e tool is able to provide. The

softness and "give" of the plastic used is

the ca us e. An analogy is that if you w ere

to weigh yourself on a bathroom scale

placed over a soft carpet, you would get

a different reading tha n if the sca le was

placed on a firm surface . Plastic grips

tend to enlarge the handle size of pliers,

which can b e a disadvantage to an

ow ner with a smaller h and.

Plastic grips should not be

considered

or treated as an

insulating feature

when

working with live wires. Tiny ho les or

cuts in the soft plastic render the tool

dangerous if only the handle is used to

isolate the user from a potential shock

hazard on an installation or repair. Plas

tic grips were not designed by the m anu

facturer for this purpose, and were

therefore not tested an d approve d for

shock protection.

Many electricians have found that

cutting tw o or mo re live wires at the

sam e time will pro du ce a short-circuit

curren t at the cutting edge. Care must be

taken to prevent this because the cur

rent will burn a hole right through the

cutter, destroying the usefulness of a

fine tool.

Diagonal Cutting Pliers. Th ese pliers

are intended for one purp ose, tha t is, to

cut wire and cab le. In the ha nd s of an

experienced installer, they can do much

more than trim conductors to length.

They can cut small bolts, trim the

sheathes of both nonmetallic and

armoured cables, prepare and trim

power tool cords, clean up e xcess

strands from terminal connections, and

form t he lo op in wires for term inal

screw s. They are particularly suited to

work in confined are as, where th e larger

side cutting pliers cannot b e used

effectively. Over the years, skilled

electricians have invented other uses

for

the se versatile cu tters , as well.

Similar to oth er typ es of pliers, diag

onal cut ters are available in various

sizes an d len gths, ranging from

4 4

in.

(11

cm ) to 8 in. (20 c m ). (See Figs. 22.19.

22.20 an d

22.21)

Both regular and high-

leverage models are available, using the

same design features produced on the

side cutters. Plastic comfort-grips are

provided by some manufacturers to

412 Application s of Electrical Con struction



FIGURE 22.19

General purpose diagonal

cutter for use with electronic and small

con

ductor circuits

FIGURE 22. 20

S tandard leverage general

purpose diagonal cutter

c

s

FIGURE

22.21

High leverage diagonal

cutters provide approximately one-third more

cutting pressure than standard mod els.

lessen han d str ess w hile using the tool.

Figure 22.22 illustrate s diago nal cu tter

operation.

Cable Cutters. Electrical cab les are

frequently assembled from multiple

strands of copper or aluminum wire.

(See Chapter Five.) Special

cable-cutting

tools allow an installer to cut o r trim

these larger conductors effectively.

Figure 22.23 illustrates a hand-operated

cutter, capable of trimming soft copper

cables up to

N o.

2/0 AWG. The str an ds

are kept in a nea t, close configuration for

easy insertion into a terminal block o r

con nec tor. Figure 22.24 illustrates a

compound lever-action cutter which

uses a ratchet assembly to provide

FIGURE 22.22 Use of diagonal cutting pliers

in a confined cable trough

FIGURE 22.23 Hand-operated cable cutter

FIGURE 22. 24 C ompound action ratchet

drive cable cutter

additional cutting force on soft copper

con duc tors up to 350 MCM. These

light

weight single-handed too ls can be car

ried in a stand ard tool po uch .

Figure 22.25 sho w s a two-h anded ,

32 in. (82 mm ) long-han dled, she ar-ty pe

cutter for copper and aluminum cables


413



FIGURE 22.25 Heavy-duty, two-h and ed cable cutter w ith fibreglass handles and rubber grips

up to 1000 MCM. Insu lated, fibreglass

handles ease the strain of operation,

while providing som e degree of pro tec

tion to the operator from live circuits.

The cutting tips can be replaced when

the y are too w orn for effective u se . This

tool was not designed to cut steel cables

or b olts. If it is used in this way, dam age

to the tool will result. The curved cutte r

design perm its an extremely neat cu t on

a cable, thereb y easing the task of insert

ing the cable into a termin al fitting.

Needle N os e Pliers. Needle

or

long

nose

pliers, as they are som etimes

called, give the installer or service

technician an extended reach into areas

or crevices where th e fingers cann ot

approach safely or effectively. They are

used to form loops on con du ctors for

termination, retrieve fallen or misplaced

parts,

hold small parts effectively for

installation, and assist in the tightening

of nuts and bolts. Num erous sizes are

available, with or without c utters , and

can be equipped by manufacturers with

comfort-grip plastic handles. Figures

22.26 and 22.27 illustrate this small but

versatile tool.

Many variations of these pliers are

prod uced . Some are equipped with wire

stripping no tche s, and som e have flat,

concave, or curved nose designs for spe

cial applications. Standard and long-

reach designs have been produced to

give installers and tec hnician s a tool to

meet any task they face.

FIGURE 22.26 S mall, 4 % in. (121 mm)

cutting long-nose pliers with comfort-grip

handles

FIGURE 22.27 Heavy-duty long-nose plier

in an 8Vi in . (211 mm) length, with comfort-

grip handles and wire-cutting jaws

Pump Pliers.

Pump pliers are another

highly useful tool in an electrician's kit

or pou ch. These pliers are to the

electrician w hat a pipe wrench is to the

plumber. The jaws are specially

designed to grip cond uit, fittings,

bolts,

nuts,

etc., in such a way tha t the re is an

abso lute m inimum of slippage when

torq ue is applied. The jaws are

positioned and locked into place by a

slanted tongue

which fits into a m atching

groove in the opposite handle.

A

wide

rang e of jaw open ings are available, and

the tong ue and groove feature ensure s

that the sett ing cannot change un der

the

heaviest pre ssu re of use.

414




Sizes ran ge from 6'/2 in.

(16.5

cm) to

16 in. (40.6 cm) in length . For maxim um

effectiveness, the pressure of turning

should be placed on the handle with the

tongue, not the section with the groove.

Jaw angle and t oo th design will the n per

mit supe rior gripping power. Applying

pressure to the grooved handle

will

lessen the tool's grip and add to th e

hand strain of th e user. Plastic comfort-

grips are produced by a number of

manufacturers. (See Fig. 22.28)

0)

FIGURE 22.28 Heavy-duty pump pliers w ith

comfort-grips and well-designed tongue and

groove jaw adjustment

C utting T ools

Wire and cable prepara tion re quires the

removal of a certain amount of insula

tion prior to termination in a conn ector

or terminal block. Many installers prefer

to us e a knife for this pu rpo se.

Knives. Figure 22.29 illu stra tes a

versatile pocket or pouch knife with two

blades. The sharpened blade can

perform traditional cutting operations,

while a blunted, seco nd blade, having a

slip-proof lock mec hanism, can be used

as a screwdriver for low-torque

installations.

A

curved, slitting blade is produc ed

in both pocket and fixed-blade config

uration s. Th e curv ed b lade pocketknife

show n in Figure 22.30 can be attac he d to

the installer's tool pouch by the handle

ring. It ser ve s as a com pac t part of th e

tool kit.

FIGURE 22.29

knife

A two-blade electrician's

FIGURE 22.30 A curved blade, folding,

cable-slitting knife

FIGURE 22.31 A heavy-duty, plastic

han

dled,

curved blade knife for line work

A larger, fixed-blade, line man's knife

can b e seen in Figure

22.31

and is m ost

suited to the difficult nature of work per

formed on line-work operations. The

extra large handle allows the us er to

wear protective gloves and still maintain

a good g rip and co ntrol of the knife while

using it.


41



FIGURE 22.32 A cable splicing kit consist

ing of a knife, scissors and pouch

Cable splicers and other installers of

small con du ctor cables make use of a

versatile scissor/knife kit. The scisso rs

are notched on the up per p art of the

blade to assist in the stripping of small

wires, and th e tw o units fit snug ly into a

pouch designed for the purpose. (See

Fig. 22.32)

Hacksaw.

Condu it op era tion s of all

size require the frequent use of a

metal-cutting hacksaw. The heavy-duty

mo del sho wn in Figure 22.33 has a

square-tube frame that holds spare

blad es for the installer. Blade tension is

adjusted by a wing-nut unit at the base

of the h andle: tension should be regu

lated to prevent u ndue b ending of the

blade while cutting.

Blades are prod uced in a wide range

of lengths and qualities to suit the saw

and task at hand. Both carbo n and high

speed steel blades are available from a

number of manufacturers.

The necessary number of teeth per

inch of blad e is determ ined by the thick

ne ss of the m aterial being cut. Thin

materials such as thinwall conduit and

armoured cable benefit from blades hav

ing 32 tee th pe r inch. Rigid con duit and

general cutting ope rations frequently

require the 24 tooth per inch blade.

Triple Tapping Tool. Installers

frequently have to clean up thread ed

holes in boxes and fittings which have

become clogged or damaged during the

con structio n pro ces s. A most useful tool

for this ta sk is pic ture d in Figure 22.34.

Its screwdriver-like design permits

one-handed operation. The most

commonly used thre ads, No.

6-32

tpi,

No. 8-32 tpi, and No. 10-32 tpi, a re

mac hined o nto the blade/shaft of the

unit.

FIGURE 22.34 A triple tapping tool for

repairing damaged No. 6-32 tpi, No. 8-32 tp

and No. 10-32 tpi threads found in m ost el'

trical equipment

FIGURE 22.33

frame hacksaw

A heavy-duty, square-tube

The b lade, m ade of high-quality tool

steel, can be b roken easily if not held at

a 90° angle to th e work, or if subje cted to

extreme torq ue d uring its use. Blades

can b e replaced if nece ssary.

416




Scratch Awl.

On many occasions,

electricians h ave to m ake hole s in m etal

and m ust first mark whe re the h oles

should b e. The awl, with

its

hardened,

sha rpe ne d steel point, is a tool m ost

suitable for this task. W hen h and held, it

is cap ab le of scribing a c lean, fine line on

a metal surface.

Many installations take place on or

over metal,

preformed-pan

ceilings,

metal stud s, and oth er lightweight shee t

metal products . Sheet metal screws (see

Chapter 21) are frequently used to

secu re boxes and cables to these sur

faces.

Starting holes for the screw s can

be m ade by striking the awl with a ham

mer and driving it into the sh eet m etal. A

heavy-duty m odel is pictured in Figure

22.35.

Plastic-handled models are produced

by several ma nufacturers for lighter

duty operat ions.

FIGURE 22.35 Heavy-duty scratch aw l

S triking T ools

Hammers form a major part of an electri

cian's tool kit. They are invaluable when

installing equipment with nails, fasten

ing cable with stap les, or creating holes

in m aso nry w alls or surfaces. Several

types have been produced to meet spe

cific job requirements.

Claw Hammer.

Claw hamm ers are

m ost useful for work on woo den frame

structu res. They drive and remove nails ,

staples, and other fasteners with a

minimum of strain on the op erator. O ne

claw ham me r, show n in Figure 22.36, has

been designed with the electrician in

mind. It has a non-conducting fibreglass

handle—a strong , shock -absorb ent sha

tha t will survive many ye ars of h ard

work, ft afso ha s a perforate d ru bb er

handle, a feature on som e claw ham me r

that provides th e user with a sure and

safe g rip. Claw ham m ers are pro duc ed in

a variety of head w eights, with the mo st

com mo n sizes being 16 oz. (454 g) and

20 oz. (567 g).

FIGURE 22.36 A straight claw, fibreglass

handled,

electrician's hammer with perforate

rubber grip

FIGURE 22.37

hammer

A w ood en handled ball pe

Ball Peen Hammer.

The ba ll peen o r

"ma chinist 's" ham mer is produced in

th e widest range of head w eights, the se

being 8 oz. (227 g ), 12 oz. (340 g), 16 oz.

(454 g), 24 oz. (680 g) an d 32 oz. (907 g).

Ball peen hammers are ideal for

heavy-duty striking operations such as

cutting with a cold chisel, p roduc ing

hole s in con cre te surfaces, o r driving

assorted fasteners into place with heavy

blows. Th ese h am m ers, one of which is

show n in Figure 22.37, are usually

equipped with strong wooden hand les.


41



Soft - face Dead Blow Hammer.

Soft-face dead blow

hamm ers are

app ropria te tools for assembling electric

motors or similar equipment where the

parts are made of cast iron. They have a

somewhat

hollowed-out

head,

containing hun dre ds of metal balls or

buckshot. The soft plastic facing on the

head c ushio ns pa rt of the blow while the

shot pellets follow up with a second,

softer

blow—a

normal hammer would

just "bounce off" the casting after

impact. The softer blow eliminates the

bounce and prevents the casting from

vibra ting or "ringing." It is this ab se nc e

of vibration that reduces metal stress on

the casting and prevents breakage.

Figure 22.38 sho w s a soft-face dead

blow hammer. The product is available

in 32 oz. (907 g) an d 48 oz. (1361 g) head

weights.

r -

FIGURE 22.3 9

P ocket-size, retractable,

steel tape measures in both imperial and

metric configurations

FIGURE 22.38

hammer

A plastic-covered dead blow

Measuring Tools

Several different typ es of m easurin g

tapes and rulers are available to the

installer of electrical equipment. The

most comm only used measuring device

is the re tractab le tap e m easure . It is nor

mally equipped with a

steel

tape, gradu

ated in either metric or imperial units,

and is prod uced in several lengths to

meet a variety of construc tion nee ds.

Replacement tap es are available and can

be used to exten d th e life of th e tool

when numbers become worn off or the

steel t ap e dam aged . Figure 22.39 illus

trates this type of tape measure.

Safety Note:

Great care must be

taken when working near live equipment

with a steel tape m easure. The tape con

ducts electricity, so contact with live

electrical parts can cause serious injury

to it or th e user.

Non<onducting

tap es a re available in

two d istinctive styles . Figure 22.40

show s a wo oden ruler, with sections thai

pivot to allow it to be op ene d to what

ever length is required. The ruler is eas

ily "folded" bac k into its com pac t form

for storage in the tool kit. It is available

FIGURE 22. 40

W ooden folding ruler

418




in both imperial and metric measure,

that

is,

in both 6 ft. and 2 m lengths.

Frequently an installer must measure

longer d istances when laying out a job

or estimating lengths of m aterial to be

used. Another tape measure, with a tape

of either non-conducting fabric or of

steel, is available in lengths of

50

ft. and

100

ft. and in lengths of

15

m,

25 m,

and

30

m.

Figure 22.41 illustrates this type of

measuring device.

FIGURE

22.41

N on-conducting fabric tape

measure and reel

S afety E quipment

Electricians or lineworkers spend a con

siderable amount of installation time

working from ladders, building struc

tures, or outdoor poles. To protect them

from falls and decrease their fatigue,

safety belts and harnesses have been

developed.

Figure 22.42 illustrates a safety belt,

made from a tough nylon m aterial and

equipped with drop-forged tongue buck

les and "D" rings. This belt is not

intended to support the worker while

performing

a

task,

but to act as a fall pre

vention device should the worker lose

his or her footing or grip during the job.

Strong,

5

/8 in. (16 mm) nylon rope is

recommended for use with the belt. This

safety line should be secured properly

FIGURE 22.42 N on-supporting, nylon mesh

safety b elt, for use w ith sturdy safety lines

to both the belt and a structure near the

worker that could withstand the stress

that would be placed on both the belt

and th e rope if the worker slipped and

fell.

Special features are required in a

body belt meant to supp ort the w orker's

weight while the job is being performed.

Additional stre ss from body movements,

pulling, tugging, twisting, and lifting

must be handled by these belts. Figure

22.43 illustrates this belt type.

Figure 22.44 illustrates the adjustable

type of pole strap frequently used when

the installer or lineworker is using the

belt to support his or her weight.

Figure 22.45 illustrates a far more

supportive belt that can provide addi

tional back support to the

worker.

This

belt is intended to reduce the physical

stress and fatigue of the user who may

be in it for extended periods of time.

Lockout Device.

Great care must be

taken when working on or around live

equipment or machines that could start

up without notice. To prevent injury

from these sources, installers frequently

place a padlock on the main power

switch supplying current to the

equipment being worked on. When a

number of trades are required to work

on one machine at the same time, each

worker needs control over the start-up

of the machine or equipment.

Figure 22.46 illustrates a device

designed to give a worker such protection


419



FIGURE 22.43 Body type safety belt designed to support the worker and carry basic

installation to ols

This lockout device can be installed

through th e padlock opening of switch

boxes and provide spaces for up to six

padlocks. In this manner, each trade can

secure the power switch in an

off

posi

tion until the equipm ent can be safely

energized or turned on.

| FIGURE 22.46 A lockout device to provide

| mu lti-trade, pow er-off security

FIGURE 22.44 A djustable pole strap for use

with body type safety belts

FIGURE 22.45 Heavy-duty body belt w ith additional back support for extended work periods

420




Tool Pouches and Kits

Several manufacturers produce leather

tool-carrying pouc hes tha t provide the

installer with a convenient me thod of

keeping the tools close at hand. Figures

22.47 and 22.48 illustra te tw o of t he

many designs available.

When filled with tools , th es e

po uch es are very heavy, so only those of

the best quality materials and

workman

ship should be considered w hen making

a p urc has e; lightweight, low-quality

pou ches will soon wear out and be com e

both a nuisance and a work hazard. A

wide, strong belt m atched to th e us er's

S

waist size should also be chosen for use

with a pouch.

Figure 22.49 illustrates some of the

tools frequently carried by installers in

their pouch es. Although pouche s are

usually purchas ed separa tely from tools,

on occasion, a manufacturer or tool sup

plier will offer a "package

deed"

whereby

the tools and a carrying pouch are

included in the purc hase price.

A high-quality tool kit, con sisting

of

tools and pouch, costs a considerable

sum of money, so care should be taken

not to shorten its useful life. Exposure to

we tness, extremes of heat, and corrosive

chemicals can ruin this valuable work

aid.

Holster-style

pouches are also availa

ble. Designed for user s of portable, bat

tery-operated drills and screwdriver-

type tools, thes e pou ches help overcome

FIGURE 22.47 A three-pocket tool pouch

with screwdriver support loops and tape

holder

FIGURE 22.48 A versati le pouch with a vari

ety of external tool sleeves, tape holder and

knife-holding snap clip

Tools o( the Electrical Trade 421



2

o

•c

LU

5

o

FIGURE 22.49 Some of the many hand

tools normally carried by installers or service

personnel in their tool pouches

FIGURE 22.50 A holster-style pouch with

com partme nts for a spare battery and bits, f<

use with battery-operated drill/driver tools

the problems of looking after tools when

not in immediate

use,

particularly if

someone is working from a ladder or

other support platform height.

Figure 22.50 illustrates a quality hol

ster-style pouch capable of supporting

the tool, extra

bits,

and spare battery

when needed. A leather thong has been

provided to secure the pouch to th e

user's leg and prevent it from bouncing

or flopping about when climbing

ladders, etc.

P ortable P ower T ools

For many years, po rtable, electric power

tools have been a major factor in both

the construction and service industries.

These tools have undergone immense

improvement over the years , as job

requirements and tool technology have

developed. New products are constantly

being designed and m ade available to

the consumer. They offer the potential

owner a wide variety of

styles,

sizes, and

features.

Quality

and

Cost.

As with hand tools,

the quality of power tools greatly affects

their reliable term of use. Lower quality

tools (often reflected by a lower

purchase price) may appear attractive

to th e inexperienced user. However they

seldom provide the balance, comfort of

use, reliability, and pow er/torque

required to complete a demanding task.

The most expensive tool is not

necessarily the best for the

job,

but cost

does provide some indication of design

forethought, materials used, and the

guarantee provided by the

manufacturer.

422




Tool life tends to be shorten ed con

siderably when

an

underpowered

or

poo rly designed tool is forced to per

form

a

task b eyond its design cap abili

ties. The need to purchase two or more

replacement tools can usually be

avoided if one prop erly designed or

sized tool

is

cho sen from th e beginning.

The quality tool will no do ubt cost mo re

initially, but when lost time and inconven

ience are counted in, the lower cost tool

is seldom ch eap.

T he Power T ool Mo tor

The heart

of

every po rtable electric

power tool is the motor, and the m ost

comm on typ e is the universal motor,

which is

a series

motor. This hard-work

ing electrical m arvel is ver y similar in

design

to a

series direct current m otor,

and it possesses most of that mo tor's

operating chara cteristics. All of its inter

nal electrical parts are connected in

a

single path, series circuit.

The term

universal

refers to

the

m otor's ability to opera te on either AC

or DC. Universal mo tors are used for

nearly all portable,

motor-driven

tools,

kitchen appliances, and hous e mainte

nance equipment such as polishers and

vacuums. Figure 22.51 illustrates th e cir

cuit for this motor.

Motor Parts.

The two main electro

magnetic pa rts of the m otor are the field

coils

and th e

armature windings.

When

current is allowed

to

enter the motor

circuit, the field coils prod uc e a strong

mag netic force. As

a

direct result

of

the

single path, series circuit in the motor,

the sam e current flows through the

arm ature w indings. The se windings

produce a stron g m agnetic force of the ir

own. Th e two m agnetic forces reac t w ith

one another and cause the armature

to

f ield windings

VAMflJLT

brush

carbon

compoun

0=^

120V

A C

,J*Tcompoun

^ g '

armatu

trigger switch

FIGURE 22.51 Circuit diagram for a basic

series universal motor

rotate with considerable torque, as its

windings are forced away from the field

poles. The more current passes through

thes e two sets of coils/windings, the

more torq ue is developed by the motor.

Figure 22.52 illustrates the pa rts of this

motor.

Motor Torque and S pee d. The series

motor will increase in torque

development as mo re curre nt flows

through the field and armature

con du ctor s. As the a rma ture windings

rot ate thro ug h th e field area , a voltage,

known

as a

counter electromotive force

(cemf),

is

induced into these w indings.

This cemf opposes the applied volt

age and limits input current

to a

level

that the motor 's conducto rs can carry

safely, w ithout ov erhea ting or burnout.

Motor manufacturers carefully design

the size of their coils and w indings to

op era te with this cemf in effect.

Reducing the spe ed

of

the mo tor

reduc es the cemf produc ed in the arma

ture. This reduction

of

cemf can be seri

ous enough

to

permit excessive input

current, to overheat the tool, to cause

severe arcing at the brush/comm utator,

and

to

prematurely burn out the tool's

motor. Con ductor dam age inside the

motor is cumulative, and the motor will

Tools

of

the Electrical Trade

42



laminated steel

armature core

cooling

fan

armature

shatt

brush connection

springs

armature coils ballbearings

field windings

F I G U R E 2 2 . 5 2 I n t e r n a l p a r t s

of a

u n i v e r s a l m o t o r

power leads

not "heal" or get better when th e tool is

in stor age . For this reason ,

be

sure

to

consider th e quality and current-carry

ing capacity of a motor's windings when

purchasing a power to ol. Most power

tools have

a

current rating stamped

on

their nameplate

to

give the prosp ective

user som e indication of the m otor cur

rent recommended by the manufacturer

for safe and continued use.

Most series motors have

a

cooling

fan attache d to the a rm ature shaft to

assist in th e cooling of the motor and its

conductors. Lower quality

or

light-duty

tools are notorious for having condu c

tors th at a re too few in number or are

undersized. These condu ctors have a

direct influence on the cost and eventual

life span of the too l. Tool o per ator s

should condition themselves to listen to

the motor's normal operating speed and

sound and

to

allow th e too l

to

perform

as much as possible within its usual rpm

rang e. Stalling the m otor or ov erloading

the tool will quickly reduc e its no rmal

operating efficiency and life span: when

speed is reduced, cooling fan efficiency

drops

off

and th e input current rises.

Motor RPM. Series m otor s, by nature-

operate

at

many thousand s

of

revolu

tions per minute (rpm ), and their

arm ature and field curren ts are one and

the sam e. When the m otor is running

without

a

load

on

it, the relationsh ip

between the armature and field

magnetic forces allows the armature to

rotate

at

speeds up

to

25 000 rpm . Any

type

of

load p laced

on

this mo tor

reduces armature speed and increases

the field and ar m ature current. The

increase

in

current causes the m otor

to

develop more torque . This process wii

continu e right up to the po int where the

m otor stalls, and m aximum torq ue is

developed. As mentioned earlier in this

chapter, care mu st be taken not to allow

the speed reduction and current

increase

to

cause overheating and

damage

to

the windings.

Certain tools used

in

the wood

and

i

424




metal indus tries, such as routers and die

grinders, take advantage of this

high

speed operation to produce clean and

efficient cuts.

Most tools favoured by th e elec trical

industry have gear drive systems within

them. A gear system reduces the output

rpm of a tool to a more useful level wh en

drilling or sawing, and at the sam e time,

increases the tool's outpu t torq ue. Tre

mendous power/torque can be devel

oped by these tools when equipped with

the proper speed-reduction gears.

A

person abou t to purch ase a power

tool should check the tool's nam eplate

for th e outp ut rpm rating. Some lower

quality tools lack sufficient gears,

thereb y increasing outp ut rpm, but

reducing the ou tput to rque of the tool

considerably. They may have a lower

purchase price, but the short life span of

such a tool and its motor soon eliminate

this apparent benefit.

Motor B earings. High arm ature rpm

and gear-drive torqu e and stress are

pre sen t thro ugh out th e life of the tool.

Lower quality tools frequently use a

sleeve-type bearing, made of sintered

bronze or similar metal.

Sintering

is a

process whereby powdered bronze

particles are compressed under great

pressure into the final shape of the

bearing. The compresse d powd er is heat

treat ed so th at it will stay in th e d esired

bearing shape . The porous bearing is

then impregnated w ith a lubricant such

as oil. Such a bearing is c onsid ered

permanently lubricated, and indeed

lubrication cannot be effectively added

to the sintered bearing material.

Sleeve-type bearing s will not stan d up to

continued hard use and should not be

considered for tools designated as

industrial grade.

Q uality power tools only use a com

bination of high-speed

needle/roller and

ball bearings. The se bearings can b e

checked and relubricated with a high-

quality bearing grease throughout the

life span of a tool, depending on the fre

quency and type of use the tool is sub

jected to. Needle/roller and ball bearings

will raise a tool's initial pu rch ase price

but add m any years of useful s ervic e to

the product.

Electric Drills

Few installers lack electric drills which

are p rodu ced in a wide variety of styles

by a number of highly respected tool

m anufa cturers. Basic differences in drills

seem to be in the materials used for

the con struction of the outer case or

housing.

Metal has been p opular for m any

years, and is still preferred by many

us ers for its ability to m aintain prop er

gear/shaft/bearing alignment within the

motor. Proper alignment contribu tes

much to th e life span of the tool.

In recent y ears, however, some

manufacturers have switched to

a glass

reinforced polycarbonate material for

their housings. This material can with

stand years of hard use without crack

ing, provide the corrosion resistance

that some metal-clad tools lack, and

make possible the "double insulated"

feature app reciated by many service

personnel.

Double insulated

means that

the too l's internal wiring has a primary

insulation while all metal p ar ts of the

tool are electrically separated from the

user by a seco nda ry system of insula

tion. This type of tool do es not r equ ire a

grounded plug and does protect the use

from electrical shock.

Figure 22.53 illus trat es a drill of th e

dou ble insulated typ e. Such a drill is pro

duced in models having a 4 in. (6 mm ),

Tools of the E lectrical Trade

42



F I G U R E 2 2 . 5 3 A % in . (10 mm) var iable

s p e e d

dri l l ,

l i ght t o m ediu m du t y , w i t h a

rev ers ing s w i t c h

3

I

2

Vs in. (10

mm),

or Vi in. (13 mm) capacity

chuck.

Many of these drills are equipped

with additional features, such as varia

ble speed control through the trigger

switch and m otor reversing. The motor

reversing feature aids in removing some

drill bits and allows the tool to be used

as a screwdriver when equipped with

the proper bit. (See Figs. 22.54 and 22.55

for diagrams of m otor reversing cir

cuits.)

Figure 22.56 features a m ore power

ful drill that has been equipped with a

heavy-duty m otor and

Chuck.

The drill is

designed to provide extra torque for

tougher jobs.

half of field winding

\

TJLQJLQJLT

trigger switch

#

120

V A C

double-pole

double-throw switch

^3",

rush

carbon

compound


• \ JU L Q _ Q JL T

FIGU R E 22. 54 A m ot or rev ers ing c i rcu i t us ing a double- po le , doub le- t hrow s w i t c h t o revers e

c urrent d i rec t ion t hrough t he armat ure w ind ings

426





trigger switch

1

£

120

V A C

AJlMiJjLr


FIGURE 22.55 A n alternate motor reversing circuit show ing direction of current through both

the field coils and armature wind ings

o

FIGURE 22.56 A heavy-duty

3

/

8

in.

(10 mm)

drill with speed control and a reversing sw itch

Safety Note: When using the se tools,

be sure not to grip them carelessly.

Many injuries have resulted when the

operator has not taken care. The drill bit

may jam, causing the tool to rotate in the

opposite direction to the bit and subject

ing the user's wrist to a great deal of

strain. Just as an installer should use the

proper size of hand tool, he or she

should also match power tools to both

the size of the task at hand and personal

size and ability.

Speed control is accomplished by

using a trigger switch with a built-in sili

cone control rectifier circuit (SCR) to reg

ulate the actual voltage that is supplied

to th e field and armature windings. This

trigger switch normally provides

Tools of th e Electrical Tra de

427



complete variable speed from zero to

full speed and provides the user with a

much greater degree of control for many

drilling operations.

On many occasions, large holes must

be drilled with high-speed steel drill bits

or hole saws, and they require the power

of a larger, two-handed power drill. Fig

ure 22.57 shows this type of drill. Care

must be taken by the operator to ensure

firm footing, balance, and a secure grip

to prevent injury during use of the tool.

FIGURE 22.57 A two-hande d powe r drill for

heavy cons truction use

Special Purpose Drills.

Electricians are

frequently forced to drill holes in

awkward or confined spaces. Several

specially designed angle drills are

available for these tasks and can be seen

in Figures 22.58, 22.59 and 22.60.

Drilling holes in brick or cement sur

faces can be time consuming and gruel

ling. Masonry drill bits such as those in

Figure 21.39 can be pu t to excellent use

in specially designed power drills that

produce both rotary and reciprocating

FIGURE 22.58 A light-duty angle dril l for

use in confined spaces

§ FIGURE 22.59 A

Vi

in. (13 mm) two sp -

3 angle

drill,

medium duty design, with full

| swivel adjustme nt of chuck direction

FIGURE 22.60 A

V?

in . (13 mm) two speeJ

angle drill, heavy-duty model

motions. As the drill bit rotates, a built-

in hammer feature causes the bit to

move in and out of the cutting surface

at

high speed. This in-and-out action

tends

to break up small stones or similar hard

spo ts in the drilling material, and

quicken the task considerably.

428




FIGURE

22.61

A light-duty hammer

dril

with a hole-depth guide

Q.

s

FIGURE 22.62 A variable, tw o speed ham

mer

drill,

medium duty, with dep th guide and

front handle grip

Figure

22.61

show s a light-duty ham

mer drill equipped with a hole-depth

guide to ensure uniform drilling depth.

A medium-duty ham mer drill can be

seen in Figure 22.62. This drill has two

separate speed ranges which can be

controlled from zero to full speed by the

trigger switch. A reversing switch allows

the tool to run in reverse so that it can

remo ve the drill bit and residu e from th e

finished hole. An adjustable handle is fit

ted to th e front sectio n of th e tool to pro

vide a bette r grip and safer control of

the tool when in use.

Both the tool shown in Figure 22.61

and the one sho wn in Figure 22.62 can be

used for straight drilling and hammer

drilling.

Heavy-duty too ls ar e available for

the installer who must drill large holes

into tough maso nry su rfaces. These

tools are also designed to operate for

long perio ds of time without undu e w ear

or o verhe ating. Figure 22.63 illustrates a

heavy-duty hammer drill that is

designed with a special type of chuck to

accept masonry bits only. It cannot be

used as a norm al typ e of drill with a con

ventional chuck.

Owners of hammer drills should peri

odically use an air hose to blow

powdered masonry particles from the

inside of the too l. Eye prote ction shou ld

be worn during all drilling and cleaning

operations.

FIGURE 22.63

rotary hamm er

A variable speed, heavy-duty

Tools of the Electrical Tra de 429



Battery-O pe rated Drivers

and Drills

When battery-operated tools were intro

duced a num ber of years ago, they ap

peared to be little mo re than interesting

toys. Battery-operated drivers and drills

we re no exception . Mo derately priced

driver drills with limited amounts of

torque are still available for casual users;

however, modern d evelopm ents in motor

and b attery technology have enabled

manufacturers to produ ce battery-pow

ered driv ers and drills with rema rkable

am oun ts of torqu e for their size.

Because these tools are

cordless,

the

installer is freed from th e ne ces sity t o

drag along a cord or to find an electrical

outlet close to the w ork area. He or she

is also able to work in outdoo r area s

away from electrical outlets.

Battery-operated tools have other

advan tages, as well. They perm it safe

work in dam p a reas, usually sourc es of

electrical shock haza rds. Many can both

drill holes and drive fasteners. Also, they

use

fasteharging,

nickel-cadmium batter

ies,

which, when cared for according t o

the tool manufacturer 's recommended

procedures and charging schedules, will

provide the tool opera tor with years of

faithful service.

Figure 22.64 shows a light-duty

driver drill with a 7.2 V ba ttery. Carrying

case, battery charger, and spare batter

ies are options for the tool.

Figure 22.65 illustrate s a hea vier

duty m odel using a 9.6 V battery. This

driver drill has two separate speeds and

five torque settings for driving screws.

Th e built-in torque-drive unit operates

much like a ratchet. It releases when the

tool has driven in the fastener or reached

the assigned torqu e setting. Both driver

drills in Figures 22.64 and 22.65 have

reverse switches for screw removal.

FIGURE 22.64 A lightw eigh t, 7.2 V, revers

ble driver drill with a

3

/s in. (10 mm ) chuck

FIGURE 22.65 A heavy-duty, 9.6

V,

revei

ble driver drill with a

3

/s in . (10 mm ) chuc*.

430




FIGURE 22.66 A variable tw o speed

cord

less driver drill with five torque settings, a

reverse switch and an electric brake

Figure 22.66 illustrates a co rdles s,

9.6

V

driver drill with two variab le

spe ed s, five torq ue settings and

an

elec

tric bra ke for fast sto pp ing w hen a fas

tene r has be en installed. Rpm ranges are

0 rpm to 400 rpm and 0 rpm to

1100

rpm.

Figure 22.67 illustrates a uniq ue

angle drill with a 7.2

V

b attery . Like its

larger cousins in the power drill family, it

is mo st suited to drilling and driving

fasteners in confined spaces.

FIGURE 22.67

7.2 V battery

A cordless angle drill w ith a

Reciprocating Saw

When installers need to cut through

wood or metal to com plete their tasks,

they can rely on a well-designed recipro

cating saw. This saw can b e fitted w ith

metal or wood cutting b lades in a variety

of lengths and too th p atte rns . Figure

22.68 illustrates a two- speed saw un it

capable of cutting through wood, fibre-

board,

plaster,

and ferrous metals.

FIGURE 22.68

ing saw

A variable speed reciprocat-

Disc Grinder

On certain occas ions, installers deal

with metal fabrications. Sharp edges,

prepa ration of openings in panels, and

removal of slag from weld s be com e tire

some ch ores when approa ched with reg

ular hand-op erated tools. A high-speed

(10 000 rpm) d isc grinder, as shown in

Figure 22.69, will easily rem ov e m etal

from surface areas.

FIGURE 22.69

disc grinder

A 4 in. (100 mm) high-spee

Tools of the E lectrical Tra de

43



A disc grinder produ ces a great

many spark s when working on ferrous

metals, so care should be taken not to

operate the unit near combustible

materials. A removable ha nd grip is pro

vided at the front end of the tool for

extra safety and co ntrol when required

and should be used whenever possible.

A

steel guard is placed a t the rea r of th e

grinding wheel to protect the o pera tor in

case the wheel should shatter and fly

apart.

A

disc grinder is a mo st useful to ol

when h and led properly, and it can b e fit

ted with a variety of wheel types and

wire brushes for working on metal.

Power Tool Maintenance

Manufacturers normally provide a book

of operating instructions and m ainte

nance tips w ith th eir too ls. By promoting

prope r care of their p rod ucts, they are

helping tool owners to gain many extra

hours of tool life. The following is a list

of tips and suggestions for tool care and

maintenance.

1.

Damage to the tool's windings is

cum ulative when the tool is over

worked and allowed to heat up. Avoid

loaning a pow er tool to inexperienced

ope rators . Any dam age they cause to

the tool will prob ably not b e de tecte d

until the

tool

stop s working properly.

2. Do not cov er th e air circulation holes

with your han ds or gloves when

using the tool. Air circulation helps

to keep the motor windings at a safe

working temperature.

3.

Check the cord on tho se tools

equip ped for plug-in op era tion . On

non-double-insulated tools, make

sure the plug has all the pro ngs

(including the gro und ) and is with

out cuts or other weaknesses that

might cause a shock to the operator.

4.

Do not use an extension cord that is

too long or has a cond ucto r tha t is

too small for the tool. Voltage loss in

these cords can cause damage to the

tool's moto r windings over a period

of tim e.

5.

Keep th e tool in a carrying ca se or

container when not in use. Doing so

will prevent dam pn ess and mechani

cal damage to th e tool. Related par ts

and a ccesso ries can also be kept in

the cas e for easy a ccess.

6. Do not u se over-size bits, san ding

disc s, hole saw s, etc., tha t will over

work the power too l. The tool was

designed to operate at a prede ter

mined power/torque level. Ignoring

that fact will cause early burnout.

7. Compressed air can be used to clean

out g rindings, chips, d ust, etc ., from

the tool's interior. Sawdust on the

windings will hold in heat and not

allow th e tool to cool properly. Use

caution and safety glasses when per

forming this clean-out. Compressed

air can be dangerou s if the pressu re

is to o high.

8. Fresh grease can be added to the

gear c ase . The factory-installed lubri

cant will be thrown off the gears by

centrifugal force after a period of

time and may need freshening up.

A

high-quality bearing grease is recom

mended.

9. As the tool ages, the ca rbon brush es

may wear dow n so much that they

need replacement. These specially

shaped inserts are unique to their

particular tool, and should be

replaced with the identical product.

10. Wipe moisture, chem icals, dust,

dirt

etc., off the tool after use and coat

chuck s and bit holders with a dry

lubricant spray. This helps to pre

vent ru st and keep the tool in proper

working order.

432




C hoosing a P ower T ool

Th ere are som e major factors to con

sider w hen choo sing a too l. The follow

ing is a list of recommendations that can

help you to make the right choice .

1. Decide wha t typ e of job or proje cts

th e tool will be used for. Doing so will

allow you to cho ose a tool in the

power/torque range needed to per

form your task comfortably and with

out undue strain on the tool.

2. Try to m atch th e tool to th e size of

you r hand , arm stren gth, e tc. A large

high-torque tool in the hands of a

pe rson unable to con trol its weight

and pow er may re sult in a painful

accident.

3.

Look at several name brands and

compare their features, power, and

price before making you r pu rcha se.

Some manufacturers copy oth ers in

appearance and design, but leave out

key features which make a co nsider

ab le difference to the ea se of use on

th e job.

4. When co mp aring tools of various

makes and sizes, the nameplate cur

rent can b e a rule-of-thumb guide

line. Generally speaking, the higher

the cu rrent rating, the mo re powerful

the tool will be.

5. Check th e size of the chuc k on drills,

tool bit or blade holders, etc., as a

guideline to the quality of the tool.

Manufacturers seldom apply heavy-

duty, quality parts to a cheaper tool.

As a rule, you get wh at you pay for.

6. Remember that ball and roller bear

ings are far superio r to sleeve ty pe

bearings. They last much, m uch

longer.

7.

As a general

rule,

avoid "packag e

deals"

where many, low cost acc es

sorie s are include d w ith the too l. It is

often better to spend your money on

the tool alone and to add parts and

acc esso ry units when and if you

require them . Some name brand

manufacturers do, however, provide

special de als that are well wo rth

looking for. Top quality pa rts ne ed ed

for th e op eration of the tool may b e

included.

8. When choosing th e tool, inquire

about the warranty or guarantee that

is provided in writing by th e manu

facturer. Find out at the same time

wh ere repa irs can be m ade: not all

tool supp liers repair tools on the sel

ling pre m ises.

9. Look at th e length and natu re of cord

and the typ e of plug on power tools.

Rubber cords tend to be fairly flexi

ble in cold weather; in contrast,

plastic c ord s can be a bit stiff and

awkward to use o utdo ors in winter

months. Three prong plugs should

be on all metal tools tha t are not

double insulated and CSA approved

for the intended purpose.

10. Look carefully at battery-operated

tools for b atte ry voltage, cost of

spare batter ies and chargers, and

time required to recharge the bat

tery. Some tools require an overnight

charge, something that can be most

inconvenient on an imp ortant job

site project. Tools shown in this

chapter are designed to charge in

one hour, and can b e pa rtially

rech arge d in m inutes if only a few

m inute s of wo rk are required to fin

ish th e job.


433



F o r R e v i e w

1.

What two features make top qual

ity tools more desirable to the

installer?

2. W hen choo sing a screwdriver for

persona l use, what features should

be considered?

3. a) What p roc ess of repair is used

to reshape the tip of a worn, stand

ard slot screwdriver?

b) What care m ust be taken while

repairing the tip of the driver?

4. Name the thre e most comm only

used sizes of square-tip drivers.

State the screw sizes they are

designed to work with.

5.

What special treatm ent is given to

the long-shaft screwdrivers that

are used in and aroun d live electri

cal equipment?

6. Name two major ap plication s or

use s of side cutting p liers.

7. What special design feature deter

mines if a pa ir of pliers is high lev

erage or not? What is the advan

tage of high leverage pliers over

standard pliers?

8. What are the advan tages and

disadvantages of comfort-grips on

the han dles of various typ es of pli

ers?

9. State two specific uses of adjusta

ble pump pliers.

10. Why are slanted tong ue and

groove pump pliers the safest to

use?

11.

What special design features are

desirab le in a

metal-cutting

hack

saw?

12. List three types of hammers used

by the electrical trade and give an

application of each type.

13. Why must ca re be taken when

using steel measuring tapes near

live electrical circu its and equip

ment?

14. What protection do es the lockout

device illustrated in Figure 22.46

provide when persons from a num

ber of tra de s are servicing electri

cal equipment and their circuits?

15.

What special advantages doe s a

properly designed tool p ouch

have over a metal or wooden tool

box?

16.

What typ e of motor is used exten

sively in m odern pow er tools, and

why is that so?

17.

What is the advantage of speed

control on a power tool and how is

speed control achieved?

18. What design features indicate that

a power tool is of high quality and

suitable for industrial use?

19. Name two precau tions you can

take to reduce the chance of elec

tric shock when using power tools.

20 . What consideration should be

given to the user's physical size

when selecting a portable power

tool?

21. What safety equipment should be

worn by the op erator of a pow er

tool such as a hammer drill?

22.

List thre e major a dva ntage s of

cordless power tools.

23. What are the two most commonly

used voltages for cordless power

tools?

24 . Why is a motor-reverse switch

desirable on electric and battery-

operated drills?

25. Why is it useful for a cordless

pow er drill to have adjustable

torqu e settings?




26. List three elec tric power too ls th at

are designed to e ase th e installa

tion of electrical equipment and

circuits.

27 .

What care must be taken with the

co rds and plugs of power-oper

ated tools?

28.

Why mu st power tools be cleaned

and blown free of wood dust and

othe r residue that h as accumu

lated on the inside?

29. What parts of a power tool require

lubrication from time to time, and

wh at lubricant is used for th e pur

pose?

30 . Which typ e of bearing is m ost

suited to long life in an industrial-

grad e pow er tool? Explain why.




Glossary of Electrical Terms

acceptable Equipm ent or installation

of equipment is accep table to th e

authority enforcing the Canadian Elec

trical Code.

accessible

Not perma nently closed in

by the structure or finish of a building;

can be remov ed without disturbing the

structure or finish of a building.

alive Co nnected to a sou rce of voltage,

or charg ed electrically to have a volt

age different from that of the earth.

alternating current (AC) A current

which reverses its direction and magni

tud e in a period ic man ner, rising from

zero to a maximum value in one direc

tion, falling to zero, and reversing in the

opp osite d irection to a maximum value

before falling again to ze ro.

ampacity

The current-carrying capac

ity of cond ucto rs ex pressed in

amperes.

amperes

(A) The com mon ly used unit

of electrical current flow in a circuit.

AWG

Am erican Wire Gauge, used to

measure solid, non-ferrous (usually

copp er or aluminum) conductors, pro

viding both gauge number and diame

ter in tho usa nd ths of an inch.

branch circuit

That pa rt of a circuit

which extends beyond the final over-

current device protecting the circuit or

system.

CEMA Can adian Electrical Manufactur

ers '

Association, which regulates sizes,

dim ensio ns, and configurations of elec

trical devices and equipm ent.

CMA Circular mil area, which indica tes

the nominal size of conductors larger

than

No.

0000 AWG.

Canadian Stand ards Ass ociation (CSA)

The association that approves and

tests electrical devices and equipm ent

to be sold and installed in Canad a.

cycles

Cycles per second, or the num

ber of pulsations occurring in an alter

nating cu rrent system w ithin one sec

ond. Consists of one positive and one

negative maximum va lue in an alternat

ing cu rrent.

direct cu rrent (DC) An electric curren t

that flows in one direction only and is

reasonably free from pulsations.

Obtained in a pulsation-free form from

a battery, it can also be produced by a

generator or obtained electronically if

alternating current is passe d through a

rectifier.

hertz (Hz)

The mea surem ent of alter

nating curre nt frequency indicating th e

num ber of cycles per seco nd.

identified

a. A white or natural grey

covering on a conductor, b. A raised

ridge on the surface insulation of some

wiring co rds , c. A silver-coloured ter

minal screw on wiring devices.

IEC

International Electro-technical

Commission. The European equivalent

to CEMA and NEMA.

436




kilowatt (kW)

A unit of power measure

ment to 1000 W.

kilovolt (kV) A unit of electric al pre s

sure equivalent to 1000 V.

line

A

term usually referring to the

input side of a switch, m eter, or co ntrol

ling device for a motor.

load

A

term usually referring to the

ou tpu t sid e of a switch , meter, or con

trolling device for a motor.

NEMA National Electrical Manufactur

ers '

Asso ciation. Th e American organi

zation that con trols the dim ensions,

sizes,

and configurations of electrical

devices and equipment.

neutral The con duc tor that divides the

secondary of a supply transformer

into two equal sections, providing two

voltages from three wires in the system.

It is norm ally wh ite or grey in co lour.

outlet

A point in th e circuit at which

current can be taken to supp ly electri

cal devices or equipment designed to

operate on that circuit.

overcurrent device

A fuse o r circuit

breaker designed to open a circuit auto

matically under predeterm ined over

load or short-circuit conditions.

overload

A

flow of cur ren t in excess of

normal, predetermined circuit capacity,

which can cause overheating or dam

age to the circuit.

primary The input side of a transfo rme r

into which voltage is placed so tha t it

may be raised o r lowered in value.

PVC

Polyvinylchloride. A plastic

material used in the manufacture of

electrical cond uit and fittings.

receptacle One or mo re female con tact

devices on a comm on moun ting

brack et for the con nection of plug-in

equipment.

resistance

The prop erty of a cond uc

tor or electrical device that o pp ose s

the flow of current through the system.

Measured in ohms.

secondary

The ou tpu t section or wind

ing of a transformer from which voltage

is taken after it has been raised or low

ered in value.

short circuit

A

circuit fault caused by

contact between two opposite sections

of an electrical circuit. An ab norm ally

low-resistance path is created, resulting

in sudden and possibly dangerous high

currents.

Underwriters' Laboratories UL) The

American equivalent to the Canadian

Standards Association. The organiza

tion test s and appro ves electrical

devices and equipment for use in the

United S tates.

voltage

(V) A unit of electrical pressure

applied t o a circuit.

wattage W)

A

unit of electrical energy

or power resulting from electrical pres

sure forcing a current throug h the

circuit.

For Reference

Canadian Electrical C ode, Part 1,

Canadian Standards Association.

Heating and Cooling Load Calculation,

Ontario Electrical League.

Intermediate Electricity, Frank J. Long,

General Pub lishing.

In troductory Electricity, Frank

J.

Long,

General Pub lishing.

Lucalox High Pressure Sodium Lamps,

8707-3,

GE Lighting.

Multi-Vapour SP30 Metal H alide Lamps,

206-81245 (4/88), GE Lighting.

Typical W iring Diagrams,

publication

Gl-2.0, A llen-Bradley.

Glossary of Electrical Terms

437



Index

Adap ters for Iampho lders, 29,

308-9

Ambient temp erature , 249

Am erican W ire Gauge (AWG),

53-54

Am pacity, 60-62

Amperage

in Oh m's Law, 9-10

rating for switches, 15

Annealing, of conductors, 53 , 250

Antioxidant chemicals, 49

Appliance

cord s ets, 67

large, 2

small, 2

Arcing, 15-16,335,346

Area of cros s-section , 54-55

B

Baseboard heater

installation, 277

overheating protection,

297,

298

type s, 277, 279

C

Cable

accessories, 99,141

acce ss to , 90

aluminum-sheathed,

140-48

applications, 139-40,148,

153,155-57,160-61

architectural symbols,

93-98

armoured, 136-41

connector, 144-45

construction, 88,136-37,

151,156

fastening to bo x, 90-91

fireproof, 151-55

fishing, 139

in concealed installations,

91-92

installation, 90,142

insulation, 88,136,151

materials,

88,136-37,151

mineral-insulated, 151-61

multi-conductor, 141-42

nonmetallic sheathed, 88-92

pliers, 99

ratings, 136,141

residential a pplications, 92

ripper, 99

single-conductor, 141,160

sizes,

88,151-54

supports, 90,138-39,147

terminating, 111,

137-38,

143, 146-47,157-59

trade names, 88,136

underground, 91,137

water-tight, 139-40,149

wiring diagram sym bols,

92,

94-98

Canadian Building Code, 153,

268-70

Canadian Electrical Code,

28-29,31-32,33,39,42,55,

65,70,71,75,84,85,88,90,

91,102,141,147,162-63,171,

174,184,188,193,199,206,

211-12,224,240,246,250,

253,

259,

306,335,

337, 346

Canadian Standards

Asso ciation (CSA),

15,37-38,

68,102,263,356,394,396,

402,433

Circuit breaker

advantages of,

241-42

disadvantages of, 42

for m oto rs, 346

GFI ty pe , 242-47

thermal overload relay,

337-43

Circular mil area , 54

Cold

flow of co ndu ctors , 49,250

lead of condu ctors , 280

Conductor

aluminum, 48-49

cable, 51,53

compound, 53,143

copper, 48, 249

cord, 52-53

forms, 49-53

heat generation factors,

249-50

installation in a lug, 55,

107-8

installation in conduit,

188-92

Insulation,

55,58-60,249

ma terials, 48-49

overheating, 84,248

single strand , 49,141

sizes,

53-55,88,238,240

steel, 49

wire, 49-50, 53

Conduit

applications and features

162,170-71,178-80,

182-83

bending hydraulically.

168-69,172, 179

ben ding man ually, 165-66.

168,172, 179

bending with heat, 180-82

condulets, 173-77,211

cutting, 184

EMT

(thin wa ll), 170-73

expan sion joints, 180

fishing, 189,192

fittings, 171,174-77

grounding, 184

installation, 179

liquid-tight flexible, 185

metallic flexible, 180,183

nonmetallic flexible, 183-84

number of conductors

allowed, 193

PVC-jacketed, 171

rigid aluminum, 163,178-3

rigid

PVC,

179-80

rigid (thickw all), 16369

secu ring to fish tap e, 191

sizes,

162-63,182, 238,

24f

supports, 163,183,184

termination, 177-78,

180.

185

threading, 164-65,179

types, 163-73,178-80, IS

types of bends, 166-67

Connector (solderless)

applications, 105

com pression, 104,106.

108-9,112

heat-shrink tubing, 119-22

insulating materials,

112.

114-19

materials, 102,108

mechanical, 107-8,169

resin-splicing kits,

115-

set-screw, 104-5

438




splice tape, 112-14,119

tools,

109-10,112

twist-on, 102-3

types, 102-8

water-tight, 140

Cord fittings

dead-front plug caps, 65-66

heavy-duty cap s, 64

removable, 67

Crimping and co mpre ssion

tool, 157-58

Current

alterna ting (AC), 15

direct (DC), 15

eddy, 142

sheath, 14M2,160

Cycle (see Frequency)

Design tem peratu re, 286

Dies

for condu ctors, 49

for con dui t, 164-65

Discharge light sources (see

Fluorescent lamp)

Drilling d evice s

hammer-driven, 391

power-driven, 391-92

Drivers and drills

battery-operated.

430-31

electric, 391,425-29

hand tools, 407-11

hex key, 410

hollow-shaft

nutdrtver,

410-11

multi-purpose

screwdriver.

409-10

Phillips scre wdrive r. 409

powe r tools , 425-31

slot screw driver, 407-9

square-tip screwdriver

409

Torx screwdriver, 409

Electrical and Electronic

Manufacturers' Association

of Canada (EEMAC). 345.3

Electric shock, 6-8.43.68

217,

234, 244-45

Electrolysis, of cond ucto rs, 46

F

Fastener

drilling devices, 391-92

hollow-wall, 392-93

masonry, 387-91

powder-actuated.

394-403

screw, 376-87

Fire endu rance test, 152-53.155

Flat-rate, hot-water heater. 3,

206, 209

Fluorescent lamp

advantages,

301-2,305

applications, 315,322-23,

327-28

ballast,

304,306

disadvantag es, 302

efficiency, 331-32

high-intensity discharge,

310,312-28

high-pressure sodium,

323-28

instant-start, 306, 308

low w attag e biaxial,

308-10

Lucalox, 317, 325-26

maintenanc e, 332

m ercu ry vapou r, 312-16

metal

ha lide, 318-23

metric sizes, 308

multi-vapou r, 328-29

ope ration , 304-5

pow er groove, 310-12

rapid -start, 305-7

starting, 302,304

tube life, 301-2

tube parts, 302-3

tungsten-halogen, 329-31

Frequency, 2

Fuse

arc-quenching m aterial,

257-59,262

circuit fault indications,

255-56

coding. 254-55

design. 250-54, 256-59,

261-62

dual-element, 261-62

ferrule-contact c artridge,

256-57

for

motors. 263,346

high-mpture capacity,

259-61

knife-blade cartridge,

257-58

M effect. 250-51

I fatigue. 258

; delay. 252.254

,258

sot 5,250-51

,

6,253-54.

256-58,

MM2

renewable-link cartridge,

258

screw -base (plug), 252,

254-55

short circuits,

5-6,250-51

sizes, 256

spiking, 258

time-delay, 251-57, 260-64

tripping level, 42

Ganging outlet boxe s, 75

Gauge, for wire and c able, 53,

55

Ground fault interrupter (GFT

features of, 43-44, 247

functions of, 42, 242

operation of, 245-47

testing of, 43,247-48

Grounding

of neutral wire, 6-8

why needed, 6-3

H

Hand tools

cuttin g, 415-17

drivers, 407-11

measuring, 418-19

plie rs, 411-15

pouches and kits, 421

striking, 417-18

High tension lines, 3

Hysteresis loss, 346

I

Industrial power supply

circuit brea kers, 241-42

conductor and conduit

size, 238, 240

dem and factor, 241

550 V and 440 V, 230-32

grounding, 234,238

metering, 233-34,24041

motor-driven, 229

120 V/208V, 230, 235-38

polypha se, 229

600 V/347V system , 231

sub-disconnect switches

233

Insulation

attic, 273,

276-77

batts,

269-70, 273

function of, 267

poured, 269,271-73

rigid, 271-72, 274

rolls, 269,271,273

4 3 9



RSI values , 268-74

vapour retarders, 272-76

Interlocking, 357-58, 360

K

Kirchhoff's Current Law, 245

Knockout

cutters, 186-87

for co ndu it, 177

in outlet boxes,

71,82

Lampholder

adapte rs, 29

candelabra, 29

circuits, 31

construction, 29

insulating link, 31

interme diate, 29

location, 31-32

medium, 28-30

miniature , 29

mogul, 28

scre w-b ase s izes, 28-29

switch mechanisms, 30

Lighting-load c alculation s, 16

Line

side,

3

term inals , 3, 20, 22, 212

Lineworkers, 411,415,419

Load, side of sw itch, 5

Locked rotor curre nt, 334,361

Loop system , 90

M

Main disconnec t switch

fuses in, 5-6

loca tion of, 3, 200

Masonry fastener

drive-in a ncho r, 391

expansion shield, 388

lead sleeve anchor, 389-91

scre w an chor, 387-88

self-drilling s hield, 388

Meter,

3,199,214,221,224-26,

233,

239, 240-41

Motor control

auto transformer starter,

364-66

conductor sizes, 335,337

direct-cu rrent, 371-74

jogging circuits , 354-56

location, 335

magnetic, 344-45,346-47,

349-50

maintain contacts, 350-51

man ual, 344

multi-speed, 360-63

need,334

overcurrent protection,

335

primary resistor starter,

361,364

reduced voltage control,

356-57

reduced voltage starters,

361-66

reversing, 357-59,370

single-phase, 370

solid-state starte r, 370-71

stat ions , 351-53

switche s, 335

thermal overload relay,

337-43

Wye-Delta starter, 367-69

Muscu lar freeze, 42

N

National E lectrical

Manu facturers' Association

(NEMA),41,260,345,347

Ohm's Law, 9-10

Outlet box

cable clamp s, 82-83

concrete-masonry-tile, 82

conductor capacity, 84-86

ganging, 76-77

grounding, 84

materials, 70, 75-76,80

octag on, 70-72

pan cak e, 72-73

sectional

plaster,

74-79

squ are , 72-74

steel stud, 77, 79

utility, 80-81

vapour barrie rs, 81

Oven

continuous clean, 131

heat control, 130-31

pyro lytic , 131-34

rotisserle, 134

self-cleaning, 131-34

timer, 132

Overload relay selection chart,

343

Oxidation

of cond uctors, 48,108,250

of fluorescent tubes, 305

Parallel circuit, resistanc e of.

9-10

Plaster ears

for receptacles, 41-42

removing, 42

Pliers

cable cutters, 413-14

diagonal cutting, 412-13

high-leverage,

411-13

long-nose, 414

pum p, 414-15

side cutting, 411-12

Plug cap

connection, 65

dead-front, 65-66

electrical ratings, 68

female, 64

for appliances, 67

grounding, 68

heavy-duty, 64

male, 64

twist-lock, 68

Powder-actuated fastener

high-velocity tool, 401

in concrete, 397-99

in maso nry and sU

399-401

low-velocity tool, 394-95

powder-charge cartric

396

safety equipm ent, 402-3

safety recommendatio

403-4

typ es, 396-97

Power

factor, 305

ratings for switches. 1

Power tool motor

bearing s, 425

parts,

423

r p m , 424-25

torqu e and speed, 423

Power tools

battery-operated drrwi

and drills, 430-31

choosing, 433

disc grinder, 431-32

electric drills , 425-29

holster-style pouches.

421-22

ma intenance, 432

motor, 423-25

quality and cost, 422-23

reciprocating saw,

431

Pry-outs, in outlet boxes. 5J4

440




R

Receptacle

combinations, 34

construction, 33

covers, 45

crow's foot, 35

direct curren t, 36

duplex, 39

electric shaver, 43

ground fault interrupter,

42-44

grou nding , 38-39

hospital grade grounding,

44-45

installation regulations, 33

locking, 38

NEMA, 41

non-locking, 37

polarize d, 41

range and drier, 36

rang es of, 33

replacement, 40

sh ap es , 34-36

split , 39-40

standardized, 41

tandem , 36

twist-lock, 35

two-prong, 34

U-ground, 34-35

Residential electric heating

adva ntage s of, 266

baseboards, 277-79

base m ent, 283-84

central heating, 266

costs of, 267, 294-95,297

end rate, 267

forced air units, 294-96

heater location, 292

inspections, 267, 274

insulation, 267-72

radiant-heating cable, 277,

279-80, 297-99

radiant-heating foil, 279-81

selecting size, 291-92

thermostat location, 292-94

unitary, 266-67

ventilating dev ices, 274,

276-77

Residential heat loss

basements, 283-84

calculations, 266, 284-86,

290-91

conc rete slab, 282

degree days and design

tem pera ture, 286-89

do ors and window s, 286, 290

fireplaces, 281-82

infiltration, 286, 290

pipes and electrical

box es, 281-82

walls and ceilings,

284,

286

windows, 280-81

Residential power supply

combination units, 202-4,

214

conductors, 199

flat-rate syst em s, 206, 209

grounding, 215, 217-18,

223-24

inspection permit, 226

installation, 203

me ter cabinet, 215

meter socket, 206,208-10

overhead, 3,199,200, 201

service, 199

service boxes, 214

service box installation, 212

service

ell,

211-12

service entrance elbows,

210-11

service mast, 206-7

size and capacity, 199,202-3

tem pora ry service, 226-27

unbalanced system, 8-9

underground,

3,199,

210,

212-13

Resistance

for co nduc tors, 61

in Ohm 's Law, 10

Root Mean Square (RMS), 251

S

Schematic wiring diagram

symbols, 348, 350

Screw fastener

Allen, 378

bolt s treng th, 386-87

cam-out, 377

construction materials,

385-86

driving configuration, 377,

379

dua l-drive, 378-79

head design, 376

hexagon,378

length and diameter, 384-85

m achin e, 379-81

neck/shoulder,

378-79

Phil lips, 377-78

point designs, 385

Robe rtson, 377

self-tapping, 382-83

shank and body, 378-79

slotted, 377

squ are recess, 377

thre ad typ es, 379-84

Torx, 378

woo d, 382-84

Series c ircuit, resis tanc e in,

Series/parallel, switch

combinations, 124-34

Service m ast

as ground, 7

installation, 204,206

requireme nts, 204

Sheath cur rents, 160

Single-phase voltage, 2

Society of Autom otive

Eng ineers (SAE), 386-87

Spiking, 258

Switch (heat control)

five heat, 124

for ovens, 130-31

infinite-heat, 128-30

seven-heat, 126-28

three-heat, double pole

124, 126

three-heat, single-pole,

124-25

Switch (light)

alternate , 25

and re ceptacle unit, 46

applications, 17

consecutive, 25

dimmer, 16, 25-26

double-pole, 17, 19

electrolier, 22-25

flush, 12

four-way, 18, 21

function of, 13

internal construction, 1

non-indicating, 21

operating m echanism, 1

30

rat ing s, 14-16

single-pole, 17-18

surface, 12

test equipm ent, 16

three-way, 18,20-21

trillte , 22-23

wiring symb ols, 17

Stroboscope effect, 302

Supply authority, 199, 203

T

Tables

air change s per hour, 29

allowable ampacities fo

Index

44



aluminum c ondu ctors, 62

allowable ampacities for

copper c ondu ctors, 61

batt insulation RSI value

data, 270

Canadian Building Code's

minimum insulation

requirements, 268

cartridge power loads,

396

common coarse and fine

thread screw sizes, 380

cost to illuminate for a

year, 332

cross-sectional a reas of

cond uit, 197

degree days and design

tem per ature s, 287-89

determining motor

conductor sizes, 338

dimen sions of bare

copp er and aluminum

stranded conductors, 57

dimen sions of insulated

cond uctors for

calculating cond uit fill,

196

dimen sions of insulated

copper and aluminum

cond uctors, 56

dimensions, weights, and

resistance of bare

copp er wire, solid, 58

dimensions, weights, and

resistance of bare

copp er wire, stranded, 59

distan ces for fasteners, 399

electrical sy mbo ls for

light sources and power

consumption, 331

low and standard watt

density heater

specifications, 293

markings and mechanical

properties of hex cap

screws, 386

maximum allowable p er

cent conduit fill, 197

maximum num ber of

cond uctors (imperial),

195

maximum n um ber of

conductors (metric), 194

metallic flexible c ond uit, 183

minimum RSI values for

various assem blies in a

building, 270

minimum size of

grounding

conductor.

231

number of conduc tors in

boxes,

85

overcurrent devices, 337

overcurrent protection,

336

resistance v alues for

building materials, 285

roll insulation RSI data,

271

RSI values for insulating

materials, 269

sizes and ratings of

magnetic motor

starters , 347

spac e for conduc tors in

boxes, 84

Three-wire system, for two

voltages, 2,4,229 , 231

Tools

battery-operated drivers

and drills, 430-31

cutting,

415-17

disc grinder, 431-32

driver family of hand

tools , 407-11

electric drills, 425-29

measuring, 418-19

plier family of hand too ls.

411-15

portable power, 422-33

po uc hes and kits, 421-22

quality, 406,

421,

422-23

reciprocating saw, 431

safety eq uipm ent. 419-20

strikin g, 417-18

Transformer

contacts, 365

current-reducing, 215.

234, 236

distribution, £4,212

step-down, 4,235,345

T rating, for incandescent

lamps, 15

Trilite, 22-24

Tubing (heat-shrink), 119-22

Tungsten-halogen lamp,

32939

U

U factor, 286

Underwriters' Laboratories

(UL),

15

V

Vapour barrie rs, 77-78,272-76

applications electrical

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