ee020-electrical installation 1-th-inst.pdf
TRANSCRIPT
SRI LANKA INSTITUTE of ADVANCED TECHNOLOGICAL
EDUCATION
Training Unit
Electrical Installation 1 Theory
No: EE 020
INDUSTRIETECHNIKINDUSTRIETECHNIK
ELECTRICAL and ELECTRONIC ENGINEERING
Instructor Manual
1
Training Unit
Electrical Installation 1
Theoretical Part
No.: EE 020
Edition: 2008 All Rights Reserved Editor: MCE Industrietechnik Linz GmbH & Co Education and Training Systems, DM-1 Lunzerstrasse 64 P.O.Box 36, A 4031 Linz / Austria Tel. (+ 43 / 732) 6987 – 3475 Fax (+ 43 / 732) 6980 – 4271 Website: www.mcelinz.com
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ELECTRICAL INSTALLATION 1-Theory
CONTENTS Page
LEARNING OBJECTIVES...................................................................................................5
1 GENERAL REQUIREMENTS ......................................................................................6
1.1 Accident safety.....................................................................................................6
1.2 Operational reliability ...........................................................................................6
1.3 General layout......................................................................................................7
2 SYMBOLS FOR INSTALLATION PLANS ....................................................................9
2.1 Cables, number of conductors and cable crossovers ..........................................9
2.2 Voltage sources, types of current ......................................................................10
2.3 Lamps, domestic equipment ..............................................................................10
2.4 Fuses, switches .................................................................................................12
2.5 Sockets and socket outlets ................................................................................12
2.6 Other equipment ................................................................................................13
2.7 Telecommunications equipment ........................................................................14
3 CIRCUIT DIAGRAMS.................................................................................................15
3.1 The general circuit diagram ...............................................................................15
3.2 The detailed wiring diagram...............................................................................15
3.3 The installation plan (location diagram) .............................................................16
4 BASIC CIRCUITS FOR ELECTRICAL INSTALLATIONS ..........................................17
4.1 Single pole switching .........................................................................................17
4.2 Two-pole and three-pole switching ....................................................................18
4.3 Single-pole two-way switching circuit.................................................................20
4.4 Multiple single pole switch units.........................................................................21
4.5 Two-way switching circuits.................................................................................22
4.6 Two-way and intermediate switching circuit (cross connections).......................24
3
4.7 Pulsed relay switching .......................................................................................25
4.8 Staircase time switch .........................................................................................26
5 CONDUITS AND ACCESSORIES .............................................................................27
5.1 Laying ................................................................................................................27
5.1.1 Instructions for laying conduits.......................................................................27
5.2 Rigid plastic conduit - grey.................................................................................29
5.3 Rigid plastic conduit - yellow or light grey (Eurogrey to RAL 7035) ...................29
5.4 Flexible plastic conduit - yellow or light grey (Eurogrey to RAL 7035) ...............30
5.5 Armoured plastic conduit - black........................................................................30
5.6 Armoured flexible plastic conduit - black............................................................31
5.7 Armoured rigid plastic conduit - grey .................................................................31
5.8 Armoured flexible plastic conduit - grey .............................................................31
5.9 Conduit with overlapping steel armour, unsheathed (Peschel conduit) .............32
5.10 Galvanized flexible conduit with or without woven sheath (Peschel hose) ........32
5.11 Steel armoured conduit ......................................................................................33
5.12 Flexible steel armoured conduit .........................................................................33
5.13 Heavy gauge black plastic conduit.....................................................................34
5.14 Wiring ducts (Trunking) ......................................................................................35
5.15 Installation ducts (cable ducts)...........................................................................37
6 LAYING CABLES .......................................................................................................38
6.1 Permanent cabling .............................................................................................38
6.1.1 NY-cables.......................................................................................................38
6.1.2 NYM parallel twin cables................................................................................38
6.1.3 NYM cable......................................................................................................39
6.1.4 Working with plaster.......................................................................................40
6.2 Cables for portable equipment...........................................................................40
6.2.1 Rules for connecting plugs and cables ..........................................................41
7 CABLE PROTECTION ...............................................................................................42
7.1 Fuses .................................................................................................................42
7.1.1 Screw cap fuses.............................................................................................42
4
7.1.2 Low voltage power fuses (NH fuses) ...........................................................46
7.1.3 Small or glass tube fuses...............................................................................47
7.1.4 Tripping behaviour of fuses............................................................................47
7.2 Cable protection switch (overload circuit breaker) .............................................49
8 MOTOR PROTECTION CIRCUIT BREAKER............................................................52
9 SWITCHES AND PLUG-IN DEVICES........................................................................53
9.1 Installation of switches .......................................................................................53
9.2 Socket and plug assemblies ..............................................................................54
5
ELECTRICAL INSTALLATION 1
LEARNING OBJECTIVES
The trainee should ...
- state the three guidelines for carrying out electrical installation work
- describe the three types of circuit diagram which are required for electrical Installation
- name four methods of laying conduit
- outline the permitted and prohibited methods of laying NY, NYM parallel twin cables
and NYM cables
- name the different methods of laying NYM cables
- state four rules concerning connecting cables for portable equipment
- name the two types of cable protection
- describe the construction of a cartridge fuse
- state the rated currents and colour marking of cartridge fuses from 2A to 100A
- describe the construction of a circuit breaker
- state the regulations for connecting switches in installations and for connecting cables
to plugs
6
ELECTRICAL INSTALLATION 1
1 GENERAL REQUIREMENTS
Every electrical installation must comply with the general requirements of the electricity
supplier.
The following rules must be obeyed:
- Installations must be accident proof.
- Operational reliability must be ensured.
- The installation must be easily accessible for inspection and testing.
1.1 Accident safety
- It must be impossible to touch "live" parts. If necessary, protective measures must be
taken against contact voltage.
- The insulation resistance between wire and wire and between wore and earth must
not be less than:
1000 Ω /V of operating voltage in dry and damp rooms
500 Ω/V of operating voltage in wet rooms and out of doors
- Electrical equipment must comply with the prevailing regulations
- A socket should be provided for each piece of portable electrical equipment (this
prevents the use of adaptors and multi-plugs, which are contrary to regulations).
1.2 Operational reliability
- Installations must be so constructed that they resist the effects of impacts and knocks,
dust, damp and humidity.
- The cables must be protected by the specified fuses against overload and short-
circuit.
7
- As many current circuits as possible should be installed on the distribution boards, so
that faults will only affect individual pieces of equipment or groups of equipment.
- Electrical machinery with loads above 1.5 kW should be installed in individual spur
circuits.
1.3 General layout
- The inside of a distribution board must be easily visible. The switches and fuses must
be labelled.
- Conduit and cables must be laid vertically and horizontally.
- The wires of only one circuit may be run (laid) in a conduit or contained within the
sheath of a cable.
Exception:
Control and Signal wires for several circuits may be run in a common sheath but must
be separated from the main power circuits.
- Several power circuits may be pulled through one junction box or distribution box
(branching box) if the cables are not terminated.
8
If there are branches or connections, the power circuits must be separated by insulating
partitions.
9
2 SYMBOLS FOR INSTALLATION PLANS
2.1 Cables, number of conductors and cable crossovers
General cable symbol
Earth cable (protective conductor)
Signal cable
Flexible cable
Number of cables
Cable crossover in single line diagram
Cable connection
Cable on plaster
Cable in plaster
Cable under plaster
Cable laid in conduit
Distribution board on plaster
Distribution board under plaster
Junction box
House connection box
General symbol for distribution board
10
2.2 Voltage sources, types of current
Source of direct current (DC) voltage
Generators
Transformers
Potential earth, protective earth
Ground
Direct current
Alternating current
Universal (d.c. or a.c )
3-phase alternating current
2.3 Lamps, domestic equipment
Lamp
Wall lamp
Lamp with built-in switch
Emergency light
Panic light
Searchlight
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Discharge lamp or tube for discharge lamp
Fluorescent tube, single tube
Electrical equipment, general
Heating equipment
Kitchen equipment
Electric cooker, general symbol
Baking oven
Hot water heater
Washing machine
Dishwasher
Electrically driven fan
Air conditioning equipment
Refrigerator
Freezer
Motor, general symbol
Motor, stating type of protection
12
2.4 Fuses, switches
Single pole fuse
Three pole fuse
Switch, general symbol
Overload circuit breaker
Protective circuit breaker with thermal trip
Pushbutton
2.5 Sockets and socket outlets
Socket
Multiple socket (e.g. triple socket)
13
Safety socket
Multiple safety socket
Switched socket
Safety socket for 3-phase alternating current
Safety plug
2.6 Other equipment
Ammeter
Voltmeter
Wattmeter
Counter
Alarm bell
Pulsed stepping switch
14
Staircase time switch
Buzzer
Hooter (horn)
Siren
Alarm lamp, signal lamp
Door opener
2.7 Telecommunications equipment
Socket for telecommunication circuits
(telephone and aerials etc.)
Telex
General telecommunications device
General telephone equipment,
domestic telephone equipment
15
3 CIRCUIT DIAGRAMS
Installation circuits are shown in circuit diagrams by standard symbols.
The types of circuit diagram are:
- The general circuit diagram.
- The detailed wiring diagram.
- The installation plan.
3.1 The general circuit diagram
This is a simplified, single line diagram of an installation.
3.2 The detailed wiring diagram
This is the exact representation of a circuit with all details.
16
3.3 The installation plan (location diagram)
The cable runs are indicated as a single line in the plan of the building, using conventional
symbols.
17
4 BASIC CIRCUITS FOR ELECTRICAL INSTALLATIONS
Switches are used for opening and closing circuits.
The following switches and switching systems are used for this purpose in electrical
installations:
- Single-pole switches
- Two-pole and three-pole switches
- Single-pole two-way switching circuit
- Multiple switch units
- Two-way switching circuits
- Intermediate switches
- Pulsed relays
- Staircase time switches
4.1 Single pole switching
The most frequently used switch in lighting circuits is the single-pole switch.
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4.2 Two-pole and three-pole switching
Two-pole switches are specified by the electricity supply authority for connecting radiators
and water heating equipment etc. Three-pole switches are required for three-phase
equipment.
19
20
4.3 Single-pole two-way switching circuit
Single-pole two-way switches are provided for the selective switching of two incandescent
lamps or groups of incandescent lamps (they have now been replaced by multiple switch
units).
21
4.4 Multiple single pole switch units
Units containing two single-pole one-way switches are used for switching two
incandescent lamps or groups of lamps either individually or together.
22
4.5 Two-way switching circuits
Changeover switches, single-pole two-way switches, are used for switching one or more
incandescent lamps on and off from two places.
23
Cable saving changeover switch circuit
This circuit is used if sockets are mounted below the switch.
24
4.6 Two-way and intermediate switching circuit (cross connections)
Intermediate switches together with two changeover switches make it possible to switch
on and off from three or more places.
25
4.7 Pulsed relay switching
Impulse relay switching is used to switch one or more loads on and off independently from
one or more places. The impulse relay is an electro-magnetically actuated switch, which is
activated by pushing any of the pushbuttons Q1, Q2 and Q3.
When one of the switches is pressed the impulse relay is activated and the three loads
light up.
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4.8 Staircase time switch
Staircase time switches are used for staircase illumination (in blocks of flats). The time
switch is started by pressing a pushbutton, and switches itself off after a set time of
several minutes.
By actuating a pushbutton switch, the armature coil pulls in and the current circuit is
closed. The current circuit remains closed until the switching contact is switched off after
the set delay period.
One can switch over to continuous illumination using the switch installed in the contactor
unit K1.
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5 CONDUITS AND ACCESSORIES
5.1 Laying
Conduits protect electrical cables against mechanical damage.
NOTE:
NY cables must always be laid in conduits.
NYM cables must be laid in conduits if the sheath gives insufficient protection.
5.1.1 Instructions for laying conduits
- An insulated conduit has the following advantages compared to a metal conduit:
it provides additional insulation.
it is resistant to breakdowns.
it is resistant to corrosion.
it is easy to work with.
no internal condensation takes place.
- For metal conduits, all conductors of each AC or three-phase AC circuit must be
contained in the same conduit (avoidance of inductive volt drop).
- AH ends of the conduits must be deburred.
Metal conduit ends must be provided with insulating sleeves or bushes.
- Conduits must be laid in such a way that no water can collect in them.
- For installations an plaster, the distance between clamps (saddles) given in the table
overleaf must not be exceeded.
Double strap clamps must be used for conduit size 21 upwards.
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Distance between saddles
Type of conduit Horizontal run Vertical run
Plastic conduit 40 cm 70 cm
Armoured plastic conduit 60 cm 80 cm
"Peschel" conduit 70 cm 100 cm
Steel conduit 100 cm 130 cm
- Close attention should be paid to the permitted number of cables in the conduits.
29
5.2 Rigid plastic conduit - grey
This is used for light mechanical loads.
Nominal sizes:
9, 11, 13.5, 16, 23, 29, 36, 42, 48
The dimensions 9, 42 and 48 are non-standard.
Properties:
Resistant to corrosion, non inflammable, acid resistant, insulating and safe against human
contact
Sizes 9 - 16 can be bent cold, at temperatures from 10°C - 70°C.
Application:
For laying below plaster of all kinds, even in damp walls.
Accessories:
Couplings, bends, ring bushes and 90° elbow.
Tools for working:
Bending spring, sawing tool and bending profile.
5.3 Rigid plastic conduit - yellow or light grey (Euro grey to RAL 7035)
This is used for medium mechanical loads.
Nominal sizes:
9, 11, 13.5, 16, 23, 36, 42, 48
Properties:
High dielectric strength of approximately 40 kV/mm, non inflammable, corrosion and acid
resistant, pressure tight, suitable for use between -10°C and 70°C
Application:
As a conduit for mounting on plaster, and for laying on wood (with saddle clamps) and
hollow ceilings
Accessories:
Couplings, bends, 90° elbow, ring bushes, saddles and junction boxes.
Tools for working:
Bend spring, sawing tool and bending profile.
30
5.4 Flexible plastic conduit - yellow or light grey (Eurogrey to RAL 7035)
This is used for light mechanical loads.
Nominal sizes:
11, 13.5, 16, 23, 36, 48
Properties:
Flexible i.e. it can be bent by hand, pressure tight, non inflammable, corrosion and acid
resistant, can be used between -10°C and 70°C, insulating and safe for human contact.
Application:
For mounting on top of, in or under plaster and four use together with stiff plastic conduits.
Accessories:
Couplings, clamps and sockets
5.5 Armoured plastic conduit - black
This is used for medium-heavy mechanical loads.
Nominal sizes:
11, 13.5, 16, 21, 29, 36, 42, 48
Properties:
Pressure tight, non inflammable, corrosion and acid resistant, heat resistant up to 70°C,
highly insulating and high dielectric strength (40 kV/mm.)
Application:
As a corrosion resistant electrical conduit for industrial purposes and for laying in
concrete.
Accessories:
Couplings, bends, clamps and junction boxes
31
5.6 Armoured flexible plastic conduit - black
Nominal sizes:
11, 13.5, 16, 21, 29, 36, 48
Properties:
Pressure tight, non inflammable, temperature resistant from -20°C to 70°C, highly
insulating, safe for human contact
Application:
For laying on and under plaster, on wood and in concrete.
Accessories:
Couplings, bends, clamps and junction boxes
5.7 Armoured rigid plastic conduit - grey
This is used for medium heavy loads
Nominal sizes:
11, 13.5, 16, 21, 29, 36, 48
Properties:
Resistant to cold fractures down to -20°C, heat resistant to 90°C. Application
For assembly into precast concrete parts, also for laying in vibrated and tamped concrete.
Accessories:
Couplings, bends, clamps and junction boxes
5.8 Armoured flexible plastic conduit - grey
This is used for medium heavy mechanical loads.
Properties:
Absolutely airtight, can be stepped on without damage and secure against fracture.
32
Application:
For laying in heavy concrete and for machine connections. It can be firmly screwed into
steel accessories.
Nominal sizes:
11, 13.5, 16, 21, 29, 36, 48
Accessories:
Couplings, bends, clamps and junction boxes
5.9 Conduit with overlapping steel armour, unsheathed (Peschel conduit)
This is used for medium mechanical loads.
Nominal sizes:
8, 14, 18, 26, 37
Properties:
Not airtight, intensive to temperature.
Application:
Only to be installed on plaster.
Accessories:
Elbows, half elbows, sleeves, clamps, ring bushes, reducers, T-pieces and inspection
couplings (with screw-on lid), junction boxes and four-way junction boxes.
5.10 Galvanized flexible conduit with or without woven sheath (Peschel hose)
Nominal sizes and accessories:
As for overlapping steel armoured conduit
33
5.11 Steel armoured conduit
This is used for heavy mechanical loads.
Nominal sizes:
(Conduit thread) Pg 11, 13.5, 16, 21, 29, 36, 42, 48
Properties:
Pressure tight, intensive to temperature
Application:
In concrete for connecting fixed machines
Accessories:
Elbows, sleeves, ring bushes, T-piece, inspection T-pieces, inspection couplings clamps,
stopping plugs, undrilled junction boxes, four-way junction boxes, threaded nipple,
reducers with small external thread, large internal thread, reducers with large external
thread and small internal thread.
5.12 Flexible steel armoured conduit
This is used for medium mechanical loads.
Nominal sizes:
As for steel armoured conduit.
Properties:
Flexible, i.e. a metal conduit which can be bent by hand, made of galvanised sheet steel
with an intermediate metal layer.
Application:
For laying under plaster and in concrete.
Accessories:
As for steel armoured conduit.
34
5.13 Heavy gauge black plastic conduit
For laying in earth and in concrete.
Properties:
PVC hard, highly insulating
Application:
Same applications as the steel armoured conduit,
When laying such conduit pipes attention must be paid to the radius of curvature, also
conduits must be laid slightly curved on the bottom of the trench, to allow for expansion.
Nominal sizes:*
Design of conduit for cable diameter:
The overall cross-sectional area of the cable should not exceed 1/3 of the internal cross-
sectional area of the conduit.
* Size shown in inches is that by which conduit is categorised and not an exact dimension.
35
Nominal
diameter in
inches
Radius of
curvature in
mm
External
diameter in
mm
Internal
diameter in
mm
Cable
diameter in
mm
Cross-
sectional
area of
cable mm²
Cross-
sectional
area of
conduit mm²
1" 350 32.0 28.0 up to 16 201 616
1 1/4" 400 40.0 35.2 up to 20 314 973
1 1/2" 500 50.0 44.0 up to 25 490 1520
2" 650 63.0 55.4 up to 32 804 2409
2 1/2" 750 75.0 66.0 up to 38 1134 3420
3" 900 90.0 79 4 up to 46 1662 4949
3 1/2" 1100 110.0 97 0 up to 56 2462 7386
4" 1250 125.0 110.0 up to 63 3116 9533
5.14 Wiring ducts (Trunking)
These are used for wiring (NYe and NYf cables etc.) in protection cubicles and distribution
boards. They are manufactured in grey slotted and unslotted. The material is high grade
PVC-hard (difficult to ignite, self-quenching when the flame is withdrawn).
Temperature resistant to 80°C.
Dimensions:
Length 2 m.
36
Fixing:
By gluing, riveting or screwing.
Advantages:
Wiring can be carried out quickly and there is protection from mechanical damage.
37
5.15 Installation ducts (cable ducts)
These are used for laying electrical cables in horizontal, vertical and overhead situations
in all areas of electrical installations. They are made of high-grade PVC, in grey and dark
grey.
Dimensions and capacity:
Height
mm
Width
mm
Width of opening
mm
Cable capacity at 1.5
mm2
15 15 11 15
25 25 13 30
40 25 13 45
40 40 30 70
40 60 35 115
40 80 35 160
40 150 90 300
40 200 140 450
60 60 35 170
60 80 35 220
60 100 35 270
60 120 55 340
60 150 90 440
60 200 140 550
80 40 30 180
80 80 65 295
Advantages:
Electrical cables can be laid with a saving of space and cost, and in a fully insulated
enclosure in the shortest possible time.
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6 LAYING CABLES
6.1 Permanent cabling
The following cables are mainly laid in buildings and out of doors.
CENELEC HO7V-U HO7V-R - A05VV-U
ÖVE Ye Ym YM Steg YM Austrian
VDE NYAe NYAm NYIF NYM German
6.1.1 NY-cables
Permitted:
In dry rooms in buildings for laying in conduits.
Not permitted:
For laying in plaster and out of doors.
NY-cables must always be protected from mechanical damage by conduits or covers
Above 10 mm², NYAm cables are used, as solid core cables of large cross section are
very stiff.
6.1.2 NYM parallel twin cables
Permitted:
In and under plaster on a fire-resistant base in dry rooms in buildings.
Not permitted:
In wooden rooms, even with fire-resistant base; in bathrooms and shower rooms; in
agricultural buildings; as metering cables, in sales rooms, stores and workshops of
warehouses and businesses.
If a parallel twin cable is used, it must be firmly fixed to the wall along its entire length by:
- Plastering,
- Gluing
39
- Clamping with insulated cable clamps.
It is not permitted to fix NYM parallel twin cables with nails or staples as the insulation of
the sheath can easily be damaged.
If two parallel twin cables are laid in parallel they should be spaced at least 2 cm apart.
The circuit and insulation resistance should be checked after any painting work has been
carried out.
6.1.3 NYM cable
Permitted:
In dry rooms in buildings and out of doors, in and under plaster.
Not permitted:
Laid in the ground.
40
6.1.4 Working with plaster
Plaster is the most frequently used material in installation work.
Tools:
The plastering float and trowel are part of the basic Installation equipment. Plaster
hardens rapidly if mixed with water, and should, therefore, be mixed immediately before
use.
NOTE:
Stir the plaster into the water and not the other way round. Too much stirring shortens the
hardening time.
If the mixed plaster is not required immediately, but is to be prepared in advance, then the
plaster can be scattered evenly over the water and left (according to the amount of
saturation, for 10 to 20 minutes). Stir just before use.
For large areas of plastering for conduit work, plaster with added sand can be used. First
mix the sand and water, then stir the plaster in.
NOTE:
Dampen the brickwork before plastering!
6.2 Cables for portable equipment
Electrical equipment which moves during operation or which is portable (e.g. hand drills,
kitchen equipment, irons and electric cookers etc.) is called portable equipment. This type
of equipment must be connected through plugs and flexible cables.
Flexible cables are, therefore, especially exposed to mechanical loads and the correct
choice of cable must be made. They must be carefully mounted and maintained. The point
at which the cable enters the equipment and the plugs is a particular danger point.
Flexible cables may have either plastic insulation (Y) or rubber insulation (G). They obtain
their flexibility by having cores made of thin or very thin copper wires.
41
6.2.1 Rules for connecting plugs and cables
- The rated current of the plug must be at least as great as the rated current of the piece
of equipment.
- To ensure that cores do not break off at the point of connection, they should be
secured by cable clamps and cable end sleeves.
- Protective earth conductors must be left longer than the other conductors, so that if the
cable clamp falls, they will break last of all.
- Extension cables must never be fitted with male connectors (plugs) at both ends.
- Extension cables must always include a protective earth conductor.
- Only one flexible cable may be connected to a plug.
- With 3-phase AC cables ensure correct phase sequence (L1-L2-L3).
- Extension cables must be matched to the rated current of the plugs to which they are
connected.
Do not use undersize leads.
- Cables rolled on drums must not carry their full current due to poor cooling and
inductance effects.
42
7 CABLE PROTECTION
Each cable is heated when current flows through it. If the current is too great during a
short-circuit overload, then the excessive heat will destroy the cable insulation. Each cable
must, therefore, be protected against short-circuits and overload. An over-current
protective device carries out this function.
There are two types of device:
- Fuses;
- Overload switches (circuit breakers).
7.1 Fuses
A fuse is a deliberately inserted section of reduced cable cross section which melts when
there is a short-circuit, over-current or earth fault, and, therefore, protects the cables and
equipment from excessive heating.
7.1.1 Screw cap fuses
Diazed fuses are manufactured for rated currents of 2 A to 200 A and a nominal voltage of
500 V
Neozed fuses are appreciably smaller than diazed fuses, but are constructed on the same
principle. They are manufactured for rated currents of 2 A to 100 A and with a nominal
voltage of 380 V.
43
The following code letters are used to identify fuse bases according to their type of
construction:
UZ - universal bases
TZ - switchboard bases, rear connection EZ - bases to be installed
FZ - free cable bases
NDZ - neozed bases
44
1. top contact
2. support wire
3. quartz sand
4. fuse wire
5. cap
6. spring
7. porcelain body
8. bottom contact
The rated current of the cartridges are standardized and are indicated by colours on the
caps In order to prevent fuse link from being wrongly used for currents which are too high,
the feet of the fuse link have different diameters, according to the current rating. The feet
of the fuse link fit the diameters of the base inserts. Therefore, fuse links with a high
current rating do not fit into base inserts suitable for low current ratings.
NOTE:
Fitting screws must not be replaced by others with higher rated fusing currents. Fuses
must not be mended or bridged.
45
Current ratings, colours for cartridges and fittings screws and sizes of screw cap fuses:
Diazed
Rated voltage 500 V
Neozed
Rated voltage 380 V
Thread Size
Rated
current A
Colour
Size Thread
2
4
6
10
16
pink
brown
green
red
grey
D 01
E 14
E 27
D II
20
25
blue
yellow
E 33
D III
35
50
63
black
white
copper
D 02
E 18
R 1 1/4" D IV 80
100
silver
red
D 03 M 30.2
R 2"
D V
125
160
200
yellow
copper
blue
46
7.1.2 Low voltage power fuses (NH fuses)
Power fuses have appreciably higher breaking currents (100 kA). The parts carrying
current (knife contacts) of the power fuse link are not covered. Therefore, they must not
be accessible to the layman, and must only be replaced by a technician. The insulated
fuse puller is used for this purpose. Power fuse links must only be pulled out or pushed in
with power removed.
Great care must be taken when inserting fuse links!
Fuse insulators are used in 3-phase networks, where the fuse links can be replaced off
lad. It is impossible to touch live parts.
Sizes of power fuses
Size Rated current of fuse links
00
0
1
2
3
6 A to 100 A
10 A to 160 A
36 A to 250 A
36 A to 400 A
300 A to 630 A
47
7.1.3 Small or glass tube fuses
These are mainly used in low power equipment (electronic equipment, electronic
equipment for entertainment), and are also used in the car industry. In contrast to other
fuses, there is no colour marking of fuse links. The data for these fuses (such as voltage,
current and breaking capacity) are given on the contact caps or on the body of the fuse.
1. metal caps
2. fuse wire
3. insulating tube
Design:
The cylindrical contact caps are insulating tube is made of glass or ceramic material.
Cap diameter: 5 2 mm.
Length: 20 mm.
Rated voltage: 250 V.
Rated current: 32 mA to 10 A.
7.1.4 Tripping behaviour of fuses
According to time taken to melt the fuse, when excessive current flows, the fuses are
classified as:
- Superfast
- Fast
- Medium fast
- Slow
48
Superfast fuses are used to protect semi-conductors.
Fast fuses melt at 3.5 times the rated current (standard Diazed fuses). This is called the
fusing factor.
Medium fast fuses have the characteristics of slow fuses for small overcurrents but the
characteristics of fast fuses for large overcurrents (standard Neozed fuse).
Slow fuses can carry high currents for a short time (motor starting period).
7.1.4.1 Graphically representation of tripping behaviour
1. superfast
2. fast
3. medium fast
4. slow
7.1.4.2 Functioning of a fuse
A better understanding of how fuses work can be achieved using the following diagram. It
shows that the current is cut-off by the fuse before it reaches the full "prospective" value
determined by the parameters of the faulty circuit. The fusing time "ζ" depends on the
characteristics of the fuse (fast or slow etc.).
49
Testing fuses
In order to test a fuse, the fuse cartridge is removed and is tested using an ohmmeter. For
a blown (open) fuse the ohmmeter reads infinity.
7.2 Cable protection switch (overload circuit breaker)
Instead of fuses, circuit breakers can be used. They are reset after tripping.
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Construction
The magnetic trip provides short-circuit protection for the cable. The thermal trip (bimetal
strip) provides over current protection.
Design:
Overload circuit breakers are made with different numbers of poles.
51
Overload circuit breakers are divided according to the setting of the magnetic and thermal
trips as follows:
L type:
This is the most frequently used circuit breaker, it is suitable for all applications and
corresponds to the tripping characteristic of a fuse of equal current rating.
Magnetic trip 5 x In Thermal trip 1.4 x In In = rated current
HL, HG type (domestic H, equipment G):
These are mainly for apartment and house installations. The magnetic trip is set to 3.1 x
In which keeps the required breaking current of the neutral and protective earth low. The
HG switch is used mainly in socket circuits.
G type:
Cable protection switches with G characteristics permit higher peak currents. They are
designed for individual pieces of equipment with high starting currents (magnetic trip
operates at 10 x In).
Graphic representation of the tripping characteristic (magnetic trip)
52
8 MOTOR PROTECTION CIRCUIT BREAKER
Motor protection circuit breakers are 3-pole overload circuit breakers where the trips are
adjustable.
Detailed wiring diagram of motor protection circuit breaker:
The thermal over current trip is set at the rated motor current. The electro-magnetic trip is
set either at 8 - 16 times the rated circuit breaker current or at 10 times the rated motor
current when connecting up (observe the connecting instructions). On short-circuits the
current may be so great that the short-circuit trip trips, but an arc is maintained between
the open switch contacts. Therefore, fuses are connected in series with the circuit
breaker. Motor protection circuit breakers are often produced without magnetic trips for
this reason.
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9 SWITCHES AND PLUG-IN DEVICES
Switches and plug-in devices must comply with the recognised rules of electrical
technology. All materials used must carry the appropriate safety sign, which means that
these materials have been tested in a recognised testing station regarding their
compliance with regulations and their safety.
9.1 Installation of switches
Switches in installations are produced as rocker switches, tumbler switches, rotary
switches, pull switches, bar switches and lockable switches for mounting on and in
plaster. They must be suitable for a rated voltage of 250 V and a rated current of at least 6
A.
Regulations for connections:
- Single pole switches must be in the live conductor (L).
- The neutral conductor may only be interrupted, together with the live conductor in a
linked two pole switch.
- In order to switch circuits containing more than two fluorescent lamps, the switches
must be rated for at least 10 A.
Single pole switches are permitted:
- In two wire circuits with fuse or overload circuit breaker rated up to 10 A or domestic
overload circuit breakers rated up to 16 A, and with rated voltages up to 250 V.
- In lighting circuits which are fused up to 25 A.
NOTE:
At locations with operating temperatures above 60°C, heat-resistant switches marked T
must be used.
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9.2 Socket and plug assemblies
The most usual plug-in devices are:
- Sockets for mounting on or in plaster of 2 and 3 pole design as: Single sockets fused
for 6 A or 10 A or not fused.
- Protected sockets for 10 A or 16 A with sprung protective contacts (2 pins and earth).
- Equipment sockets for hand tools and electrical heating equipment.
- Sealed sockets that may be switched off for damp rooms (garage sockets).
- Encapsulated plug-in assemblies (shrouded plug and socket) with earthing pin for
damp rooms, out of doors and in rough locations. CEE shrouded plugs and sockets.
This international standard plug and socket system is suitable for rated currents of 16 A,
32 A, 125 A and 200 A, with a rated voltage of 24 V - 750 V DC or AC and a frequency up
to 500 Hz.
CEE equipment has a colour marking according to the rated voltage.
24 V - violet 220 V - blue
42 V - white 380 V - red
110 V - yellow 500 V - black
The pin and socket of the protective earth contact have a larger diameter than the live
conductor contacts. This ensures that even if the shroud breaks (groove or projection), lt
is not possible to insert the plug pins into the incorrect sockets.
There is a "pilot contact" in the middle of the insert for 63 A and 125 A plugs, which
enables an electrical interlock to be made.
This contact closes after the other contacts.
CEE power plugs are:
- Technically complete, as they are created by the cooperation of Standards
Committees of European countries.
- Reliable for the future, as they are used in all European countries.
55
- Safe to operate, as the thicker protective earth contacts guarantee that poles cannot
be confused or the plug used for the wrong system.
- Accident proof as they are fully insulated made of high-quality plastic material
(Makrolon) largely insensitive to temperature or resistant to fracture.
Regulations for connection:
- Plugs must be constructed for a rated voltage of 250 V and a minimum current of 10
A.
- Portable equipment may be switched on and off by means of the plugs and sockets, if
the following ratings are not exceeded:
For DC 250 V/10 A.
For AC 250 V/16 A.
For 3-phase AC 380 V/10 A.
- Only shrouded plugs and sockets should be used for connecting large loads.
- In rooms where protective measures are required, only protected sockets with earth
wires may be used, apart from sockets for low voltages.
- At locations with operating temperatures above 60°C, heat resistant equipment
sockets marked T must be used.
- Plugs and sockets for connecting extension cables (couplings) must be mounted so
that the plug-in (male) contacts are not live with the connection uncoupled e.g.,
extension cables with plugs at both ends).
- Plugs and sockets must be constructed so that there is no strain on the terminals of
the flexible cable.
- Wall sockets should be mounted at least 25 cm above the floor.
The following are not permitted:
- Lamp holders which incorporate socket outlets.
- Multiplugs, even with protected plugs.
- Connection of more than one extension cable to one plug.
56
EE 020
Electrical Installation 1
Theoretical Test
57
EE 020
ELECTRICAL INSTALLATION 1
TEST 1
1. State three rules that must be obeyed in electrical installation.
2. State the conditions under which cables for more than one power circuit may be drawn
through the same junction or distribution box.
3. What is meant by ?
4. Name three different types of circuit diagram.
5. State what is meant by "a general circuit diagram".
6. State what is meant by the installation plan.
7. List the types of switches and switching circuits which are used in electrical
installations.
8. What is the application of two-way switches?
9. State what is meant by the two-way and intermediate switching.
10. What is the following circuit used for?
58
EE 020
ELECTRICAL INSTALLATION 1
TEST 2
1. What is the purpose of conduits?
2. Name the advantages of an insulated conduit compared to a metal conduit.
3. Name two types of conduits used where the mechanical loading is light.
4. What are the properties of armoured black-plastic conduit?
5. State the application of steel armoured conduit.
6. What is the relationship between the cross sectional area of the conduit and the
maximum cross sectional area of the cables if contains?
7. Where is the wiring duct used?
8. Is it permissible to lay NY cable in plaster or outdoors?
9. Is it permitted to use NYM cable in damp places?
10. Make a sketch showing the methods of laying cables and conduits.
59
EE 020
ELECTRICAL INSTALLATION 1
TEST 3
1. What is meant by the term portable electric equipment?
2. Explain what is meant by cable protection.
3. What is the function of a fuse?
4. Name two different screw cap fuse systems with their current and voltage rates.
5. Make a sketch showing the construction of fuse cartridge.
6. What is the application of small or glass-tube fuses?
7. Name four different types of fuses, in the order of their fusing time.
8. State how fuses may be tested.
9. What is an L-type switch?
10. Draw a detailed wiring diagram of a motor overload trip.
60
EE 020
ELECTRICAL INSTALLATION 1
TEST 1
(Solution)
1. Installations must be accident proof.
Operational reliability must be ensured.
The installations must be easily visible.
2. Either a) The second cable must not be joined in the junction box
or b) The circuits are separated by an insulating partition.
3. Three cables following the same path.
4. The general circuit diagram.
The detailed wiring diagram.
The installation plan.
5. This is the simplified, single line diagram of an installation.
61
6. The cable runs are indicated as a single line in the plan of the building, using
abbreviated symbols.
7. - Single pole switches
- Two-pole and three-pole switches.
- Group switches.
- Multi-circuit switches. Changeover switches.
- Intermediate switches.
- Current impulse relay.
- Staircase time switches.
8. Changeover switches are used for switching one 'or more incandescent lamps on and
off from two places.
62
9. Intermediate switches together with two two-way switches make it possible to switch
on and off from three or more places.
10. It is used for staircase illumination (in blocks of flats).
63
EE 020
ELECTRICAL INSTALLATION 1
TEST 2
(Solution)
1. To protect electrical cables against mechanical damage.
2. - It provides additional insulation.
- It is resistant to breakdowns.
- It is resistant to corrosion.
- it is easy to work with.
3. - Rigid plastic conduit - grey.
- Flexible plastic conduit - yellow or light grey.
4. Pressure-tight, non inflammable, corrosion and acid resistant, heat resistant up to
70°C, highly insulating and high electrical strength (40 kV/mm).
5. In concrete for connecting fixed machines.
6. The cross-sectional area of the cable should not exceed 1/3 of the internal cross-
sectional area of the conduit.
7. These are used to give mechanical protection to installations using NYe, NYf etc.
cable.
8. No.
9. No.
64
10. Methods of laying.
65
EE 020
ELECTRICAL INSTALLATION 1
TEST 3
(Solution)
1. Portable electrical equipment (e.g. hand drills, kitchen equipment, irons and electrical
cookers etc.).
2. Each cable is heated when current flows through it. If the current is too great during
short-circuit or overload, then the excessive heat will destroy the cable insulation.
Each cable must therefore, be protected against short-circuits and overload. An
overload circuit breaker carries out this function.
3. A fuse is a deliberately inserted section conductor of reduced cross section which
melts when there is short-circuit, over current or earth fault, and, therefore, protects
the cables and equipment from excessive heating.
4. Diazed fuses are manufactured for rated currents of 2 A to 200 A and a nominal
voltage of 500 V.
Neozed fuses are manufactured for rated currents of 2 A to 100 A and with a nominal
voltage of 380 V.
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5. Construction of fuse cartridge
1. top contact
2. support wire
3. quartz sand
4. fuse wire
5. cap
6. spring
7. porcelain body
8. bottom contact
6. These are mainly used in light current equipment (electronic equipment, electronic
equipment for entertainment), and are also used in the car industry.
7. Superfast; Fast; Medium fast; Slow fuses.
8. In order to test a fuse, the fuse cartridge is removed and tested using an ohmmeter,
for a blown fuse the ohmmeter reads infinity.
67
9. This is the most frequently used circuit breaker, which is suitable for all applications
and corresponds to the tripping characteristic of a fuse of equal current rating.
Magnetic trip 5 x In
Thermal trip 1.4 x In
In = rated current
10. With thermal trips With thermal trips and magnetic trips
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KEY TO EVALUATION
PER CENT
MARK
88 – 100
1
75 – 87
2
62 – 74
3
50 – 61
4
0 – 49
5