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B S I

B S * 5 3 4 5 : P A R T x L

03 H L b 2 4 6 6 9 0373412 L72 m

BS

5345 :

Part 1 : 1989

UDC 696.6 621.3 - 7 614.83

British Standards

I n s t i t u t i o n

No

part of

t h i s

publication may be p h o t W i e d or otherwise reproduced without

the

prior

permission

in writing of BSI

-

British StandardCode of practice

for

Selection, installationand

maintenance of

electrical

apparatus for use in potentially

explosive atmospheres (other than mining

applications or explosives processing

and manufacture)

Part l .General

recommendations

Code de bonne pratique pour sélection, installat ion e t entretien des matériels électriques à utiliser dans

les atmosphères explosibles ( à l’exception des applications dans les mines ou du traitement

ou de la fabrication des explosifs)

Partie l . Recommandations générales

Richtl inie f i r Auswahl, Einrichtung und nstandhaltung von elektrischen Betriebsmitteln für explosible

Atmosphären (außer der Verwendung ¡m Bergbau oder in der Sprengstoffverarbeitung und -herstellung)

Teil l . Allgemeine Empfehlungen

.

_.

British Standards Institution

y _

ritish Standards Institute on ERC Specs and StandardsPYRIGHT British Standards Institute on ERC Specs and Standardscensed by Information Handling Services

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B S I B S * 5 3 4 5 :

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03 m

L b 2 4 b b 9 0373433 O09 W

BS

5345

: Par t

1 :

1989

Foreword

This Part of

BS

5345 has been prepared under the direction

of t h e General Electrotechnical Engineering Standards

Policy Committee and is a revision of

BS

5345 : Part 1 :

1976, hich

i s

withdrawn. Before 1976, installations were

made in accordance wi th CP 1003. However, CP 1003 has

now been declared obsolescent and wi ll eventually be

withdrawn and should not be used for new installations.

Many industrial processes involve the generation,

processing, handling and storage of flammable and

potentially explosive gases, vapours and mists. Where such

materials may be present appropriate precautionshave to

be taken to design or locate electrical apparatus o that

electrical arcs, sparks, hot surfaces or frictional sparks

produced by such apparatus do not cause ignition.

Several techniques are available for the protection of

electrical apparatus situated in hazardous areas. These

techniques are described in this Part of BS 5345, which

takes into account the developments that have taken place

in area classification and the design, manufacture and use

of electrical apparatus for hazardous areas since its first

edition.

This revision of 6s 5345 :Part

I

has taken into account

the requirements of apparatus specifications

BS 5501

and

BS 4683. Although written largely with BS 5501 in mind,

it is recognized that apparatus in accordance wit h

BS

4683

and some earlier standards* is still manufactured and that

such equipment wil l no doubt continue to be in use for

a

number

of

years

t o

come.

BS 5345 is divided into nine P a r k t BS 5345

:

Parts 3 to

9

deal wit h the selection, installation and maintenance

recommendations appropriate to the types of protection

tha t may be used to achieve safe operation of equipment

in potentially explosive atmospheres.

BS

5345

:

Parts 1

and 2 provide basic recommendations applicable to al l

Parts. The lis t of Parts

i s

as follows:

Part 1

Par t 2

Part 3

Part

4

Part 6

Part 6

Part 7

Part 8

Part

9*

General recommendations

Classification of hazardous areas

Installation and maintenance requirements for

electrical apparatus wi th type of protection

d.. Flameproof enclosure

Installation and maintenance requirements or


'i'.

Intrinsically safe electrical apparatus and

systems


electrical apparatus protected by pressurization

'P' and by continuous dilution, and for

pressurized rooms



'e'.

Increased safety

Insta llation and maintenance requirements or

electrical apparatus wi th type of protection N


electrical apparatus with type ofprotection

S .Special protection



'o'.

Oil-immersed apparatus, and with type of

protection 'q'. Sand-filled apparatus

Compliance wi th a British Standard does not of i t se l f

confer immunity from

legal

obligations.

These earller spectfications are listed in appendix

A.

t B S

5345

wil l not now contain

a

tenth Part dealing with

the

use of gas detectors. This wi ll be the subject

of

a

separate standard.

..ZJ&~~eparation.

ritish Standards Institute on ERC Specs and Standards

Services

PYRIGHT British Standards Institute on ERC Specs and Standardscensed by Information Handling Services

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BSI

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0373414 T 4 5

m

BS 5345

:

Par t

1

: 1989

Contents

Page

Foreword

Inside front cover

Committees responsible

Back cover

Section one.General

1

Scope 2

2

3 requirements 3

4 Classification of hazardousreas 3

5 Types ofrotection

6ight metals as constructionaterials 3

Section two. Selection of apparatus

7

Procedure for selectinglectricalpparatus 5

8

7

9 Interconnection of apparatus 8

Section hree. General nstallation

recommendations

10 9

1 1 Access for inspection 9

12 Plansnd 9

13 9

14 Installationof apparatus 9

15 Integrity ofnsulation 9

16 Automatic overcurrentrotection 9

17 Earthingndarth faul t protection 10

18 Isolation 10

190

20 Portable and transportable apparatus and i t s

connections 13

Section four. Inspection, maintenance, esting

and repair

21

22

23solation

24 Precautions concerning the use

of

igniting

agencies 14

25 Initial anderiodicnspections 14

26 Init ial anderiodicesting 15

27aintenanceecommendations6

Section f i ve. Properties of flammable iquids,

vapours andgases

28 17

29 Melting point and boilingoint 17

30

Rela t ive

vapourensity 17

31 point 17

32lammableexplosive) limits 17

33 Flammableexplosive) range8

34 Effect of environments with other than normal

atmosphericonditions

18

35 gnition temperature

36 Apparatus group

37 Recommendations and notes concerning

individual materials

38 General considerations

Section six. Marking of apparatus

39 General

40 Marking requirements fo r apparatus

41 Examples of marking of apparatus

42 General notes on marking

Page

18

18

18

19

27

27

27

28

Appendices

A

Relevant International, European and British

Standards and details of the national certify ing

authority and

i t s

certification standards0

B Frictional sparking risks with

light

metals and

their alloys 33

C

Degrees ofrotectiony enclosures3

D Bibliography of dataources for table 7 36

E Calculation of the flammable lim its for

a

mixturef gases 37

Tables

1 Types of protection

2 Selection of apparatus and systems according

to zone of risk

3 Relationship between T class and maximum

surface temperature

4 Relationship between apparatus group,

the former gas group and apparatus

lass

5 Example of schedule for ini tia l inspection

6 Example of schedde for subsequent

7 Data for flammable materials or use wi th

8 Protection against contact and ingress of

9 Protection against ngress of water

inspections

electrical equipment

foreign bodies

10

Most frequently used degrees of protection

11 Components of the industrial gas mixture

12 Flammable limits of simpler mixtures

4

5

6

7

15

15

20

34

35

36

38

39

Figures

1 Flammable limits of hydrogen,carbon

monoxide and methane containing various

amountsfarbon dioxide and nitrogen 40

2 Flammable limits of ethane, ethylene and

benzene containing various amounts f

carbonioxidenditrogen 40

”

_c_

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Code o f practice.

Section

one

Section one. General

1 Scope

This Part of BS 5345

gives

recommendations for the

selection, installation and maintenance of electrical

apparatus for use in areas where flammable mater ial(s) are

generated, processed, handled, stored or otherwise

encountered which couldgive rise to explosive atmospheres.

This standard relates o the precautions necessary to avoid

ignition of an explosive atmosphere resulting rom electrical

arcs and sparks, hot surfaces or frict ional sparks from

electrical apparatus and installations.

This standard does not cover the following:

(a)

inherently explosive situations,e.g. explosives

manufacturing and processing;

(b) underground mining applications;

(c) dust atmospheres* or atmospherescontaining a

mixture of dusts and gaseshapours;

(d l areas where abnormal atmospheric conditions occur

(see clause

34);

(e)

precautions against the effects of static electricity

(see

BS 5958);

I f ) precautions against the effects of lightning

(but see 19.2.12 and BS 6651);

(g)

precautions against the effects of high frequency

electromagnetic radiation

(see BS

6656);

(h) precautions against ox ic hazards associatedwith

flammable materials;

NOTE. The toxic risks ssociated with flammable materials

apply to concentrations that are usually ery much less than

t h e lower flammable limit.

( i )

additional requirements for the installation of

electric surface heating systems (see BS 6351 .

This standard is applicable to al l new permanent

installations and, where reasonably practicable, to changes

to installations complying with earlier standards. The

recommendations or maintenance are applicable to

all

installations.

The recommendations of his standard are also applicable

to those installations that are semi-permanent or temporary.

However, in certain circumstancesalternative safety

measures and procedures may need o be adopted to

achieve the same

level

of safety

as

that recommended in

this standard.

Appendix A contains, for information, a l i s t of relevant

international, European and British Standards, together

with details of the national certifying authority and i t s

certification standards.

\

NOTE. The titles of the publications referred

o in

this standard

are liste d on page

44

and the inside back cover.

BS

6467

cor

tains a specifi cati on for elec

and a guide to i t s selection and use.

, t r ic i I appara

t B S 4056, now with draw n, uses the same test method .

2 Definitions

For the purposes of this Part of BS

5345,

and of the other

Parts of the standard generally, theollowing definitions

apply.

NOTE. Further definitions that re particularly relevant to the

specific types of prote ction are included

in

the appropriate Parts

of this British Standard.

2.1

explosive atmosphere. A mixture with air, under

atmospheric conditions, of flammable substances in the

form of gas, vapour or mist in such proportions that it can

be exploded by excessive temperatures, arcs or sparks

(the danger

is

a real one).

2.2

potentially explosive atmosphere. An atmosphere that

could become explosive (the danger

is

a

potential one).

2.3 flammable mist. A free suspension in air of droplets

of a liquid whose vapour is flammable.

2.4 hazardous area. An area in which explosive atmospheres

are, or may

be

expected to be, present in quantit ies such as

to require special precautions for the construction and use

of electrical apparatus.

2.5 non-hazardousarea. An area in which explosive

atmospheres are not expected to be present in such

quantities thatspecial precautions or the construction

and use of electrical apparatus are necessary.

2.6 flash point. The minimum temperature a t which a .

material

gives

off sufficient vapour to fo rm n explosive

atmosphere within the apparatus used for flash poin t

determination (see 31.1).

2.7

ignition temperature. The lowest temperature of

a

flammable

gas

or vapour a t which ignition occurs when

tested

as

described in International Electrotechnical

Commission (IEC) publication IEC

79-4t.

NOTE. Ignition temperature

was

formerly

known

as auto-ignition

or spontaneous ignition temperature.

2.8

flammable material.

A

gas, vapour, liquid or solid that

can react continuously wi th atmospheric oxygen and hat

may therefore sustain fire or explosion whensuch reaction

is

initiated

by a

suitable spark, flame or hot surface.

NOTE. Many liquids and olids, though regardedas flammable,

nevertheless do not normally burn. The appl icat ionf heat to such

materia ls serves to release vapour that mayburn with atmospheric

oxygen. The heatof the subsequent reaction

erves

t o release

further vapour for combustion. Flame may propagate through

suspensions of dusts by this mechanism. Liquids can lso give rise

t o lammable mists (see38.3).

2.9 apparatus (or system) certification. A formal

attestation by

a

recognized testingstation that a prototype

or sample of apparatus (or system), constructed o the

certification documents, complies wi th a standard.

NOTE. Although strictly

t

s the apparatus design rather thanhe

individual apparatus that s the subject

of

certification, the term

'certified apparatus' and variants upon

his

have gained acceptance.

This

is

reflected in the standard.

l tus with protection by enclosure for use in the presence of combustible dusts,

2


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2.10 component certification. A formal attestation by a

recognized testingstation that a component, constructed

to the certification documents, complies wi th a standard.

NOTE. The note to 2.9 applies here in respect of components.

2.11 maximum surface temperature. The highest

temperature that i s attained in service under the most

adverse conditions (but wi th in ecognized tolerances) by

any part or any surface of an electrical apparatus, which

would be able to produce an ignition of he surrounding

explosive atmosphere.

NOTE. The most adverse condit ions nclude recognized overloads

and any fault condit ion recognized n the standard for the type of

protecti on concerned and those abnormal operating conditions

recognized for the produc t concerned.

2.12

temperature

class

(T

class). One of six values of

temperature allocated to electrical apparatus derived rom

a system of classification according o the maximum

surface temperature of the apparatus.

2.13 apparatus group. The group assigned t o electrical

apparatus to indicate i t s suitabil ity for use in mines or

surface industry.

NOTE. For surface indust ry applicatiorl s the group may be

subdiv ided fo r specific gases.

2.14

type of protection. The measures applied in the

construction of electrical apparatus to prevent ignition

of surrounding explosive atmosphere by such apparatus.

NOTE. Formerl y it was com mon for an individual it em of apparatus

t o

employ one type of protecti on on ly; increasingly, apparatus may

now employ t w o or mo re types of pr otecti on. Thus

a

rotating

machine may incorporate a m oto r carcass in type of pro tection 'd'

(flameproof enclosure) and a terminal box in type of protection 'e '

(increased safety). It has become com mon usage to refer to

'explosio n-protected' apparatus rather than to any one ty pe of

protection.

(See

also section two.)

2.15

degrees of protection provided by enclosures ( o f

electrical apparatus). The measures applied to the

enclosures of electrical apparatus o provide:

( a ) the protection of persons against contact with or

approach to l ive parts and against contactwith moving

parts (other thansmooth rotating shafts and the like)

inside the enclosure andhe protection of the apparatus

against ingress of solid foreign bodies;

(b) the protection of the apparatus inside the enclosure

against harmful ingress of water.

2.16 electrical protection. The measures applied to

BS

5345 : Par t 1 : 1989

S e c t i o n o n e

ments

of

the Health and Safety a t Work etc. Act 1974.

More specific requirementsare imposed in certain

classes

of premises and legal advice should be sought. It should be

noted that the Health and Safety at Work etc. Act 1974

applies to all offshore installations operating n control led

waters designated under the United Kingdom Continental

Shelf Act 1964.

4 Classification

of

hazardous areas

This standard

s

based on the concept, which

is

accepted

international ly, of dealing with the risk of fire and

explosion by area classification. This concept recognizes

the differing degrees of probabil ity wi th which

concentrations of flammable

gas

or vapour may arise in

installations in terms of both the frequency of occurrence

and the probable durat ion of existence on each occasion.

The detailed considerations that should be taken into

account in area classification are described in

BS 5345 :

Part

2.

For completeness, the definitions appropria te o

area classification are repeated here.

Zone

O

Zone in which an explosive atmosphere

i s

continuously present, or present for long

periods.

Zone 1 Zone in which an explosive atmosphere i s

likely to occur in normal operation.

Zone

2

Zone in which an explosive atmosphere s not

likely to occur in normal operation, and f

it

occurs it will

ex is t

only for

a

short time.

NOTE. Area classification n this standard deals only with risks

due to flammable gases, vapours and mists.

When the hazardous areas of a plant have been classified,

the remainder will be defined a s non-hazardous. In a non-

hazardous area normal electrical techniquesapply

(but

see 7.1).

5 Types of protection

There are a t present nine accepted types of Protection for

electrical apparatus for use in hazardous areas.A

description of each type

i s

given in table

l .

The relevant

equipment specifications, where they xist, should b e

referred to for precise definitions of he type of protection.

Apparatus may

be

protected by one or more types of

circuits to control the effects of overcurrent and earth fault. protection (see

42.4).

. .

I 6 Lightetalssonstruction materials

I

NOTE.

IE C

79-3 tandardizes an apparatus and a test m ethod.

Particular consideration should be given to the location of

an apparatus that incorporates light metals in the

construction of i t s enclosure. The propensityof such

conditions of frictional contact has been well established.

3 Statutory requirements

materials to give rise to sparking that i s incendivender

Electrica l installations in hazardous areashave to complyReference should

e

made to appendix B for urther

with a l l relevant statutory requirements.nstallations in detailed guidance.

Great Britain a t places of work are subject to the require-


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S e c t i o n

one

r---

1

Table 1. Types

@ f rotection

Title

Flameproof

enclosure

Intrinsically-safe

apparatus or system

Pressurization,

continuous dilution

and pressurized

rooms

Increased safety

Type of

protection N

Special protection

Oil-immersion

Powder/sand f ill ing

Encapsulation

Description

A method

of

protection where the enclosure fo r electrical apparatus

will withstand an internal explosion of the flammable gas or vapour

(for which it is designed) that may enter it, without suffering

damage and without communicating the internal flammation to the

explosive atmosphere for which it

i s

designed, through any joints or

structural openings in the enclosure.

A protection technique based upon the restriction of electrical

energy within apparatus and in the interconnecting wiring, exposed

to

a

potentially explosive atmosphere, to

a

level below that which

can cause ignition by either sparking or heating effects. Because of

the method by which intrinsic

safe ty is

achieved it is necessary that

not only the electrical apparatus exposedo the potentially

explosive atmosphere, but also other (associated) electrical

apparatus with which

it

i s

interconnected, is suitably constructed.

A

method of protection using the pressure of a protective gas to

prevent the ingress of an explosive atmosphere o a space that may

contain

a

source of ignition and, where necessary,

using

continuous

dilution of an atmosphere within a space that contains a source of

emission of

gas,

which may form an explosive atmosphere.

A method of protection by which additional measures are applied

to an electrical apparatus to give increased security against the

possibility of excessive temperatures and of the occurrence of arcs

and sparks during the service ife of he apparatus. I t applies only

to an electrical apparatus, no parts of which produce sparksor arcs

or exceed the lim it ing temperature* in normal service.

A type of protection applied to an electrical apparatus such that,

in normal operation, it is not capable of igniting a surrounding

explosive atmosphere, and a fau lt capable of causing ignit ion is

not likely to occur.

A concept for those types of electrical apparatus that,

by

their

nature, do not comply with the constructional or other requirements

specified for apparatus wi th established types of protection, but that

nevertheless can be shown, where necessary by

test,

to

be

suitable

for use in hazardous areas in prescribed zones.

A

method of protection where electrical apparatus s made safe by

oil-immersion in the sense that an explosive atmosphere above he

oil or outside the enclosure wi ll no t be ignited.

A

method of protection where the enclosureof electrical apparatus

i s fil led with mass of granular material such

that,

if an arc occurs,

the arc will not be liable to ignite the outer flammable atmosphere.

A

type of protection in which parts that could ignite an explosive

atmosphere by either sparking or heating are enclosed in a compound

in such a way that this explosive atmosphere cannot

be

ignited.

Part of

ES

5345

3

4

5

6

7

8

9t

9t

t t

For defin iti on of 'l imiti ng temperature' see

3.5

o f

BS

5345

:

Part

6 : 1976.

t

In preparation.

t t

Although the existence of type of protection 'm' is acknowledged here and

ES

5501 : Part 8 has been published con taining the

equipment specification, consideration has yet to

be

given to recommendations for

i t s

selection, ins tallation and maintenance etc.

for incorporation in ES 5345. The recommendations in this standard do not therefore necessarily cover ty pe of prot ectio n 'm'.

NOTE

l . Other types of prot ectio n are under consideration internationally. These may include typ e of p rot ectio n

h

hermetically sealed.

NOTE 2.

Whereas in

OS

6941 the type

of

protectton

i s

known

as

type

N,

in

IEC

publication

79-1

5 t is designated typ e n'.

4


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Sect ion two

Section two. Selection

of apparatus

7

Procedure

or

selecting electrical

apparatus

7.1 General

Apparatus for use in hazardous

areas

should be selected

in accordance with each of the following criteria':

(a) classification of area;

(b) temperature classification;

(c)

apparatus group;

(d) environmental conditions.

Selection procedures according to the above criteria are

recommended in 7.2 to 7.5.

Special considerations may be required for non-hazardous

area apparatus that i s associated w ith hazardous area

apparatus (see appropriate Parts

of BS

5345,

e.g.

Parts

4

and 6 for intr insic safety and increased safety apparatus,

respectively).

7.2

Selection according to classification of area

Reference should be made to clause 4 and to BS 5345 :

Part

2

for details of area classification that results in the

division of the hazardous area in to one or more zones.

Having established

he

zones, the types of protection to be

applied to the electrical apparatus should be selected in

accordance wi th table

2.

7.3 Selection according to temperature classification

When selecting apparatus according o temperature

classification, the maximum surface temperature of the

T

class

of the apparatus (or, where the apparatus

s

marked

with

a

particular maximum surface temperature, that

temperature) should not exceed the igni tion temperature

of the gases or vapours involved.

NOTE.

However, BS 5501, subject t o certain specified conditions,

permits the surface temperature of certain small componentsf

apparatus, e.g. transi stors or resi stors used in intrinsically-s afe

electrical circuits, t o exceed the temperatureclass marked on

t h e

apparatus if there is no direct or indirect risk of ignition fromhese

components.

Table 7 gives ignition temperatures for

a

range of

flammable materials. Apparatus intended or use with

materials no t given in table

7,

or where this tabledoes not

list the ignition temperature, should be installed only when

expert advice confirms i t s suitabili ty for use with those

materials.

The

T class is

normally assigned to apparatus on the basis of

temperature rise

t es t s

assuming

that

the apparatus may be

used in

a

local ambient temperatureno t exceeding

40

"C.

In special cases, apparatus may be designed on request to

operate in a local ambient temperature of more than40 OC.

In this case the maximum permitted local ambient

temperature will be clearly marked on the apparatus. The

T class wil l have been assigned on the basis of temperature

rise tes ts and the assumption hat the apparatus may

operate a t temperatures up to the maximum permitted

local ambient temperature.

When apparatus which has had a T class assigned assuming

a

40 "C maximum ambient temperature s to be used a t

a

higher local ambient temperature, for example, because it

i s

mounted on

a

hot surface, the maximum surface

temperature of the apparatus should not exceed the

igni tion temperatures of the gases or vapours likely to be

present.

It s

also important to check with the manufacturer

on the suitability of

the

apparatus to operate a t these

higher temperatures. For example, when apparatus s to be

mounted under pipe-lagging,

t

i s

virtually unaffected by

the air temperature, but may fail due to heat from the pipe.

The permitted maximum surface temperatures classified

according to BS 5501

:

Part 1 and BS 4683

:

Part 1 are

given in table 3.

~~~

Table 2. Selection of apparatus and systems

according to zone of risk

Zone

-

O

1

2

Type of protection

'ia' intrinsically-safe apparatus or

system

'S '

special protection specifically

certif ied for use in Zone

O )

Any explosion protection

suitable for Zone

O

and

'd' lammable enclosure

'ib' intrinsically-safe apparatus or

'P'

pressurization,continuous

'e' increasedsafety

'S '

special protection

Any explosion protection suitable

for Zones O or 1 and

N type of protection N t

'o'

oil-immersion

'q'

sand filling8

system

dilution and pressurized rooms

Part of

BS 5345

4

8

7

9*

9*

Alternatively, apparatus that in normal operation s no t

capable of producing ignition capable rcs, sparks or

surface temperatures may lso be acceptable or use in

Zone 2 where it has been assessed

by

persons who should :

(a) be familiar with the requirements of any relevant

standards andcodes of practice and their current

interpretations;

(b ) have access

to

all inform ation necessary t o carry

out theassessment;

(c) where necessary, utili ze similar test appar atus and

test procedures

to

those used by recognized testing

stations.

t Whereas in BS 6941 the type of protection

is

kno wn as

type N, n IE C pubilcation 79-15 it s designated ty pe 'n'.

*

In

preparation.

8 The use of apparatus wit h typ e

of

protection 'q' in

Zone

1

is under consideration.

Special conditions for afe use apply to any type f certified ex plosion-protected apparatus wh ere the certification number has a suffix

marking of 'B' o r 'X', and these conditions may affect the select ion of suchpparatus.

.A

.

-

r,


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Section

two

Table

3.

Relationship between

T

class and maximum surface

temperature

T

class

T l

T2

T3

T4

T5

T6

Max imu m surface

temperature

O C

450

300

200

135

1

O0

85

An example can be given of the relationship between

T

class

and ignition temperature. Cyclohexanehas an

ignit ion temperature (see also clauses

35

and

38)

f

259 C

and, therefore, assuming

a

maximum environmental

temperature of 40 C , apparatus wi th a temperature class

T2

(¡.e.

300 C ) would not be suitable, whereas apparatus

with

a

temperature class of T3 (¡.e. 200 C ) would be

suitable.

NO TE . In special cases, apparatus can be marked witha particular

temperat ure as wel l as one of the six

T

classes. Fo r example,

in

the

case cited above, if the apparatus were markedwith a temperature

of 259 "C, as well as the temperature class of T2,

it

would still be

suitable for use

in

areas where a potentially explosive atmosphere

of cyclohexane might form.

In the

case

of some items of apparatus with type of

protection

e (e.g.

motors) the maximum temperature

should not exceed the 'limi ting temperature', which may

be determined by the thermal stability of materials used

in the apparatus (see

BS

5345 : Part

6) .

7.4

Selection according to apparatus group

7.4.1

App aratus groups and subdivisions. BS

5501 divides

electrical apparatus into two basic groups.

(a) Group I:electrical apparatus for mines susceptible

to firedamp.

(b)Group

II:

electrical apparatus for places with

a

potentia lly explosive atmosphere, other than mines

susceptible t o firedamp.

Some types of Group

I

apparatus with, for example.

types of protect ion 'd', 'i' and

S *

may be further

subdivided according o the nature of the potentially

explosive atmosphere for which it

i s

intended. These

subdivisions are given in BS 5501

as

A,

B

and C .

NOTE. For brevity BS 5501 states apparatus group and

subdivision collectiv ely, e.g. Gro up IIA, dropping theword

'subdivision'.

7.4.2

Use of apparatus in poten t ia l ly exp losive

atmospheres.

Apparatus that has no subdivision in i t s

group may be used wit h any of the flammable materials

listed in table

7

subject to consideration

of

the

recommendations of 7.3 and

7.5.

Appraratus that has a subdivision in

i t s

group should be

used only with the materials allocated o tha t subdivision

(see

table 7) subject to consideration of the recommend-

ations of 7.3 and 7.5 and 7.4.2(c).

Apparatus with

a

particular subdivision may be used wi th

flammable materials allocated o a lower subdivision

subject

to

consideration of the recommendationsof

7.3

and 7.5,

e.g.

Group l l B apparatus may be used with

flammable materials allocated o Group I IA , and Group I I C

apparatus may be used wit h flammable materials allocated

to Group I IA and Group

IIB.

Apparatus that has subdivisions in t s group and which i s

intended for use wi th flammable materials not given in

table 7 should be installed only when expert advice

confirms

i t s

suitability for use with those materials.

NOTE. In BS 229 and

BS 1259

flammable gases and v apours are

grouped or classified, respectively, according to th e ex pe ri men ta l

data for lim iti ng safe gaps or igniting c urrents measured under

precisely specified conditions. In he case of

ES

1259, many

materials are classified according to their chemical similaritywith

gases and vapours t ha t are already c lassified on th e basis of

experimental data. Neither method of grouping takes nto account

the need for surface temperature classification, since ignition

temperatures generally are not rel ate d o other combustion

characteristics.

It

is therefore inaccurate

o

assume that any

particular apparatus complying with the design requirements for

a group of gases could be used safely with all flammable materials

allocated to that group. For his reason, instead of group ing gases.

an apparatus itself s now grouped according o design criteria

specified in the appropriate Parts

of BS 4683

and BS

5501.

The relationship between the apparatusgroup and the

former

gas

group and apparatus lass

is

given i n table

4.

Apparatus with type of protect ion

S'

may be subdivided as

shown

above where

it

uses either or

both

techniques of typesof protect ion

'd' or 'i'.

.:

c


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Table 4. Relationship between apparatus group, the former gas group

and apparatus

class

Repres entat ive gas

Methane

Propane

Ethylene

Hydrogen

Acetylene

Carbon disulphide

1

r

pparatus group Formerormer

BS

5501

I "

I A

I B

I IC

I IC

I C

gas group

apparatus

in BS 229

c lan

in

B5 4683 ES 1259

I*

I

I *

I A

II 2c

I IB

III 2d

I G

IV 2e

Not allocated

I V t

2f

Not allocated

I V t 2f

For underground mining applications.

t Although

a

gas Group IV was allocated, the standard excluded construction

requirements for apparatus to e used in this group.

7.5 Selectiolx according to environmental condit ions

Current standards for the types of protection listed in

table 1 require that apparatus is normally tested in air and

under normal atmospheric conditions. However, oxygen

enrichment or variations of pressure or temperature may

adversely affect the type o f protection afforded to the

apparatus. In such

cases care

should be taken to ensure

that the apparatus has been evaluated by

a

competent

authority

(see A.4)

for the specific conditions of use'.

Apparatus and

its

component parts should

e

constructed

so

as

to guard against electricaland mechanical fai lure in

the intended conditions of use. The integrity of some

electrical apparatusmay be affected when required to

operate under temperature or pressure conditions outside

those for which the apparatus has been constructed. In

such conditions fur ther advice should be sought.

Particular attent ion should be given to the need for

protection against the weather, the ngress of liquids and

particulate matter, corrosion, the effect of solvents and the

effect of heat from adjacent plant (see also appendix

C

and 27.3 o

27.5).

Attention is drawn to the risks that can arise wi th apparatus

in to which process fluids may be introduced, e.g. pressure

switches or canned electric motor pumps. Under fau lt

conditions, e.9. diaphragm or can failure,

the

flu id may be

released inside the apparatus under considerable ressure

which may cause any or all of the following:

(a) rupture of

he

apparatus enclosure;

(b)

an immediate ignition risk;

(c) transmission of

t h e

fluid along the insideof the

cable into a non-hazardous area.

Preferably such apparatus shouldbe designed

so

that the

process flu id containment

s

in

a

separate enclosure from

the electrical apparatus, but where this is not possible

apparatus designed to be vented is acceptable. Failing his

a special sealing joint should be used or a length of mineral

insulatedmetal sheathed cable shouldbe introduced

n

the

cable run.

8 Certification

8.1 General

Notwithstanding he statements in this clause concerning

cert ification, apparatus shouldbe selected wi th

a

type of

protectionas recommended in table2 for the appropriate

zone.

.

".

BS

5345

: P a r t 1

: 1989

Section two

NOTE l . The t erm 'apparatus' can

be

generally said to include

systems

also.

NOTE 2 . See definition s in

2.9

and 2.10.

8s 5501 and BS 4683 : Part 2 and Part 4 require apparatus

to be certified. When conformity wi th EEC Directives

is

required, certif ication is to be carried out by an 'approved

body' listed

by

the Commission. (See A.4 for details

of

the

'approved body' in the United Kingdom.)

In practice for Zone O and Zone 1 applications certified

apparatus ¡s.generally used as an aid to satisfying he

statutory requirements listed in clause 3 (but see 8.2).

For apparatus designed o

BS 4683 :

Part

3

certification

i s

optional.

Apparatus certified to standards other than British

Standards or CENELEC European Standards or BASEEFA

Standards falls outside the scope of

t h i s

standard. Such

apparatus may, however, be used, but inorder to ensure i t s

correct application and insta llation reference should be

made to the relevant nat ional code of practice that deals

with these aspects. In cases of doubt about the application

or instal lat ion of such apparatus expert advice should be

sought.

Cer tified apparatus normally bears t h e authority's

certification mark in addi tion to ll other marking required

by the indiv idual standard (see clause 42 for notes on

marking to

BS

5501).

NOTE 3. BASEEFA has ssued cert if i cates to BASEEFAstandards

when there was no acceptable published British Standard.

of this standard.

NOTE

4.

For information

on

marking o f apparatus see section six

8.2 Uncertified apparatus for Zone

O

and Zone 1

In exceptional circumstances,e.g. research, development,

pilot plantand other new projects work, where suitable

certified apparatus i s not obtainable, other apparatus may

be used in Zone

O

and Zone l . The users of such apparatus

should obtain

a

'document of conformity' to how that the

apparatus

has

been examined and, where necessary, tested

by

a

competent body (using techniques and acilities

similar to those normally used by a national certifying

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Sect ion

two

author ity for the type of protection concerned) andhas

been found t o comply with the requirements of the

appropriate standard or the particular type

of

protection.

Such apparatus would not, however, bear the mark of

a

national certifying authority.

8.3 Assessment of

Ex

components

(see

also 42.3)

A number of components have been assessed fo r use in

potentially explosive atmospheres and may have been given

a Component Certificate. Such componentsmay be used

wi th other apparatus where either the certificate for tha t

apparatus identifies the relevant component or where the

apparatus including the component has been assessed.

Particular attention should always be given to the selection

and use of components.

9

Interconnection

of

apparatus

The safety of individual pieces of apparatus may be

influenced by any other apparatus with which

it is

interconnected. For such system considerations, reference

should be made to the Parts of

B S 5345

covering individual

protection concepts.


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BS 5345

:

Part

1

: 1989

Section three

Section three. General installation recommendations

10 General

In addition o any recommendations there may be for

installations in non-hazardous areas, further recommend-

ations for installations in hazardous areas as

a

consequence

of the nature of the environment and that are generally

applicable to

al l

types of protection are described in

clauses 11to 20.

The explosion protection of some installations, for

example, those using electric surface heating, pressurization

'P',

etc.

i s dependent on the overall design of the completed

system. In such cases, the appropriate design codes or

standards should be used for guidance to carry ou t the

installation

(see

A.3 and/or other Parts of BS 5345).

Alterations to apparatus or systems may invalidate any

certificate or other documentation relating to that

apparatus or system. Such alterations shouldbe made only

with the agreement of the owner, occupier or other

responsible persons who are in control of the premises, in

consultation with the manufacturer where appropriate.

There may be special condit ions for safe use listed in he

certification documents (see 42.2) that will affect the

method of installation and it

i s

important to ensure that

such conditions are properly met.

1

1

Access for inspection

Installations should be designed and the apparatus and

materials installed with a view to providing

ease

of access

for inspection and maintenance.

12 Plans and records

For each si te

a

responsible person should maintain plansor

records of the following items:

(a )

the classification and extent of hazardous areas

together wi th the other information

as

recommended

in 7.4 of BS 5345 : Part 2 : 1983;

(b) records sufficient t o enable the explosion-protected

equipment to be maintained in accordance wi th itstype

of protection.

Clause

1.3

of BS 5501

:

Part 1 : 1977 ndicates that devices

in which, according to

t h e

manufacturer's specifications, .

none of the values 1.2 V , 0.1 A, 20

pJ

or 25 mW

i s

exceeded need not be certified or marked. The most

widespread use of such apparatus is in intrinsically-safe

systems where the use of simple apparatus such as

thermocouples and switches

s

usually covered by

these

rules. A comprehensive recordof such apparatus and

systems should be maintained so that it may be properly

inspected for compliance wi th the relevant safety

documentation.

13 Electrical ratings

Electrical apparatus and materials should

be

installed, used

and maintained within their electrical ratings or power,

voltage, current, frequency, duty and such other

characteristics where non-compliancemight jeopardize the

safety of the installation.

In respect of electrical apparatus from non-UK suppliers,

because of the differing nature of the supply networks,

special care should

be

taken to ensure that:

(a) the

voltage and frequency rating are appropriate t o

the supply system on which the apparatus is t o be used;

(b) the temperature classificationhas been established

for the correct voltage, frequency,etc.

14 Installation

of

apparatus

All apparatus should be installed wi th due regard to the

possibility of external mechanicaldamage affecting the

type of protection of the apparatus. Where equipment is

to

be

installed in areas of high mechanical risk, additional

measures such as the provision of guards for light

transmitting parts may be necessary. However, additional

measures should not impair the integrity of the type of

protection (see, for example, BS 5345 : Part 3).

Special conditions for safe use apply to any type of

explosion-protected apparatus where thecertificate

number has a suffix marking and these conditions may

affect certain featuresof the installation. The certification

documents shouldbe studied to ascertain the conditions

of installation. The manufacturers shouldlso have

provided clear nstallation instructions.

15 Integrity of insulation

Care should be taken during installation to maintain the

degree of electrical insulation provided by the construction

of the apparatus so that the possibility of accidental

sparking or arcing

s

avoided.

16 Automatic overcurrent protection

In general,

al l

circuits and apparatus in hazardous areas

should

be

provided with automatic means of disconnection

in the event of overcurrent (short circuitand overload)

conditions. However, apparatus w ith part icular t y p e s of

protect ion may have additional and/or alternative

requirements, and reference should be made o the

recommendations n the appropriate Parts of B S 5345.

Suitable protection should be fitted where there

is

a danger

that three-phase apparatus may be subjected o

excess

current duringsingle-phase operation.

9


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Section three

17

Earthing and earth ault protection

17.1 Earthing of power systems

Earthing of power dist ribution systems should be in

accordance wi th appropriate recommendations,

e.g.

CP

1013, Fifteenth editionof the IEE ‘Regulations for

electrical installations’ (the Wiring Regulations),

1981

or

the I E E Recommendations for the Electrical and

Electronic Equipment

of

Mobile and Fixed Offshore

Installations (1983).

High voltage systems, e.g.

3.3

kV and 6.6 kv, should have

earth fault protection n addition o overcurrent protection.

17.2

Earthing of intrinsically-safe electrical systems/

apparatus

‘i’

Detailed recommendations are given in

BS

5345

:

Part 4.

17.3 Lightning protection

Recommendations or lightning protectionof structures

are given in

BS 6651 (see

also

19.2.12).

17.4

Electrostatic phenomena

Recommendations or the avoidance of ignition risks due

to

s t a t i c

electr icity are given in

BS 5958.

17.5

Cathodic protection

Recommendations for cathodic protect ion ystems are

given in

CP

1021.

17.6

Protective multiple earthing (PME)

Where the power supply

s

directly from

a

system that

is

protected by protective mul tiple earthing,

special

precautions may be required within the hazardous area and

specialist advice should be sought.

17.7 Interconnection of earthing ystems

The power, lightning, andstat ic earthing systems, where

they ex is t in the same area, should be effectively connected

together to ensure

as

far

as

possible that all metal work in

a

part icular area i s a t the same potentia l under al l conditions

(see

BS

5345

: Part

4

for special recommendations for type

of protection ‘i‘).

18

Isolation

At

a

suitable point or points outside thehazardous area

there should be single or multiple means of isolating

electrical supplies to the hazardous area.

Suitable means of iso lat ion should be provided for each

circu it or group of circuits, to include

all

circuit conductors

(inc luding neutral conductors). Where the means of

isolation is located inside the hazardous rea

it

should be

provided with an appropriate

type

of protection.

Labelling shouldbe provided immediately adjacent to each

means of isolation to permit rapid identification

f

the

circuit or group ofcircuits thereby controlled. There

should be effective measures to prevent the restoration

of

supply t o the apparatus whils t the risk of exposing

.

l o

unprotected

l ive

conductors to an explosive atmosphere

continues.

BS

5345

:

Part 4 hould be referred to for isolation

recommendations for circuits for apparatus and systems

with type

of

protection

’i’.

19 Wiring systems

19.1 General

The types

of

cable that in principle may be used for

installations in hazardous areas are described in this clause.

The detailed recommendations for permitted types of cable

and their accessories are described in the Parts of BS 5345

dealing wi th individual types of protection.

For

a

Zone

O

installation, cables wi ll be either part of an

‘ia’ system

(see

BS 5345 : Part 4 r as recommended for

type of protection

S’

for Zone

O

(see BS

5345

:

Part 8) .

Types of wiring system that should be used in Zone 1 and

Zone

2

areas are:

(a)

cables drawn into conduit systems (see 19.4);

(b) cables that are otherwise suitably protectedagainst

mechanical damage.

NOTE. The sheath

o f

a metal sheathed cable should no t be used

as

the

neutral

conductor.

Examples of the types of cable that are in accordance with

the recommendations

of

(b ) are:

(1 ) thermoplastics or elastomer insulated screened or

armoured cable with or without a lead sheath and with

polyviny lchloride (PVC), chlorosulphonated

polyethylene (CSP), polychloroprene (PCP), chlorinated

polyethylene (CPE) or similar sheath overall;

(2 )

cables enclosed n

a

seamless aluminium sheath with

or without armour, with an outer protective sheath

(see

also appendix

B);

(3) mineral insulated metal sheathed cable

(see

also

appendix

B);

(4)

thermoplastics or elastomer insulated flexib le cable

or cord with

a

flexible metallic screen or armour and

a

PVC, CSP, PCP, CPE or similar sheath overall;

(5)

thermoplastics insulated cable wi th semi-rigidsheath.

For type of protection

‘i‘

and for apparatus used in Zone

2

only, other cables may be used (see

BS

5345

:

Parts 4 and

7).

19.2 General installat ion recommendations o r wiring

systems

19.2.1

The cable entry to the apparatus should maintain

the integrity of the type of protection of he apparatus.

Certain

t y p e s

of cable employ materials that can exhibi t

significant cold flow’ characteristics which could have

adverse effects on the protection of theapparatus. Where

such cable is to be used a suitable cable entry device should

be employed, e.g. certified glands not employing

compression seals or other certified cable entry devices

suitable for use wit h these cables.

19.2.2 Unused cable entries in electrical apparatus should

be closed with plugs suitable for the type of protection of

the apparatus.


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1 : 1989

Sec t ion th ree

19.2.3

Where accessories, e.g. a junction box, are used for

the interconnection of cables, only those accessories that

are

suitable for the zone concerned should be used.

19.2.4

Electrical continui ty between metallic enclosures

and conduit, armour or cable sheaths and armour, or across

any joints in the conduit or armour, should be maintained

by the integrity of the joint i t se l f . If external bonding is

necessary, it should be connected directly across the joint.

19.2.5

Where circuits traverse

a

hazardous area in passing

from one non-hazardous area o another, the wiring system

in the hazardous area should

b e

in accordance with the

recommendations of this standard.

19.2.6

Except for trace heating, fortuitous contact between

conduit or the metallic armouring/sheathing of cables and

pipework or equipment containing flammable gases, vapour

or l iquids should be avoided. The insulation provided by a

non-metallic outer sheath on

a

cable will usually be

sufficient to avoid this.

19.2.7

A wiring system should be installed, so far as is

practicable, in positions that wi ll prevent it being exposed

to mechanical damage and to corrosive or solvent agencies

and to the effects of heat. Where exposure of this nature is

unavoidable, appropriate protective measures should

be

taken.

19.2.8

All apparatus connections andwiring systems

whose functions are not immediately apparent shouldbe

clearly marked to enable their relationship to any

associated apparatus, connections and wir ing systems to

be clearly recognized.

19.2.9

Where cables or conduit pass through a floor, wall,

parti tion or ceiling that forms a gas or fire barrier, the hole

provided for them should be made good wi th material

determined as incombustible in accordance with the

method of

BS

476 : Part 4 to the full thickness of the

floor, wall, partition or ceiling. Alternatively, cable glands

or cable transits may be used for this purpose.

19.2.10

Where trunking, ducts, pipes or trenches are used

to accommodate cables, precautions should

be

taken to

prevent the passage of flammable gases, vapours or liquids

from one area to another and to prevent the collection of

flammable gases, vapours or liquids i n trenches. Such

precautions may involve the sealingof trunking, ducts and

pipes and the adequate ventilation or sandfilling of

trenches.

19.2.1 1

For terminal connections to fixed apparatus that

may be required to be moved a small distance, e.g. motors

on slide rails, cables arranged to permit the necessary

movement without detriment t o the cable, or one of t he

types of cable suitable for transportable apparatus, may

be

used. If flexible conduit is used, i t and i t s fittings should

be so constructed and assembled that damage to the cable

consequent upon its use i s avoided. Adequate earthing or

bonding should be maintained other than by means of the

flexible conduit.

19.2.12

Where an overhead line provides power or

telecommunication services to apparatus in

a

hazardous

area it should be terminated in a non-hazardous area and

c

“

the service continued by buried cable. Suitable surge

protection apparatus should be fit ted

a t

or near the

terminal point. The armouring or metal sheathing of the

cable should be electrically continuous, and the end

adjacent to the point of connection with the overhead line

should be bonded to the earth electrode of the surge

protection apparatus. l n addition,

t h e

armouring or metal

sheathing should be independently earthed as near as

possible to the lightning protective system, i f any,

associated with the hazardous area (see also

BS

6651

).

NOTE. Guidance on the application

of

surge diverters for

alternating current power circuits

i s

given in

ES 2914.

19.3 Environmental factors affecting choice of wiring

system

19.3.1 Insulating materials may be attacked by certain

chemicals, and where contact may be sufficiently long that

deterioration could result from such exposure, then

consideration shouldbe given to the use of

a

suitable means

of protection, e.g.

a

protective sheath.

19.3.2 Where cables may be subjected to excessive flexing,

consideration shouldbe given to the avoidance of fracture,

e.g. when using mineral insulated cable, by forming

a

cable

into a loop close to the point of termination.

19.3.3

Where electrolytic corrosion of metal sheath may

result from contact with walls or other surfaces o which

the cable is attached, it should be kept clear of such

surfaces or covered with

a

protective sheath.

19.3.4

Cables, whether or no t manufactured in accordance

with

a

British Standard,

are

not necessarily intended for

wet conditions. Where such conditions persist, the cable

manufacturer shouldbe consulted so that the correct

construction may be supplied.

19.4

Conduit systems

Conduit should

be

selected from the following:

(a) screwed heavy gauge steel, solid drawn or seam

welded in accordance with

BS 31

or BS 4568;

(b)

lexible conduit of metal or composite material

construction,

e.g.

metal conduit with a plastics outer

jacket,

of heavy or very heavy mechanical strength

classification in accordance wi th BS 731 : Part

1.

NOTE l.he use

of

plastics condui t

of

sufficient strength with

apparatus having specific types

of

protection

i s

discussed in the

appropriate Parts

of

BS 5345.

NOTE 2.

Attention is drawn

to

the recommendations of clause 6

with respect to the use of light metals as construction materials.

In installations where vibration, relative movement or

excessive stresses may be a potential source of fracturing

or loosening of joints, the use of flexible conduit

as

recommended in (b)above may be considered.

All conduits should have corrosion resistance qualities

commensurate with the environment in which they wi ll

be

installed.

Where a run of conduit, irrespective of size, passes from

a

hazardous area t o

a

non-hazardousarea,

a

stopper box or

sealing device should be inserted

a t

the hazardous area

boundary or, failing this, on the side remote from the

hazardous area.

11


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NOTE 3. T h e use of a sealing device i s essential to the maintenance

of

certain types of p rotecti on

(see

appropriate Parts

of

BS

5345).

Elbows of the solid ype may be used for the immediate

connection of conduit to apparatus.

Surface mounted solid drawn orseam welded conduit

should

be

supported by spacing saddles.

Al l join ts in an assembly

of

conduit should

be

prepared

before or after assembly so that the development of rust

i s

inhibited and earth continuity and bonding

is

maintained.

The flexible condui t section shouldbe fitted with

terminating ittings, appropriate to the classification of the

conduit , that maintain he ingress protection of he

condui t system. The flexible conduitsection should not

be used

as

the sole means of maintaining the continuity of

the protective conductor provided by he rigid system.

The metall ic portion of he conduit should

be

electrically

bonded to the rigid system by either

a

separate conductor

or the terminat ing devices.

NOTE

4. For additional recommendations for conduit systems

that are relevant to particular types of pro tection ,

see

the

appropri ate Parts of

BS

5345.

19.5 Cable systems

19.5.1 General. Conductors may be of copper or

aluminium, but plain aluminium hould not be used for

conductors wit h cross-sectional areas

less

than

16

mm2

(see

also

8.7

for precautions on the use of aluminium in

E x 'd' flameproof enclosures).

Cable runs should, where practicable,be uninterrupted.

Where discontinuities cannot be avoided, the oint, in

addition to being mechanically and electrically suitable

for the situation, should

be

encapsulated or made in a

compound-f illed oint box or be protected in accordance

with the requirements of the zone.

NOTE.

Certain typ es of prot ection require specific types

of

cable

glands; reference shoul d

be

made to relevant Parts of

B S

5345 for

details.

A l l

cables should be provided with adequate mechanical

protection. Cables should be adequately supported

throughout thei r ength, care being taken to avoid excessive

pressure when

cleats

are used. Horizontal cables may be

carried on supports or cable trays

or

through protective

troughs or tubes. Rising cables should be clipped, cleated

or otherwise attached to suitable supports hat provide

adequate mechanical protection and support.

Where single core metal sheathed or armoured cables are

used, precautions should be taken to avoid dangerous

sheath voltages or currents.

19.5.2

PVC

covered and/or insulated cables.

Attention

i s

drawn to the fact that

as

temperature decreases, PVC

becomes increasingly sti ff and b rit tle wi th he result that,

if

PVC cables are bent too sharply or are struck a t

temperatures of about

O

OC or lower, there is a risk for

most PVC cables of shattering the PVC. It s advisable to

store PVC cable a t temperatures above

O

'C for

a t leas t

24

h prior to installation.

19.5.3 Paper nsulated cables.

Where paper insulated

armoured cables are used, and part icularly where such

cables may be exposed to high temperature, preference

should

be

given to non-drainingcables complying wi th

BS 6480

: Part 1. In the case of other

t y p e s

of paper

insulated armouredcables, vertical runs should be avoided.

Cable boxes,

if

necessary, should be arranged for sealing

the cable insulation and should be provided with adequate

means for ensuring the earthcontinuity of metallicsheath

andlor armour.

Adequate arrangements should be made to ensure that

cable boxes can be filled with he necessary compound

or insulating

oil

according to their design.

19.5.4 Mineral insulated metal sheathed cables.

Cable

terminations should incorporate

a

seal

for the cable

insulation and, where necessary, means of ensuring

adequate earth continuity.

NOTE.

Certain t ypes of prot ection require specific types

of

seal.

Reference should

be

made to the relevant Parts of

BS

5345 for

details.

Seals

in which compound

i s

used should not be exposed

to

temperatures that may, in the course of normal working,

affect the satisfactory func tioning of such compound.

Where there i s a risk of mineral insulated cables being

exposed to excessive voltages suchas inductive surges,

surge suppression shouldbe fitted. Where surge suppression

devices are installed in hazardous areas, they should be

suitably explosion-protected.

19.5.5

Al um ini um sheathed cables.

Aluminium sheathed

cables, unless further sheathed with

a

protective covering,

should no t be installed in contact with walls or floors.

Consideration should

be

given to the avoidance of frict ional

contact with

such

cables

(see

appendix

B).

19.5.6 Cables wi th low smoke produ cing insu la t ion.

Cables complying wi th

BS 6724

are not necessarily

intended for wet conditions see also

19.3.4).


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20

Portable and transportable apparatus

and its connections

Portable and transportable apparatus should ave a type of

protection appropriate to the zone(s) of use. During use

such apparatus should no t be transferred from

a

zone of

lower risk to a zone of higher risk unless it

is

suitably

protected for the higher risk. Additional ly, t h e apparatus

group andT class should be appropriate to all of the gases

and vapours in which the apparatusmay be used.

Ordinary industrial portable or transportable apparatus

should no t be used in a hazardous

area

unless i t s use i s

undertaken undera controlled procedure and the specific

location has been assessed to ensure that potentially

flammable gas or vapour i s absent during

the

period of use.

Should plugs and sockets be in

a

hazardous area, they

should be suitable for use in the particular zone of risk and

should have mechanical and/or electrical inter-locking to

prevent danger during insertion or removal of the plug.

In many cases the type of cable to be used wil l

be

stated

on the apparatus certificate. In cases where this i s not

so,

the cable should be suitable for rough usage and other

adverse environmental conditions, e.g. elevated

temperatures, presence of solvents. I t should also be

suitable for the circuit protective arrangements, e.g. where

earth monitoring

is

used, the necessary number of

conductors should be included. Where the apparatus needs

t o

be earthed, the cable may include an earthed flexible

metallic screen in addition t o the earth conductor.


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Section four

Section four. Inspection, maintenance, testing and repair

21 General

To minimize the risk of igni tion of an explosive atmosphere

by electrical apparatus, efficient inspection, maintenance

and testing

of

the apparatus, systems and installations are

essential.

I t

should

be

noted that correct functional

operation does not itself indicate conformity wi th the

recommendations fo r the safe use of apparatus. The general

recommendations fo r inspection, maintenance and testing

that are applicable to

al l

types of protection are described

in clauses

22

to

27.

Those recommendations that apply

only

to specific types cf protect ion are described in the

appropriate Parts of

BS

5345.

2,2

ersonnel

The inspection, testing, maintenance, replacement and

repair of apparatus, systems and installations should

be

carried out only by persons whose training includes

instruction on the various typesof protection involved.

A,ppropriate refresher training shouldbe given from time

to time.

2:3 solation of apparatus

23.1 General

Ampparatus should not be opened in a hazardous area unti l

it has been disconnected from

i t s

source of supply

(see

clause

18)

and effective measures, such

as

the locking of

the disconnector in the open position or fuse removal or

other acceptable method, have been taken to prevent

i t s

being made

a l i ve

before re-assembly. However, apparatus

with type of protection ‘i’or certain low power apparatus

w’ith type of protection

N

may be opened whilst energized

provided that the specific recommendations

of

the clauses

dealing with maintenance in

BS

5345 : Parts

4

and

7

are

followed. Particular attention should be paid in the case of

an apparatus that may be

l ive

even after

it

has been

disconnected from

a

source of supply. For example,

electrically driven rotating machinery may produce

a

voltage

a t

the terminals until it i s stationary, and power

capacitors even though fitted wi thdischarge resistors take

a finite time to bring the terminal voltage o a harmless

value.

Where, for purposes of electrical testing,

it

s

essential to

restore the supply before

he

apparatus is re-assembled,

then this work should be under a controlled procedure and

the specific location assessed to ensure that potentially

flbmmable gas or vapour is absent. For the testing of

intrinsically-safe electrical apparatus and systems,

see

B S 5345

:

Part 4.

23.2 Field replacement of batteries

Batteries should preferably be replaced in a non-hazardous

area. Where batteries have to be replaced in a hazardous

area this should be done under a controlled procedure (see

clause 24). However, batterieswith type of protection

‘i’

may be replaced in

a

hazardous

area

provided

that

any

limiting resistor associated with the battery

is

not dis-

connected. Other batteries shouldbe transported through

; :A, ”

a hazardous area only under a controlled procedure unless

other precautions

are

taken to prevent the occurrence of

ign ition capable arcs and sparks.

Replacement batteries should be in accordance wit h the

certification documents.

Batteries of

all

types no t being used should be removed

promptly from the hazardous area.

24

Precautions concerning he use of

igniting agencies

No operation involving the use of a source of ignition,

e.g. welding, brazing, unprotected apparatus etc., should

be attempted in

a

hazardous area un ti l the conditions have

been made safe by the control of the flammable material

that may

give

rise to the r isk. Such operations should be

undertaken only on the issue of

a

gas free certificate

confirming that adequate control measures have been

taken and that tests have been made and will be repeated

a t

suff iciently frequent intervals t o ensure that the safe

conditions are maintained.

25 Initial and periodic inspections

All electrical apparatus, systems and installations should be

inspected prior to commissioning to confi rm that the

selection and installation i s appropriate and in accordance

with

BS

5345. Examples of some of the items that should

be included in an initial inspection are given in table 5.

Following any replacement, repair, mod ifica tion or

adjustment, the items concerned should be inspected to

ensure that the appropriate recommendations of this

standard have been maintained.

If

a t

any time there

is a

change in the area classification or

in the characteristic of the flammable materialused in the

area, or if any apparatus

i s

moved from one location to

another, an inspection should be made t o ensure

that

the

type of protection, apparatus group and

T

class, where

appropriate, are suitable for the revised conditions.

The extent, complexity and frequency of inspection of

apparatus, systems and nstallations when n use should

be determined

by

those whose training and experience

wi ll enable them to recognize any potentia l hazards and

who are familiar with the operation and the environmental

conditions under which the apparatus s used.

The frequency of inspection depends on the type of

equipment, the factors governing t s deterioration, and the

findings of previous inspections. Examplesof factors that

can affect the deterioration of apparatus or otherwise lead

to an unsafe condition are given

in

table 6.

I t

s

therefore recommended hat once the apparatushas

been taken into use, ini tia l intervals between inspections

should

be

of

a

reasonably short duration and tha t

a

system

be established to enable subsequent inspection intervals o

be reviewed and modif ied in the light of operational

experience. Where inspection intervals and methodsare

already established and are found

by

experience to be

satisfactory for similar apparatus and environments, these

may be used. It is recommended that

a n

inspection record

14


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Section

four

system be operated

so

that the review of inspection

frequencies

i s

effective.

When large numbers of similar items such as luminaires,

junction boxes etc. are installed, it may be feasible to carry

out inspections on a sample basis provided that the degree

of sampling in addition to the inspection frequency

s

subjected to review.

26 Init ial and periodic testing

Al l

electrical apparatus, systems and installations should

be tested prior to commissioning and these tests should

include the following:

(a)

insulat ion resistance measurement;

(b ) earth electrode resistance measurement;

(c)

earth loop impedance measurement;

NOTE.

It ma y be advantageous to make the earth loop

impedance measurement with bot h a substantial cur rent and

wit h an intrinsically-safe tester t o enable the measurement to

be made wit h the ntrinsically-safe tester alone for subsequent

tests and to allow those results to be compared wi th the ini tial

test results.

It

should be noted that tests made with an

intri nsicall y-safe tester may not necessarily ident ify c ertain bad

connect ions because of the

low

test current.

(d) setting and, where appropriate, operation of

protect ive devices.

The results of

all t e s ts

should be recorded and included n

the record

of

inspections described n clause

25.

The testing of apparatus, systems and nstallations when in

use should be under the control of those whose experience

will enable them to recognize the potential hazards and

who are familiar with operation and the environmental

conditions under which the apparatus

is

to be used.

Test procedures shouldbe designed to cause the minimum

disturbance to the installation or system.

Diagnostic testingand recording of results of such

functions

as

time, operating voltage, circui t resistance,

insulat ion resistance

etc.

should be used where possible to

show trends in electrical condition and to aid the

determination of both he nature and frequency of

subsequent

t es t s

and inspections.

The frequency of testing depends on the type of equipment

or system, the factors governing t s deterioration and in

particular the findings of previous

tests.

Factors that may

affect the deterioration of apparatus are identified in

table

6

and

as

these should be taken into account in

determining the frequency of inspection the frequency of

testing wi ll not be greater than, and in fact may be

less

than, the frequency of inspection for the relevant apparatus

or system. The frequency of testing should be established

and reviewed in a manner similar to that recommended for

the frequency of inspection.

Testing in continuously operating plant and on similar

apparatus or systems may be undertaken on a sample basis

subject to review similar to that recommended for

inspections conducted on a sample basis.

Tests should

be

made in such a way that low energy or

ÏÖW

voltage apparatus and circuits

re

not subject

t o

damage by

-

- -

excess voltage. For testing electrical systems with type of

protection i',

see

BS

5345

:

Fart

4.

Tests should be undertaken under a controlled procedure

to ensure that the specific ocation has either been

assessed for the absence of a flammable gas or vapour, or

that t h e

t e s t

method

i s

non-incendive.

Table 5. Example of schedule

for

initial inspection

Initi al inspection items

Apparatus appropriate or the area classification

Correct temperature classification

Appropriate apparatus group or subgroup

Correct circuit identification

Maintenance of integrity of enclosure

Cable entries and stoppers tc. are complete and

appropriate

to

the enclosure

Electrical connectionsare tight

Satisfactory earthing, bonding etc.

Correct rating ofapparatus and components

Damage to apparatus or wiring systems

Adequate environmental protection,e.g. against

weather, mechanical damage

No unauthorized modifications

NOTE. Items

are

not

listed in any order of pr io ri ty ,

Where integrity

of

type of protection

is

dependent

on electrical protection, this should be verified ini tiall y.

Table

6.

Example

of

schedule for subsequent

inspections

Factors

affecting integrity

of

apparatus, systems

and

installations

Corrosion of enclosures, fixings, cable entries etc.

Damage to apparatus

or

wiring systems

Undue accumulation of dust and ir t

Loose electrical connections, ncluding hose for

earthing, bonding

etc.

Loose fixings, glands, conduit, stoppers

etc.

Condition ofenclosure gaskets and fastenings

Leakage of oil or compound

Condition of bearings

Inadvertent contactbetween rotating and fixed parts

Integrity of guards

Incorrect amp ratings or

ype

Undue vibration

Malfunction of relays and protective devices

Unauthorized modificationsor adjustments

Inappropriate maintenance,e.g. not inaccordance

wi th manufacturer's recommendations

NOTE.

Items are not listed in any order

of

pr ior i ty ,

Where integrity o f type of protection is dependent

on electrical protection, this should be verified init ially .


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Part

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1989

Sect ion four

It should be borne in mind hat certain

t es t

instruments

that incorporate

a

power source, when used to

test

isolated

bs 5345 p1.pdf

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