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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 _
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B S I B S * 5 3 4 5 :
P A R T S 1
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withdrawn.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withdrawn and should not be used for new installations.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
electrical apparatus wi th type of protection
'i'.
Intrinsically safe electrical apparatus and
systems
Installation and maintenance requirements or
electrical apparatus protected by pressurization
'P' and by continuous dilution, and for
pressurized rooms
Installation and maintenance requirements or
electrical apparatus wi th type of protection
'e'.
Increased safety
Insta llation and maintenance requirements or
electrical apparatus wi th type of protection N
Installation and maintenance requirements or
electrical apparatus with type ofprotection
S .Special protection
Installation and maintenance requirements or
electrical apparatus wi th type of 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.
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BSI
B S X 5 3 4 5 : P A R T * L O3 m L b 2 4 b b 9
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_
1
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E S 1
B S X 5 3 4 5 :
P A R T * 3
03
m 3624669 O373435
983
m
8s 5345
:
Par t 1
:
1989
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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BSI BS*5345:
P A R T L O3
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0373436 818 m
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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BSI BS*5345: P A R T * %
03 m 36246690373437754
m
BS 5345
:
P a r t 1
:
1989
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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BS 5345
:
P a r t 1
:
1989
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
.
-
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BS
5345 P a r t
1
1989
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'.
.:
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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
7
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BSI BS*5345: P A R T * L 03 m 1 b 2 4 b b 9 0373421
185
m
BS
5345 : Par t
1
:
1989
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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B S I
B S * 5 3 4 5 :
P A R T W I 03
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l b 2 4 b b 9 0373423 T58
W
BS
5345
:
Part
1
:
1989
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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BS
5345 : P a r t
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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BSI B S X 5 3 4 5 :
P A R T * L O3
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b T 3 m
BS 5345 :
P a r t 1 : 1989
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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BS
5345 : Part
1
: 1989
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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E S 1 B S X 5 3 4 5 : P A RT *L
O3
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BS
5345
:
Part
1
:
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