IEC 60079-14:2007

IEC 60079-14
Edition 4.0 2007-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 14: Electrical installations design, selection and erection

Atmosphères explosives –
Partie 14: Conception, sélection et construction des installations électriques

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IEC 60079-14
Edition 4.0 2007-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 14: Electrical installations design, selection and erection

Atmosphères explosives –
Partie 14: Conception, sélection et construction des installations électriques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XD
CODE PRIX
ICS 29.260.20 ISBN 2-8318-9491-3

– 2 – 60079-14 © IEC:2007
CONTENTS
FOREWORD.8
INTRODUCTION.10

1 Scope.13
2 Normative references .13
3 Terms and definitions .16
3.1 General .16
3.2 Hazardous areas .16
3.3 Flameproof enclosure.17
3.4 Increased safety.17
3.5 Intrinsic safety - General .18
3.6 Intrinsic safety parameters .19
3.7 Pressurization .19
3.8 Type of protection 'n' .19
3.13 Electrical supply systems .20
3.14 Equipment.21
4 General .21
4.1 General requirements.21
4.2 Documentation .22
4.3 Assurance of conformity of equipment .23
4.3.1 Equipment with certificates according to IEC standards .23
4.3.2 Equipment without certificates according to IEC standards .23
4.3.3 Selection of repaired, second hand or existing equipment .23
4.4 Qualifications of personnel .23
5 Selection of equipment (excluding cables and conduits) .24
5.1 Information requirements.24
5.2 Zones.24
5.3 Relationship between Equipment protection levels (EPLs) and zones.24
5.4 Selection of equipment according to EPLs.25
5.4.1 Relationship between EPLs and types of protection.25
5.4.2 Equipment for use in locations requiring EPL 'Ga' or 'Da'.26
5.4.3 Equipment for use in locations requiring EPL ‘Gb’ or 'Db' .26
5.4.4 Equipment for use in locations requiring EPL ‘Gc’ or ‘Dc’.26
5.5 Selection according to equipment grouping .26
5.6 Selection according to the ignition temperature of the gas, vapour or dust
and ambient temperature.27
5.6.1 General .27
5.6.2 Gas or Vapour .27
5.6.3 Dust .27
5.7 Selection of radiating equipment for dust.30
5.7.1 Ignition process .30
5.7.2 Safety measures in zone 20 or 21.30
5.7.3 Safety measures in zone 22 .31
5.8 Selection of ultrasonic equipment for dust .31
5.8.1 Ignition process .31
5.8.2 Safety measures.31

60079-14 © IEC:2007 – 3 –
5.9 External influences.31
5.10 Light metals as construction materials.32
5.10.1 Gas or vapour.32
5.10.2 Dust .32
5.11 Transportable, Portable and Personal equipment .33
5.11.1 General .33
5.11.2 Transportable and Portable equipment - Gas.33
5.11.3 Personal Equipment - Gas.33
5.11.4 Dust .33
5.12 Selection of rotating electrical machines.34
5.12.1 General .34
5.12.2 Motors fed from a converter supply.34
5.13 Luminaires .34
5.14 Plugs and socket outlets for dust.34
5.14.1 General .34
5.14.2 Mounting .34
5.14.3 Location .35
6 Protection from dangerous (incendive) sparking .35
6.1 Danger from live parts .35
6.2 Danger from exposed and extraneous conductive parts.35
6.2.1 TN type of system earthing .35
6.2.2 TT type of system earthing .35
6.2.3 IT type of system earthing .35
6.2.4 SELV and PELV systems.35
6.2.5 Electrical separation .36
6.2.6 Above hazardous areas .36
6.3 Potential equalization .36
6.3.1 General .36
6.3.2 Temporary bonding.37
6.4 Static electricity.37
6.4.1 Gas .37
6.4.2 Dust .38
6.5 Lightning protection.38
6.6 Electromagnetic radiation .38
6.7 Cathodically protected metallic parts .38
6.8 Ignition by optical radiation.39
7 Electrical protection.39
7.1 General .39
7.2 Rotating electrical machines.39
7.3 Transformers.39
7.4 Resistance heating devices .40
8 Emergency switch-off and electrical isolation.40
8.1 Emergency switch-off .40
8.2 Electrical isolation .40
9 Wiring systems .41
9.1 General .41
9.2 Aluminium conductors .41
9.3 Cables.41

– 4 – 60079-14 © IEC:2007
9.3.1 Cables for fixed wiring .41
9.3.2 Cables supplying transportable and portable equipment .41
9.3.3 Flexible connections for dust .42
9.3.4 Flexible cables .42
9.3.5 Non-sheathed single cores .42
9.3.6 Overhead lines .42
9.3.7 Avoidance of damage .43
9.3.8 Cable surface temperature .43
9.3.9 Flame propagation.43
9.3.10 Connections of cables to equipment .43
9.4 Conduit systems.44
9.5 Cable and conduit systems.45
9.5.1 EPL 'Ga' .45
9.5.2 EPL 'Da' .45
9.5.3 Cable and conduit systems for EPL ‘Gb’, ‘Gc’, ‘Db’ and ‘´Dc’ .45
9.6 Installation requirements .45
9.6.1 Circuits traversing a hazardous area .45
9.6.2 Protection of stranded ends.45
9.6.3 Unused cores .45
9.6.4 Unused openings.45
9.6.5 Fortuitous contact.45
9.6.6 Jointing .46
9.6.7 Openings in walls .46
9.6.8 Passage and collection of flammables .46
9.6.9 Static build-up for dust.46
9.6.10 Accumulation of combustible dust.46
10 Additional requirements for type of protection 'd' – Flameproof enclosures .47
10.1 General .47
10.2 Solid obstacles.47
10.3 Protection of flameproof joints .47
10.4 Cable entry systems.48
10.4.1 General .48
10.4.2 Selection of cable glands.48
10.5 Conduit systems.50
10.6 Motors.50
10.6.1 Motors with a converter supply .50
10.6.2 Reduced-voltage starting (soft starting) .50
11 Additional requirements for type of protection ‘e’ – Increased safety.51
11.1 Degree of ingress protection of enclosures (IEC 60034-5 and IEC 60529).51
11.2 Wiring systems.51
11.2.1 General .51
11.2.2 Cable glands .51
11.2.3 Conductor terminations.52
11.2.4 Combinations of terminals and conductors for general connection
and junction boxes .52
11.3 Cage induction motors.52
11.3.1 Mains-operated .52
11.3.2 Winding temperature sensors .53
11.3.3 Machines with rated voltage greater than 1 kV.53

60079-14 © IEC:2007 – 5 –
11.3.4 Motors with converter supply .54
11.3.5 Reduced-voltage starting (soft starting) .54
11.4 Luminaires .54
12 Additional requirements for types of protection 'i' – Intrinsic safety .54
12.1 Introductory remark .54
12.2 Installations to meet the requirements of EPL ‘Gb’ or ‘Gc’ .55
12.2.1 Equipment .55
12.2.2 Cables.56
12.2.3 Termination of intrinsically safe circuits .59
12.2.4 Earthing of intrinsically safe circuits.60
12.2.5 Verification of intrinsically safe circuits .61
12.3 Installations to meet the requirements of EPL 'Ga'.63
12.4 Special applications .64
13 Additional requirements for pressurized enclosures.65
13.1 Type of protection 'p' .65
13.1.1 General .65
13.1.2 Ducting.65
13.1.3 Action to be taken on failure of pressurization .66
13.1.4 Multiple pressurized enclosures with a common safety device .68
13.1.5 Purging.68
13.1.6 Protective gas .68
13.1.7 Wiring systems .69
13.2 Motors.69
13.2.1 Motors with a converter supply .69
13.2.2 Reduced-voltage starting (soft starting) .69
13.3 Type of protection 'pD'.69
13.3.1 Sources of protective gas .69
13.3.2 Automatic switch-off .70
13.3.3 Alarm.70
13.3.4 Common source of protective gas.70
13.3.5 Switching on electrical supply.70
13.3.6 Motors with a converter supply .71
13.4 Rooms for explosive gas atmosphere .71
13.4.1 Pressurized rooms and analyser houses.71
14 Additional requirements for type of protection 'n' .71
14.1 General .71
14.2 Degree of ingress protection of enclosures (IEC 60034-5 and IEC 60529).72
14.3 Wiring systems.72
14.3.1 General .72
14.3.2 Cable glands .72
14.3.3 Conductor terminations.73
14.4 Motors.73
14.4.1 Machines with rated voltage greater than 1 kV.73
14.4.2 Motors with converter supply .73
14.4.3 Reduced-voltage starting (soft starting) .74
14.5 Luminaires .74
15 Additional requirements for type of protection 'o'– Oil immersion .74
16 Additional requirements for type of protection 'q' – Powder filling.74

– 6 – 60079-14 © IEC:2007
17 Additional requirements for type of protection 'm' – Encapsulation.74
18 Additional requirements for type of protection 'tD' – Protection by enclosure .74
18.1 Practices A and B.74
18.2 Practice A .74
18.3 Practice B .75
18.4 Motors supplied at varying frequency and voltages.75

Annex A (normative) Verification of intrinsically safe circuits with more than one
associated apparatus with linear current/voltage characteristics .76
Annex B (informative) Methods of determining the maximum system voltages and
currents in intrinsically safe circuits with more than one associated apparatus with
linear current/voltage characteristics (as required by Annex A) .77
Annex C (informative) Determination of cable parameters.80
Annex D (informative) Safe work procedure guidelines for explosive gas atmospheres .82
Annex E (normative) Potential stator winding discharge risk assessment – Ignition risk
factors .83
Annex F (normative) Knowledge, skills and competencies of 'Responsible Persons',
'Operatives' and 'Designers'.84
Annex G (informative) Examples of dust layers of excessive thickness .87
Annex H (normative) Frictional sparking risks with light metals and their alloys.88
Annex I (informative) Introduction of an alternative risk assessment method
encompassing “equipment protection levels” for Ex equipment .89

Bibliography.94

Figure 1 – Correlation between the maximum permissible surface temperature and
depth of dust layers .29
Figure 2 – Selection chart for cable entry devices into flameproof enclosures for
cables complying with item b) of 10.4.2 .49
Figure 3 – Earthing of conducting screens .57
Figure B.1 – Series connection – Summation of voltage.78
Figure B.2 – Parallel connection – Summation of currents .78
Figure B.3 – Series and parallel connections – Summations of voltages and
summations of currents.79
Figure G.1a − Excessive layer on top of equipment .87
Figure G.1b − Excessive layer on top of equipment due to low ignition temperature of
the dust .87
Figure G.1c − Excessive layer at the sides of equipment.87
Figure G.1d − Completely submerged equipment .87
Figure G.1 – Examples for dust layers of excessive thickness with the requirement of
laboratory investigation.87

Table 1 – Equipment protection levels (EPLs) where only zones are assigned .24
Table 2 – Relationship between types of protection and EPLs .25
Table 3 – Relationship between gas/vapour or dust subdivision and equipment group .26
Table 4 – Relationship between gas or vapour ignition temperature and temperature
class of equipment.27

60079-14 © IEC:2007 – 7 –
Table 5 – Limitations of areas .38
Table 6 – Minimum distance of obstruction from the flameproof flange joints related to
the gas group of the hazardous area.47
Table 7 – Assessment for T4 classification according to component size and ambient
temperature .63
Table 8 – Determination of type of protection (with no flammable release within the
enclosure).65
Table 9 – Use of spark and particle barriers.66
Table 10 – Action to be taken when the pressurization with the protective gas fails for
electrical equipment without an internal source of release .67
Table 11 – Summary of protection requirements for enclosures .70
Table 12 – Dust tightness practice A.75
Table 13 – Dust tightness practice B.75
Table I.1 – Traditional relationship of EPLs to zones (no additional risk assessment) .91
Table I.2 – Description of risk of ignition protection provided .92

– 8 – 60079-14 © IEC:2007
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 14: Electrical installations design, selection and erection

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60079-14 has been prepared by subcommittee 31J: Classification
of hazardous areas and installation requirements, of IEC technical committee 31: Equipment
for explosive atmospheres.
This fourth edition cancels and replaces the third edition published in 2002 and constitutes a
technical revision with respect to gases and vapours and incorporates the requirements for
dusts from IEC 61241-14 (2004). The incorporation of requirements for dust is without
technical change.
The significant technical changes with respect to the previous edition are as follows:
• Knowledge, skills and competencies of "Responsible Persons”, “Operatives" and
"Designers" are explained in Annex F.
• Equipment Protection Levels (EPLs) have been introduced and are explained in the new
Annex I.
• Dust requirements included from IEC 61241-14, Ed. 1.0.

60079-14 © IEC:2007 – 9 –
NOTE Dust requirements are included as an interim presentation for the purpose of this edition and will be refined
in a next edition with other required technical changes.
The text of this standard is based on the following documents:
FDIS Report on voting
31J/150/FDIS 31J/152/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60079 series, under the general title Explosive atmospheres, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 10 – 60079-14 © IEC:2007
INTRODUCTION
Preventive measures to reduce the explosion risk from flammable materials are based on
three principles, which shall be applied in the following order:
1) Substitution
2) Control
3) Mitigation
Substitution involves, for example, replacing a flammable material by one which is either not
flammable or less flammable.
Control involves, for example:
a) reducing the quantity of flammables;
b) avoiding or minimising releases;
c) controlling the release;
d) preventing the formation of an explosive atmosphere;
e) collecting and containing releases; and
f) avoiding ignition sources.
NOTE 1 With the exception of item f), all of the above are part of the process of hazardous area classification.
Mitigation involves, for example:
1) reducing the number of people exposed;
2) providing measures to avoid the propagation of an explosion;
3) providing explosion pressure relief;
4) providing explosion pressure suppression; and
5) providing suitable personal protective equipment.
NOTE 2 The above items are part of consequence management when considering risk.
Once the principles of substitution and control (items a) to e)) have been applied, the
remaining hazardous areas should be classified into zones according to the likelihood of an
explosive atmosphere being present (see IEC 60079-10 or IEC 61241-10). Such
classification, which may be used in conjunction with an assessment of the consequences of
an ignition, allows equipment protection levels to be determined and hence appropriate types
of protection to be specified for each location.
For an explosion to occur, an explosive atmosphere and a source of ignition need to co-exist.
Protective measures aim to reduce, to an acceptable level, the likelihood that the electrical
installation could become a source of ignition.
By careful design of the electrical installation, it is frequently possible to locate much of the
electrical equipment in less hazardous or non-hazardous areas.
When electrical equipment is to be installed in areas where dangerous concentrations and
quantities of flammable gases, vapours, mists or dusts may be present in the atmosphere,
protective measures are applied to reduce the likelihood of explosion due to ignition by arcs,
sparks or hot surfaces, produced either in normal operation or under specified fault
conditions.
Many types of dust that are generated, processed, handled and stored, are combustible.
When ignited they can burn rapidly and with considerable explosive force if mixed with air in
the appropriate proportions. It is often necessary to use electrical apparatus in locations

60079-14 © IEC:2007 – 11 –
where such combustible materials are present, and suitable precautions must therefore be
taken to ensure that all such apparatus is adequately protected so as to reduce the likelihood
of ignition of the external explosive atmosphere. In electrical apparatus, potential ignition
sources include electrical arcs and sparks, hot surfaces and frictional sparks.
Areas where dust, flyings and fibres in air occur in dangerous quantities are classified as
hazardous and are divided into three zones according to the level of risk.
Combustible dust can be ignited by equipment in several ways:
• by surfaces of the apparatus that are above the minimum ignition temperature of the dust
concerned. The temperature at which a type of dust ignites is a function of the properties
of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the
geometry of the heat source;
• by arcing or sparking of electrical parts such as switches, contacts, commutators, brushes,
or the like;
• by discharge of an accumulated electrostatic charge;
• by radiated energy (e.g. electromagnetic radiation);
• by mechanical sparking or frictional sparking associated with the apparatus.
In order to avoid dust ignition hazards it is necessary that:
• the temperature of surfaces on which dust can be deposited, or which would be in contact
with a dust cloud, is kept below the temperature limitation specified in this standard;
• any electrical sparking parts, or parts having a temperature above the temperature limit
specified in this standard:
• are contained in an enclosure which adequately prevents the ingress of dust, or
• the energy of electrical circuits is limited so as to avoid arcs, sparks or temperatures
capable of igniting combustible dust;
• any other ignition sources are avoided.
Several types of protection are available for electrical equipment in hazardous areas (see
IEC 60079-0), and this standard gives the specific requirements for design, selection and
erection of electrical installations in explosive atmospheres.
This part of IEC 60079 is supplementary to other relevant IEC standards, for example
IEC 60364 series as regards electrical installation requirements. This part also refers to
IEC 60079-0 and its associated standards for the construction, testing and marking
requirements of suitable electrical equipment.
This standard is based on the assumption that electrical equipment is correctly installed,
tested, maintained and used in accordance with its specified characteristics.
Inspection, maintenance and repair aspects play an important role in control of hazardous
area installations and the user’s attention is drawn to IEC 60079-17 and IEC 60079-19 for
further information concerning these aspects.
In any industrial installation, irrespective of size, there may be numerous sou
...