IEC 60079-0:2017

Explosive atmospheres - Part 0: Equipment - General requirements

IEC 60079-0:2017 specifies the general requirements for construction, testing and marking of Ex Equipment and Ex Components intended for use in explosive atmospheres. The standard atmospheric conditions (relating to the explosion characteristics of the atmosphere) under which it may be assumed that Ex Equipment can be operated are:
-temperature –20 °C to +60 °C;
-pressure 80 kPa (0,8 bar) to 110 kPa (1,1 bar); and
-air with normal oxygen content, typically 21 % v/v.
This part of IEC 60079 and other standards supplementing this standard specify additional test requirements for Ex Equipment operating outside the standard temperature range, but further additional consideration and additional testing may be required for Ex Equipment operating outside the standard atmospheric pressure range and standard oxygen content. Such additional testing may be particularly relevant with respect to Types of Protection that depend on quenching of a flame such as ‘flameproof enclosures “d”’ (IEC 60079-1) or limitation of energy, ‘intrinsic safety “i”’ (IEC 60079-11). This seventh edition cancels and replaces the sixth edition, published in 2011. This edition constitutes a technical revision. Refer to the Foreword of the document for a complete listing of the technical changes between edition 7.0 and the previous edition of the document.
Keywords: Ex Equipment and Ex Components intended for use in explosive atmospheres
The contents of the interpretation sheet 1 of April 2019, of the interpretation sheet 2 of June 2019 and the corrigendum 1 of January 2020 have been included in this copy.

Explosionsgefährdete Bereiche - Teil 0: Betriebsmittel - Allgemeine Anforderungen

Atmosphères explosives - Partie 0: Matériel - Exigences générales

IEC 60079-0:2017 spécifie les exigences générales de construction, d'essais et de marquage de l’appareil Ex et des Composants Ex destinés à être utilisés dans des atmosphères explosives. Les conditions atmosphériques normales (relatives aux caractéristiques d’explosion de l’atmosphère) dans lesquelles, par hypothèse l’appareil Ex peut être utilisé, sont les suivantes:
-température de –20 °C à +60 °C;
-pression de 80 kPa (0,8 bar) à 110 kPa (1,1 bar); et
-air avec teneur normale en oxygène, typiquement 21 % v/v.
La présente partie de la norme IEC 60079 et les autres normes qui la complètent spécifient des exigences d’essai supplémentaires pour les appareils Ex fonctionnant hors de la plage normale de températures, une attention supplémentaire ultérieure et des essais complémentaires pouvant toutefois être exigés pour les appareils Ex fonctionnant hors de la plage normale de pressions atmosphériques et de la teneur normale en oxygène. De tels essais complémentaires peuvent se révéler pertinents, notamment pour les modes de protection qui dépendent de l’extinction d’une flamme, tels qu’une «enveloppe antidéflagrante «d»» (IEC 60079-1), ou de la limitation de l’énergie, tels que la «sécurité intrinsèque «i»» (IEC 60079-11). Reportez-vous à l'avant-propos du document pour une liste complète des modifications techniques entre l'édition 7.0 et édition précédente du document.
Mots-clés: l’appareil Ex et des Composants Ex destinés à être utilisés dans des atmosphères explosives.
Le contenu de la feuille d'interprétation 1 d'avril 2019, la feuille d'interprétation 2 de juin 2019 et le corrigendum 1 de janvier 2020 a été pris en considération dans cet exemplaire.

Eksplozivne atmosfere - 0. del: Oprema - Splošne zahteve

General Information

• Status: Published
• Publication Date: 12-Dec-2017
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: TC 31 - Equipment for explosive atmospheres
• Drafting Committee: WG 22 - TC 31/WG 22
• Current Stage: PPUB - Publication issued
• Start Date: 22-Dec-2017
• Completion Date: 13-Dec-2017
• Ref Project: oSIST IEC 60079-0:2018 - Explosive atmospheres - Part 0: Equipment - General requirements

Relations

• Corrected By: IEC 60079-0:2017/COR1:2020 - Corrigendum 1 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/COR2:2013 - Corrigendum 2 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revised: IEC 60079-0:2017/ISH2:2019 - Interpretation Sheet 2 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revised: IEC 60079-0:2017/ISH1:2019 - Interpretation Sheet 1 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/ISH1:2013 - Interpretation sheet 1 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/COR1:2012 - Corrigendum 1 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/ISH2:2014 - Interpretation sheet 2 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/ISH3:2018 - Interpretation sheet 3 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 60079-0:2011/ISH4:2019 - Interpretation Sheet 4 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60079-0 ®
Edition 7.0 2017-12
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 0: Equipment – General requirements

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
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Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

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IEC 60079-0 ®
Edition 7.0 2017-12
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 0: Equipment – General requirements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.260.20 ISBN 978-2-8322-5204-8

 IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60079-0
Edition 7.0  2017-12
EXPLOSIVE ATMOSPHERES –
Part 0: Equipment – General requirements

INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 31: Equipment for
explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
31/1455/DISH 31/1464/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

___________
Interpretation sheet of Subclause 16.6 of IEC 60079-0:2017
The TC31/CAG requested (Resolution 2 of 2018-04-19) that WG22 prepare an interpretation
sheet based on IECEx Decision Sheet DS2018/002 addressing the assignment of entry point
and branching point temperatures of electrical rotating machines.
Details of interpretation:
requirements
Interpretation of Subclause 16.6: Temperature at branching point and entry point:
Question: Subclause 16.6 of IEC 60079-0:2017 states “When the temperature under rated
conditions is higher than 70 °C at the entry point or 80 °C at the branching point of the
conductors, information shall be marked on the equipment exterior to provide guidance to the
user on the proper selection of cable and cable gland or conductors in conduit.”
ICS 29.260.20
– 2 – IEC 60079-0:2017/ISH1:2019
 IEC 2019
It is not normal practice for electrical rotating machines to be tested with the cable entry
devices and cables that might be used in an actual installation, but with the cables available
at the manufacturer’s test area. In many cases, there will be no formal entry device as the
cables will enter via the space reserved for fixing of a gland plate.
How shall the relevant entry point and branching point temperatures be determined?
Interpretation: The use of the maximum internal air space temperature to represent the
maximum service temperature of terminal box gaskets and seals, the cable branching point
temperature, and the entry point temperature reflects the normal practice of testing electrical
rotating machines without prior knowledge of the actual glands and cables to be used for
installation. The production of heat from the electrical rotating machine connections is
generally insignificant with respect to the production of heat from the machine windings and
core.
Further amplification:
1) The entry point of the cable where the temperature is measured should be sealed so far
as possible to ensure that there is minimum air-circulation which can reduce the measured
temperature.
2) This is not intended to apply to any gasket between the terminal box and the frame of the
electrical rotating machine, where higher temperatures may be recorded, but only to the
gasket between the terminal box and its lid.
Although written in the context of electrical rotating machines, there may be other types of
equipment where an equivalent approach is applicable

 IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60079-0
Edition 7.0  2017-12
EXPLOSIVE ATMOSPHERES –
Part 0: Equipment – General requirements

INTERPRETATION SHEET 2
This interpretation sheet has been prepared by IEC technical committee 31: Equipment for
explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
31/1469/DISH 31/1486/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

___________
Question:
How shall marking be shown for equipment covered by both the electrical and non-electrical
standards (IEC 60079 and ISO 80079 series)?
Answer:
Equipment which includes both an electrical part and a non-electrical part shall have
combined marking. For example:
Ex db h IIA T4 Gb
Ex h tb IIIC T135 °C Db
ICS 29.260.20
– 2 – IEC 60079-0:2017/ISH2:2019
 IEC 2019
It will be clearer for the user that the combined risk of the electrical part and the non-electrical
part, covered by a single certificate, has been assessed for the complete equipment, stating
one EPL, one equipment Group and one temperature class for Gas and the same for Dust
(but showing a maximum surface temperature instead of a temperature class). It is also noted
that Ex Components are not marked with either a temperature class (Group II) or a maximum
surface temperature (Group III).
For equipment where separate certificates have been prepared, with one for the electrical
parts, and one for the non-electrical parts, it is appropriate to have separate electrical and
non-electrical marking strings, each with its own associated certificate number.
NOTE Additional guidance on the marking of assemblies is given in IEC TS 60079-46.

– 2 – IEC 60079-0:2017 RLV  IEC 2017
CONTENTS
FOREWORD . 9
1 Scope . 16
2 Normative references . 18
3 Terms and definitions . 21
4 Equipment grouping . 21
4.1 General . 39
4.2 Group I . 39
4.3 Group II . 40
4.4 Group III . 40
4.5 Equipment for a particular explosive gas atmosphere . 40
5 Temperatures . 40
5.1 Environmental influences . 40
5.1.1 Ambient temperature . 40
5.1.2 External source of heating or cooling . 41
5.2 Service temperature . 41
5.3 Maximum surface temperature . 42
5.3.1 Determination of maximum surface temperature . 42
5.3.2 Limitation of maximum surface temperature . 42
5.3.3 Small component temperature for Group I or Group II electrical
equipment. 42
5.3.4 Component temperature of smooth surfaces for Group I or Group II
electrical equipment . 44
6 Requirements for all electrical equipment . 45
6.1 General . 45
6.2 Mechanical strength of equipment . 45
6.3 Opening times . 45
6.4 Circulating currents in enclosures (e.g. of large electrical machines) . 46
6.5 Gasket retention . 46
6.6 Electromagnetic and ultrasonic energy radiating equipment . 46
6.6.1 General . 46
6.6.2 Radio frequency sources . 46
6.6.3 Ultrasonic sources . 47
6.6.4 Lasers, luminaires, and other non-divergent continuous wave optical
sources. 47
7 Non-metallic enclosures and non-metallic parts of enclosures . 47
7.1 General . 48
7.1.1 Applicability . 48
7.1.2 Specification of materials . 49
7.2 Thermal endurance . 50
7.2.1 Tests for thermal endurance . 50
7.2.2 Material selection . 50
7.2.3 Alternative qualification of elastomeric sealing O-rings . 50
7.3 Resistance to ultraviolet light . 51
7.4 Electrostatic charges on external non-metallic materials . 51
7.4.1 Applicability . 51

7.4.2 Avoidance of a build-up of electrostatic charge on for Group I
or Group II electrical equipment . 51
7.4.3 Avoidance of a build-up of electrostatic charge on equipment for Group
III . 54
7.5 Accessible metal Attached external conductive parts . 55
8 Metallic enclosures and metallic parts of enclosures . 55
8.1 Material
...

IEC 60079-0 ®
Edition 7.0 2017-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 0: Equipment – General requirements

Atmosphères explosives –
Partie 0: Matériel – Exigences générales
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International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

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IEC 60079-0 ®
Edition 7.0 2017-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 0: Equipment – General requirements

Atmosphères explosives –
Partie 0: Matériel – Exigences générales

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-5065-5

 IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60079-0
Edition 7.0  2017-12
EXPLOSIVE ATMOSPHERES –
Part 0: Equipment – General requirements

INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 31: Equipment for
explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
31/1455/DISH 31/1464/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

___________
Interpretation sheet of Subclause 16.6 of IEC 60079-0:2017
The TC31/CAG requested (Resolution 2 of 2018-04-19) that WG22 prepare an interpretation
sheet based on IECEx Decision Sheet DS2018/002 addressing the assignment of entry point
and branching point temperatures of electrical rotating machines.
Details of interpretation:
requirements
Interpretation of Subclause 16.6: Temperature at branching point and entry point:
Question: Subclause 16.6 of IEC 60079-0:2017 states “When the temperature under rated
conditions is higher than 70 °C at the entry point or 80 °C at the branching point of the
conductors, information shall be marked on the equipment exterior to provide guidance to the
user on the proper selection of cable and cable gland or conductors in conduit.”
ICS 29.260.20
– 2 – IEC 60079-0:2017/ISH1:2019
 IEC 2019
It is not normal practice for electrical rotating machines to be tested with the cable entry
devices and cables that might be used in an actual installation, but with the cables available
at the manufacturer’s test area. In many cases, there will be no formal entry device as the
cables will enter via the space reserved for fixing of a gland plate.
How shall the relevant entry point and branching point temperatures be determined?
Interpretation: The use of the maximum internal air space temperature to represent the
maximum service temperature of terminal box gaskets and seals, the cable branching point
temperature, and the entry point temperature reflects the normal practice of testing electrical
rotating machines without prior knowledge of the actual glands and cables to be used for
installation. The production of heat from the electrical rotating machine connections is
generally insignificant with respect to the production of heat from the machine windings and
core.
Further amplification:
1) The entry point of the cable where the temperature is measured should be sealed so far
as possible to ensure that there is minimum air-circulation which can reduce the measured
temperature.
2) This is not intended to apply to any gasket between the terminal box and the frame of the
electrical rotating machine, where higher temperatures may be recorded, but only to the
gasket between the terminal box and its lid.
Although written in the context of electrical rotating machines, there may be other types of
equipment where an equivalent approach is applicable

 IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60079-0
Edition 7.0  2017-12
EXPLOSIVE ATMOSPHERES –
Part 0: Equipment – General requirements

INTERPRETATION SHEET 2
This interpretation sheet has been prepared by IEC technical committee 31: Equipment for
explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
31/1469/DISH 31/1486/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

___________
Question:
How shall marking be shown for equipment covered by both the electrical and non-electrical
standards (IEC 60079 and ISO 80079 series)?
Answer:
Equipment which includes both an electrical part and a non-electrical part shall have
combined marking. For example:
Ex db h IIA T4 Gb
Ex h tb IIIC T135 °C Db
ICS 29.260.20
– 2 – IEC 60079-0:2017/ISH2:2019
 IEC 2019
It will be clearer for the user that the combined risk of the electrical part and the non-electrical
part, covered by a single certificate, has been assessed for the complete equipment, stating
one EPL, one equipment Group and one temperature class for Gas and the same for Dust
(but showing a maximum surface temperature instead of a temperature class). It is also noted
that Ex Components are not marked with either a temperature class (Group II) or a maximum
surface temperature (Group III).
For equipment where separate certificates have been prepared, with one for the electrical
parts, and one for the non-electrical parts, it is appropriate to have separate electrical and
non-electrical marking strings, each with its own associated certificate number.
NOTE Additional guidance on the marking of assemblies is given in IEC TS 60079-46.

– 2 – IEC 60079-0:2017  IEC 2017
CONTENTS
FOREWORD . 8
1 Scope . 15
2 Normative references . 16
3 Terms and definitions . 18
4 Equipment grouping . 36
4.1 General . 36
4.2 Group I . 36
4.3 Group II . 36
4.4 Group III . 36
4.5 Equipment for a particular explosive gas atmosphere . 37
5 Temperatures . 37
5.1 Environmental influences . 37
5.1.1 Ambient temperature . 37
5.1.2 External source of heating or cooling . 37
5.2 Service temperature . 37
5.3 Maximum surface temperature . 38
5.3.1 Determination of maximum surface temperature . 38
5.3.2 Limitation of maximum surface temperature . 38
5.3.3 Small component temperature for Group I or Group II electrical

equipment. 39
5.3.4 Component temperature of smooth surfaces for Group I or Group II
electrical equipment . 40
6 Requirements for all equipment . 41
6.1 General . 41
6.2 Mechanical strength of equipment . 41
6.3
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Eksplozivne atmosfere - 0. del: Oprema - Splošne zahteveExplosionsgefährdete Bereiche - Teil 0: Betriebsmittel - Allgemeine AnforderungenAtmosphères explosives - Partie 0: Matériel - Exigences généralesExplosive atmospheres - Part 0: Equipment - General requirements29.260.20Electrical apparatus for explosive atmospheresICS:Ta slovenski standard je istoveten z:IEC 60079-0 Ed. 7.0oSIST IEC 60079-0:2018en,fr,de01-april-2018oSIST IEC 60079-0:2018SLOVENSKI
STANDARD
IEC 60079-0 Edition 7.0 2017-12 INTERNATIONAL STANDARD NORME INTERNATIONALE Explosive atmospheres –
Part 0: Equipment – General requirements
Atmosphères explosives –
Partie 0: Matériel – Exigences générales INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE
ICS 29.260.20
ISBN 978-2-8322-5065-5
– 2 – IEC 60079-0:2017  IEC 2017 CONTENTS FOREWORD . 8 1 Scope . 15 2 Normative references . 16 3 Terms and definitions . 18 4 Equipment grouping . 36 4.1 General . 36 4.2 Group I . 36 4.3 Group II . 36 4.4 Group III . 36 4.5 Equipment for a particular explosive gas atmosphere . 37 5 Temperatures . 37 5.1 Environmental influences . 37 5.1.1 Ambient temperature . 37 5.1.2 External source of heating or cooling . 37 5.2 Service temperature . 37 5.3 Maximum surface temperature . 38 5.3.1 Determination of maximum surface temperature . 38 5.3.2 Limitation of maximum surface temperature . 38 5.3.3 Small component temperature for Group I or Group II electrical equipment. 39 5.3.4 Component temperature of smooth surfaces for Group I or Group II electrical equipment . 40 6 Requirements for all equipment . 41 6.1 General . 41 6.2 Mechanical strength of equipment . 41 6.3 Opening times . 41 6.4 Circulating currents in enclosures (e.g. of large electric machines) . 42 6.5 Gasket retention . 42 6.6 Electromagnetic and ultrasonic energy radiating equipment . 42 6.6.1 General . 42 6.6.2 Radio frequency sources . 42 6.6.3 Ultrasonic sources . 43 6.6.4 Lasers, luminaires, and other non-divergent continuous wave optical sources. 44 7 Non-metallic enclosures and non-metallic parts of enclosures . 44 7.1 General . 44 7.1.1 Applicability . 44 7.1.2 Specification of materials . 44 7.2 Thermal endurance . 45 7.2.1 Tests for thermal endurance . 45 7.2.2 Material selection . 46 7.2.3 Alternative qualification of elastomeric sealing O-rings . 46 7.3 Resistance to ultraviolet light . 46 7.4 Electrostatic charges on external non-metallic materials . 47 7.4.1 Applicability . 47 7.4.2 Avoidance of a build-up of electrostatic charge for Group I or Group II . 47 oSIST IEC 60079-0:2018

7.4.3 Avoidance of a build-up of electrostatic charge for Group III . 49 7.5 Attached external conductive parts . 50 8 Metallic enclosures and metallic parts of enclosures . 51 8.1 Material composition . 51 8.2 Group I . 51 8.3 Group II . 51 8.4 Group III . 52 8.5 Copper Alloys . 52 9 Fasteners . 52 9.1 General . 52 9.2 Special fasteners . 53 9.3 Holes for special fasteners . 53 9.3.1 Thread engagement . 53 9.3.2 Tolerance and clearance . 53 9.4 Hexagon socket set screws . 54 10 Interlocking devices . 54 11 Bushings . 54 12 (Reserved for future use) . 54 13 Ex Components . 54 13.1 General . 54 13.2 Mounting . 55 13.3 Internal mounting . 55 13.4 External mounting . 55 13.5 Ex Component certificate . 55 14 Connection facilities . 55 14.1 General . 55 14.2 Type of protection . 56 14.3 Creepage and clearance . 56 15 Connection facilities for earthing or bonding conductors . 56 15.1 Equipment requiring earthing or bonding . 56 15.1.1 Internal earthing . 56 15.1.2 External bonding. 56 15.2 Equipment not requiring earthing . 56 15.3 Size of protective earthing conductor connection . 56 15.4 Size of equipotential bonding conductor connection . 57 15.5 Protection against corrosion . 57 15.6 Secureness of electrical connections . 57 15.7 Internal earth continuity plate . 57 16 Entries into enclosures . 57 16.1 General . 57 16.2 Identification of entries . 57 16.3 Cable glands . 58 16.4 Blanking elements. 58 16.5 Thread adapters . 58 16.6 Temperature at branching point and entry point . 59 16.7 Electrostatic charges of cable sheaths . 59 17 Supplementary requirements for electric machines . 60 17.1 General . 60 oSIST IEC 60079-0:2018

– 4 – IEC 60079-0:2017  IEC 2017 17.2 Ventilation. 60 17.2.1 Ventilation openings . 60 17.2.2 Materials for external fans . 60 17.2.3 Cooling fans of rotating electric machines . 60 17.2.4 Auxiliary motor cooling fans . 61 17.2.5 Room ventilating fans . 61 17.3 Bearings . 62 18 Supplementary requirements for switchgear . 62 18.1 Flammable dielectric . 62 18.2 Disconnectors . 62 18.3 Group I – Provisions for locking . 63 18.4 Doors and covers . 63 19 Reserved for future use . 63 20 Supplementary requirements for external plugs, socket outlets and connectors for field wiring connection . 63 20.1 General . 63 20.2 Explosive gas atmospheres . 64 20.3 Explosive dust atmospheres . 64 20.4 Energized plugs . 64 21 Supplementary requirements for luminaires . 64 21.1 General .
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