Explosive atmospheres - Part 25: Intrinsically safe electrical systems

IEC 60079-25:2020 contains the specific requirements for design, construction and assessment of intrinsically safe systems, Type of Protection “i”, intended for use, as a whole or in part, in locations in which the use of Group I, II or III Ex Equipment is required.
This document supplements and modifies the general requirements of IEC 60079-0 and the intrinsic safety standard IEC 60079-11. Where a requirement of this standard conflicts with a requirement of IEC 60079-0 or IEC 60079-11, the requirement of this standard takes precedence.
The installation requirements of Group II or Group III systems designed in accordance with this standard are specified in IEC 60079-14.
This third edition cancels and replaces the second edition published in 2010 and constitutes a technical revision.
The contents of the corrigendum of October 2020 have been included in this copy.

Atmosphères explosives - Partie 25: Systèmes électriques de sécurité intrinsèque

IEC 60079-25:2020 contient les exigences spécifiques de conception, de construction et d’évaluation des systèmes de sécurité intrinsèque, de mode de protection "i", destinés à être utilisés, en tout ou en partie, dans des atmosphères qui exigent l’emploi de matériel Ex du Groupe I, II ou III. Le présent document complète et modifie les exigences générales de l’IEC 60079-0 et de la norme de sécurité intrinsèque IEC 60079-11. En cas de contradiction entre une exigence de la présente norme et une exigence de l’IEC 60079-0 ou de l’IEC 60079-11, l’exigence de la présente norme prévaut.
Les exigences d’installation pour les systèmes du Groupe II ou du Groupe III conçus conformément à la présente norme sont spécifiées dans l’IEC 60079-14.
Cette troisième édition annule et remplace la deuxième édition parue en 2010 et constitue une révision technique.
Le contenu du corrigendum d'octobre 2020 a été pris en considération dans cet exemplaire.

General Information

Status
Published
Publication Date
25-Jun-2020
Current Stage
PPUB - Publication issued
Completion Date
26-Jun-2020
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IEC 60079-25
Edition 3.0 2020-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 25: Intrinsically safe electrical systems
Atmosphères explosives –
Partie 25: Systèmes électriques de sécurité intrinsèque
IEC 60079-25:2020-06(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60079-25
Edition 3.0 2020-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 25: Intrinsically safe electrical systems
Atmosphères explosives –
Partie 25: Systèmes électriques de sécurité intrinsèque
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-8512-1

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60079-25:2020  IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 9

2 Normative references ...................................................................................................... 9

3 Terms and definitions ...................................................................................................... 9

4 Descriptive system document ........................................................................................ 11

5 Grouping and temperature classification ........................................................................ 11

6 Levels of Protection ....................................................................................................... 11

6.1 General ................................................................................................................. 11

6.2 Level of Protection “ia” .......................................................................................... 12

6.3 Level of Protection “ib” .......................................................................................... 12

6.4 Level of Protection “ic” .......................................................................................... 12

7 Non-intrinsically safe circuits ......................................................................................... 12

8 Interconnecting wiring / cables used in an intrinsically safe system ............................... 12

8.1 General ................................................................................................................. 12

8.2 Cables containing a single intrinsically safe circuit ................................................ 12

8.3 Cables containing more than one intrinsically safe circuit ...................................... 12

9 Requirements of single and multi-circuit cables ............................................................. 13

9.1 General ................................................................................................................. 13

9.2 Dielectric strength ................................................................................................. 13

9.2.1 Cables containing a single intrinsically safe circuit ......................................... 13

9.2.2 Cables containing more than one intrinsically safe circuit .............................. 13

9.3 Intrinsic safety parameters of cables ..................................................................... 13

9.4 Conducting screens .............................................................................................. 14

9.5 Types of multi-circuit cables .................................................................................. 14

9.5.1 General ......................................................................................................... 14

9.5.2 Type A cable ................................................................................................. 14

9.5.3 Type B cable ................................................................................................. 14

9.5.4 Type C cable ................................................................................................. 14

10 Enclosures .................................................................................................................... 14

11 Earthing and bonding of intrinsically safe systems ......................................................... 14

12 Assessment of an intrinsically safe system .................................................................... 15

12.1 General ................................................................................................................. 15

12.2 Systems containing only apparatus certified to IEC 60079-11 ............................... 15

12.3 Systems containing apparatus not separately evaluated to IEC 60079-11 ............. 15

12.4 Systems containing a single power source ............................................................ 15

12.5 Systems containing more than one power source .................................................. 16

12.5.1 General ......................................................................................................... 16

12.5.2 Systems containing linear and non-linear sources of power ........................... 16

12.6 Simple apparatus .................................................................................................. 18

12.7 Assessment of capacitance, inductance and cable L/R ......................................... 18

12.7.1 General ......................................................................................................... 18

12.7.2 Unspecified Parameters ................................................................................. 18

12.7.3 Output Parameter adjustments for Level of Protection ................................... 18

12.7.4 Effect of combined lumped capacitance and inductance ................................ 18

12.7.5 Determination of L/R ...................................................................................... 18

12.8 Faults in multi-circuit cables .................................................................................. 19

---------------------- Page: 4 ----------------------
IEC 60079-25:2020  IEC 2020 – 3 –

12.9 Type verifications and type tests ........................................................................... 19

13 Predefined systems ....................................................................................................... 19

Annex A (informative) Assessment of a simple intrinsically safe system ............................... 20

Annex B (informative) Assessment of circuits with more than one power source .................. 22

Annex C (informative) Interconnection of non-linear and linear intrinsically safe circuits ...... 25

C.1 General ................................................................................................................. 25

C.2 Assessment of the output characteristics of the power sources ............................. 25

C.3 Assessment of interconnection possibilities and resultant output

characteristics ...................................................................................................... 28

C.4 Determination of intrinsic safety and the use of graphs ......................................... 31

C.5 Verification against IEC 60079-11 ......................................................................... 33

C.6 Illustration of the procedure .................................................................................. 33

C.7 Limit curves for universal source characteristic ..................................................... 37

Annex D (informative) Verification of inductive parameters .................................................. 48

Annex E (informative) Example format for a descriptive system document ........................... 50

Annex F (informative) Use of simple apparatus in systems .................................................. 52

F.1 General ................................................................................................................. 52

F.2 Use of apparatus with ‘simple apparatus’ .............................................................. 53

Annex G (normative) FISCO systems ................................................................................... 54

G.1 General ................................................................................................................. 54

G.2 System requirements ............................................................................................ 54

G.2.1 General ......................................................................................................... 54

G.3 Additional requirements of “ic” FISCO systems ..................................................... 55

Bibliography .......................................................................................................................... 57

Figure 1 – Systems analysis ................................................................................................. 17

Figure B.1 – Power sources connected in series ................................................................... 23

Figure B.2 – Power sources connected in parallel ................................................................. 24

Figure B.3 – Power sources not deliberately connected ........................................................ 24

Figure C.1 – Equivalent circuit and output characteristic of resistive circuits ......................... 26

Figure C.2 – Output characteristic and equivalent circuit of a source with trapezoidal

characteristic ........................................................................................................................ 28

Figure C.3 – Current and/or voltage addition for interconnections ......................................... 31

Figure C.4 – Example of an interconnection .......................................................................... 33

Figure C.5 – Sum characteristics for the circuit as given in Figure C.4 .................................. 35

Figure C.6 – Current and/or voltage addition for the example given in Figure C.4 ................. 36

Figure C.7 – Limit curve diagram for universal source characteristic − Group IIC .................. 42

Figure C.8 – Limit curve diagram for universal source characteristic – Group IIB .................. 47

Figure D.1 – Typical inductive circuit .................................................................................... 49

Figure E.1 – Typical block diagram for IS system descriptive system document .................... 51

Figure G.1 – Typical system ................................................................................................. 56

Table A.1 – Simple system analysis ...................................................................................... 21

Table C.1 – Parameters necessary to describe the output characteristic ............................... 26

Table C.2 – Assignment of diagrams to equipment Groups and inductances ......................... 32

---------------------- Page: 5 ----------------------
– 4 – IEC 60079-25:2020  IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
EXPLOSIVE ATMOSPHERES –
Part 25: Intrinsically safe electrical systems
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, Technical Reports,

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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

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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 60079-25 has been prepared by subcommittee 31G: Intrinsically

safe apparatus, of IEC technical committee 31: Equipment for explosive atmospheres.

This third edition cancels and replaces the second edition published in 2010 and constitutes a

technical revision.

The significance of the changes between IEC 60079-25, Edition 2 (2010) and IEC 60079-25,

Edition 3 (2019) are as listed below:
---------------------- Page: 6 ----------------------
IEC 60079-25:2020  IEC 2020 – 5 –
Type
Changes Clause Minor and Extension Major
editorial technical
changes changes
References to ‘electrical systems’ changed to ‘systems’ 1
and note added that installation requirement for Group I
are being considered.
Normative references updated to remove references that 2
were outdated or not mentioned in the body of the
standard.
Reference to IEC Electropedia and ISO Online Browsing 3
platform added, abbreviations dropped from title.
Definition of ‘system designer’ deleted, definitions of
‘certified intrinsically safe electrical system’, and
‘uncertified intrinsically safe electrical system’ dropped.
‘Intrinsically safe electrical system’ changed to 3.1
‘intrinsically safe system’.
Definition for ‘multi-circuit cable’ added. X
3.2
‘Maximum’ changed to ‘total’ on definitions of cable 3.4, 3.5
capacitance and cable inductance.
‘Maximum’ deleted on definition of cable inductance to 3.6
resistance ratio.
FISCO changed to definition from abbreviation. 3.9
The requirement for the system designer to sign and date
the document dropped, editorial changes for clarity made,
and a reference to Annex E made to show typical
descriptive system documents.
Title of clause changed to ‘Grouping and temperature 5
classification’, ambient temperature range added to things
to be included in the system document and reworded for
clarity.
Notes moved and reworded among the clauses. 6.1, 6.2,
6.3, 6.4
Changed from ‘Ambient temperature rating’ which was 7
moved to Clause 5, and new section renamed ‘Non-
intrinsically safe circuits’ added.
Clause reorganized into sections and some rewording 8
done for clarity.
Title changed to ‘Requirements of single and multi-circuit 9
cables’.
Requirement for insulation thickness moved into this 9.1
clause, and it now applies to all cables.
Title changed to ‘Dielectric strength’ and consolidation of 9.2
requirements for single circuit and multi-circuit cables.
Requirement for dielectric testing changed to twice the
circuit voltage with a minimum of 500VAC.
Dielectric strength requirements for single circuit cables 9.2.1
consolidated here.
Dielectric strength requirements for multi- circuit cables 9.2.2
consolidated here.
C1
Multi-circuit cables shall not be used for intrinsically safe 9.2.2
circuits with voltages exceeding 90 V.
Title changed to ‘Intrinsic safety parameters of cables’ 9.3
---------------------- Page: 7 ----------------------
– 6 – IEC 60079-25:2020  IEC 2020
Type
Changes Clause Minor and Extension Major
editorial technical
changes changes
Title changed to ‘Enclosures’ 10
C2
Most of the old Clause 12 moved to IEC 60079-14. 11
This clause was Clause 13 in the previous edition, and the 12
entire clause has been re-arranged for clarity and easier
reading.
This General clause has been re-written in list format to 12.1
make it easier to understand, and analysis of single and
multiple power supplies moved to 12.4 and 12.5
respectively.
This clause added to clarify fault applications in 12.2
assemblies of certified equipment.
This clause added to provide guidance on how to handle 12.3
non-certified items in larger assemblies.
Analysis of single power source information consolidated 12.4
here and amplified.
Analysis of multiple power sources information 12.5
consolidated in this clause. Information added for clarity.
The circuit analysis example dropped in text for simple 12.6
apparatus, new Annex F added with more information.
Section added to provide more information on determining 12.7
capacitance, inductance and L/R that was moved from
Annex A.
Requirements for Type A, B, and C cables reworded for 12.8
clarity.
Information on evaluation of capacitance and inductance Annex A
moved to 12.7.
Changed from normative to informative Annex B
Reordered and rewritten for greater clarity. Annex C
Annex updated for clarity. Annex E
C3
The former Annex F on surge protection has been
Annex F
removed.
Annex G in the previous edition was on testing of cable Annex G
parameters and has been removed from this edition.
Annex G is now FISCO systems.

NOTE The technical changes referred to include the significance of technical changes in the revised IEC Standard,

but they do not form an exhaustive list of all modifications from the previous version. More guidance may be found

by referring to the Redline Version of the standard.
---------------------- Page: 8 ----------------------
IEC 60079-25:2020  IEC 2020 – 7 –
Explanations:
A) Definitions
Minor and editorial changes clarification
decrease of technical requirements
minor technical change
editorial corrections

These are changes which modify requirements in an editorial or a minor technical way. They

include changes of the wording to clarify technical requirements without any technical change,

or a reduction in level of existing requirement.
Extension addition of technical options

These are changes which add new or modify existing technical requirements, in a way that new

options are given, but without increasing requirements for equipment that was fully compliant

with the previous standard. Therefore, these will not have to be considered for products in

conformity with the preceding edition.
Major technical changes addition of technical requirements
increase of technical requirements

These are changes to technical requirements (addition, increase of the level or removal) made

in a way that a product in conformity with the preceding edition will not always be able to fulfil

the requirements given in the later edition. These changes have to be considered for products

in conformity with the preceding edition. For these changes additional information is provided

in clause B) below.

NOTE These changes represent current technological knowledge. However, these changes should not normally

have an influence on equipment already placed on the market.
B) Information about the background of ‘Major Technical Changes’

B1 – A limitation of 90 V for multi-circuit system has been added since for this voltage level a

dielectric test of at least 500 V AC or 700 V DC is normally used to validate the insulation.

B2 – Most of the earthing and bonding requirements have been removed and moved to

IEC 60079-14, and the surge protection requirements that were in the old Clause 12 were added

here in Clause 11. The rest of the old Clause 12 was also removed and moved to IEC 60079-

14.

B3 – The former Annex F on surge protection has been removed and will be covered in

IEC 60079-14. Annex F is now Simple Apparatus, which was Annex H in the previous edition.

The text of this standard is based on the following documents:
FDIS Report on voting
31G/318/FDIS 31G/321/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.

---------------------- Page: 9 ----------------------
– 8 – IEC 60079-25:2020  IEC 2020

A list of all parts in the IEC 60079 series, published 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

stability 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.
---------------------- Page: 10 ----------------------
IEC 60079-25:2020  IEC 2020 – 9 –
EXPLOSIVE ATMOSPHERES –
Part 25: Intrinsically safe electrical systems
1 Scope

This part of IEC 60079 contains the specific requirements for design, construction and

assessment of intrinsically safe systems, Type of Protection “i”, intended for use, as a whole or

in part, in locations in which the use of Group I, II or III Ex Equipment is required.

NOTE 1 This standard is intended for use by the designer of the system e.g. a person who could be a manufacturer,

a specialist consultant or a member of the end-user’s staff.

This document supplements and modifies the general requirements of IEC 60079-0 and the

intrinsic safety standard IEC 60079-11. Where a requirement of this standard conflicts with a

requirement of IEC 60079-0 or IEC 60079-11, the requirement of this standard takes

precedence.

The installation requirements of Group II or Group III systems designed in accordance with this

standard are specified in IEC 60079-14.

NOTE 2 Group I installation requirements are presently not provided in IEC 60079-14. Installation requirements for

Group I are being considered.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements

IEC 60079-11, Explosive atmospheres – Part 11: Equipment protection by intrinsic safet

...

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