SIST EN 60079-26:2005

Electrical apparatus for explosive gas atmospheres -- Part 26: Construction, test and marking of Group II Category 1 G electrical apparatus

Specifies the particular requirements for construction, test and marking for electrical apparatus of Group II intended for use in Zone 0. This electrical apparatus, within the operational parameters specified by the manufacturer, ensures a very high level of protection that includes rare faults related to the apparatus or two faults occurring independently of each other. It is intended for use in Zone 0 hazardous areas, in which explosive gas atmospheres caused by mixtures of air and gases, vapours or mists under normal atmospheric conditions are present continuously, for long periods or frequently.

Elektrische Betriebsmittel für gasexplosionsgefährdete Bereiche -- Teil 26: Konstruktion, Prüfung und Kennzeichnung elektrischer Betriebsmittel der Gruppe II Kategorie 1 G

Matériel électrique pour atmosphères explosives gazeuses -- Partie 26: Construction, essais et marquage des matériels électriques de Groupe II Catégorie 1 G

Spécifie les prescriptions particulières pour la construction, les essais et le marquage des matériels électriques du Groupe II destinés à être utilisés en Zone 0. Lorsqu'ils sont utilisés dans le domaine opérationnel spécifié par le constructeur, de tels matériels assurent un très haut niveau de protection même dans les cas rares de défaut dû au matériel, ou de deux défauts indépendants l'un de l'autre. Ils sont destinés à une utilisation dans des emplacements dangereux de Zone 0, dans lesquels des atmosphères explosives gazeuses formées d'un mélange d'air et de gaz, de vapeurs ou de brouillards dans des conditions atmosphériques normales sont présentes continuellement, durablement ou fréquemment.

Električne naprave za eksplozivne plinske atmosfere - 26. del: Konstrukcija, preskušanje in označevanje električnih naprav skupine II kategorije 1G (IEC 60079-26:2004, spremenjen)

General Information

• Status: Withdrawn
• Publication Date: 31-Mar-2005
• Withdrawal Date: 16-Dec-2009
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: EXP - Electrical apparatus for explosive atmospheres
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 07-Dec-2009
• Due Date: 30-Dec-2009
• Completion Date: 17-Dec-2009
• Directive: 94/9/EC - Directive 94/9/EC of the European Parliament and the Council of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres
• Ref Project: EN 60079-26:2004 - Electrical apparatus for explosive gas atmospheres - Part 26: Construction, test and marking of Group II Category 1 G electrical apparatus

Relations

• Revised: SIST EN 60079-26:2007 - Explosive atmospheres -- Part 26: Equipment with equipment protection level (EPL) Ga
• Effective Date: 13-May-2010
• Replaces: SIST EN 50284:2000 - Special requirements for construction, test and marking of electrical apparatus of equipment group II, Category 1 G
• Effective Date: 06-May-2014
• Replaces: SIST EN 50284:2000 - Special requirements for construction, test and marking of electrical apparatus of equipment group II, Category 1 G
• Effective Date: 28-Jan-2023

Standards Content (Sample)

SLOVENSKI SIST EN 60079-26:2005

STANDARD
april 2005
Električne naprave za eksplozivne plinske atmosfere - 26. del: Konstrukcija,
preskušanje in označevanje električnih naprav skupine II kategorije 1G (IEC
60079-26:2004, spremenjen)
Electrical apparatus for explosive gas atmospheres – Part 26: Construction, test
and marking of Group II Category 1 G electrical apparatus
ICS 29.260.20 Referenčna številka
SIST EN 60079-26:2005(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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EUROPEAN STANDARD EN 60079-26
NORME EUROPÉENNE
EUROPÄISCHE NORM December 2004

ICS 29.260.20 Supersedes EN 50284:1999


English version


Electrical apparatus for explosive gas atmospheres
Part 26: Construction, test and marking
of Group II Category 1 G electrical apparatus
(IEC 60079-26:2004, modified)


Matériel électrique pour atmosphères Elektrische Betriebsmittel für
explosives gazeuses gasexplosionsgefährdete Bereiche
Partie 26: Construction, essais et Teil 26: Konstruktion, Prüfung und
marquage des matériels électriques Kennzeichnung elektrischer Betriebsmittel
de Groupe II Catégorie 1 G für Gruppe II Kategorie 1 G
(CEI 60079-26:2004, modifiée) (IEC 60079-26:2004, modifiziert)






This European Standard was approved by CENELEC on 2004-04-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2004 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60079-26:2004 E

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EN 60079-26:2004 - 2 -
Foreword
The text of document 31/483/FDIS, future edition 1 of IEC 60079-26, prepared by IEC TC 31,
Electrical apparatus for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote and
was approved by CENELEC as EN 60079-26 on 2004-04-01.
Directive 94/9/EC requires equipment classification according to categories. Therefore, in all clauses
where the text of IEC 60079-26 uses the term "Zone 0 Equipment", or equivalent, this shall be
interpreted as referring to equipment of Category 1 G.
To this end, a draft amendment, prepared by the Technical Committee CENELEC TC 31, Electrical
apparatus for explosive atmospheres - General requirements, was submitted to the formal vote and was
approved by CENELEC for inclusion into EN 60079-26 on 2004-09-22.
This European Standard supersedes EN 50284:1999.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2005-06-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2007-04-01
__________
Endorsement notice
The text of the International Standard IEC 60079-26:2004 was approved by CENELEC as a European
Standard with agreed common modifications as given below.
COMMON MODIFICATIONS
Replace the title by:
Electrical apparatus for explosive gas atmospheres – Part 26: Construction, test and marking of Group II
Category 1 G electrical apparatus.
Replace Clause 6 by:
6  Marking
6.1  General
The apparatus shall be marked according to the requirements of the Directive 94/9/EC for equipment
Group II, Category 1 G and according to the type of protection as defined in the applicable standard.
Apparatus intended for installation in the boundary wall between areas requiring different categories
shall have both categories marked on the label separated by a “/” and the corresponding symbols for
each type of protection separated by a “/”. In the case where the apparatus group or temperature class
differ for the two types of protection, the complete designation of each rating shall be used and
separated by a “/”.

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- 3 - EN 60079-26:2004
Where more than one type of protection is used in accordance with 4.2.4, the symbols for the types of
protection shall be joined with a “+”.
6.2  Examples of marking
a) Apparatus which is intended to be completely installed inside the Zone 0 area for example:
II 1 G Ex ia IIC T6
or
II 1 G Ex d+e IIB T4
b) Associated apparatus, which is installed outside the hazardous area and providing external
electrical circuits protected by intrinsic safety “ia” according to EN 50020, which can be connected
to Category 1 apparatus , for example:
II (1) G [Ex ia] IIC
NOTE 1  No designation of the temperature class is required, as this apparatus is located outside the hazardous area.
c) Equipment which is installed in the boundary wall between areas requiring different categories,
both categories are marked on the label separated by a slash for example:
II1/2 G Ex d IIC T6
or
II 1/2 G Ex ia/d IIC T6
NOTE 2  Intrinsic safety “ia” apparatus in Zone 0 with a flameproof “d” compartment in Zone 1.
or
II 1/2 G Ex d+e/d IIB T4
NOTE 3  Two independent types of protection flameproof “d” and increased safety “e” in Zone 0 with a flameproof “d”
compartment in Zone 1.
The documentation shall state which parts of the apparatus are suitable for installation in each zone.
__________

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EN 60079-26:2004 - 4 -
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application 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.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1) 2)
IEC 60079-0 – Electrical apparatus for explosive gas EN 60079-0 2004
atmospheres
Part 0: General requirements

1) 2)
IEC 60079-1 – Electrical apparatus for explosive gas EN 60079-1 2004
atmospheres
Part 1: Flameproof enclosures 'd'

1) 2)
IEC 60079-10 – Part 10: Classification of hazardous areas EN 60079-10 2003

1)
IEC 60079-11 – Part 11: Intrinsic safety "i" - -

1) 2)
IEC 60079-14 – Part 14: Electrical installations in EN 60079-14 2003
hazardous areas (other than mines)

1) 2)
IEC 60079-18 – Part 18: Construction, test and marking of EN 60079-18 2004
type of protection encapsulation "m"
electrical apparatus

1) 2)
IEC 60695-11-10 – Fire hazard testing EN 60695-11-10 1999
Part 11-10: Test flames - 50 W horizontal
and vertical flame test methods
__________


1)
Undated reference.
2)
Valid edition at date of issue.

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NORME CEI
INTERNATIONALE
IEC



60079-26
INTERNATIONAL


Première édition
STANDARD

First edition

2004-03


Matériel électrique pour atmosphères
explosives gazeuses –
Partie 26:
Construction, essais et marquage
des matériels électriques de Groupe II
utilisables en Zone 0

Electrical apparatus for explosive
gas atmospheres –
Part 26:
Construction, test and marking
of Group II Zone 0 electrical apparatus
 IEC 2004 Droits de reproduction réservés  Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
CODE PRIX
Q
PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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60079-26  IEC:2004 – 3 –
CONTENTS
FOREWORD.5

1 Scope.9
2 Normative references.11
3 Terms and definitions .11
4 Requirements for design and construction.11
4.1 General.11
4.2 Protection measures against ignition hazards of the electrical circuits .13
4.3 Apparatus with moving parts .23
4.4 Isolated conductive components .25
4.5 Non-conductive enclosures and accessible non-conductive components .25
4.6 Mechanical connection.27
5 Type tests.29
5.1 Standardized types of protection .29
5.2 Separation elements.29
5.3 Temperature evaluation.29
6 Marking.29
6.1 General.29
6.2 Examples of marking .29
7 Information for use.31

Bibliography .33

Figure 1 – Example of a partition wall with a conductor bushing being considered gas
diffusion tight .17
Figure 2 – Example of a separation element with a cylindrical shaft joint and natural
ventilation .23

Table 1 – Separation elements .21

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60079-26  IEC:2004 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

ELECTRICAL APPARATUS FOR EXPLOSIVE GAS ATMOSPHERES –

Part 26: Construction, test and marking
of Group II Zone 0 electrical apparatus


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, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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 60079-26 has been prepared by IEC technical committee 31:
Electrical apparatus for explosive atmospheres.
The text of this standard is based on the following documents:
FDIS Report on voting
31/483/FDIS 31/494/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.

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60079-26  IEC:2004 – 7 –
The committee has decided that the contents of this publication will remain unchanged until
2006. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.

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60079-26  IEC:2004 – 9 –
ELECTRICAL APPARATUS FOR EXPLOSIVE GAS ATMOSPHERES –

Part 26: Construction, test and marking
of Group II Zone 0 electrical apparatus



1 Scope
This part of IEC 60079 specifies the particular requirements for construction, test and marking
for electrical apparatus of Group II intended for use in Zone 0 as defined in IEC 60079-10.
This electrical apparatus, within the operational parameters specified by the manufacturer,
ensures a very high level of protection that includes rare faults related to the apparatus or two
faults occurring independently of each other.
NOTE 1 A malfunction may result from a failure of the component parts of the electrical apparatus or from
anticipated externally applied influences. Two independent malfunctions which may occur more frequently and
which, separately, would not create an ignition hazard but which, in combination, could create a potential ignition
hazard, should be regarded as occurring together to form a rare fault.
This electrical apparatus is intended for use in Zone 0 hazardous areas, in which explosive gas
atmospheres caused by mixtures of air and gases, vapours or mists under normal atmospheric
conditions are present continuously, for long periods or frequently.
This standard also applies to apparatus mounted across the boundary between Zone 0 and
Zone 1.
EXAMPLE: In the wall of a storage vessel.
This standard also applies to apparatus installed outside Zone 0, but electrically connected to
apparatus inside Zone 0 (associated apparatus).
This standard supplements the general requirements in IEC 60079-0 and the requirements of
the standardized types of protection, in accordance with the IEC 60079 series, to adapt the
level of safety provided by those standards to the very high level of risk in Zone 0.
NOTE 2 In designing apparatus for operation in explosive gas atmospheres under conditions other than the
atmospheric conditions given in IEC 60079-0, this standard may be used as a guide. However, additional testing is
recommended related specifically to the intended conditions of use. This is particularly important when the types of
protection ‘Flameproof enclosure’ (IEC 60079-1) and ‘Intrinsic safety’ (IEC 60079-11) are applied.
NOTE 3 The classification of hazardous areas in zones is defined in IEC 60079-10.
NOTE 4 There may be other non-electrical sources of ignition (for example ultrasonic, optical or ionizing radiation)
that are not addressed by this standard; these should also be taken into consideration (see, for example, EN 1127-1).

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60079-26  IEC:2004 – 11 –
2 Normative references
The following referenced documents are indispensable for the application 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:, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-1, Electrical apparatus for explosive gas atmospheres – Part 1: Flameproof
enclosures "d"
IEC 60079-10, Electrical apparatus for explosive gas atmospheres – Part 10: Classification of
hazardous areas
IEC 60079-11, Electrical apparatus for explosive gas atmospheres – Part 11: Intrinsic safety “i”
IEC 60079-14, Electrical apparatus for explosive gas atmospheres – Part 14: Electrical
installations in hazardous areas (other than mines)
IEC 60079-18:, Electrical apparatus for explosive gas atmospheres – Part 18: Encapsulation
“m”
IEC 60695-11-10, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical
flame test methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0 and the
following apply.
3.1
Zone 1 types of protection
protection measures for electrical apparatus for use in Zone 1 in accordance with IEC 60079-14
4 Requirements for design and construction
4.1 General
The apparatus shall comply with the requirements of 4.2 for the electrical circuits and with the
requirements of 4.3 to 4.6 for mechanical and electrostatic ignition hazards.

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60079-26  IEC:2004 – 13 –
4.2 Protection measures against ignition hazards of the electrical circuits
4.2.1 General
The apparatus shall comply with the requirements of either
a) 4.2.2 or 4.2.3 in the event of two faults occurring independently of each other in a single
apparatus means of protection; or
b) 4.2.4 or 4.2.5 in the event of a failure of one apparatus means of protection, by the
provision of a second independent means of protection.
Electrical connections and permanently connected cables of the apparatus sited within Zone 0
shall comply with the same level of protection required by this standard, e.g. an Ex “e” cable
additionally protected by a flameproof conduit or an Ex “e” cable provided with an earth
leakage protection.
NOTE 1 Detailed cable and installation requirements for non-intrinsically safe circuits in Zone 0 are given in
IEC 60079-14.
NOTE 2 Because of ignition hazards which can arise from faults and/or transient circulating currents in the
potential equalization system, galvanic isolation in the power and signal connections to the apparatus according to
4.2.2, 4.2.3 and 4.2.4 is preferred. Consideration should also be given to minimize the effect of transient fault
currents in the potential equalization network by the use of electrical protection equipment such as sensitive earth
leakage monitors.
4.2.2 Intrinsic safety as a sole means of protection
Intrinsically safe electrical apparatus located in Zone 0 and intrinsically safe electrical circuits
of associated apparatus entering Zone 0 shall comply with the requirements of IEC 60079-11,
intrinsic safety “ia”.
NOTE Intrinsic safety “ib” in accordance with IEC 60079-11 may be considered as one of two independent means
of protection according to 4.2.4.
4.2.3 Encapsulation as a sole means of protection
Electrical apparatus which is protected by encapsulation in Zone 0 shall comply with the
requirements of IEC 60079-18, encapsulation “ma”.
NOTE Encapsulation “mb” in accordance with IEC 60079-18 may be considered as one of two independent means
of protection according to 4.2.4.
4.2.4 Application of two independent Zone 1 types of protection
Electrical apparatus shall comply with the requirements of two independent Zone 1 types of
protection. If one type of protection fails, the other type of protection shall continue to function.
The independent types of protection shall not have a common mode of failure except as
specified in this clause.
An example of a common mode failure is if an Ex “d” enclosure with arcing contacts inside it is
used inside an Ex “e” enclosure. If the Ex “d” enclosure is compromised, then arcing inside the
enclosure will also compromise the Ex “e” enclosure.
NOTE Combined Zone 1 types of protection should depend on different physical protection principles. For example
the combination of Ex “d” and Ex “q” both depend on the avoidance of flame propagation and may not be useful in
combination. In practice, some combinations may not be useful, for example the combination of oil and powder
filling.
Where combined types of protection are used, it shall be possible for each type of protection to
be tested individually (see 5.1).

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60079-26  IEC:2004 – 15 –
Both types of protection shall be assessed using the most arduous fault condition of the other
type of protection. When combining intrinsic safety, type of protection “ib”, with other types of
protection, the second type of protection shall be assessed, with the most arduous fault
condition applied to the intrinsically safe circuit.
When using two types of protection, which rely both on the same parameter (for example, the
creepage distance combining Ex “ib” with Ex “e”), the most stringent requirement of both types
of protection shall be applied.
If two types of protection are combined which both rely on the enclosure, one of the following
shall be met:
a) if two enclosures are used (one totally enclosed within the other), each enclosure shall
comply with the requirements of the respective type of protection; or
b) if only one enclosure is used, the enclosure and the cable entries shall meet the impact test
requirements of 26.4.2 of IEC 60079-0, using the Group I values.
Examples of combinations of two independent types of protection are as follows:
– inductive transmitters (for example proximity switches, electrical position sensors) with
intrinsic safety “ib” enclosed by encapsulation “mb”. The connections to intrinsically safe
“ib” circuits can be protected by the increased safety “e”;
– a lamp with the bulb designed as increased safety “e”, the lamp circuit with the switch as
intrinsic safety “ib”. These components may be incorporated in a flameproof enclosure “d”;
– measuring transducers with intrinsic safety “ib” and a flameproof enclosure “d”;
– apparatus with electrical circuits of intrinsic safety “ib”, additionally protected by a powder
filling “q”;
– electromagnetic valves with encapsulation “mb”, enclosed by a flameproof enclosure “d”;
– increased safety “e”, with pressurized apparatus “px”.
4.2.5 Application of a Zone 1 type of protection and a separation element
4.2.5.1 General
Apparatus which is mounted through or forming part of the boundary wall to Zone 0 and
containing electrical circuits which do not comply with the requirements of intrinsic safety “ia” or
encapsulation “ma” shall comply at least with one of the Zone 1 types of protection.
Additionally, they shall contain a mechanical separation element as part of the apparatus to
seal off the electrical circuits of the apparatus from Zone 0.
If the type of protection fails, the separation element shall
a) prevent flame propagation through the apparatus into Zone 0,
b) maintain its safety characteristics,
c) not be heated above the temperature class of the apparatus.
Separation elements consist of a partition wall, possibly combined with a flameproof joint or an
air gap with natural ventilation.

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60079-26  IEC:2004 – 17 –
4.2.5.2 Partition walls
Partition walls shall be constructed of either
a) corrosion resistant metals, glass or ceramics, which are specified in the manufacturer’s
documentation; or
b) other materials as long as the same level of safety can be demonstrated. In this case, the
apparatus shall be marked with an “X” in accordance with item i) of 29.2 of IEC 60079-0,
and the manufacturer’s instructions shall clearly specify the material and its thermal and
mechanical properties to enable the user to confirm the suitability for the particular
application.
If the wall thickness is less than 1 mm, the apparatus shall be marked with an “X” with a
special condition for safe use that the material shall not be subject to environmental conditions
which might adversely affect the partition wall. If the partition wall is under constant vibrational
stress (for example vibrating membranes), the minimum endurance limit at maximum
amplitude shall be defined in the documentation.
NOTE 1 A wall thickness less than 1 mm is only permitted in combination with intrinsic safety “ib”, or a flameproof
joint or natural ventilation, see 4.2.5.3.
NOTE 2 For glass or ceramics, a minimum thickness of 1/10 of the diameter/maximum dimension but not less
than 1 mm is recommended.
In addition to the requirements of 4.2.5.1-4.2.5.3 metallic partition walls with a thickness ≥
1 mm may be provided with suitable conductor bushings, see Figure 1. To avoid a critical
concentration of explosive gas atmosphere diffusing from Zone 0 into the enclosure containing
the electrical circuits, the leakage rate through the bushing shall be low compared to the
leakage rate from the enclosure into the free atmosphere. This can be achieved, for example,
by using a glass or ceramic bushing as shown in Figure 1.
NOTE 3 Using a standard enclosure with an IP67 rating according to IEC 60529, a bushing with a leakage rate
-2 –4 5
equivalent to a helium-leakage rate less than 10 Pa×l/s (10 mbar×l/s) at a pressure difference of 10 Pa (1 bar)
is sufficient.
Metallic sleeve, corrosion
resistant (wall thicknness ≥1 mm)
Bushing insulator (e.g. melted
≥10 mm glass, brazed ceramics)
Less hazardous
area
“ia” circuit
Ex “ia” circuit
Zone 0
Non-“ia”
Non-“ia” supply circuit
circuit
(e.g. Ex “e”)
Partition wall
Welded
(≥1 mm)
(joint ≥1 mm)
Electrical apparatus
IEC  133/04

Figure 1 – Example of a partition wall with a conductor bushing
being considered gas diffusion tight

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60079-26  IEC:2004 – 19 –
4.2.5.3 Requirements depending on the thickness of the partition wall
The combinations of separation elements and additional protective
...