SIST EN IEC 60079-18:2025

SLOVENSKI STANDARD
01-december-2025
Eksplozivne atmosfere - 18. del: Zaščita opreme z zalivanjem z zalivno maso "m"
(IEC 60079-18:2025)
Explosive atmospheres - Part 18: Equipment protection by encapsulation "m" (IEC
60079-18:2025)
Explosionsgefährdete Bereiche - Teil 18: Geräteschutz durch Vergusskapselung „m“
(IEC 60079-18:2025)
Atmosphères explosives - Partie 18: Protection du matériel par encapsulage "m" (IEC
60079-18:2025)
Ta slovenski standard je istoveten z: EN IEC 60079-18:2025
ICS:
29.260.20 Električni aparati za Electrical apparatus for
eksplozivna ozračja explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60079-18

NORME EUROPÉENNE
EUROPÄISCHE NORM October 2025
ICS 29.260.20 Supersedes EN 60079-18:2015; EN 60079-
18:2015/A1:2017; EN 60079-18:2015/AC:2018-09
English Version
Explosive atmospheres - Part 18: Equipment protection by
encapsulation "m"
(IEC 60079-18:2025)
Atmosphères explosives - Partie 18: Protection de l'appareil Explosionsgefährdete Bereiche - Teil 18: Geräteschutz
par encapsulage "m" durch Vergusskapselung "m"
(IEC 60079-18:2025) (IEC 60079-18:2025)
This European Standard was approved by CENELEC on 2025-07-24. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60079-18:2025 E

European foreword
The text of document 31/1858/FDIS, future edition 5 of IEC 60079-18, prepared by TC 31 "Equipment
for explosive atmospheres" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 60079-18:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-10-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-10-31
document have to be withdrawn
This document supersedes EN 60079-18:2015 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a standardization request addressed to CENELEC by the
European Commission. The Standing Committee of the EFTA States subsequently approves these
requests for its Member States.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60079-18:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60079-1 NOTE Approved as EN 60079-1
IEC 60079-2 NOTE Approved as EN 60079-2
IEC 60079-5 NOTE Approved as EN 60079-5
IEC 60079-6 NOTE Approved as EN 60079-6
IEC 60079-10-1 NOTE Approved as EN IEC 60079-10-1
IEC 60079-10-2 NOTE Approved as EN 60079-10-2
IEC 60079-14 NOTE Approved as EN IEC 60079-14
IEC 60079-26 NOTE Approved as EN IEC 60079-26
IEC 60079-28 NOTE Approved as EN 60079-28
IEC 60086-1 NOTE Approved as EN IEC 60086-1
IEC 60622 NOTE Approved as EN 60622
IEC 60664-1 NOTE Approved as EN IEC 60664-1
IEC 60747-5-5 NOTE Approved as EN IEC 60747-5-5
IEC 61951-1 NOTE Approved as EN 61951-1
IEC 61951-2 NOTE Approved as EN 61951-2
ISO 13849-1 NOTE Approved as EN ISO 13849-1
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60079-0 - Explosive atmospheres - Part 0: Equipment EN IEC 60079-0 -
- General requirements
IEC 60079-7 - Explosive atmospheres - Part 7: Equipment EN 60079-7 -
protection by increased safety "e"
IEC 60079-11 - Explosive atmospheres - Part 11: Equipment EN IEC 60079-11 -
protection by intrinsic safety "i"
IEC 60079-15 - Explosive atmospheres - Part 15: Equipment EN IEC 60079-15 -
protection by type of protection "n"
IEC 60127 series Miniature fuses EN IEC 60127 series
IEC 60243-1 - Electric strength of insulating materials - EN 60243-1 -
Test methods - Part 1: Tests at power
frequencies
IEC 60691 - Thermal-links - Requirements and EN IEC 60691 -
application guide
IEC 60730-2-9 - Automatic electrical controls - Part 2-9: EN IEC 60730-2-9 -
Particular requirements for temperature
sensing control
IEC 60738-1 - Thermistors - Directly heated positive EN IEC 60738-1 -
temperature coefficient - Part 1: Generic
specification
IEC 61140 - Protection against electric shock - Common EN 61140 -
aspects for installation and equipment
IEC 61558-1 - Safety of transformers, reactors, power EN IEC 61558-1 -
supply units and combinations thereof - Part
1: General requirements and tests
IEC 61558-2-6 - Safety of transformers, reactors, power EN IEC 61558-2-6 -
supply units and combinations thereof - Part
2-6: Particular requirements and tests for
safety isolating transformers and power
supply units incorporating safety isolating
transformers for general applications
Publication Year Title EN/HD Year
IEC 62326-4-1 - Printed boards - Part 4: Rigid multilayer EN 62326-4-1 -
printed boards with interlayer connections -
Sectional specification - Section 1:
Capability detail specification - Performance
levels A, B and C
ANSI/UL 248 series Standard for low-voltage fuses - -
ANSI/UL 746A - Polymeric Materials - Short Term Property - -
Evaluations
ANSI/UL 796 - Printed-Wiring Boards - -
IPC-A-600 - Acceptability of Printed Boards - -
IPC-6012 - Qualification and Performance Specification - -
for Rigid Printed Boards
IEC 60079-18 ®
Edition 5.0 2025-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 18: Equipment protection by encapsulation "m"

Atmosphères explosives –
Partie 18: Protection de l’appareil par encapsulage "m"
ICS 29.260.20  ISBN 978-2-8327-0471-4

IEC 60079-18:2025-06(en-fr)
– 2 – IEC 60079-18:2025 © IEC 2025
CONTENTS
FOREWORD . 5
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 General requirements . 11
4.1 Level of Protection (Equipment Protection Level (EPL)) . 11
4.2 Rated voltage and maximum prospective current . 11
4.3 Additional requirements for Levels of Protection "ma" and "mb" . 11
5 Requirements for compounds . 11
5.1 General . 11
5.2 Specification . 12
5.3 Properties of the compound . 12
5.3.1 Water absorption . 12
5.3.2 Dielectric strength . 12
6 Temperatures . 12
6.1 General . 12
6.2 Maximum surface temperature . 13
6.3 Service temperature of the compound . 13
6.4 Temperature limitation of the "m" equipment . 13
7 Constructional requirements . 13
7.1 General . 13
7.2 Determination of faults . 14
7.2.1 Fault examination . 14
7.2.2 Components considered as not subject to fail . 14
7.2.3 Isolating components . 15
7.2.4 Infallible separation distances . 15
7.3 Free space in the encapsulation . 16
7.3.1 Group III "m" Equipment . 16
7.3.2 Group I and Group II "m" Equipment . 17
7.4 Thickness of the compound. 18
7.4.1 "m" Equipment . 18
7.4.2 Windings for electrical machines . 20
7.4.3 Rigid, multi-layer printed wiring boards with through connections . 20
7.5 Switching contacts . 21
7.5.1 General . 21
7.5.2 Level of Protection "ma" . 21
7.5.3 Level of Protection "mb" . 21
7.5.4 Level of Protection "mc" . 21
7.6 External connections . 22
7.6.1 General . 22
7.7 Protection of bare live parts . 22
7.8 Cells and batteries . 22
7.8.1 General . 22
7.8.2 Prevention of gassing . 22
7.8.3 Protection against inadmissible temperatures and damage to the cells
or batteries . 22

IEC 60079-18:2025 © IEC 2025 – 3 –
7.8.4 Reverse current . 23
7.8.5 Current limitation . 23
7.8.6 Protection against the polarity inversion and deep discharge of the cells . 23
7.8.7 Charging of cells or batteries . 24
7.8.8 Requirements for safety devices for cells or batteries . 24
7.9 Protective devices . 24
7.9.1 General . 24
7.9.2 Electrical protective devices . 25
7.9.3 Thermal protective devices . 26
7.9.4 Built-in protective devices . 26
8 Type tests . 27
8.1 Tests on the compound . 27
8.1.1 Water absorption test . 27
8.1.2 Dielectric strength test . 27
8.2 Tests on the apparatus . 27
8.2.1 Test sequence . 27
8.2.2 Maximum temperature . 27
8.2.3 Thermal endurance test . 27
8.2.4 Dielectric strength test . 28
8.2.5 Cable pull test . 29
8.2.6 Pressure test for Group I and Group II "m" Equipment . 29
8.2.7 Test for resettable thermal protective device. 30
8.2.8 Sealing test for built-in protective devices . 30
9 Routine verifications and tests . 31
9.1 Visual inspections . 31
9.2 Dielectric strength test . 31
10 Marking . 32
Annex A (informative) Basic requirements for compounds for "m" Equipment . 33
Annex B (informative) Allocation of test samples . 34
Annex C (normative) Dielectric strength test between circuits and environment . 35
C.1 General . 35
C.2 Batch test procedure . 35
Bibliography . 36

Figure 1 – Dimensional key for thickness through the compound . 19
Figure 2 – Minimum distances for multi-layer printed wiring boards . 21
Figure 3 – Fitting of blocking diodes . 23
Figure A.1 – Basic requirements for compounds for "m" Equipment . 33

Table 1 – Distances through the compound . 16
Table 2 – Minimum thickness of compound adjacent to free space for Group III "m"
Equipment . 17
Table 3 – Minimum thickness of compound adjacent to free space for Group I and
Group II "m" Equipment . 18
Table 4 – Thickness of the compound . 19
Table 5 – Minimum distances for multi-layer printed wiring boards . 20
Table 6 – Test pressure . 30

– 4 – IEC 60079-18:2025 © IEC 2025
Table B.1 – Allocation of test samples . 34

IEC 60079-18:2025 © IEC 2025 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 18: Equipment protection by encapsulation "m"

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 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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60079-18 has been prepared by IEC technical committee 31: Equipment for explosive
atmospheres. It is an International Standard.
This fifth edition cancels and replaces the fourth edition published in 2014 and
Amendment 1:2017. This edition constitutes a technical revision.
This International Standard is to be used in conjunction with IEC 60079-0, Explosive
atmospheres – Part 0: Equipment – General requirements.
Users of this document are advised that interpretation sheets clarifying the interpretation of this
document can be published. Interpretation sheets are available from the IEC webstore and can
be found in the "history" tab of the page for each document.

– 6 – IEC 60079-18:2025 © IEC 2025
This edition includes the following significant technical changes with respect to the previous
edition:
Type
Explanation of the significance of the changes Clause Minor and Extension Major
editorial technical
changes changes
Specification has been extended for clarification. Curing 5.2b)  C1
conditions have been added
Dielectric strength test according to ANSI/UL 746A has 5.3.2 X
been added as alternative
Restructure of Clause 6 6 X
Deletion of the additional protective measures as they are 7.1 X
given in IEC 60079-0
For the Level of Protection "mc" faults need to be 7.2.1  C1
considered regarding the separation distances
The NOTE was changed to an EXAMPLE for clarification of 7.2.1 X
track failures
Intermediate failure conditions for components are not 7.2.1 X
considered
Clarification made about faults 7.2.1 X
Another possibility for the construction of transformer 7.2.3 X
according to IEC 60079-7 EPL "eb" added
Rating of component shall not be exceeded was added as 7.5.1  C1
clarification
Additional enclosure changed to "arc chamber" housing 7.5.1, X
7.5.2,
7.5.3
Consideration of fault conditions has been added 7.5.2  C1
Additional requirements for "ma" Equipment deleted Former X
7.6.2
NOTE 2 added for protection of bare live parts 7.7 X
Note 1 and Note 2 have been changed to normative text for
7.9.1 X
clarification
Requirement regarding the thermal coupling moved from 7.9.1 X
7.9.3 to 7.9.1 as this is applicable for all temperature
monitoring devices
The surface temperature determination for EPL Da has 8.2.2 X
been deleted, because this is given in IEC 60079-0
Acceptance criteria for the Dielectric strength test aligned 8.2.4.2 X
with the TC 31 Good Working Practice

IEC 60079-18:2025 © IEC 2025 – 7 –
Explanation of the types of significant changes:
A) Definitions
1 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.
2 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.
3 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 item 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’
C1 It is recognized that the new requirements were, in many cases, already applied. The
change is to ensure that they are uniformly and consistently applied.

The text of this International Standard is based on the following documents:
Draft Report on voting
31/1858/FDIS 31/870/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all the parts in the IEC 60079 series, published under the general title Explosive
atmospheres, can be found on the IEC website.

– 8 – IEC 60079-18:2025 © IEC 2025
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IEC 60079-18:2025 © IEC 2025 – 9 –
EXPLOSIVE ATMOSPHERES –
Part 18: Equipment protection by encapsulation "m"

1 Scope
This part of IEC 60079 gives the specific requirements for the construction, testing and marking
of electrical Ex Equipment, parts of electrical Ex Equipment and Ex Components with the Type
of Protection encapsulation "m" (hereinafter referred to as "m" Equipment) intended for use in
explosive gas atmospheres or explosive dust atmospheres.
For Levels of Protection "mb" and "mc", this document applies where the rated voltage does
not exceed 11 kV AC or DC.
RMS
For Level of Protection "ma", this document applies where the rated voltage does not exceed
1 kV AC or DC.
RMS
This document does not take account of any hazard due to an emission of flammable or toxic
gas from the dust.
This document supplements and modifies the general requirements of IEC 60079-0. Where a
requirement of this document conflicts with a requirement of IEC 60079-0, the requirement of
this document takes precedence.
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 60079-7, Explosive atmospheres – Part 7: Equipment protection by increased safety "e"
IEC 60079-11, Explosive atmospheres – Part 11: Equipment protection by intrinsic safety "i"
IEC 60079-15, Explosive atmospheres – Part 15: Equipment protection by type of protection "n"
IEC 60127 (all parts), Miniature fuses
IEC 60243-1, Electric strength of insulating materials – Test methods – Part 1: Tests at power
frequencies
IEC 60691, Thermal-links – Requirements and application guide
IEC 60730-2-9, Automatic electrical controls – Part 2-9: Particular requirements for temperature
sensing controls
IEC 60738-1, Thermistors – Directly heated positive temperature coefficient – Part 1: Generic
specification
– 10 – IEC 60079-18:2025 © IEC 2025
IEC 61140, Protection against electric shock – Common aspects for installation and equipment
IEC 61558-1, Safety of transformers, reactors, power supply units and combinations thereof –
Part 1: General requirements and tests
IEC 61558-2-6, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-6: Particular requirements and tests for safety isolating transformers and power supply
units incorporating safety isolating transformers for general applications
IEC 62326-4-1, Printed boards – Part 4: Rigid multilayer printed boards with interlayer
connections – Sectional specification – Section 1: Capability detail specification – Performance
levels A, B and C
ANSI/UL 248 (all parts), Standard for low-voltage fuses
ANSI/UL 746A, Polymeric Materials – Short Term Property Evaluations
ANSI/UL 796, Printed-Wiring Boards
IPC-A-600, Acceptability of Printed Boards
IPC-6012, Qualification and Performance Specification for Rigid Printed Boards
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
3.1
encapsulation "m"
Type of Protection whereby parts that are capable of igniting an explosive atmosphere by either
sparking or heating are fully enclosed in such a way as to avoid ignition of a dust layer or
explosive atmosphere under operating or installation conditions
3.2
free surface
compound surface exposed to the explosive atmospheres and/or dust layers
Note 1 to entry: Unless a compound surface is in contact with and covered by a non-metallic or metallic enclosure,
the compound surface is a free surface.
3.3
switching contact
mechanical contact, designed to make and break an electrical circuit

IEC 60079-18:2025 © IEC 2025 – 11 –
3.4
adhesion
moisture, gas and dust tight permanent bonding of a compound to a surface
Note 1 to entry: Adhesion provides a seal to prevent the ingress of the explosive atmosphere between the enclosure
and the compound.
4 General requirements
4.1 Level of Protection (Equipment Protection Level (EPL))
Electrical equipment with encapsulation "m" shall be one of the following:
a) Level of Protection "ma" (EPL Ma, Ga, Da),
b) Level of Protection "mb" (EPL Mb, Gb, Db), or
c) Level of Protection "mc" (EPL Gc, Dc).
The requirements of this document apply to all Levels of Protection for encapsulation "m" unless
otherwise stated.
4.2 Rated voltage and maximum prospective current
The following shall be specified such that the limiting temperature is not exceeded for the
relevant Level of Protection "ma", "mb" or "mc":
a) The rated voltage, and
b) The maximum available short-circuit current of the supply to which the Ex Equipment can
be connected.
4.3 Additional requirements for Levels of Protection "ma" and "mb"
Components without additional protection shall be used only if they cannot damage the
encapsulation mechanically or thermally in the case of any fault conditions specified in this
document.
Alternatively, where a fault of an internal component can lead to failure of encapsulation "m"
due to increasing temperature, the requirements of 7.9 shall apply.
5 Requirements for compounds
5.1 General
The documentation shall specify the compound(s) used and the processing method(s), including
measures to prevent the formation of voids.
See Annex A for basic requirements for compounds for "m" equipment.
As a minimum, those properties of the compound(s) on which encapsulation "m" depends shall
be included in the Schedule Drawings according to the requirements of IEC 60079-0.
NOTE Proper selection of the compound allows for the expansion of components during operation and in the event
of allowable faults.
– 12 – IEC 60079-18:2025 © IEC 2025
5.2 Specification
The specification for the compound shall include the following:
a) the name and address of the manufacturer of the compound,
b) the exact and complete reference of the compound and if relevant, percentage of fillers and
any other additives, the mixture ratios and the type designation, the curing method, curing
temperature, duration of curing,
c) if applicable, any treatment of the surface of the compound(s), for example varnishing,
d) if applicable, to obtain correct adhesion of the compound to a component or enclosure, any
requirement for pre-treating of the component or enclosure for example cleaning, etching,
e) the dielectric strength in accordance with IEC 60243-1 or ANSI/UL 746A at the maximum
service temperature of the compound determined according to 8.2.2 a) if available; if not
available, the requirements of 5.3.2 shall be applied,
f) the continuous operating temperature (COT) other than for plastic materials,
g) in the case of "m" Equipment where the compound is part of the external enclosure or the
compound is a plastic material, the temperature index TI value as defined by IEC 60079-0.
As an alternative to the TI, the relative thermal index (RTI-mechanical) may be determined
in accordance with ANSI/UL 746B,
h) the colour of the compound used for the test samples, where the compound specification
will be influenced by changing the colour,
i) Thermal conductivity if utilizing the alternative test method in 6.3.
This document does not require that conformity to the manufacturer's specification of the
compound be verified.
5.3 Properties of the compound
5.3.1 Water absorption
Either the compound shall be tested in accordance with 8.1.1 or, if this test is not performed,
the certificate number for the equipment shall include the "X" suffix in accordance with the
marking requirements of IEC 60079-0 and the Specific Conditions of Use listed on the certificate
shall detail the precautions necessary to protect the compound in the product from moisture.
5.3.2 Dielectric strength
Where the dielectric strength according to IEC 60243-1 or ANSI/UL 746A at the maximum
service temperature according to 8.2.2 a), of the compound is not available from the material
manufacturer, a test shall be performed in accordance with 8.1.2.
This document does not require that conformity to the manufacturer's specification of the
compound be verified.
6 Temperatures
6.1 General
The following temperatures shall be considered:
• Maximum surface temperature and
• Service temperature of the compound.

IEC 60079-18:2025 © IEC 2025 – 13 –
6.2 Maximum surface temperature
The maximum surface temperature shall be determined in accordance with IEC 60079-0 under
normal operation and under the conditions defined in 7.2.1.
The maximum surface temperature shall be determined using the test method given in 8.2.2 in
accordance with the supply conditions specified in 4.2.
NOTE This temperature is used to determine either the temperature class for explosive gas atmospheres or the
maximum surface temperature in degrees Celsius for explosive dust atmospheres of the equipment, or both.
6.3 Service temperature of the compound
The service temperature of the compound, determined in accordance with IEC 60079-0, shall
not exceed the maximum value of the COT of the compound.
The hottest component shall be determined. The maximum temperature in the compound,
adjacent to the hottest component, shall be determined using the test method given in 8.2.2 for
normal operation.
As alternatives, the temperature of the hottest component in normal operation may be
determined by calculation, manufacturer’s specification, or by testing the component under
intended application conditions prior to encapsulating the component if the thermal conductivity
of the compound is greater than that of air.
NOTE Thermal conductivity of air is most often defined as 0,025 W/m × K (standard conditions).
6.4 Temperature limitation of the "m" equipment
Where temperature limitation is required to satisfy 6.2 or 6.3, protective devices according to
7.9 shall be used.
7 Constructional requirements
7.1 General
Where the compound forms part of the external enclosure it shall comply with the requirements
of IEC 60079-0 for non-metallic enclosures and non-metallic parts of enclosures.
If the surface of the compound is totally or partly surrounded by an enclosure and the enclosure
is part of the protection, the enclosure or parts of the enclosure shall comply with the enclosure
requirements of IEC 60079-0.
Appropriate action shall be taken to accommodate the expansion of components and
compounds during normal operation and in the event of faults according to 7.2.
In 7.2 to 7.9 the requirements differ according to whether the compound adheres to the
enclosure. Where adhesion is specified, the aim is to prevent the ingress of explosive
atmospheres and moisture at the boundary surfaces (for example, enclosure-compound,
compound-parts that are not completely embedded in the compound, such as printed wiring
boards, connection terminals). Where adhesion is required to maintain the Type of Protection,
it shall be maintained after completion of all the prescribed tests. The choice of the compound(s)
to be used for a specific application is dependent on the task each compound has to perform.
Testing a compound once for a given application will not qualify that compound for all
applications.
– 14 – IEC 60079-18:2025 © IEC 2025
7.2 Determination of faults
7.2.1 Fault examination
When tested in accordance with IEC 60079-0, encapsulation "m" shall be maintained in the
case of
a) the most unfavourable output load and
b) up to two internal countable faults for Level of Protection "ma", and up to one internal
countable fault for Level of Protection "mb", taking into account 7.2.2, 7.2.3 and 7.2.4.
No faults are taken into account for Level of Protection "mc" except for separation distances
according to 7.2.4 and 7.4.3.
EXAMPLE Faults can include the failure of any component and a fault between tracks in the printed wiring board,
but not the opening of a track provided it is designed properly in accordance with IPC-2221.
Components which are:
– in accordance with 7.2.2 are not considered to fail;
– used within the ratings specified by the component manufacturer shall be considered to fail
as a countable fault; and,
– used outside their ratings shall be considered to fail as a non-countable fault.
The failure of some components can result in an unstable condition, for example, alternating
between high and low resistance. In those cases, the most onerous condition shall be
considered. An intermediate failure condition need not be considered.
If a fault leads to one or more subsequent faults, for example, due to the overload of a
component, the primary and subsequent fault(s) shall be considered to be a single fault.
7.2.2 Components considered as not subject to fail
For Levels of Protection "ma" and "mb" the following components shall be considered as not to
fail if they are encapsulated according to the requirements of this document, if they are suitable
for the service temperature and if they are not operated at more than 2/3 of their rated voltage,
rated current and rated power as applicable, related to the rating of the device, the mounting
conditions and the temperature range specified:
– resistors,
– single-layer, spirally wound coils,
– plastic foil capacitors,
– paper capacitors,
– ceramic capacitors,
– semiconductors.
Semiconductors which are used for a protective function for encapsulation "m" shall additionally
satisfy the requirements of 7.9.
Resistors which are used as a protective device according to 7.9 shall additionally comply with
the current limiting resistors of IEC 60079-11 for Level of Protection "ia" or "ib".
For Levels of Protection "ma" and "mb" windings that comply with IEC 60079-7, including also
those that have wire diameters of less than 0,25 mm shall be considered as not subject to
failure if they are encapsulated according to the requirements of this document.

IEC 60079-18:2025 © IEC 2025 – 15 –
7.2.3 Isolating components
The following components for the segregation of different circuits shall be considered to provide
isolatio
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