EN 60079-18:2009

SLOVENSKI STANDARD
01-marec-2010
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Explosive atmospheres -- Part 18: Equipment protection by encapsulation m
Explosionsfähige Atmosphäre -- Teil 18: Geräteschutz durch Vergusskapselung m
Atmosphères explosives -- Partie 18: Protection du matériel par encapsulage m
Ta slovenski standard je istoveten z: EN 60079-18:2009
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60079-18
NORME EUROPÉENNE
December 2009
EUROPÄISCHE NORM
ICS 29.260.20 Supersedes EN 60079-18:2004 + corr. April 2006 and EN 61241-18:2004

English version
Explosive atmospheres -
Part 18: Equipment protection by encapsulation "m"
(IEC 60079-18:2009 + corrigendum 2009)

Atmosphères explosives -  Explosionsfähige Atmosphäre -
Partie 18: Protection du matériel Teil 18: Geräteschutz
par encapsulage "m" durch Vergusskapselung "m"
(CEI 60079-18:2009 + corrigendum 2009) (IEC 60079-18:2009 + Corrigendum 2009)

This European Standard was approved by CENELEC on 2009-10-01. 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, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

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

Central Secretariat: Avenue Marnix 17, B - 1000 Brussels

© 2009 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60079-18:2009 E
Foreword
The text of document 31/784/FDIS, future edition 3 of IEC 60079-18, prepared by IEC TC 31, Equipment
for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote and was approved by
CENELEC as EN 60079-18 on 2009-10-01.
This European Standard supersedes EN 60079-18:2004 + corrigendum April 2006 and
EN 61241-18:2004.
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) 2010-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2012-10-01
This European Standard has been prepared under a mandate given to CENELEC by the European
Commission and the European Free Trade Association and covers essential requirements of
EC Directive ATEX (94/9/EC). See Annex ZZ.
CENELEC/TC 31 as the responsible committee has concluded that this new edition of EN 60079-18 does
not contain substantial changes regarding the ESRs.
The State of the Art is included in Annex ZY “Significant changes between this European Standard and
EN 60079-18:2004".
Annexes ZA, ZY and ZZ have been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60079-18:2009 + corrigendum June 2009 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 standards indicated:
IEC 60079-1 NOTE  Harmonized as EN 60079-1:2007 (not modified).
IEC 60079-2 NOTE  Harmonized as EN 60079-2:2007 (not modified).
IEC 60079-5 NOTE  Harmonized as EN 60079-5:2007 (not modified).
IEC 60079-6 NOTE  Harmonized as EN 60079-6:2007 (not modified).
IEC 60079-10 NOTE  Harmonized as EN 60079-10:2003 (not modified).
IEC 60079-14 NOTE  Harmonized as EN 60079-14:2008 (not modified).
IEC 60079-26 NOTE  Harmonized as EN 60079-26:2007 (not modified).
IEC 60079-28 NOTE  Harmonized as EN 60079-28:2007 (not modified).
IEC 60086-1 NOTE  Harmonized as EN 60086-1:2007 (not modified).
IEC 60622 NOTE  Harmonized as EN 60622:2003 (not modified).
IEC 60664-1 NOTE  Harmonized as EN 60664-1:2007 (not modified).
IEC 61241-10 NOTE  Harmonized as EN 61241-10:2004 (not modified).
IEC 61951-1 NOTE  Harmonized as EN 61951-1:2003 (not modified).

- 3 - EN 60079-18:2009
IEC 61951-2 NOTE  Harmonized as EN 61951-2:2003 (not modified).
IEC 61960-1 NOTE  Harmonized as EN 61960-1:2001 (not modified).
__________
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  When 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 - Explosive atmospheres - EN 60079-0 2009
Part 0: Equipment - General requirements

1) 2)
IEC 60079-7 - Explosive atmospheres - EN 60079-7 2007
Part 7: Equipment protection by increased
safety "e"
1) 2)
IEC 60079-11 - Explosive atmospheres - EN 60079-11 2007
Part 11: Equipment protection by intrinsic
safety "i"
1) 3)
IEC 60079-15 - Explosive atmospheres - EN 60079-15 200X
Part 15: Equipment protection by type of
protection "n"
1) 2)
IEC 60079-26 - Explosive atmospheres - EN 60079-26 2007
Part 26: Equipment with equipment protection
level (EPL) Ga
1) 2)
IEC 60079-31 - Explosive atmospheres - EN 60079-31 2009
Part 31: Equipment dust ignition protection by
enclosure "t"
IEC 60127 Series Miniature fuses EN 60127 Series

1) 2)
IEC 60243-1 - Electrical strength of insulating materials - EN 60243-1 1998
Test methods -
Part 1: Tests at power frequencies

1) 2)
IEC 60691 - Thermal-links - Requirements and application EN 60691 2003
guide
1)
IEC 60730-2-9 - Automatic electrical controls for household - -
(mod) and similar use -
Part 2-9: Particular requirements for
temperature sensing controls
1) 2)
IEC 60738-1 - Thermistors - Directly heated positive EN 60738-1 2006
temperature coefficient -
Part 1: Generic specification
1) 2)
IEC 61241-11 - Electrical apparatus for use in the presence of EN 61241-11 2006
combustible dust -
Part 11: Protection by intrinsic safety 'iD'

1)
Undated reference.
2)
Valid edition at date of issue.
3)
To be ratified.
- 5 - EN 60079-18:2009
Publication Year Title EN/HD Year

1) 2)
IEC 61558-2-6 - Safety of power transformers, power supply EN 61558-2-6 2009
units and similar -
Part 2-6: Particular requirements for safety
isolating transformers for general use

1) 2)
IEC 62326-4-1 - Printed boards - EN 62326-4-1 1997
Part 4: Rigid multilayer printed boards with
interlayer connections - Sectional
specification - Section 1: Capability Detail
Specification - Performance levels A, B and C

1)
ISO 62 - Plastics - Determination of water absorption - -

1)
ANSI/UL 248-1 - Standard for low-voltage fuses - - -
Part 1: General requirements
1)
ANSI/UL 746B - Standard for polymeric materials - Long-term - -
property evaluations
Annex ZY
(informative)
Significant changes between this European Standard and EN 60079-18:2004
The significant changes with respect to EN 60079-18:2004 are as listed below.
Type
Minor and Extension Substantial
editorial change
changes regarding
a
ESR´s
Incorporation of level of protection "mc" X
Equipment protection levels (EPL Ma, Ga, Da, Mb, Gb, Db,
X
Gc, Dc)
Incorporation of the dust requirements X
Incorporation of switching contacts for level of protection
X
"ma"
a
ESR = Essential Health and Safety Requirements (Annex II of Directive 94/9/EC)

General conclusion on the change of the State of the Art by this standard
CENELEC/TC 31 as the responsible committee has concluded that this new edition of EN 60079-18 does
not contain substantial changes regarding the ESRs.

- 7 - EN 60079-18:2009
Annex ZZ
(informative)
Coverage of Essential Requirements of EC Directives
This European Standard has been prepared under a mandate given to CENELEC by the European
Commission and the European Free Trade Association and within its scope the standard covers only the
following essential requirements out of those given in Annex II of the EC Directive 94/9/EC:
– ER 1.0.1, ER 1.0.2 (partly), ER 1.0.5 (partly)
– ER 1.1 (partly)
– ER 1.2.4, ER 1.2.8
– ER 1.3.1
– ER 1.6.4 (partly)
– ER 2.0.1 (partly)
– ER 2.0.2.1 (partly), ER 2.0.2.3 (partly)
– ER 2.1.1.1 (partly), ER 2.1.1.2 (partly)
– ER 2.1.2.1 (partly), ER 2.1.2.3 (partly)
– ER 2.2.1.1 (partly), ER 2.2.1.2 (partly)
– ER 2.2.2.1 (partly), ER 2.2.2.2 (partly)
– ER 2.3.1.1, ER 2.3.1.2
– ER 2.3.2.1, ER 2.3.2.2
Compliance with this standard provides one means of conformity with the specified essential
requirements of the Directive concerned.
WARNING: Other requirements and other EC Directives may be applicable to the products falling within
the scope of this standard.
__________
IEC 60079-18 ®
Edition 3.0 2009-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 18: Equipment protection by encapsulation “m”

Atmosphères explosives –
Partie 18: Protection du matériel par encapsulage «m»

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 29.260.20 ISBN 2-8318-1036-2
– 2 – 60079-18 © IEC:2009
CONTENTS
FOREWORD.4
1 Scope.6
2 Normative references .6
3 Terms and definitions .7
4 General .9
4.1 Level of protection (Equipment protection level (EPL)) .9
4.2 Additional requirements for level of protection “ma”.9
4.3 Rated voltage and prospective short circuit current .9
5 Requirements for compounds .9
5.1 General .9
5.2 Specification .9
5.3 Properties of the compound.10
5.3.1 Water absorption .10
5.3.2 Dielectric strength .10
6 Temperatures .10
6.1 General .10
6.2 Determination of the limiting temperature .10
6.2.1 Maximum surface temperature.10
6.2.2 Temperature of the compound .10
6.3 Temperature limitation.10
7 Constructional requirements .11
7.1 General .11
7.2 Determination of faults .11
7.2.1 Fault examination .11
7.2.2 Components considered as not subject to fail .12
7.2.3 Isolating components.12
7.2.4 Infallible separation distances.12
7.3 Free space in the encapsulation .13
7.3.1 Group III “m” equipment.13
7.3.2 Group I and Group II “m” equipment .14
7.4 Thickness of the compound .15
7.4.1 “m” equipment .15
7.4.2 Windings for electrical machines .17
7.4.3 Rigid, multi-layer printed wiring boards with through connections .17
7.5 Switching contacts .18
7.5.1 Level of protection “ma”.18
7.5.2 Level of protection “mb”.18
7.5.3 Level of protection “mc” .18
7.6 External connections .19
7.6.1 General .19
7.6.2 Additional requirements for “ma” equipment .19
7.7 Protection of bare live parts.19
7.8 Cells and batteries .19
7.8.1 General .19
7.8.2 Prevention of gassing .19
7.8.3 Protection against inadmissible temperatures and damage to the cells .20

60079-18 © IEC:2009 – 3 –
7.8.4 Reverse current.20
7.8.5 Current limitation .20
7.8.6 Protection against the polarity inversion and deep discharge of the
cells .20
7.8.7 Charging of cells or batteries.21
7.8.8 Requirements for control safety devices for cells or batteries .21
7.9 Protective devices .21
7.9.1 General .21
7.9.2 Electrical protective devices .22
7.9.3 Thermal protective devices .23
7.9.4 Built-in protective devices.23
8 Type tests .23
8.1 Tests on the compound .23
8.1.1 Water absorption test .23
8.1.2 Dielectric strength test.24
8.2 Tests on the apparatus.24
8.2.1 Test sequence.24
8.2.2 Maximum temperature .24
8.2.3 Thermal endurance test.24
8.2.4 Dielectric strength test.25
8.2.5 Cable pull test .25
8.2.6 Pressure test for Group I and Group II electrical equipment.26
8.2.7 Test for resettable thermal protective device .26
8.2.8 Sealing test for build-in protective devices.27
9 Routine verifications and tests.27
9.1 Visual inspections .27
9.2 Dielectric strength test.27
10 Marking .27
Annex A (informative) Basic requirements for compounds for “m” equipment .29
Annex B (normative) Allocation of test samples .30
Bibliography.31

Figure 1 – Dimensional key for thickness through the compound .16
Figure 2 – Minimum distances for multi-layer printed wiring boards.18
Figure 3 – Fitting of blocking diodes .20
Figure A.1 − Basic requirements for compounds for “m” equipment.29

Table 1 – Distances through the compound .13
Table 2 – Minimum thickness of compound adjacent to free space for Group III “m”
equipment.13
Table 3 – Minimum thickness of compound adjacent to free space for Group I and
Group II “m” equipment.14
Table 4 – Thickness of the compound.16
Table 5 – Minimum distances for multi-layer printed wiring boards.17
Table 6 – Test pressure .26
Table B.1 − Allocation of test samples .30

– 4 – 60079-18 © IEC:2009
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) 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 60079-18 has been prepared by IEC technical committee 31:
Equipment for explosive atmospheres.
This third edition cancels and replaces the second edition of IEC 60079-18 (2004) and
IEC 61241-18 (2004), and constitutes a technical revision.
The significant technical changes with respect to the previous edition are as follows:
– Incorporation of level of protection “mc”
– Equipment protection levels (EPL Ma, Ga, Da, Mb, Gb, Db, Gc, Dc)
– Incorporation of the dust requirements
– Incorporation of switching contacts for level of protection “ma”

60079-18 © IEC:2009 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
31/784/FDIS 31/801/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 standard is to be read in conjunction with IEC 60079-0:2007, Explosive atmospheres –
Part 0: Equipment – General requirements.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The list of all parts of IEC 60079 series, under the general title Explosive atmospheres, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of June 2009 have been included in this copy.

– 6 – 60079-18 © IEC:2009
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 equipment, parts of electrical equipment and Ex components with the
type of protection encapsulation “m” intended for use in explosive gas atmospheres or
explosive dust atmospheres.
This part applies only for encapsulated electrical equipment, encapsulated parts of electrical
equipment and encapsulated Ex components (hereinafter always referred to as “m”
equipment) where the rated voltage does not exceed 11 kV.
The application of electrical equipment in atmospheres, which may contain explosive gas as
well as combustible dust simultaneously may require additional protective measures.
This standard does not apply to dusts of explosives, which do not require atmospheric oxygen
for combustion, or to pyrophoric substances
This standard does not take account of any risk due to an emission of flammable or toxic gas
from the dust.
This standard supplements and modifies the general requirements of IEC 60079-0. Where a
requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of
this standard shall take precedence.
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, 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 60079-26, Explosive atmospheres – Part 26: Equipment with equipment protection level
(EPL) Ga
IEC 60079-31, Explosive atmospheres – Part 31: Equipment dust ignition protection by
enclosures “t”
IEC 60127 (all parts), Miniature fuses

60079-18 © IEC:2009 – 7 –
IEC 60243-1, Electrical strength of insulating material – Test methods – Part 1: Tests at
power frequencies
IEC 60691, Thermal-links – Requirements and application guide
IEC 60730-2-9, Automatic electrical controls for household and similar use – Part 2-9:
Particular requirements for temperature sensing controls
IEC 60738-1, Thermistors – Directly heated positive temperature coefficient – Part 1: Generic
specification
IEC 61241-11, Electrical apparatus for use in the presence of combustible dust – Part 11:
Protection by intrinsic safety ‘iD’
IEC 61558-2-6, Safety of power transformers, power supply units and similar – Part 2:
Particular requirements for safety isolating transformers for general use
IEC 62326-4-1, Printed boards – Part 4: Rigid multilayer printed boards with interlayer
connections – Sectional specification – Section 1: Capability detail specification – Perform-
ance levels A, B and C
ISO 62, Plastics – Determination of water absorption
ANSI/UL 248-1, Standard for low-voltage fuses – Part 1: General requirements
ANSI/UL 746B, Standard for polymeric materials – Long term property evaluations
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0 and the
following definitions specific to encapsulation “m” apply.
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 enclosed in a compound in such a way as to avoid ignition of a
dust layer or explosive atmosphere under operating or installation conditions
3.2
compounds
any thermosetting, thermoplastic, epoxy resin or elastomeric materials with or without fillers
and/or additives, in their solid state
3.3
temperature range of the compound
range of temperatures within which, the properties of the compound, in either operation or
storage, permit compliance with the requirements of this standard
3.4
continuous operating temperature (COT) of the compound
temperature range within which, according to the details given by the manufacturer, the
properties of the compound, during operation, satisfy the requirements of this standard on a
permanent basis during the foreseen lifetime of the equipment

– 8 – 60079-18 © IEC:2009
3.5
encapsulation
process of applying the compound to enclose any electrical device(s) by suitable means
3.6
free surface
compound surface exposed to the explosive atmospheres and/or dust layers
3.7
normal operation
operation of equipment conforming electrically and mechanically with its design specification
and used within the limits specified by the manufacturer
NOTE 1 The limits specified by the manufacturer may include persistent operational conditions, for example
operation of a motor on a duty cycle.
NOTE 2 Variation of the supply specifications within stated limits and any other operational tolerance is part of
normal operation.
3.8
void
unintentional space created as a consequence of the encapsulation process
3.9
free space
intentionally created space surrounding components or space inside components
3.10
switching contact
mechanical contact, which makes and breaks an electrical circuit
3.11
adhesion
moisture, gas and dust tight permanent bonding of a compound to a surface
3.12
countable fault
fault, which occurs in parts of electrical equipment conforming to the constructional require-
ments
3.13
infallible separation or insulation
separation or insulation between electrically conductive parts that is considered as not subject
to short circuits as specified in IEC 60079-18. The probability of such fault modes occurring in
service or storage is considered to be so low that they are not to be taken into account
3.14
non-countable fault
fault, which occurs in parts of electrical equipment not conforming to the constructional
requirements of IEC 60079-18
3.15
solid insulation
insulation material, which is extruded or moulded, but not poured
NOTE Insulators fabricated from two or more pieces of electrical insulating material, which are solidly bonded
together may be considered as solid. Varnish and similar coatings are not considered to be solid insulation.

60079-18 © IEC:2009 – 9 –
4 General
4.1 Level of protection (Equipment protection level (EPL))
Electrical equipment with encapsulation “m” shall be either
a) level of protection “ma” (EPL “Ma, Ga, Da”),
b) level of protection “mb” (EPL “Mb, Gb, Db”) or in
c) level of protection “mc” (EPL “Gc, Dc”).
The requirements of this standard shall apply to all levels of protection “m” (EPL`s) unless
otherwise stated.
4.2 Additional requirements for level of protection “ma”
The working voltage at any point in the circuit shall not exceed 1 kV.
Components without additional protection shall be used only if they cannot damage the
encapsulation mechanically or thermally in the case of any specified fault.
Alternatively, where a fault of an internal component may lead to failure of the encapsulation
“m” due to increasing temperature, the requirements of 7.9 shall apply.
4.3 Rated voltage and prospective short circuit current
The rated voltage and the prospective short circuit current shall be specified such that the
limiting temperature is not exceeded for the relevant level of protection “ma”, “mb” or “mc”.
5 Requirements for compounds
5.1 General
The documentation shall specify the compound(s) used and the processing method(s).
As a minimum, those properties of the compound(s) on which the encapsulation “m” depends
shall be provided.
NOTE Due consideration should be given in the selection of compounds to allow for the expansion of components
during operation and in the event of allowable faults.
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,
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, any requirement
for pre-treating of the component for example cleaning, etching,
e) the dielectric strength in accordance with IEC 60243-1 at the maximum temperature of the
equipment determined according to 8.2.2 if available. If not available, the requirements of
5.3.2 shall be applied,
f) temperature range of the compound(s) (continuous operating temperature),
g) in the case of “m” equipment where the compound is part of the external enclosure, the
temperature index TI value as defined by IEC 60079-0. As an alternative to the TI, the

– 10 – 60079-18 © IEC:2009
relative thermal index (RTI-mechanical impact) 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.
NOTE It is not a requirement of this standard that conformity to the manufacturer’s specification of the compound
needs to be verified.
5.3 Properties of the compound
5.3.1 Water absorption
If the equipment is to be exposed to dampness, the compound shall be tested in accordance
with 8.1.1. If this test is not performed, the equipment shall be marked “X” in accordance with
the marking requirements of IEC 60079-0 and the restriction of use to dry environments
clarified in the instructions.
5.3.2 Dielectric strength
Where the dielectric strength according to IEC 60243-1 is not available at the maximum
temperature of the equipment as defined according to 8. 2. 2, s ee 5.2 e), a test shall be
performed in accordance with 8. 1. 2.
6 Temperatures
6.1 General
The maximum value of the continuous operating temperature of the compound shall not be
exceeded under normal operation. The maximum surface temperature, determined in
accordance with IEC 60079-0 shall not be exceeded under normal operation and under fault
conditions as defined in 7.2.1. The “m” equipment shall be protected in such a way that the
encapsulation “m” is not adversely affected under these fault conditions.
NOTE Normal operation includes operation at the extremes of voltage tolerances of the supply normally 90 % to
110 % if not otherwise specified.
6.2 Determination of the limiting temperature
6.2.1 Maximum surface temperature
The maximum surface temperature shall be determined using the test method given in 8.2 . 2
in accordance with the supply conditions specified in 4.3. This temperature shall be used to
determine the temperature class for explosive gas atmosphere or the maximum surface
temperature in degrees Celsius for explosive dust atmosphere of the equipment.
6.2.2 Temperature of the compound
The hottest component(s) shall be determined. The maximum temperature in the compound,
adjacent to the hottest component(s), shall be determined using the test method given in
8.2.2 for normal operation.
As an alternative the determination of the temperature of the hottest component may be
done by calculation, manufacturer’s specification or by a practical test prior to encapsulating
the components.
6.3 Temperature limitation
Where the equipment may be subject to fault in accordance with 7.2.1, or where there is the
possibility of an increased temperature, for example by an unfavourable input voltage in
accordance with 7.2.1 or an unfavourable load, this shall be taken into account in determining
the limiting temperatures.
60079-18 © IEC:2009 – 11 –
When a protective device is required to limit temperatures for safety reasons, it shall be an
internal or external, electrical or thermal device, as defined in 7. 9.
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 parts of non metallic 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
If additional protective measures are required to be provided by the user in order to satisfy the
requirements of this standard, for example, additional mechanical protection, to indicate this
specific condition of use the equipment shall be in accordance with the “specific conditions of
use” marking requirements of IEC 60079-0.
Appropriate action shall be taken to accommodate the expansion of components during
normal operation and in the event of faults according to 7. 2.
In 7. 2 t o 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, etc.). Where adhesion is required to maintain the type of
protection, it shall be maintained after completion of all the prescribed tests.
NOTE The choice of the compound(s) to be used for a specific application is dependent on the task each
compound has to perform. In general, testing a compound once is not sufficient for universal use for encapsulation
“m”.
7.2 Determination of faults
7.2.1 Fault examination
The encapsulation “m” shall not be invalidated even under the most adverse input rating, but
between 90 % and 110 % of the rating and most adverse output load and up to two internal
countable faults for level of protection “ma”, and up to one internal countable fault for level of
protection “mb.
No faults are taken into account for level of protection “mc”.
NOTE Examples of faults are: a short circuit in any component; the failure of any component and a fault in the
printed wiring board.
Components meeting the requirements of 7.2.2 are not considered to fail and infallible
separation distances shall only be considered to fail in accordance with 7. 2. 4.
The failure of some components may result in an unstable condition, for example, alternating
between high and low resistance. In those cases, the most onerous condition shall 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.

– 12 – 60079-18 © IEC:2009
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 standard, 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 or rated power specified by the manufacturer of the respective
component:
– resistors, if they comply with the current limiting resistors of IEC 60079-11,
– single-layer, spirally wound coils,
– plastic foil capacitors,
– paper capacitors,
– ceramic capacitors,
– shunt semiconductors, if they are used in accordance with the shunt safety assemblies of
IEC 60079-11,
– series semiconductor devices used to limit current:
– a single device is adequate for level of protection “mb”
– two devices shall be used for level of protection “ma”.
For levels of protection “ma” and “mb” coils, motor windings and transformers 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 standard.
7.2.3 Isolating components
The following components for the segregation of different circuits shall be considered to
provide isolation and are not considered to fail across the segregation:
• optocouplers and relays, if the rated insulation voltage conforms to 2U + 1 000 V r.m.s.
+5
% or 1 500 V r.m.s. whichever is greater (U is the sum of the rated r.m.s. voltages of
both circuits);
• transformers, complying with IEC 61558-2-6 or IEC 60079-11.
7.2.4 Infallible separation distances
It is not necessary to consider the possibility of a fault occurring as described in 7. 2 . 1 i n
respect of voltage breakdown, if the distances between bare current-carrying parts
– of the same circuit, or
– of a circuit and earthed metal parts, or
– of two separate circuits (sum of the working voltages shall be taken as the voltage for
Table 1; where one of the working volt
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