IEC 60079-11:2006

IEC 60079-11
Edition 5.0 2006-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 11: Equipment protection by intrinsic safety "i"

Atmosphères explosives –
Partie 11: Protection de l’équipement par sécurité intrinsèque «i»

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IEC 60079-11
Edition 5.0 2006-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 11: Equipment protection by intrinsic safety "i"

Atmosphères explosives –
Partie 11: Protection de l’équipement par sécurité intrinsèque «i»

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XE
CODE PRIX
ICS 29.260.20 ISBN 2-8318-8749-6

 IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
IEC 60079-11
Edition 5.0  2006-07
EXPLOSIVE ATMOSPHERES –
Part 11: Equipment protection by intrinsic safety "i"

INTERPRETATION SHEET 1
This interpretation sheet has been prepared by subcommittee 31G: Intrinsically-safe
apparatus, of IEC technical committee 31: Equipment for explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
31G/310/DISH 31G/313/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.
___________
Background
The maximum surface temperature shall be determined as follows:
All current-limiting devices external to the cell or battery shall be short-circuited for the test.

Any external sheath (of paper or metal, etc.) not forming part of the actual cell enclosure shall
be removed for the test. The temperature shall be determined on the outer enclosure of each
cell or battery and the maximum figure taken. The test shall be carried out both with internal
current-limiting devices in circuit and with the devices short-circuited using 10 cells in each
case. The 10 samples having the internal current-limiting devices short-circuited shall be
obtained from the cell/battery manufacturer together with any special instructions or
precautions necessary for safe use and testing of the samples.
The intent of the cited paragraphs is to simulate an internal short inside a cell, by shorting the
cell’s external terminals for the purpose of thermal assessment.
It was found that two details have been misinterpreted in this subclause:
a) The subjects of this subclause are cells or batteries, while the intent is clearly to
simulate internal shorts inside cells and not inside batteries in which case the shorts
could be interpreted as being external to the cell(s) within a battery.
ICS 29.260.20
– 2 – IEC 60079-11:2006/ISH1:2019

 IEC 2019
b) It is unclear what constitutes a current limiting device that protects against internal

shorts.
A separator with shutdown function may be interpreted as a current limiting device that

protects against internal shorts by its function, but since it is a constructional part of the cell

that is not removable without invalidating the functionality of the basic cell, it is not a current
limiting device for the purposes of implementing the standard. Conversely, a CID (Current

interruption device), for example, is a switch that is triggered by increased pressure inside the

cell, and the cell’s functionality is not invalidated by the absence of the CID.

The reference to internal current limiting devices that protect against internal shorts in edition

6 was included to address unknown future cell technologies which could include such current

limiting devices, however at this time no such current limiting devices are known.
Question
For either Level of Protection “ia” or “ib”, what are the current limiting devices that are
required to be disabled (or equivalent e.g. not fitted, short-circuited or removed) by IEC
60079-11:2006, Subclause 10.5.3 b), and what are the current limiting devices that need not
be disabled?
Answer
All discrete protective devices that can be schematically represented as individual devices
apart from the cell are to be disabled for the purposes of testing according to IEC 60079-
11:2006, Subclause 10.5.3 b), regardless if they are located inside the cell or if they are
external to the cell. This includes, but is not limited to resistors, fuses, resettable fuses (NTC,
PTC, PPTC), CID (current interruption device), semiconductors, etc.
Features that provide essential cell functions, such as a separator with shutdown function or
the ohmic resistance of the electrolyte, are not considered current limiting devices in the
sense of this clause and need not be shorted or removed, and such cells can be considered
for Level of Protection “ia”.
60079-11  IEC:2006 – – 2 –3 – 60079-11 © IEC:2006
CONTENTS
FOREWORD.6

Scope.8
2 Normative references.10
3 Terms and definitions .11
4 Grouping and classification of intrinsically safe apparatus and associated apparatus .16
5 Levels of protection and ignition compliance requirements of electrical apparatus.16
5.1 General .16
5.2 Level of protection "ia" .16
5.3 Level of protection "ib" .17
5.4 Level of protection "ic" .17
5.5 Spark ignition compliance .18
5.6 Thermal ignition compliance .18
5.7 Simple apparatus.22
6 Apparatus construction .22
6.1 Enclosures .23
6.2 Facilities for connection of external circuits .23
6.3 Separation distances .27
6.4 Protection against polarity reversal .38
6.5 Earth conductors, connections and terminals .38
6.6 Encapsulation.40
7 Components on which intrinsic safety depends.40
7.1 Rating of components .40
7.2 Connectors for internal connections, plug-in cards and components .41
7.3 Fuses .41
7.4 Primary and secondary cells and batteries .42
7.5 Semiconductors.46
7.6 Failure of components, connections and separations.47
7.7 Piezo-electric devices .48
7.8 Electrochemical cells for the detection of gases .48
8 Infallible components, infallible assemblies of components and infallible
connections on which intrinsic safety depends.48
8.1 Mains transformers.48
8.2 Transformers other than mains transformers.50
8.3 Infallible windings .5 1
8.4 Current-limiting resistors.52
8.5 Blocking capacitors.52
8.6 Shunt safety assemblies .53
8.7 Wiring, printed circuit board tracks, and connections. .54
8.8 Galvanically separating components .56

60079-11 © IEC:200660079-11  IEC:2006 – – 3 –5 –
9 Diode safety barriers.57
9.1 General . 57
9.2 Construction .57
10 Type verifications and type tests .57
10.1 Spark ignition test.57
10.2 Temperature tests .62
10.3 Dielectric strength tests .62
10.4 Determination of parameters of loosely specified components.63
10.5 Tests for cells and batteries.63
10.6 Mechanical tests.65
10.7 Tests for apparatus containing piezoelectric devices .65
10.8 Type tests for diode safety barriers and safety shunts .66
10.9 Cable pull test .67
10.10 Transformer tests .67
11 Routine verifications and tests .67
11.1 Routine tests for diode safety barriers.67
11.2 Routine tests for infallible transformers .68
12 Marking .68
12.1 General .68
12.2 Marking of connection facilities .69
12.3 Warning markings .69
12.4 Examples of marking .70
13 Documentation .7 1

Annex A (normative) Assessment of intrinsically safe circuits.72
Annex B (normative) Spark test apparatus for intrinsically safe circuits .94
Annex C (informative) Measurement of creepage distances, clearances and separation
distances through casting compound and through solid insulation.103
Annex D (informative) Encapsulation .106
Annex E (informative) Transient energy test .110
Annex F (normative) Alternative separation distances for assembled printed circuit
boards and separation of components .113

Bibliography .117

Figure 1 – Separation of intrinsically safe and non-intrinsically safe terminals .25
Figure 2 – Example of separation of conducting parts.30
Figure 3 – Determination of creepage distances .34
Figure 4 – Creepage distances and clearances on printed circuit boards.35
Figure 5– Examples of independent and non-independent connecting elements.39
Figure 6 – Infallible solder connection of surface mount component in accordance
with 8.7 c) 3). .55
Figure A.1 – Resistive circuits .75
Figure A.2 – Group I capacitive circuits .76
Figure A.3 – Group II capacitive circuits .77
Figure A.4 – Inductive circuits of Group II .78

60079-11  IEC:2006 – – 4 –7 – 60079-11 © IEC:2006
Figure A.5 – Group I inductive circuits .79
Figure A.6 – Group IIC inductive circuits.80
Figure A.7 – Simple inductive circuit.8 1
Figure A.8 – Simple capacitive circuit .8 1
Figure A.9 – Equivalent capacitance.93
Figure B.1 – Spark test apparatus for intrinsically safe circuits.97
Figure B.2 – Cadmium contact disc .98
Figure B.3 – Wire holder .98
Figure B.4 – Example of a practical design of spark test apparatus.99
Figure B.5 – Example of an explosion pressure switch.100
Figure B.6 – Example of automatic stopping by means of an explosion pressure switch .1 01
Figure B.7 – Arrangement for fusing tungsten wires.102
Figure B.8 – Circuit diagram for fusing tungsten wires .102
Figure C.1 – Measurement of clearance .103
Figure C.2 – Measurement of composite distances .103
Figure C.3 – Measurement of creepage.104
Figure C.4 – Measurement of composite creepage .105
Figure D.1 – Examples of encapsulated assemblies conforming to 6.3.4 and 6.6 .107
Figure D.2 – Applications of encapsulation without enclosure.108
Figure E1 – Example of test circuit .112
Figure E2 – Example of output waveform.112

Table 1 – Exclusion of specific clauses of IEC 60079-0 .8
Table 2 – Assessment of temperature classification according to component size and
ambient temperature .19
Table 3 – Temperature classification of copper wiring (in a maximum ambient
temperature of 40 °C).20
Table 4 – Temperature classification of tracks on printed circuit boards (in a maximum
ambient temperature of 40 °C) .21
Table 5 – Clearances, creepage distances and separations .29
Table 6 – Minimum foil thickness or minimum wire diameter of the screen in relation to
the rated current of the fuse .49
Table 7 – Compositions of explosive test mixtures adequate for 1,0 safety factor.59
Table 8 – Compositions of explosive test mixtures adequate for 1,5 safety factor.59
Table 9 – Routine test voltages for infallible transformers .68
Table 10 – Text of warning markings .69
Table A.1 – Permitted short-circuit current corresponding to the voltage and the
apparatus group.82
Table A.2 – Permitted capacitance corresponding to the voltage and the apparatus
group .87
Table A.3 – Permitted reduction of effective capacitance when protected by a series
resistance .93

60079-11 © IEC:200660079-11  IEC:2006 – – 5 –9 –
Table F.1 – Clearances, creepage distances and separations for level of protection ”ia”
and “ib” when ingress protected, and special conditions of material and installation are
fulfilled. 115
Table F.2 – Clearances, creepage distances and separations for level of protection”ic”
when ingress is protected by an enclosure or by special conditions of installation . 116

– 6 –                   60079-11 © IEC:2006
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 11: Equipment protection by intrinsic safety "i"

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
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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 60079-11 has been prepared by subcommittee 31G: Intrinsically
safe apparatus, of IEC technical committee 31: Equipment for explosive atmospheres.
This fifth edition cancels and replaces the fourth edition published in 1999 and constitutes a full
technical revision.
The significant changes with respect to the previous edition are listed below:
– introduction of level of protection “ic” (this level of protection has been introduced to allow
removal of the 'energy limitation' concept from 60079-15);
– introduction of Annex F that allows reduction in segregation distance requirements when
the pollution degree has been reduced by installation or enclosure;
– introduction of alternative spark test apparatus construction when used with high current
circuits;
– introduction of Annex E that provides a method for transient energy test;

60079-11  IEC:2006 – 7 –
– changes in the table of 'Temperature classification of tracks on PCB's' to allow correlation
with IPC-2152;
– allowing alternative methods of rating resistors when used to limit the discharge from
capacitance;
– introduction of methods to deal with the spark ignition energy consideration when high
current low voltage cells and batteries are used;
– introduction of tests to measure the maximum pressure in sealed battery containers;
– introduction of methods to deal with fault application on voltage enhancement IC's;
– introduction of infallible connection methods for SMD's (surface mount devices);
– introduction of alternative methods to deal with the spark ignition energy in circuits with
both inductance and capacitance;
– introduction of alternative high voltage test for transformers;
– introduction of methods to assess the reduction of effective capacitance when protected
by series resistances;
– introduction of Group I data for permitted short circuit current and permitted capacitance in
the tables of Annex A.
The text of this standard is based on the following documents:
FDIS Report on voting
31G/159/FDIS 31G/161/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 supplements and modifies the general requirements of IEC 60079-0, except as
indicated in Table 1 (see Scope).
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60079 series, under the general title: Explosives 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 interpretation sheet 1 of December 2019 have been included in this copy.

60079-11  IEC:2006 – – 8 –15 – 60079-11 © IEC:2006
EXPLOSIVE ATMOSPHERES –
Part 11: Equipment protection by intrinsic safety "i"

1 Scope
This part of IEC 60079 specifies the construction and testing of intrinsically safe apparatus
intended for use in an explosive gas atmosphere and for associated apparatus, which is
intended for connection to intrinsically safe circuits which enter such atmospheres.
This type of protection is applicable to electrical apparatus in which the electrical circuits
themselves are incapable of causing an explosion in the surrounding explosive atmospheres.
This standard is also applicable to electrical apparatus or parts of electrical apparatus located
outside the explosive gas atmosphere or protected by another type of protection listed in
IEC 60079-0, where the intrinsic safety of the electrical circuits in the explosive gas
atmosphere may depend upon the design and construction of such electrical apparatus or parts
of such electrical apparatus. The electrical circuits exposed to the explosive gas atmosphere
are evaluated for use in such an atmosphere by applying this standard.
The requirements for intrinsically safe systems are provided in IEC 60079-25. The
requirements for intrinsically safe concepts for fieldbus are provided in IEC 60079-27.
This standard supplements and modifies the general requirements of IEC 60079-0, except as
indicated in Table 1. Where a requirement of this standard conflicts with a requirement of
IEC 60079-0, the requirements of this standard shall take precedence.
If associated apparatus is placed in the explosive gas atmosphere, it must be protected by an
appropriate type of protection listed in IEC 60079-0, and then the requirements of that method
of protection together with the relevant parts of IEC 60079-0 also apply to the associated
apparatus.
Table 1 – Exclusion of specific clauses of IEC 60079-0
Intrinsically Associated
safe apparatus
Clause or subclause of IEC 60079-0
apparatus
4.2.2 Group II – Surface temperature marking Applies Excluded
5.3 Maximum surface temperature Applies Excluded
5.4 Surface temperature and ignition temperature Applies Excluded
5.5 Small components Applies Excluded
6.3 Opening times Excluded Excluded
7.1.1 Applicability Applies Excluded
7.1.2 Specification of materials Applies Excluded
7.1.3* Plastic materials Excluded Excluded
7.2* Thermal endurance Excluded Excluded
7.3 Electrostatic charges on external non-metallic materials of Applies Excluded
enclosures
7.3.2 Avoidance of a build-up electrostatic charge Applies Excluded
7.4 Threaded holes Excluded Excluded

60079-11 © IEC:200660079-11  IEC:2006 – – 9 –17 –
Table 1 (continued)
Intrinsically Associated
safe apparatus
Clause or subclause of IEC 60079-0
apparatus
8.1 Material composition Applies Excluded
8.2 Threaded holes Excluded Excluded
9 Fasteners Excluded Excluded
10 Interlocking devices Excluded Excluded
11 Bushings Excluded Excluded
12 Materials used for cementing Excluded Excluded
14 Connection facilities and terminal compartments Excluded Excluded
15 Connection facilities for earthing or bonding conductors Excluded Excluded
16.5 Conductor temperature Excluded Excluded
17 Supplementary requirements for rotating electrical machines Excluded Excluded
18 Supplementary requirements for switchgear Excluded Excluded
19 Supplementary requirements for fuses Excluded Excluded
20 Supplementary requirements for plugs and sockets Excluded Excluded
21 Supplementary requirements for luminaires Excluded Excluded
22 Supplementary requirements for caplights and handlights Excluded Excluded
23.1 Batteries Applies Excluded
26.4 Tests of enclosures Applies Excluded
26.5.1 Temperature measurement Applies Excluded
26.5.2 Thermal shock test Excluded Excluded
26.5.3 Small component ignition test Applies Excluded
26.6 Torque test for bushings Excluded Excluded
26.7* Non-metallic enclosures or non-metallic parts of enclosures Excluded Excluded
26.8* Thermal endurance to heat Excluded Excluded
26.9* Thermal endurance to cold Excluded Excluded
26.10* Resistance to light Excluded Excluded
26.11* Resistance to chemical agents for Group I electrical apparatus Excluded Excluded
26.12 Earth continuity Excluded Excluded
26.13 Surface resistance test of parts of enclosures or non-metallic Applies Excluded
materials
26.14 Charging tests Applies Excluded
26.15 Measurement of capacitance Applies Excluded
Annex A Ex cable glands Excluded Excluded
* indicates that these requirements apply for 6.1.2a) only.

60079-11  IEC:2006 – – 10 –19 – 60079-11 © IEC:2006
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 60079. For dated references, only the edition cited
applies. For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-0:2004, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-7, Explosive atmospheres – Part 7: Equipment protection by increased safety "e"
IEC 60079-25, Electrical apparatus for explosive gas atmospheres – Part 25: Intrinsically safe
systems
IEC 60079-27, Electrical apparatus for explosive gas atmospheres – Part 27: Fieldbus
intrinsically safe concept (FISCO) and Fieldbus non-incendive concept (FNICO)
IEC 60085, Electrical insulation – Thermal classification
IEC 60112, Method for the determination of the proof and the comparative tracking indices of
solid insulating materials
IEC 60127 (all parts), Miniature fuses
IEC 60317-3, Specifications for particular types of winding wires – Part 3: Polyester enamelled
round copper wire, class 155
IEC 60317-7, Specifications for particular types of winding wires – Part 7: Polyimide enamelled
round copper wire, class 220
IEC 60317-8, Specifications for particular types of winding wires – Part 8: Polyesterimide
enamelled round copper winding wire, class 180
IEC 60317-13, Specifications for particular types of winding wires – Part 13: Polyester or
polyesterimide overcoated with polyamide-imide enamelled round copper wire, class 200
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60664-1:2002, Insulation coordination for equipment within low-voltage systems – Part 1:
)
Principles, requirements and tests
Amendment 1 (2000)
Amendment 2 (2002)
___________
)
A consolidated edition 1.2 exists, that comprises IEC 60664-1 and its amendments 1 and 2.

60079-11 © IEC:200660079-11  IEC:2006 – – 11 –21 –
IEC 60664-3:2003, Insulation coordination for equipment within low-voltage systems – Part 3:
Use of coating, potting or moulding for protection against pollution
ANSI/UL 248-1, Low-Voltage Fuses – Part 1: General Requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions in IEC 60079-0, as well as the
following apply.
3.1 General
3.1.1
intrinsic safety “i”
type of protection based on the restriction of electrical energy within apparatus and of
interconnecting wiring exposed to the potentially explosive atmosphere to a level below that
which can cause ignition by either sparking or heating effects
3.1.2
associated apparatus
electrical apparatus which contains both energy-limited and non-energy-limited circuits and is
constructed so that the non energy-limited circuits cannot adversely affect the energy-limited
circuits
NOTE 1 Associated apparatus may be either:
a) electrical apparatus which has an alternative type of protection included in this standard for use in the
appropriate explosive gas atmosphere,
b) electrical apparatus not so protected and which therefore is not to be used within an explosive gas atmosphere,
for example, a recorder which is not of itself in an explosive gas atmosphere but is connected to a thermocouple
situated within an explosive gas atmosphere where only the recorder input circuit is energy limited.
[Definition 3.2 of IEC 60079-0]
NOTE 2 For the purposes of this standard associated apparatus is also electrical apparatus which contains both
intrinsically safe circuits and non-intrinsically safe circuits and is constructed so that the non-intrinsically safe
circuits cannot adversely affect the intrinsically safe circuits and includes
a) electrical apparatus which has another type of protection listed in IEC 60079-0 for use in the appropriate
explosive gas atmosphere, or
b) electrical apparatus not so protected and which, therefore, shall not be used within an explosive gas atmosphere,
for example a recorder which is not itself in an explosive gas atmosphere, but is connected to a thermocouple
situated within an explosive atmosphere where only the recorder input circuit is intrinsically safe, or
c) chargers or interfaces not used in the hazardous area, but which are connected to hazardous area equipment in
the safe area for charging, data downloading, etc.
[IEV 426-11-03, modified]
3.1.3
intrinsically safe apparatus
electrical apparatus in which all the circuits are intrinsically safe circuits
3.1.4
intrinsically safe circuit
circuit in which any spark or any thermal effect produced in the conditions specified in this
standard, which include normal operation and specified fault conditions, is not capable of
causing ignition of a given explosive gas atmosphere

60079-11  IEC:2006 – – 12 –23 – 60079-11 © IEC:2006
3.1.5
simple apparatus
electrical component or combination of components of simple construction with well-defined
electrical parameters which is compatible with the intrinsic safety of the circuit in which it is used
3.2
coating
insulating material such as varnish or dry film laid on the surface of the assembly
NOTE Coating and base material of a printed board form an insulating system that may have properties similar to
solid insulation.
[Definition 3.5 of IEC 60664-3]
3.3
conformal coating
electrical insulating material applied as a coating to loaded printed wire boards to produce a
thin layer conforming to the surface in order to provide a protective barrier against deleterious
effects from environmental conditions
[Definition 2.1 of IEC 61086-1]
3.4
control drawing
drawing or other document that is prepared by the manufacturer for the intrinsically safe or
associated apparatus, detailing the electrical parameters to allow for interconnections to other
circuits or apparatus
3.5
diode safety barrier
assemblies incorporating shunt diodes or diode chains (including Zener diodes) protected by
fuses or resistors or a combination of these, manufactured as an individual apparatus rather
than as part of a larger apparatus
3.6
entity concept
method used to determine acceptable combinations of intrinsically safe apparatus and
associated apparatus through the use of intrinsically safe parameters assigned to connection
facilities
3.7
faults
3.7.1
countable fault
fault which occurs in parts of electrical apparatus conforming to the constructional require-
ments of IEC 60079-11 (this standard)
3.7.2
fault
any defect of any component, separation, insulation or connection between components, not
defined as infallible by IEC 60079-11, upon which the intrinsic safety of a circuit depends
3.7.3
non-countable fault
fault which occurs in parts of electrical apparatus not conforming to the constructional
requirements of IEC 60079-11
60079-11 © IEC:200660079-11  IEC:2006 – – 13 –25 –
3.8
normal operation
operation of apparatus 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, e.g. operation of a
motor on a duty cycle
NOTE 2 Variation of the supply voltage within stated limits and any other operational tolerance is part of normal
operation
[Definition 3.19 of IEC 60079-0]
NOTE 3 This includes opening, shorting and earthing of the external interconnecting cable.
3.9
free space
intentionally created space surrounding components or space inside components
3.10
fuse rating
I
n
current rating of a fuse as specified in IEC 60127, ANSI/UL 248-1 or in the manufacturer's
specification
3.11
infallibility
3.11.1
infallible component or infallible assembly of components
component or assembly of components that is considered as not subject to certain fault modes
as specified in IEC 60079-11
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.
3.11.2
infallible connection
connections, including joints and interconnecting wiring and printed circuit board tracks, that
are not considered according to IEC 60079-11 as becoming open-circuited in service or
storage
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.
3.11.3
infallible separation or insulation
separation or insulation between electrically conductive parts that is considered as not
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