IEC 60079-11:2011/ISH3:2016
(Main)Intrepretation sheet 3 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
Intrepretation sheet 3 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
Feuille d'intreprétation 3 - Atmosphères explosives - Partie 11: Protection de l'équipement par sécurité intrinsèque "i"
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Standards Content (Sample)
IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60079-11
Edition 6.0 2011-06
EXPLOSIVE ATMOSPHERES –
Part 11: Equipment protection by intrinsic safety "i"
INTERPRETATION SHEET 3
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:
ISH Report on voting
31G/253/ISH 31G/255/RVD
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.
___________
Question
Regarding IEC 60079-11:2011 Edition 6.0 (2011-06), some clauses specifically indicate
whether or not the requirement is applicable or not applicable to level of protection “ic”.
However, many other clauses include no indication one way or the other, resulting in potential
inconsistencies when applied. In the interest of improving consistency, what are the
requirements in IEC 60079-11:2011 Edition 6.0 (2011-06) that are applicable to level of
protection “ic”?
Answer
In answering this question, the following considerations were taken:
1) Requirements in IEC 60079-11 Edition 6.0 (2011-06) indicating that the requirements are
applicable to level of protection “ic” are considered “Applicable”;
2) Requirements in IEC 60079-11 Edition 6.0 (2011-06) indicating that the requirements are
not applicable to level of protection “ic” are considered “Not applicable”;
3) Regarding requirements in IEC 60079-11 Edition 6.0 (2011-06) other than those
referenced in 1) and 2) above:
• determine if the intent of these requirements for levels of protection "ia" and "ib" is to
address fault (abnormal) conditions; and
ICS 29.260.20
IEC 60079-11:2011-06/ISH3:2016-07(en-fr)
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• if the intent is to address fault (abnormal) conditions, then the requirements are
considered not applicable for level of protection "ic".
Based on the above considerations, the following informative table (similar in concept to
Annex B of IEC 60079-0:2011 on Ex Components) provides guidance regarding which
requirements in IEC 60079-11 Edition 6.0 (2011-06) are applicable to level of protection “ic”.
Additional background
As additional background details, the following seven key issues of principle were taken into
account when developing the above answer:
1) Objective of the original transfer of type of protection “nL” to “ic”: The objective of the
original transfer of type of protection “nL” to “ic” (as first included in IEC 60079-11 Fifth
Edition) was not to substantially revise the applicable requirements, except where
the maintenance team MT 60079-11 made specific reference to level of protection “ic” in a
given clause. Examples of this include 7.1, which simplifies the rating requirements for
level of protection “ic” protective components from “nL” requirements; and 6.2.1, which
increases the separation distances for level of protection “ic” terminals (to align with
IEC 60079-14) from “nL” requirements. This objective approach is consistent with how the
transfer of other IEC 60079-15 types of protection have been handled, and are still being
handled in other IEC 60079 series standards.
2) Common applications of a level of protection “ic” circuit that protects an arcing part: The
following are common applications of a level of protection “ic” circuit that protects an
arcing part:
• The circuit does not exit the device.
• The circuit exits one device and is interconnected via a wiring method to another
device, with both devices and the interconnecting wiring method being part of a
system.
• The circuit exits a device via a receptacle, with entity parameters provided for field
connection to the receptacle.
• The circuit exits a device via a terminal block, with entity parameters provided for field
connection to the terminal block.
For all the above applications, the level of protection "ic" circuit does not begin until
after the last protective component that establishes the necessary voltage and current
limitation. For other circuitry in the device, another type of protection, such as “nA” or
“ec”, is applied. It is also possible for an entire apparatus to be only ”Ex ic”.
3) Remarks in the draft I-SH: In the draft I-SH, the intent is for all Remarks to only be for
issues specific to level of protection “ic”. The few exceptions to this are for Remarks
highlighting requirements that, while applicable to all types of protection “i”, represent a
significant change in requirements from type of protection “nL” to “ic”.
4) Transient effects on level of protection “ic” circuits: For level of protection “ic” circuits, the
effects of transients are only addressed for diode safety barriers. This is because
connection of such barriers is to unspecified equipment. For other level of protection “ic”
circuit applications, no additional evaluation is required regarding the effects of transients
based on the following considerations:
• the presence of an explosive atmosphere is only under abnormal conditions; and
• the circuit complies with the applicable safety requirements of the relevant industrial
standards.
5) Separation distances for level of protection “ic” circuits: Separation distances are only
applicable to the level of protection “ic” circuit and to the protective components that
establish the level of protection “ic” circuit. Where separation distances are required,
separations that do not comply with the values of Table 5 or Annex F are to be shorted as
part of the evaluation, if the shorting may impair intrinsic safety.
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6) Protective components for level of protection “ic” circuits: Voltage and current limiting
protective components comply with the applicable requirements for components on which
intrinsic safety depends (e.g. 7.1).
7) IEC/TC 31 MT 60079-15 support: The MT 60079-15 convener has been involved in the
development of the content of this I-SH, and supports it based on the current
IEC 60079-11 Edition 6.0 (2011-06) text.
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The following informative table provides guidance regarding which requirements in
IEC 60079-11 Edition 6.0 (2011-06) are applicable to level of protection “ic”.
Informative guide for level of protection “ic” evaluations
NOTE 1 In some cases, where a clause is indicated as “Applicable” to level of protection “ic”, it is applicable in
its entirety. In other cases, the clause is only applicable in part. Remarks are provided to indicate which parts of a
given clause are applicable to level of protection “ic”, along with indicating general explanatory content regarding
the application of the clause to level of protection “ic”.
NOTE 2 Where a clause is indicated as being not applicable, in its entirety or in part, consideration is still given
regarding the applicability of other IEC 60079-11 and IEC 60079-0 clauses, including the applicable safety
requirements of the relevant industrial standards in accordance with IEC 60079-0.
Clause Requirement Applicability Remark
1 Scope Applicable
2 Normative references Applicable
3 Terms and definitions Applicable For “ic” circuits, Ui, Ii, Pi are maximum
values possible in normal operation. Uo, Io,
Po are determined in normal operation, but
with the most onerous rated load for each
case attached. Reduction of maximum
voltage from Um can be achieved with a
transformer that complies with the
applicable requirements of this standard.
The same equipment designed for “ic”, and
also designed for “ia” or “ib”, can have
different parameters for connection to “ic”
circuits versus connection to “ia” or “ib”
circuits. Even though these are all the
same “type of protection”, just with varying
EPLs, the requirements under “Multiple
types of protection” in IEC 60079-0 applies.
4 Grouping and Applicable While “nL” was only a Gc type of
classification of protection, “ic” is for both Gc and Dc.
intrinsically safe
apparatus and associated
apparatus
5 Levels of protection and ignition compliance requirements of electrical apparatus
5.1 General Applicable Opening, shorting and earthing of an “ic”
circuit at output terminals intended for field
wiring are considered normal operating
conditions.
5.2 Level of protection "ia" Not applicable Addresses safety factors and fault
conditions for "ia".
5.3 Level of protection "ib" Not applicable Addresses safety factors and fault
conditions for "ib".
5.4 Level of protection "ic" Applicable A safety factor of 1.0 with no fault condition
is applicable for "ic".
5.5 Spark ignition Applicable
compliance
5.6 Thermal ignition compliance
5.6.1 General Applicable Temperature testing is to be under worst
case normal operating conditions.
5.6.2 Temperature for small Applicable
components for Group I
and Group II
5.6.3 Wiring within intrinsically Applicable Requirement is addressed by testing
safe apparatus for Group according to 5.6.1, or addressed according
I and Group II to the applicable safety requirements of the
relevant industrial standards.
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Clause Requirement Applicability Remark
5.6.4 Tracks on printed circuit Applicable Requirement is addressed by testing
boards for Group I and according to 5.6.1, or addressed according
Group II to the applicable safety requirements of the
relevant industrial standards.
5.6.5 Intrinsically safe Applicable Temperature classification to be based on
apparatus and component the temperature of the surface exposed to
temperature for Group III dust.
5.7 Simple apparatus Applicable
6 Apparatus construction
6.1 Enclosures Applicable
6.2 Facilities for connection of external circuits
6.2.1 Terminals Applicable NOTE As with “ia” and “ib”, due to
IEC 60079-14 installation requirements,
circuits that exit a piece of equipment via a
terminal block, with entity parameters
provided for field connection to the terminal
block, maintain the following:
‒ at least 50 mm separation distance
between terminals for “ic” circuits and
terminals for non-intrinsically safe
circuits.
‒ at least 6 mm separation distance
between terminals for separate
intrinsically safe circuits.
‒ at least 3 mm separation distance
between terminals for intrinsically safe
circuits and earthed parts, if connection
to earth has not been considered in the
safety analysis.
This separation distance requirement is
different from previous Ex “nL”
requirements.
6.2.2 Plugs and sockets Applicable
6.2.3 Determination of Applicable
maximum external
inductance to resistance
ratio (L /R ) for
o o
resistance limited power
source
6.2.4 Permanently connected Applicable
cable
6.2.5 Requirements for Applicable Applicable except regarding protective
connections and circuitry for functions such as charging in
accessories for IS the non-hazardous area.
apparatus when located in
As there is no application of faults, the
the non-hazardous area
ratings of components may be ensured
without additional protection.
6.3 Separation distances
6.3.1 General Applicable Applicable to “ic” circuit and protective
components only. Where separation
distances are less than required, they are
to be shorted if the shorting may impair
intrinsic safety.
NOTE For example, an "ic" circuit is the
circuit after the last protective component
that establishes the necessary voltage and
current limitation.
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Clause Requirement Applicability Remark
6.3.2 Separation of conductive Applicable Applicable to "ic" circuit and protective
parts components only.
Any use of an interposing insulating
partition or earthed metallic partition is only
required to comply with the safety
requirements of the relevant industrial
standard.
6.3.2.1 Distances according to Applicable Regarding transformers, only applicable
Table 5 between external connections. Remaining
construction features of transformers are
only required to comply with the applicable
safety requirements of the relevant
industrial standards.
6.3.2.2 Distances according to Applicable Regarding transformers, only applicable
Annex F between external connections.
NOTE Remaining construction features of
transformers are only required to comply
with the applicable safety requirements of
the relevant industrial standard. Through
solid insulation of conductors are required
to comply with Table 5.
6.3.3 Voltage between Applicable For “ic”, the effects of transients are only
conductive parts addressed for diode safety barriers
because connection is to unspecified
equipment. For other “ic” applications, no
additional evaluation is required regarding
the effects of transients based on the
following considerations:
• The presence of an explosive
atmosphere is not likely to occur in
normal operation.
• The circuit complies with the applicable
safety requirements of the relevant
industrial standards.
Where separation of conductive parts is
required, separations that do not comply
with the values of Table 5 or Annex F may
be shorted as part of the evaluation if it
may impair intrinsic safety.
6.3.4 Clearance Not Applicable Any use of an interposing insulating
partition or earthed metallic partition is only
required to comply with the safety
requirements of the relevant industrial
standard. See 6.3.2.
6.3.5 Separation distances Applicable
through casting
compound
6.3.6 Separation distances Applicable
through solid insulation
6.3.7 Composite separations Applicable Applicable, except regarding the 1/3
restriction for composite separations, as
this restriction is based on fault
considerations.
6.3.8 Creepage distance Applicable Applicable, except regarding the 1/3
restriction for composite separations, and
the partition restrictions above 1,575 V.
Any use of an interposing insulating
partition or earthed metallic partition shall
comply with the safety requirements of the
relevant industrial standard. See 6.3.2.
6.3.9 Distance under coating Applicable
IEC 2016
Clause Requirement Applicability Remark
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