IEC 60079-11:2011/ISH4:2019
(Main)Interpretation Sheet 4 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
Interpretation Sheet 4 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
Feuille d'interprétation 4 - Atmosphères explosives - Partie 11: Protection de l'équipement par sécurité intrinsèque "i"
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IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
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IEC 60079-11
Edition 6.0 2011-06
EXPLOSIVE ATMOSPHERES –
Part 11: Equipment protection by intrinsic safety "i"
INTERPRETATION SHEET 4
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/293/DISH 31G/296/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.
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The wording in the intrinsic safety standard, IEC 60079-11 (2011), with respect to the
enclosure requirements for intrinsically safe apparatus for Group III where the separation is
accomplished by meeting the requirements for clearance or creepage distances of Table 5 or
Annex F, according to Subclause 6.1.3a), is ambiguous. This observation may lead to
different interpretation by different test laboratories.
This issue was discussed at the Busan, Republic of Korea meeting of the MT in October 2018.
The MT agreed at that meeting that this interpretation should also be applied to
IEC 60079-11:2011.
Because the title of Subclause 6.1.2.3 is “Apparatus complying with Annex F”, an
interpretation has been made that the additional tests required by 6.1.2.3a) only apply when
Annex F is used. The potential for compromising infallible creepage and clearance distances
exists when Annex F is applied, but also exist when Table 5 is applied.
IEC 60079-11:2011-06/ISH4:2019-04(en-fr)
– 2 – IEC 60079-11:2011/ISH4:2019
IEC 2019
The wording of IEC 60079-11 is:
6.1.3 Enclosures for Group III apparatus
Where the intrinsic safety of intrinsically safe apparatus can be impaired by ingress of dust or
by access to conducting parts, for example if the circuits contain infallible creepage distances,
an enclosure is necessary by one of the following:
a) Where separation is accomplished by meeting the requirements for clearance or creepage
distances of Table 5 or Annex F, the enclosure shall provide a degree of protection of at
least IP5X, according to IEC 60529. For such enclosures the [requirements of] 6.1.2.3 a)
shall additionally apply.
The text of the referenced clause is:
6.1.2.3 Apparatus complying with Annex F
Apparatus meeting the separation requirements of Tables F.1 or F.2 shall be provided with
protection to achieve pollution degree 2. This can be achieved by one of the following:
a) an enclosure meeting the requirements of IP54 or greater according to the intended use
and environmental conditions in accordance with IEC 60529. For such enclosures the
clauses of IEC 60079-0 identified in Table 1 additionally apply.
Question
For Groups IIIA, IIIB, and IIIC, where Annex F is not applied and the creepage or clearance
distances of Table 5, Column 2 or Column 5 are relied upon for intrinsic safety, do all the
applicable enclosure requirements of IEC 60079-0 listed in Table 1, including thermal
endurance and resistance to impact, apply?
Interpretation
Yes, for Groups IIIA, IIIB, IIIC, the “Tests of enclosures” requirements of IEC 60079-0 apply
for intrinsically safe apparatus for which the creepage and clearance distances are assessed
against either Table 5 or Annex F.
This does not apply where the separations are protected by means other than an enclosure,
such as encapsulation or conformal coating as described in 6.1.3b) of IEC 60079-11.
NOTE These tests are specified in the following subclauses of IEC 60079-0:2011; 6.2, 6.5, 7.1.1, 7.1.2.1, 7.1.2.2,
7.1.2.3, 7.2, 7.3, 12, 16, 26.4.1, 26.4.1.1, 26.4.1.2, 26.4.1.2.1, 26.4.1.2.2, 26.4.2, 26.4.3, 26.4.4, 26.5.2, 26.7,
26.8, 26.9, 26.10, 26.16, as well as Annex C and Annex F.
IEC 2019
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
IEC 60079-11
Edition 6.0 2011-06
ATMOSPHERES EXPLOSIVES –
Partie 11: Protection de l'équipement par sécurité intrinsèque "i"
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