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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 6
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/311/DISH 31G/314/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.
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Background
The second and third paragraphs of IEC 60079-11:2011, Subclause 10.5.3 b) state the
following:
The maximum surface temperature shall be determined as follows:
For “ia” and “ib” all current-limiting devices external to the cell or battery shall be short-
circuited for the test. 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. If the internal current limiting devices protect against
internal shorts then these devices need not be removed. However, such devices shall only be
considered for Level of Protection “ib”.
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.
29.260.20
IEC 60079-11:2011-06/ISH6:2019-12(en-fr)
– 2 – IEC 60079-11:2011/ISH6:2019
IEC 2019
It was found that two details have been misinterpreted in these paragraphs:
a) The subjects of the paragraphs 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.
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
60079-11:2011, 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-
11:2011, 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”.
IEC 2019
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
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IEC 60079-11
Edition 6.0 2011-06
ATMOSPHÈRES EXPLOSIVES –
Partie 11: Protection de l'équipement par sécurité intrinsèque "i"
FEUILLE D'INTERPR É TA TI O N 6
Cette feuille d’interprétation a été établie par le sous-comité 31G: Matériels à sécurité
intrinsèque, du comit
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