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.
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.
Source: IEC 60079-11 Edition 6.0 2011-06 EXPLOSIVE ATMOSPHERES – Part 11: Equipment protection by intrinsic safety “i” INTERPRETATION SHEET 6
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