The Role of IECEx ExTAG Decision Sheets
10 May 2018
In my previous article (Hazardex March 2018) I highlighted the role of European Notified Bodies in providing common interpretations of procedures relating to ATEX certification by issuing “Clarification Sheets”. I also alluded to the IECEx having a similar system of issuing “Decision Sheets”.
Ron Sinclair MBE
The Decision Sheet (DS) can relate to the certification process, or it can relate to a common clarification of a requirement in a standard. It cannot introduce new requirements or remove existing requirements covered by standards. That is a matter for the Maintenance Team (MT) for the particular standard, which works under the authority of IEC standards committee TC 31 and its sub-committees.
Draft DSs can be prepared by any member certification body (ExCB) or testing laboratory (ExTL) within the IECEx System, or can be proposed by the standards MT or the IECEx Secretariat. All draft DSs are subject to comment and vote by the members of IECEx ExTAG and, where deemed appropriate relating to the content, by the overall Management Committee of IECEx. There is also consultation with the relevant MT, if the DS relates to clarification of a requirement in the standard.
If the MT believes that the DS is of sufficient import, the MT can also issue an official clarification in the standard itself, a document known as an I-Sh, or Interpretation Sheet. After such a publication, IECEx may decide to delete the DS. I-Sh documents are automatically supplied with all future purchases of the standard. For those already owning the standard, the availability of I-Sh documents can be checked on the IEC standards web site.
The format of a DS usually follows the pattern of an introduction section, providing some background as to why the DS has been created, followed by a discrete Question and a related Answer.
DS 2017/01 was published in June last year, following a proposal from the convenor of one of the MTs, and the background information explains that there is not as much clarity as required relating to whether or not cable transit devices should be tested exactly like cable glands. Certainly the standards can be read that way, but some transit devices have appeared on the market that would obviously fail such requirements. After significant background detail we read:
QUESTION: Do all cable transit devices or entry devices need to fulfil the requirements for cable glands according IEC 60079-0 Clause 16 and Annex A and any other additional requirements in the applicable Type of Protection standards?
ANSWER: Yes, the requirements for cable glands have to be applied to all cable transit devices or entry devices, where the cable(s) are designated to connect different Ex Equipment enclosures or to lead into an Ex Equipment enclosure.
All certificates issued by ExCBs for cable transit devices will now follow this requirement. Meanwhile, the relevant MTs are looking at clarifying the texts in their next editions.
My colleagues at SGS Baseefa proposed the draft for DS 2017/004 which was published in November last year. We had become concerned that some certificates appeared to allow combinations of terminals in increased safety junction boxes that would exceed the marked temperature class. This was because the necessary de-rating information for the individual terminals was not shown in the certificate.
As soon as more than between ten and fifteen terminals are included in a single enclosure, it is necessary to apply a de-rating to the individual terminals in order to control temperatures. This relates not only to the heat produced by the current passing through the terminals, but also the heat produced by the current in the enclosed wiring. In large boxes with many terminals, the rating of the individual terminals may need to be reduced to less than 30% of the current rating marked on the terminal. This is not usually a problem, as such junction boxes are normally used for marshalling instrumentation wiring carrying less than 1 A, but the certificate can sometimes not make the de-rating clear.
A lot more background information is provided, but the meat of the DS is:
QUESTION: In arrangements where there is a necessity to de-rate terminals (typically when an enclosure contains more than 10 to 15 terminals) is it necessary to indicate this de-rating in the information provided as part of the certificate?
ANSWER: Yes. IEC 60079-0 contains the requirement in 6.1 b) that the equipment should comply with the normal industrial standards for the application, in addition to the specific Ex requirements of the IEC 60079 series. Such industrial standards would be presumed to include a requirement that the rating of the equipment is marked.
For the full background information to these decisions, and to see all other published DSs, please go to www.iecex.com and follow the links to Publications, then ExTAG Decision Sheets. All are free to download.
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