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Ex Assemblies

Author : RON SINCLAIR MBE, CHAIR, CENELEC TC31 COMMITTEE

23 August 2018

For ATEX, we have had guidance on how to handle documentation for assemblies for many years.  The latest incarnation of that guidance can be found in the “ATEX 2014/34/EU” Guidelines document at section 44.  This confirms that assemblies “placed on the market as a combined unit” are to be treated as if each assembly is a new equipment.  

It allows certain relaxation on Conformity Assessment Procedures, based on the documentation that is available for the constituent parts of the assembly, but does require that an overall risk assessment is completed and documented.

IECEx also created an internal procedure for dealing with assemblies at the International level.  DS 2015/001A is available to download from http://www.iecex.com/publications/extag-decision-sheets/. 

This document concentrates on the use of IEC 60079-14 for the interconnection of electrical units forming part of the overall assembly, but did, for the first time, acknowledge, internationally, the commercial need to provide single documentation covering an assembly.  Because the scope of this document was limited, the subject was immediately referred to the standards committee IEC TC31 who took it on board to produce a more comprehensive document with a wider scope.

IEC TS 60079-46 was published a year ago in August 2017.  (A TS is subject to review within three years to determine if it should be cancelled, amended, or immediately transformed to a full international standard.)  Although a TS rather than a standard, IECEx adopted it immediately for certification purposes.

The definition of an assembly in the TS is:
“pre-manufactured combination of Ex Equipment, together with other parts as necessary, that are electrically or mechanically interconnected that are pre-assembled prior to being placed into service at the end-user site, and that can be disassembled and then re-assembled at the end-user site”

You will notice that emphasis is placed on the use of “Ex Equipment”, which would already have its own certification, but also allows for “other parts” that might receive assessment only as part of the assembly.  This aligns with the similar requirements in the ATEX Guidelines. 

The TS also puts emphasis on a risk assessment process for the assembly, and IECEx has relied on certification bodies having experience with the non-electrical equipment standard ISO 80079-36 to justify their capability to work with IEC TS 60079-46.

The process of risk assessment is the same for both standards, just with different risks to be taken into consideration.  Part 46 does not provide a set of tables for the risk assessment, but it would make sense to use the tables in Part 36 as the format.  This method clearly guides the assembler and the certifier down a route that will unambiguously define the capability of the assembly in terms of Equipment Protection Level, Equipment Group and Temperature Class.

It was agreed that it would not be helpful to try and squeeze all the detailed information related to the constituent parts on to a common assembly label.  The detail can remain in the certificate and the instructions.

Assemblies for ATEX are marked with the basic ATEX legal code comprising the hexagon symbol, the Notified Body number related to QA activities (if there is one), the ATEX Group (I or II) and the Category, plus the summary information from the risk assessment.

IEC TS 60079-46 does not, of course, require the ATEX Marking, but does use the standard number in place of the protection concepts in the marking string.

Thus a simple assembly comprising a certified pump, a certified motor and a non-certified coupling might have constituent parts labelled:
Motor Ex db IIB T4 Gb
Pump Ex hb IIA T5 Gb
Coupling Ex hc IIC T6 Gc (assessed as part of the assembly)

The overall coding would then be:
Ex 60079-46 IIA T4 Gc

The use of a standard number as part of the code may seem odd if you have not met it before, but it is the way that Miners’ Caplights and Trace Heating components are marked, as they are not allocated a concept letter either.

About the author

SGS Baseefa Technical Manager Ron Sinclair MBE is chairman of BSI Committee EXL/31, responsible for the UK input to both European and International standards for Electrical Equipment for use in potentially explosive atmospheres. He is also chairman of Cenelec TC31, represents electrical standardisation interests on the European Commission’s ATEX Standing Committee and chairs the IECEx Service Facility Certification Committee.


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