GAMBICA Guide - Internal arc fault capability of assemblies

16 January 2017


Assemblies that are correctly operated, properly maintained, well designed and verified in accordance with the IEC 61439 series very rarely incur an internal arcing fault in service. However, as fault levels increase, the potential consequences when such a fault occurs become more severe. This, together with the ongoing pursuit for ever greater safety, is bringing internal arcing faults within assemblies to the fore.

In the belief that their personnel will be ‘safe’, increasingly, users of low-voltage assemblies are calling for them to comply with IEC/TR 61641; Enclosed low-voltage switchgear and Controlgear assemblies — Guide for testing under conditions of arcing due to internal fault. Since the document is a TR (Technical Report) it cannot be ‘complied with’ in the way that a full Standard can.

Whilst in some circumstances specifying that equipment has to ‘comply’ with IEC/TR 61641 will lead to greater operator safety and reduced down time in the event of an arcing fault within an assembly, it is not a ‘cure for all ails’. Before specifying ‘compliance’ with this requirement an objective assessment should be carried out considering the whole application to determine if ‘compliance’ with IEC/TR 61641 brings worthwhile benefits. The factors to be considered are varied and at times very subjective. They include: what enhanced safety does ‘compliance’ with IEC/TR 61641 offer for the application being considered; when is an internal arcing fault most likely to occur, and; are there better options for increasing operator safety and process security.

Making the right choice in respect of an assembly ‘complying’ with IEC/TR 61641 is complex. It requires a good understanding of the intended application for the assembly, knowledge of the design and use of assemblies and a detailed understanding of IEC/TR 61641. In addition, a skill in assessing risks is necessary. Gambica has prepared this guide to assist users of low-voltage assemblies in making the right choice in respect of an internal arc fault capability for their application