Essential changes in the product standard for low voltage MCC and switchgear

Since the main objective of a product standard is to ensure the safety of the equipment during its operational life, new editions of such a standard are expected to advance the general safety. This is done by adding requirements where the former standard ran short and by narrowing down the ways to interpret the text in order to make the specified properties of assemblies from different manufacturers comparable. The restructuring of the former document, IEC60439-1, started in 1999. While the interpretation of TTA was stretched by manufactures in a way that is hard to recognise for the user, the committee decided to abandon the terms TTA and PTTA. In general, type testing is replaced by design verification. Particularly for temperature rise testing it implemented exact ways for temperature rise verification three new methods are developed: testing with current; derivation (from a tested design) of ratings for similar variants; calculation. This paper gives a qualitative overview of the improvements of the new IEC 61439-1 and -2 that has been published beginning this year, compared to the former standard. The new 61439 series is intended to be extended with a specifiers guide to enable the user to make a comprehensive specification of the switchgear he requires. To cover also internal arcing the in 2008 published technical report for testing under conditions of internal arcing, document IEC/TR 61641, is als incorporated in this paper.