IEC switchgear & controlgear - internal arc withstand a designer´s and user´s view

The testing of both high-voltage (HV) switchgear and controlgear and low-voltage (LV) assemblies under conditions of arcing due to an internal fault has been included in IEC documents for many years. The publication in 2003 of IEC 62271-200 “AC metal-enclosed switchgear and controlgear for rated voltages above 1000V and up to and including 52kV” introduced the designation of Internal Arc Classified (IAC) equipment and specifies a type test for conditions of internal arcing. This type test has greatly facilitated the use of HV IAC classified switchgear and controlgear thus providing safer working conditions. IEC 62271-200 makes no distinction between HV equipment used primarily for the distribution of electrical energy (switchgear) and the supply of power to loads (controlgear). For this reason the expression “HV switchgear and controlgear” is used throughout IEC standards and also in this paper. For LV the term “assemblies” is used and includes all switchgear and controlgear circuits.IEC/TR 61641 "Enclosed low-voltage switchgear and controlgear assemblies guide for testing under conditions of arcing due to internal fault" Edition 2.0 was published in 2008 and introduced the designation of arc-proof assemblies. This Technical Report provides guidance for testing LV assemblies. Although the document is still a Technical Report and not an international standard, it contributes to enhancing safety. The specifying of IAC classified switchgear and controlgear and arc-proof LV assemblies must be considered as just one of the steps in providing safe working conditions in electrical installations. Many other issues must be considered as well. IEC has published ISO/IEC Guide 51 which deals with risk analysis. This document provides very useful guidelines to help engineers define the solution which best meets the requirements. As with any feature associated with any type of equipment or installation, it is essential to know the c- - onditions under which the feature is considered to be implemented, and when it is not. Probably the most dangerous situations occur when people think that there is no risk associated with a particular activity. Reduction of risk requires a good understanding of what that risk is.