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Entry type: FAQ Entry ID: 21656724, Entry date: 05/08/2014

Fuses and miniature circuit breakers for the short-circuit protection of auxiliary contacts

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What are the consequences if the short-circuit protection of auxiliary contacts is provided with fuses or miniature circuit breakers that are not rated according to their technical data?




All current ratings of fuses and miniature circuit breakers (MCBs) for the protection of auxiliary contacts as stated in our documentation / technical data is based on test conditions according to IEC 60947-5-1. In this standard a test current of not less than 1kA is specified for the short-circuit test of auxiliary contacts. Contact welding is not permitted during such tests.
A short-circuit current of 1kA would require a control transformer with a power of > 6,3kVA, which means the IEC test conditions do not reflect practical conditions. However there is no option available other than the obedience of fuse- or MCB-ratings as shown in our technical documentation. 


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