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Siemens AG
Entry type: FAQ, Entry ID: 21656724, Entry date: 05/08/2014
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Fuses and miniature circuit breakers for the short-circuit protection of auxiliary contacts

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QUESTION:

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?

 

 

ANSWER:

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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