Trip-free

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Under free release is meant a mechanism that the influenceable from the outside 'free' or unblockierbare triggering ensures a fuse.

This means that the fuse can also be triggered when the switch lever or trigger is fixed in the ON position - e.g. B. by holding, gluing or wedging. The security function cannot be restricted by these measures.

General

According to DIN VDE 0660, a switch lock for electrical fuses (which have a mechanism for switching off) is required, which is provided with a trip-free mechanism. Typical examples are motor protection switches , line circuit breakers , residual current circuit breakers and the like.

The fuse is 'free' in its 'release' - hence the term.

Commonly found wrong explanation

In several sources, trip-free is described as "... restarting is prevented as long as the cause of the shutdown still exists ...". However, this is clearly wrong. To do this, the fuse would have to determine whether the fault is still present without putting the circuit under voltage / current. When switching on, the circuit is first closed; If the error persists, it will be recognized again and the fuse trips again, even if the switch is still held in the ON position. If the bimetal of a fuse has not cooled down enough after the last fault so that it is still in the trigger area, it will also switch the fuse off immediately, regardless of whether the fault is still present or has been rectified.

literature

  • Wilfried Knies, Klaus Schierack: Electrical systems engineering. 5th edition, Carl Hanser Verlag, Munich and Vienna, 2006, ISBN 3-446-40574-7 (!! incorrect explanation !!)
  • Div. Authors: Electrical engineering. various editions, Verlag Europa-Lehrmittel, ISBN 978-3-8085-3435-9 (!! incorrect explanation !!)