In line circuit breakers with a combined overcurrent/short-circuit current tripping device, tripping should take place in a well defined manner in the case of an overcurrent and in the case of a short-circuit current. For this purpose, gaps (A, B) need to be set precisely. If the housing is made from a cost-effective housing material such as thermosetting plastic it is subject to shrinkage. As a result, the mentioned gaps may change. An armature (24) is mounted in such a way that it changes its rest rotary position in the event of shrinkage of the housing. A magnet yoke (28) as part of the overcurrent/short-circuit current tripping device is mounted and shaped in such a way that the rotation is compensated for precisely, so that the mentioned gaps do not change despite the shrinkage.