Abstract: A low voltage circuit breaker has an insulating housing which is split along a parting line into an upper part and a lower part. Disposed in the housing is an electromagnetic tripping device which comprises a fixed magnet yoke and a movably disposed armature. By means of trunnion (pivot) pins of rectangular cross-section the armature is mounted in bearing openings designed in the form of pocket-like cutouts in the wall surfaces of the lower part which limit the pole channels of the circuit breaker. The bearing surface of the bearing openings associated with a narrow surface of each trunnion pin may be composed of two subsurfaces disposed at an angle to each other so that an edge-like bearing results. For the attachment of the magnet yoke there is provided on the lower part of the housing an island-like projection which is spaced from the wall surfaces and against which the central part of the magnet yoke is caused to rest by a spring element.