Abstract: A low voltage circuit breaker has an electromagnetic overcurrent tripping device consisting of a magnetic yoke, relative to the pole surfaces of which an armature is movably arranged. The spacing of the armature from the pole surfaces is established by a stop member carried on a stationary support. The stop member is in the form of a disc having pairs of pins on its opposite sides which are mounted on connecting lines which are perpendicular to each other. Which of the four stop surfaces of the stop member is set in place is decided by rotating the stop member by 180.degree. when it is facing one way or by reversing it, and rotating it 180.degree. in its new position to choose between the other surfaces. Both sides of the stop member carry markings for the tripping current level, the effective one being always readable in the upright position.