Abstract: The limiting circuit breaker comprises a Thomson effect propelling device for opening of the contacts.The main contact bridge is securedly united to an operating rod surrounded by an annular opening coil of the propelling device. The latter comprises an opening disk which is movable in relation to the rod and an annular piston securedly united to the rod, springs being disposed between the disk and the piston, so as to return the disk to the rest position facing the coil at the end of the opening travel.

Abstract: An instantaneous solid-state trip device has two threshold values providing an upper and a lower tripping threshold. A current increase rate detector determines, when a short-circuit occurs, the prospective peak current value and, if the peak value corresponding to the electrodynamic withstand of the circuit breaker is liable to be exceeded, causes a change of threshold to bring about tripping, as soon as the lower threshold is exceeded. This high-speed tripping favours short-circuit current limiting. When a short-circuit of a lesser importance occurs, the current variation is lower and the instantaneous trip release only trips when the upper threshold is exceeded. In most cases, this upper threshold is not reached and tripping selectivity can be easily achieved in the usual way. A break in the circuit connecting the sensor to the trip unit also causes the circuit breaker to trip.