A circuit breaker for multi-phase power includes an opening-closing apparatus configured to open and close each phase of the multiphase power, a detection unit configured to detect a fault current in at least one phase of an electrical installation being protected by the circuit breaker, a plurality of connecting bars disposed on a load side of the circuit breaker, and a short circuiter disposed on the connecting bars and configured to produce a short circuit between the connecting bars if a fault current is detected by the fault-current detection unit. When a fault current occurs, a tripping signal can be transmitted by the detection system to the short circuiter. The circuit breaker is also fully operational, even without a function-activated short circuiter.