A protective device breaks an electrical circuit when a stated electric current that passes through it is exceeded. A protective device may include both the tripping unit and the breaking unit or it may simply represent the breaking unit if the tripping unit is specified individually as a protective device tripping unit.
A circuit breaker is a mechanical switching protective device capable of making, carrying, and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking, current under specified abnormal circuit conditions such as those of short circuit.