The circuit breaker at the normal condition, uses for close or open a circuit, When the urgent thing happed, under the relay protection installment control, can automatically breakdown the malfunction equipment or separation the circuit.

One kind which can release the thunder and lightning or concurrently can release the electrical power system switching surge energy, protects the electrician equipment to be exempt from the instantaneous overvoltage harm, can also interrupt the after flow, does not send causes the electrical fittings which the system earth short-circuits (to see chart).