The MCB (Miniature Circuit Breaker, small circuit breaker) mainly consists of a contact system, operating mechanism, bimetallic strip, electromagnetic trip unit, arc extinguishing chamber, terminal block and insulating housing, etc. When operating normally, the current passes through the internal contacts of the MCB, and the circuit remains conductive. When the circuit is overloaded and the current exceeds the rated value for a long time, the bimetallic strip bends due to continuous heating, pushing the tripping mechanism to act and causing the contacts to separate, thereby cutting off the circuit. When a short circuit occurs in the circuit, a large fault current is generated instantaneously. The electromagnetic trip unit quickly generates magnetic force and pushes the trip mechanism, causing the contacts to disconnect rapidly. When the contacts separate, an arc is generated. The arc extinguishing chamber divides, cools and extinguishes the arc through structures such as metal grating plates, reducing the impact of the arc on the equipment. After the fault is eliminated, the MCB can be re-closed through the handle for reuse. MCB is mainly used in residential, commercial buildings and small industrial power distribution systems, providing overload and short-circuit protection for lines and electrical equipment.