Low-voltage circuit breaker (once called automatic switch) is a type of switch that can not only switch on and off normal load current and overload current, but also switch on and off short circuit current. In addition to the control function in the circuit, the low-voltage circuit breaker also has certain protection functions, such as overload, short circuit, undervoltage and leakage protection. There are many types of low-voltage circuit breaker classification, according to the use of category, selective type (adjustable protection device parameters) and non-selective type (adjustable protection device parameters), according to the arc extinguishing medium, there are air type and vacuum type (domestic air type). Low voltage circuit breakers have a large capacity range, with a minimum storage of 4A and a maximum storage of 5000A. Low voltage circuit breaker is widely used in low voltage distribution system at all levels of feed line, all kinds of mechanical equipment power control and electrical terminal control and protection.