When short circuit occurs, the high current, usually 10 to 12 times, generates the magnetic field customer service spring, the release pulls the operation mechanism to move, and the switch trips instantaneously. When overload occurs, electrorheological (ER) increases and heat increases. Bimetal sheets deform to a certain extent to promote the action of the mechanism. The larger the current, the shorter the action time.

The main component of the leakage protector is a magnetic ring inductor. Fire wire and zero wire are wound several times on the magnetic ring by parallel winding method, and there is a secondary coil on the magnetic ring. When the same phase of the fire line and zero line in normal operation, the current generated by the magnetic flux just offset, in the secondary coil will not induce voltage.

If a line has leakage or no zero connection, the current passing through the fire line and the zero line in the magnetic ring will be unbalanced, and the flux passing through the magnetic ring will be generated. The voltage will be induced in the secondary coil, and the trip will be made by the electromagnet.

Low-voltage circuit breakers, also known as automatic air switches, can be used to turn on and break load circuits, or to control motors that do not start frequently. It is an important protective device in low-voltage distribution network. Its function is equivalent to the sum of some or all functions of switch, over-current relay, Voltage-loss relay, thermal relay and leakage protector.

Low-voltage circuit breaker has many protective functions (overload, short circuit, under-voltage protection, etc.), adjustable action value, high breaking capacity, easy operation, safety and other advantages, so it is widely used. The structure and working principle of low-voltage circuit breaker are composed of operating mechanism, contacts, protective devices (various trippers), arc extinguishing system, etc.