Low-voltage circuit breakers are mostly used for frequent switching and starting motors, to protect electrical appliances and motors. When they have serious overload and short circuit. When under-voltage and other faults occur, the circuit can be automatically cut off. Therefore, LV circuit breaker is an important protective device in low-voltage power grid.

Low-voltage household circuit breaker has many protective functions, such as overload, short circuit and under-voltage. LV circuit breaker has many advantages, such as adjustable action value, strong breaking ability, easy operation and safety, so it is widely used.

Low voltage household circuit breaker is composed of operating mechanism, contacts, protection device, arc extinguishing system, etc.

The contacts of LV circuit breakers are operated manually or electrically to complete opening or closing. When the main contact is closed, the free release mechanism locks the main contact in the position of closing. The coil of overcurrent release and the thermal element of thermal release are in series with the main circuit, and the coil and voltage of undervoltage release are in parallel.

When the circuit is short-circuited or seriously overloaded, the armature of the over-current tripper is sucked, which makes the free tripper move and drives the main contact to disconnect the power supply.

When serious overload occurs in the circuit, the heating element of the thermal release makes the bimetal sheet bend upward, pushing the free release to move, thus driving the main contact to cut off the power supply.

When the circuit is under-voltage, the undervoltage tripper releases the armature, which can also act as a free tripper and drive the main contact to cut off the circuit.

The calendar release is for remote use. In normal operation, its coil is powered off. When long-distance operation is needed, the calendar button can be pressed. The calendar release coil gets electricity, so the armature can be attracted to drive the free release action, thus driving the main contact to cut off the power supply.

Five Steps for Correct Selection of Low Voltage Circuit Breakers

(1) The rated current of the household circuit breaker is determined by the calculated current of the circuit.
(2) The short-circuit setting current of the circuit breaker should avoid the normal starting current of the circuit.
(3) Check the breaking capacity of low-voltage circuit breaker according to the maximum short-circuit current of the line.
(4) According to the minimum short-circuit current of the circuit, the sensitivity of the action of the circuit breaker should be checked, that is, the minimum short-circuit current of the circuit should be no less than 1.3 times of the short-circuit setting current of the circuit breaker.
(5) According to the short circuit impulse current (i.e. the maximum instantaneous value of the full short circuit current) on the line, the rated short circuit switching capacity of the circuit breaker (the expected peak value of the maximum current) should be checked, that is, the latter should be greater than the former.