Maintenance Method of Molded Case Circuit Breaker

The main contacts of low-voltage circuit breakers are operated manually or electrically. After the main contact is closed, the free release mechanism locks the main contact at the closing position. The coil of the overcurrent release and the thermal element of the thermal release are in series with the main circuit, and the coil and the power supply of the 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 tripping mechanism act and the main contact disconnects the main circuit.

When the circuit is overloaded, the thermal element of the thermal release bends the bimetal sheet, pushes the free release mechanism to move, and the main contact disconnects the main circuit.

When the circuit is under-voltage, the armature of the under-voltage tripper is released, which also makes the free tripping mechanism act and the main contact disconnects the main circuit.

When the release button is pressed, the armature of the release device is sucked, so that the free release mechanism can move and the main contact can disconnect the main circuit. 

(1) rated voltage

The rated voltage on the circuit breaker nameplate refers to the rated voltage of the main contacts of the circuit breaker, which ensures that the contacts work normally for a long time.

(2) rated current

The rated current on the nameplate of the contactor is the rated current of the main contactor of the circuit, which ensures the normal operation of the contactor for a long time.

(3) trip current

The tripping current is the current setting value for the overcurrent tripper to operate. When the circuit is short-circuited or the load is seriously overloaded and the load current is greater than the tripping current, the main contact of the circuit breaker breaks off.

(4) Curve of overload protection current and time

The curve of overload protection current and time is inverse time characteristic curve. The bigger the overload current is, the shorter the action time of thermal release is.

(5) Rated Voltage of Undervoltage Releaser Coil

The rated voltage of the undervoltage release coil must be equal to the rated voltage of the line.