Working principle of plastic-case circuit breaker

The working principle of the MCCB mainly involves the protection mechanism that automatically cuts off the circuit when the current exceeds the safety setting. This includes several key components:

Main contact and trip mechanism: The main contact of the moulded case circuit breaker can be closed manually or electrically. After closing, the free trip mechanism locks the main contact in the closing position. This mechanism is the core of the circuit breaker and is responsible for disconnecting the main circuit when an abnormal current is detected. 12

Overcurrent and thermal release: When the circuit occurs short circuit or serious overload, the coil of the overcurrent release will sense too much current, and quickly absorb the armature, so that the release mechanism acts, thus disconnecting the main circuit. At the same time, the thermal element of the thermal release will heat up under overload, which causes the bimetal sheet to bend and then push the release mechanism. 12

Undervoltage and shunt trip: When the circuit undervoltage or press the shunt trip button, the corresponding trip will release the armature, also make the free trip mechanism action, disconnect the main circuit.

Electronic trip device: In more advanced moulded case circuit breakers, an electronic trip device may also be included, which collects current signals through the built-in transformer and quickly sends out a trip signal when abnormal current is detected, controlling the trip coil action to achieve rapid power failure. 4

These mechanisms work together to ensure that when the circuit is abnormal, the MCCB can cut off the circuit in time to protect the safety of equipment and personnel.