Complete internal structure diagram of plastic case circuit breakerThe main contact of the circuit breaker is closed by manual operation. After the main contact is closed, the free release mechanism locks the main contact at the closing position. The thermal element of the thermal release contacts with the free release mechanism. When the circuit is overloaded, the thermal element of the thermal release bends the bimetal sheet, pushes the action of the free release mechanism, and the main contact disconnects the main circuit.