The main contacts of a low-voltage circuit breaker are closed either manually or electrically. Once closed, a free-tripping mechanism locks the main contacts in the closed position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, while the coil of the undervoltage release is connected in parallel with the power supply.
In the event of a short circuit or severe overload, the armature of the overcurrent release is attracted, actuating the free-tripping mechanism and causing the main contacts to disconnect the main circuit.
During an overload, the thermal element of the thermal release heats up, causing the bimetallic strip to bend; this actuates the free-tripping mechanism, causing the main contacts to disconnect the main circuit.
In the event of undervoltage, the armature of the undervoltage release is released, which also actuates the free-tripping mechanism, causing the main contacts to disconnect the main circuit.
When the shunt trip button is pressed, the armature of the shunt release is attracted, actuating the free-tripping mechanism and causing the main contacts to disconnect the main circuit.
