Plastic-case (plastic insulator to serve as the housing of the device) circuit breakers are also known as plastic-case circuit breakers, suitable for use as branch circuit protection switches, capable of automatically cutting off the current after the current exceeds the trip setting, used to isolate between conductors and grounded metal parts all parts are sealed in the plastic case, auxiliary contacts, undervoltage derailleurs and sub-excitation derailleurs are mostly modular. Due to the very compact structure, the moulded case circuit breakers are basically not accessible, so maintenance is not generally considered.

Multi-purpose manual operation, with electric switching options for large capacities. Due to the application of electronic overcurrent tripping, moulded case circuit breakers can also be divided into Class A and Class B. Class B has good three-stage protection, but Class A products with thermomagnetic release have a higher market share due to price factors.

Generally thermal magnetic moulded case circuit breakers are non-selective circuit breakers with only two types of protection: overload long delay and short circuit instantaneous. Most of the moulded case circuit breakers are manually controlled and operated, but there are also important parts with motors that can operate the operating mechanism.

Plastic case circuit breaker working principle.

The main contacts of the low-voltage circuit breaker are closed manually or electrically. After the main contact is closed, a free tripping mechanism locks the main contact in the closed position. The coil of the overcurrent release device and the thermal element of the thermal release device are connected in series with the main circuit and the coil of the undervoltage release device is connected in parallel with the power supply.

When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release device is pulled in, causing the free tripping mechanism to move and the main contact to break the main circuit.

When the circuit is overloaded, the heat generating element of the thermal decoupler bends the bimetal, pushing the free decoupling mechanism into motion and the main contact disconnects the main circuit.

When the circuit is under-voltage, the armature of the under-voltage current striker is released, which also makes the free realization of the decoupling need mechanism to carry out the action, and the main contact is in the disconnection of the main circuit.

When the split trip button is pressed, the armature of the split trip is attracted, the free trip mechanism is activated and the main contact disconnects the main circuit.