Plastic case (using plastic insulator as the shell of the device) circuit breaker is also known as device type circuit breaker. It is suitable for protection switch of branch circuit. It can automatically cut off the current when the current exceeds the jump-off setting. It is used to isolate all parts between conductors and grounding metal parts, which are sealed in the plastic case, auxiliary contacts, undervoltage trippers and excitation trippers, etc. Modularization. Because the structure is very compact, the plastic case circuit breaker can hardly be repaired, so maintenance is generally not considered.

Most of them are operated manually and electrically operated in large capacity. Due to the application of electronic over-current tripper, plastic case circuit breaker can also be divided into A and B types. B type has good three-stage protection characteristics, but due to price factors, the market share of A type products using thermal magnetic tripper is higher.

There are two kinds of over-current trippers: thermal magnetic type and electronic type. Generally, thermal magnetic type plastic case circuit breakers are non-selective circuit breakers. There are only two protection modes: overload long delay and short-circuit instantaneous. Electronic plastic case circuit breakers have four protection functions: overload long delay, short-circuit short delay, short-circuit instantaneous and grounding fault.

Some new products of electronic plastic case circuit breakers also have regionally selective interlocking function. Most plastic case circuit breakers are operated manually, and some are operated with motor.

Working principle:

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.

     HKM1 Molded Case Circuit Breaker