Miniature Circuit Breaker: What Is It?

- Aug 01, 2020-

Miniature Circuit Breaker: What Is It?

Miniature circuit breaker What is it?

What is MCB?

A Miniature Circuit Breaker (MCB) is an automatically operated electrical switch used to protect low voltage electrical circuits from damage caused by excess current from an overload or short circuit. MCBs are typically rated up to a current up to 125 A, do not have adjustable trip characteristics, and can be thermal or thermal-magnetic in operation.


Working Principle Miniature Circuit Breaker

There is two arrangement of operation of a miniature circuit breaker. One due to the thermal effect of over current and other due to electromagnetic effect of over current. The thermal operation of the miniature circuit breaker is achieved with a bimetallic strip whenever continuous overcurrent flows through MCB, the bimetallic strip is heated and deflects by bending.

This deflection of the bimetallic strip releases a mechanical latch. As this mechanical latch is attached to the operating mechanism, it causes to open the miniature circuit breaker contacts.

But during short circuit conditions, the sudden rising of current causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing the immediate release of the latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of the miniature circuit breaker working.