There are three mechanisms provided in a single miniature circuit breaker to make it switched off. If we carefully observe the picture beside, we will find there are mainly one bi – metallic strip, one trip coil and one hand operated on – off lever.

Electric electric current carrying path of a miniature circuit breaker shown in the picture is like follows:

-First left hand side power terminal

-Secondly bimetallic strip

– Then electric current coil or trip coil

-Then moving contact – then fixed contact

-Lastly right had side power terminal. All are arranged in series.

How to reset a circuit breaker or trip?

There are two contacts one is fixed and the other moveable. When the current exceeds the predefined limit a solenoid forces the moveable contact to open (i.e., disconnect from the fixed contact) and the MCB turns off thereby stopping the current to flow in the circuit.

In order to restart the flow of current the MCB is manually turned on. This mechanism is used to protect from the faults arising due to over current or over load.

To protect against fault arising due to over heating or increase in temperature a bi-metallic strip is used. MCBs are generally designed to trip within 2.5 millisecond when an over current fault arises. In case of temperature rise or over heating it may take 2 seconds to 2 minutes for the MCB to trip.

MCB Internal Part