Mini circuit breakers are triggered by overcurrent – electrical current that exceeds a designated safe current and makes use of a relatively robust mechanical mechanism designed to minimise failures and false alarms.

Excess current causes the bimetallic strip within the MCB to heat, bend, and trip.
This releases a switch that moves the electrical contact points apart to confine the arc (electrical discharge). The arc is divided and cooled by an insulated metal strip called the arc chute. The contacts close again once the fault has been fixed and the MCBs are reset.