MCB (Miniature Circuit Breaker) is a distribution box that is fixed or provided in every apartment in modern societies. Instead of MCB box, a 32 Ampere DP switch was fixed that had an on-off switch. MCB box concept didn’t exist as they were not aware of such a thing as MCB.
Mini circuit breakers are triggered by over current - 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.
MCB is the key component for the safety and efficient functioning of electric machines and is used in most electrical appliances that are used for industrial or domestic purposes. In domestic usage, appliances like lights, heaters, and fans require MCB to constantly check and protect the connection.