MCB is an automatically operated electrical switch. Miniature circuit breakers are intended to prevent damage to an electrical circuit as a result of excess current. They are designed to trip during an overload or short circuit to protect against electrical faults and equipment failure. These are an alternative to fuses and are used to protect circuits from excess current.

The miniature circuit breakers (MCBs) are automatic switches that open when the current flowing through them exceeds the value for which they have been set. MCBs are more sensitive to current than fuses. They immediately detect any abnormality and switch off the electrical circuit automatically. This prevents any permanent damage to electrical appliances and human beings.