What an MCCB is

A moulded case circuit breaker carries higher currents than a miniature circuit breaker and is used at the main distribution and sub-distribution level. Its trip unit can usually be adjusted, so the protection can be set to the circuit rather than fixed at the factory.

Where MCCBs are used

Main and sub-main distribution boards

Motor feeders and motor control centres

Generator and transformer outgoing circuits

Panel boards in industrial installations

Selection points

Rated current and frame size

Breaking capacity at the point of installation

Adjustable thermal and magnetic settings

Accessories: auxiliary contacts, shunt trip, undervoltage release

Coordination with the upstream and downstream devices

Why coordination matters

In a well-coordinated installation, only the device nearest the fault trips. If the settings are not coordinated, a fault on a small final circuit can trip the main incoming breaker and shut down the whole building.