Molded Case Circuit Breakers (MCCB): A Complete Selection Guide

A molded case circuit breaker (MCCB) protects higher-capacity circuits than an MCB, handling rated currents from 63A up to 1600A or more with much greater breaking capacity.

Frame size and rated current

The frame size sets the maximum current the breaker body can handle, while the rated current is the trip threshold. A 250A frame, for example, can be fitted with adjustable ratings from 100A to 250A.

Breaking capacity matters

Choose a breaking capacity (Icu/Ics) higher than the prospective short-circuit current at the point of installation. Walax MCCBs are available up to 50kA, suitable for most commercial and light-industrial boards.

Thermal-magnetic vs electronic trip units

• Thermal-magnetic – simple and economical, ideal for basic distribution protection.
• Electronic – adjustable overload and short-circuit settings, ground-fault and communication options.

Selecting the right MCCB

Match the frame size to the load, confirm the breaking capacity against the fault level, and consider adjustable settings where coordination with downstream breakers is required.