When should I use MCCB instead of MCB?

You should use a Molded Case Circuit Breaker (MCCB) instead of a Miniature Circuit Breaker (MCB) for applications involving high currents (typically over 100A), in main power distribution panels, and whenever you need adjustable protection settings for specific loads like large motors or generators.

In short, use an MCB for final circuits (like lighting and sockets) and an MCCB for main distribution and high-power equipment.