MCB
Distribution Protection · Also: Miniature circuit breaker, Breaker, Circuit breaker
In short
The switch that trips when a circuit overloads or shorts — replaces old rewirable fuses.
Notes
Each lighting or power circuit usually has its own MCB in the DB. If it trips, something on that circuit drew too much current or shorted.
MCBs are rated in amps (for example 10A lighting, 20A sockets). Do not upsize a breaker to “stop tripping” without finding the real fault.