Quick answer
An MCB trips due to overload or a short circuit. Unplug appliances on that circuit, reset it, and plug them back one at a time to find the cause.
An MCB (the individual switches in your consumer unit) trips when a circuit is carrying too much current or there is a short circuit fault. If an MCB trips, switch it fully off then back on to reset it. If it trips again immediately, there is a short circuit — do not keep resetting it. Switch off all appliances on that circuit and try again. If it holds, plug appliances back one at a time until it trips — that last appliance is the cause. If the MCB trips with nothing plugged in, the fault is in the wiring and you need an electrician. If a specific MCB trips frequently under normal use, the circuit may be overloaded and needs assessment by an electrician.
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