Quick answer
If your consumer unit main switch trips instantly with nothing plugged in, the most likely cause is a fault in the wiring between the meter and the consumer unit, a failed main switch itself, or a serious earth fault on the incoming supply cables. Switch everything off at the individual circuit breakers first, then try the main switch alone. If it still trips immediately, do not keep resetting it. Call a Part P registered electrician straight away, as this fault is upstream of your consumer unit and can indicate a dangerous condition.
When your main breaker, sometimes called the main switch or incomer, trips the moment you turn it on, it is telling you there is a fault it cannot get past. The fact that nothing is plugged in and all your individual circuit breakers are off is actually an important clue. It means the fault is almost certainly not in your sockets, lights, or appliances. The problem is in the main switch itself, in the wiring between your electricity meter and the consumer unit, or in the neutral or earth connections at the very top of the board.
Here is what is safe for you to check before calling anyone.
First, make sure every individual circuit breaker inside the consumer unit is in the off position. Push them all down if you have a standard board, or move them all to off. This completely isolates your house wiring.
Second, check whether any RCDs, which are the wider switches in the middle of many boards, are also in the off position. Make sure they are.
Third, with everything else off, try the main switch once more. If it trips again instantly, do not keep trying. Repeatedly forcing a tripped breaker can cause damage or create a more dangerous situation.
Fourth, look for anything obvious. A burning smell, discolouration around the main switch, or visible damage to the cables entering the top of the board are all signs you should not touch anything further.
Fifth, check whether your neighbours have power. If they do not, the fault may be with your supply, and you should call your Distribution Network Operator, which in England is usually UK Power Networks, Northern Powergrid, or Western Power Distribution depending on your area.
If your neighbours have power and the main switch still trips with everything isolated, this is not a job for a homeowner. The cables entering your consumer unit from the meter are not switched off by anything inside your property. They are always live. You need a Part P registered electrician or a qualified electrical contractor to investigate safely. Do not attempt to open the consumer unit casing or touch any of the connections at the top of the board yourself.
⚡ North London Electrician
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