Why has half my house lost power?

Most modern consumer units split circuits across two RCDs. If one RCD trips, all circuits protected by it lose power — which is typically about half the house.

What is the difference between an RCD and an MCB?

An MCB protects against overload and short circuits on a single circuit. An RCD protects against earth faults (which can cause electric shocks) and typically covers multiple circuits.

Should I upgrade to an RCBO board?

An RCBO consumer unit gives each circuit its own combined RCD and MCB protection, so a fault on one circuit will not affect others. It is worth considering if you experience frequent tripping.

Caution

Updated 30 August 2026

Half The House Has No Electricity

Some rooms have power and others do not — the house is partially without electricity.

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What's happening?

When roughly half your home loses power, it often means one of the RCDs in a split-load consumer unit has tripped. Modern UK consumer units typically split circuits across two RCDs, so if one trips, approximately half the house loses power.

What usually causes it?

One of two RCDs in a split-load consumer unit has tripped
Multiple MCBs have tripped on the same side of the board
Loose neutral connection on the main busbar
A fault on one circuit causing the RCD to trip and affect all circuits on that side
Water ingress affecting multiple circuits

Is it dangerous?

This indicates a potential fault that needs investigation. While not an immediate emergency, the underlying cause could be a serious wiring fault, especially if the RCD will not reset. If you notice burning smells or the problem recurs frequently, treat it as urgent.

Can I fix it myself?

Open your consumer unit cover and look for a tripped RCD — a larger switch usually positioned at the top or side. Try resetting it once. If it trips again, switch off all the MCBs on that side, reset the RCD, then switch MCBs back on one at a time. The MCB that causes the RCD to trip again identifies the faulty circuit.

When should you call an electrician?

Call an electrician if the RCD will not reset, if you cannot identify the faulty circuit, or if this happens repeatedly. An electrician should also be called if your consumer unit does not have RCD protection, as this may indicate it needs upgrading.

What will the electrician actually do?

Test the RCD to ensure it is functioning correctly
Isolate and test each circuit to find the fault
Perform insulation resistance tests on the faulty circuit
Repair the underlying fault — loose connection, damaged cable, or faulty appliance
Recommend a consumer unit upgrade if the board is outdated