RCBO Keeps Tripping Causes and Fixes

An RCBO trips for one of three reasons. Overload — too much current drawn by connected loads for the circuit rating. Short-circuit — a dead fault between conductors, producing a high fault current. Earth leakage — current taking an unintended path to earth that exceeds the device's rated residual operating current, typically 30 mA on domestic circuits. Identifying which of the three is occurring before touching anything is the starting point for every diagnosis (BS 7671 Reg 531.3.2).

The GN3 subdivision approach gives a reliable sequence. Start by removing all loads and portable appliances from the circuit, then reset the RCBO. If it holds with no loads, reconnect them one at a time — the one that trips it is the load fault. If it trips immediately with nothing connected, the fault is in the fixed wiring or an accessory.

Once the fault is narrowed down properly, the fix is usually straightforward. Replace the failed outside socket. Dry and remake the light fitting. Repair the damaged flex. Replace the faulty appliance. Re-terminate the loose conductors. If the issue is overload, rework the circuit use or review the design rather than pretending the symptom is random. Where a cable has been penetrated by a nail or screw, any repair must also restore mechanical protection to the standard required by Reg 522.6.203 — conduit, capping, or re-routing outside the wall zone is required, not just re-jointing the conductors.

Some RCBO faults are not really small-fix jobs. Repeated moisture problems, signs of age across the installation, or multiple questionable alterations may mean the client needs a broader inspection or a more substantial remedial plan.

That is when it is worth stepping back and moving from a quick reactive visit into a clearer recommendation, whether that is an EICR or a bigger consumer unit upgrade.