Nuisance tripping is one of the most common calls we take from homeowners. It is rarely random. Something is either drawing more current than the circuit is rated for, or a small amount of current is leaking to earth. Working out which one it is decides whether you are looking at a five-minute fix or a proper investigation.
Overload or earth leakage?
An MCB (the smaller switches) trips on overload or a short circuit. An RCD trips when it detects an imbalance between live and neutral — usually moisture, a failing appliance element or damaged cable insulation.
If the whole side of the board goes off, you are looking at the RCD. If a single switch drops, the fault is confined to that circuit.
The half-split test you can do safely
Unplug everything on the affected circuit, reset, then reintroduce appliances one at a time. Kettles, immersion heaters, washing machines, tumble dryers and outdoor lighting are the usual culprits because they combine heat, water and age.
- Reset the board with all appliances unplugged
- Add one appliance at a time, waiting a minute between each
- Note which item causes the trip and stop using it
- If it trips with nothing plugged in, the fault is in the fixed wiring
When to stop and book a visit
If the board will not reset at all, if you can smell heat, or if the tripping happens with no appliances connected, stop resetting it. Repeatedly forcing a device back on hides the fault rather than fixing it. We use insulation resistance and earth loop testing to find where the leakage actually is, rather than guessing.
Common questions
- Is it safe to keep resetting the trip?
- Once or twice to identify an appliance is reasonable. If it trips again immediately, leave it off and get the circuit tested.
- Can a light bulb blowing trip the board?
- Yes. A filament or LED driver failing can produce a brief surge that takes out the lighting MCB. If it happens repeatedly on the same fitting, the fitting is suspect.
- Does an old fuse box need replacing if it trips?
- Not automatically, but rewireable fuse boards give you no earth leakage protection at all, so an upgrade is usually worth quoting alongside the repair.
- How long does fault finding take?
- Most domestic faults are isolated within a couple of hours. Intermittent ones can take longer, and we will tell you before the clock keeps running.
If your board keeps tripping, send us the make of the unit and which switch is dropping — it usually tells us a lot before we arrive.
Related guides
- RCD Will Not Reset: How to Find the CircuitAn RCD that will not stay in is holding back a live earth-leakage fault somewhere on its side of the board.
- Half the House Has No PowerA house split neatly in two is a board-level symptom, not a coincidence.
- RCD vs RCBO: What the Difference Means at HomeThe difference is not protection quality — it is how much of your house goes dark when something leaks.