An RCD that trips is doing its job — it has detected current leaking somewhere it shouldn't. The question is whether that leak is a one-off, a failing appliance, or a fault in the fixed wiring.
What an RCD actually does
An RCD (residual current device) compares the current flowing out to the current coming back. If a small amount goes missing — typically 30mA — it assumes that current has found another path, possibly through a person, and disconnects in a fraction of a second.
That sensitivity is what makes it a life-saving device, and also why it can be triggered by faults that would otherwise go unnoticed for years.
The most common causes
In our experience across Cornish homes, tripping usually traces back to one of a handful of things:
- A faulty appliance — kettles, washing machines, fridges and immersion heaters are frequent culprits
- Water ingress into outdoor sockets, garden lighting or an outbuilding supply
- Damp or deteriorated cable insulation, common in older properties and coastal buildings
- Too many circuits sharing one RCD, so small leakages add up until the device trips
- A damaged cable, often from a nail, screw or a shelf fixing
What you can safely check yourself
Unplug everything on the affected circuit, reset the RCD, then plug items back in one at a time. If it trips as a particular appliance goes back on, you have found your culprit.
If the RCD will not reset with everything unplugged, or trips again immediately, stop there. That points to a fault in the fixed wiring and needs testing with proper instruments.
How we find it
We isolate the installation and take insulation resistance readings circuit by circuit, which shows where current is leaking rather than guessing. Once the circuit is identified we can narrow it down to a section, an accessory or a specific piece of equipment, and give you a fixed price to put it right.
If the board itself is the underlying problem — one RCD covering the whole house, for example — we will say so, and explain what a modern board would change.
Common Questions
Resetting once to see if it holds is reasonable. Repeatedly resetting a device that keeps tripping is not — it is telling you there is a genuine fault, and the protection may be all that stands between that fault and someone getting a shock.
This article is general guidance, not a substitute for inspection and testing of your specific installation. If you're unsure, call us on 07496 242488 — advice over the phone is free.
