An RCD (Residual Current Device) trips when it detects an imbalance between the live and neutral currents in the circuits it protects — usually indicating that current is leaking to earth. This is a safety feature, not a fault in itself, but persistent tripping needs to be investigated.
Why Does an RCD Trip?
An RCD will trip when:
1. A faulty or damaged appliance allows current to flow to earth through its casing or damaged cable
2. Moisture in an outdoor or bathroom circuit causes current leakage
3. Deteriorated cable insulation — particularly in older properties — develops tracking between live and earth
4. A legitimate electric shock hazard — someone contacting live parts
The vast majority of domestic RCD trips are caused by a faulty appliance.
How to Identify the Cause: Step by Step
Step 1 — Note Which RCD Has Tripped
Open your consumer unit and identify which RCD is down. Note which circuits it covers (these may be labelled on the board, or an electrician can identify them for you).
Step 2 — Unplug All Appliances on Affected Circuits
Unplug everything connected to the circuits protected by the tripped RCD — including appliances on extension leads. Go room by room.
Step 3 — Reset the RCD
With everything unplugged, try to reset the RCD. If it holds, the fault is in one of the appliances or portable equipment.
Step 4 — Plug Appliances Back In One at a Time
Reconnect appliances one at a time, leaving time between each. The RCD will trip again when the faulty appliance is connected. Isolate and remove that appliance.
Step 5 — If the RCD Trips with Nothing Plugged In
If the RCD trips even with nothing connected, the fault is in the fixed wiring — cables, sockets, light fittings or the consumer unit itself. This requires professional investigation.
Common Culprits
- Washing machine or dishwasher — water ingress or motor insulation failure
- Fridge freezer — compressor insulation deterioration
- Outdoor equipment — water ingress in weatherproof cables or fittings
- Bathroom extractor fans — water damage in damp environments
- Electric lawn mowers and power tools — cable damage
Nuisance Tripping
If an RCD trips regularly but you cannot identify a faulty appliance, it may be due to cumulative earth leakage — many modern appliances have small intentional earth leakage currents which can add up on a single RCD. An electrician can measure total leakage current and, if necessary, recommend splitting circuits or upgrading to an RCBO board.
Persistent Tripping — Call an Electrician
If you cannot identify the cause of persistent RCD tripping, call Onyx Electrical Solutions on 07000 000000. We use insulation resistance testing and circuit tracing equipment to locate the source of the fault quickly.