What causes an RCD to trip?

An RCD that trips again (and again) after reset is a ‘constantly tripping RCD’. The problem is unlikely to be the RCD. The problem is most likely an electrical appliance causing the RCD to trip; the RCD is ‘doing its job’; the RCD is removing the supply to an unsafe electrical circuit.

How to find the cause

The approach is to remove (disconnect) as many electrical appliances from the circuit as possible and then connect them back into the circuit one at a time. The faulty appliance will cause the RCD to trip; this will show you which appliance is faulty (causing the RCD to trip).

"You should remove (unplug) all electrical appliances. If it is not possible to unplug an appliance, turn the appliance off."
  • After unplugging all appliances, or turning them off, see if the RCD will reset. If the RCD will reset, the fault is with one of the appliances; if the RCD trips again the fault is with the electrical circuit and you will need to speak to a qualified electrician for advice.
  • Plug each appliance in one at a time. After plugging the appliance in, or turning an appliance on, reset the RCD; keep plugging the appliances in, and resetting the RCD, until the RCD trips.
  • Connecting the appliances one at a time, and resetting the RCD in-between, will show you the which appliance is causing the RCD to trip. You should then repair, or replace, the faulty appliance.
"Plugging each appliance in one at a time is not a 100% guarantee of finding the faulty appliance"
  • If the faulty appliance is cheap to replace, for instance a kettle, replacing the appliance is often cheaper than calling a qualified electrician to look into the problem further. If replacing the cheap appliance does not allow the RCD to be reset call a qualified electrician.
  • If the faulty appliance is expensive, for instance a home cinema centre, call a qualified electrician. The electrician will look into the tripping RCD to ensure the expensive appliance is causing the RCD to trip. The electrician will also know what else can be done to stop the RCD tripping without replacing the expensive appliance; this will probably be cheaper than replacing the appliance.

Written by Gareth Pope
Qualified Electrician with 30 years experiance.
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