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RCD keeps tripping: recognising an earth leakage fault and tracing the circuit

Does the residual current device trip without any clear reason? With a targeted method you find the circuit causing the leakage.

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Unlike an ordinary fuse, an RCD does not react to excessive current, but to a leakage current: electricity that flows away through an unwanted path, for example to earth. If it trips, it protects people against that leakage current.

Below you can read what an earth leakage is, how to systematically trace the circuit that is tripping the RCD, and at what point you should have a professional test the installation.

What an earth leakage fault is

The residual current device, also known as an earth leakage circuit breaker, compares the current entering the circuit with the current leaving it. As soon as there is a difference, because part of the current leaks to earth, it interrupts the circuit. This prevents you from receiving a dangerous shock on contact.

An earth leakage fault often arises from moisture in an appliance or socket, from damaged insulation on a cable, or from an outdated device whose internal insulation is failing. Damp rooms and outdoor connections are typical culprits.

Digital multimeter with pliers and circuit breakers on a white background
Photo: ERIC MUFASA / Pexels

Tracing the circuit with the leakage

Work methodically. First switch off all circuit breakers behind the residual current device. Then reset the residual current device and switch the circuits back on one by one. The circuit that trips the residual current device again is the circuit with the problem.

Once you know which circuit is faulty, unplug the appliances on that circuit and test again. If the residual current device now stays on, the leakage was in one of those appliances. If it still trips without any appliances connected, the problem lies in the wiring or a fixed connection on that circuit.

When a professional is needed

If you cannot find the circuit, or the residual current device trips even though no appliances are connected to the circuit, then the fault is in the fixed installation and you should have it tested. An earth leakage fault in the wiring is traced with measuring equipment, not by guesswork.

Also call immediately if the residual current device keeps tripping straight away, if moisture is involved at the consumer unit or connections, or if you can no longer get the installation working. In that case, contact us by phone for an urgent callout.

Points to watch with an earth leakage fault

Moisture is suspect number one

Water in sockets, outdoor connections or wet rooms often causes leakage current.

Circuits one by one

Switch the circuits on separately to isolate the faulty one.

Testing appliances

Reconnect the appliances on the faulty circuit one by one.

Leakage in the wiring

If the empty circuit still trips, the problem lies in the installation.

Tracing the earth leakage fault step by step

  1. 1

    Switch everything off

    Switch off all the circuit breakers downstream of the residual current device.

  2. 2

    Reset the RCD

    Reset the residual current device while the circuits are still switched off.

  3. 3

    Switch circuits back on one by one

    Switch the circuits on one by one until the residual current device trips again.

  4. 4

    Isolate the cause

    Test the appliances on that circuit. If the leak persists, have the wiring checked.

RCD or ordinary fuse?

RCD

  • Responds to leakage current to earth
  • Protects people against electrocution
  • Often moisture or damaged insulation as the cause
  • Trace the circuit, measure the wiring if needed

MCB

  • Responds to too much current in the circuit
  • Protects the cabling against overheating
  • Often overload or short circuit as the cause
  • Reduce the load on the circuit or have the fault checked

Frequently asked questions

What is the difference between an RCD and an ordinary fuse?
An MCB protects the circuit against too much current and safeguards the cabling. The RCD or residual current device responds to current flowing away to earth and protects people against an electric shock. So each does something different.
How do I find which circuit is tripping the RCD?
Switch off all MCBs behind the RCD, reset the RCD and switch the circuits on one by one. The circuit at which the RCD trips again contains the leakage. Then test the appliances on that circuit individually.
Why does my RCD mainly trip in damp weather?
Moisture is a common cause of leakage current. In rain or high humidity, water in an outdoor connection, socket or junction box can form a path to earth. Have the connections concerned checked and dried, otherwise the problem will return.
Can I safely keep living in my home if the RCD trips now and then?
An RCD that trips is doing its job, but it points to a leakage you need to resolve. Do not keep forcing it. If it trips repeatedly or you cannot find the cause, have the installation tested by a professional.

Read also

Cannot get the RCD stable?

If you cannot find the leakage or the device keeps tripping, we test the circuits and trace the earth leakage fault. Call us for an urgent call-out.

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