Why Does My RCD Keep Tripping?

If an RCD in your consumer unit keeps tripping, it usually indicates that the device is detecting residual current or that there is a fault somewhere within the installation or connected equipment.

An occasional trip may be associated with a particular appliance or event, but an RCD that repeatedly trips should not simply be ignored or continuously reset.

This guide covers some of the common reasons an RCD may trip and how the affected area can be identified.

What Causes an RCD to Trip?

An RCD monitors the balance of current flowing through the conductors passing through it.

Under normal conditions, these currents should balance.

If current flows through an unintended path to earth, an imbalance can occur. If the residual current reaches the RCD's operating threshold, the device disconnects the supply.

There are numerous possible causes.

1. A Faulty Appliance

A faulty appliance is one of the first things to consider when an RCD suddenly begins tripping.

Possible examples include:

• Washing machines

• Dishwashers

• Tumble dryers

• Kettles

• Ovens

• Refrigerators and freezers

• Electric showers

• Outdoor electrical equipment

• Extension leads

• Power supplies and chargers

An appliance can develop an insulation or earth-leakage fault even if it appears to operate normally.

If the RCD consistently trips when one particular appliance is used, that appliance should be investigated.

2. Moisture or Water Ingress

Water and electricity are a particularly problematic combination.

Moisture entering electrical equipment can cause leakage to earth and result in an RCD operating.

Areas particularly worth considering include:

• Outdoor sockets

• External lighting

• Garden equipment

• Garages

• Sheds

• Bathrooms

• Kitchens

• Outdoor junction boxes

If the problem begins following heavy rain or damp weather, outdoor electrical equipment may require investigation.

3. A Wiring Fault

The problem may be within the fixed electrical installation rather than an appliance.

Damaged cables, insulation faults, incorrect connections or other wiring problems can result in residual current.

Proper electrical testing may therefore be required to determine the cause.

4. Neutral-to-Earth Faults

Neutral-to-earth faults can cause RCD operation and can sometimes be difficult to diagnose without appropriate test equipment.

These faults can occur within:

• Fixed wiring

• Accessories

• Appliances

• Junction boxes

• Consumer units

A neutral-to-earth fault should be properly investigated rather than assuming that the RCD itself is defective.

5. Multiple Appliances Creating Cumulative Leakage

Modern electrical equipment can have small amounts of normal protective-conductor current or earth leakage.

Individually, each piece of equipment may not cause the RCD to operate.

However, where one RCD protects numerous circuits and many electronic devices, the combined leakage can become significant.

This is one reason installations using individual RCBO protection can offer advantages compared with older arrangements where one RCD protects a large group of circuits.

6. An RCD Protecting Several Circuits

Many older split-load consumer units use one RCD to protect several MCB-controlled circuits.

For example, a single RCD might protect a combination of:

• Socket circuits

• Kitchen circuits

• Outdoor circuits

• Other final circuits

A fault on one of those circuits can cause the RCD to disconnect all of the circuits it protects.

This can make it appear that several circuits have failed when the actual problem is confined to one circuit or connected appliance.

7. A Faulty RCD

RCDs are electrical and mechanical devices and can develop faults.

However, an RCD that trips should not automatically be assumed to be defective.

The installation and connected equipment should be properly tested before replacing the RCD simply because it is operating.

Replacing a functioning RCD without identifying the underlying fault may result in the replacement device behaving in exactly the same way.

My RCD Trips When I Turn One Appliance On

If the RCD repeatedly trips when a particular appliance is switched on, the appliance may require investigation.

Stop using equipment suspected of having an electrical fault until it has been appropriately checked.

Don't attempt to solve the problem by bypassing the RCD or removing required protective measures.

My RCD Trips When It Rains

If RCD tripping appears to correspond with wet weather, equipment exposed to external conditions should be considered.

Potential sources include:

Outdoor sockets

External lights

Garden equipment

Sheds and garages

Outdoor junction boxes

Water ingress or damaged equipment can create leakage paths that cause an RCD to operate.

The affected installation should be inspected and tested.

My RCD Trips at Random

Intermittent RCD tripping can be more difficult to diagnose.

The fault may only appear when:

• A particular appliance operates

• Heating elements become hot

• A refrigeration compressor starts

• Outdoor equipment becomes wet

• Several devices operate simultaneously

• A timer switches equipment on

• A particular circuit is energised

Keeping track of what equipment was operating when the RCD tripped can sometimes help an electrician narrow down the cause.

RCD Trips Immediately After Resetting

If an RCD trips immediately after being reset, don't repeatedly force or hold it in the ON position.

A persistent fault may still be present.

Further investigation may be required before the affected circuits can safely remain energised.

How Do Electricians Find an RCD Fault?

Finding the cause of RCD tripping can involve systematically investigating the installation and carrying out appropriate electrical tests.

Depending on the circumstances, this can include testing:

• Individual circuits

• Insulation resistance

• Protective conductors

• Connected appliances

• RCD operation

• Neutral and earth connections

Suitable electrical test equipment and knowledge of the installation are required.

Does a Tripping RCD Need Replacing?

Not necessarily.

An RCD tripping can actually indicate that it is responding to a condition it is designed to detect.

Replacing it should therefore not be the first assumption.

If testing establishes that the RCD itself is defective, the correct compatible replacement will need to be identified.

When looking for a replacement, check:

• Manufacturer

• Model number

• Consumer unit range

• Current rating

• Residual-current rating

• RCD type

• Number of poles

See our How to Find the Correct Replacement RCD guide for more information.

Should I Upgrade From an RCD and MCB Consumer Unit to RCBOs?

Some older consumer units have one or two RCDs protecting groups of circuits.

Newer consumer units commonly use individual RCBOs, allowing residual-current and overcurrent protection to be provided on a circuit-by-circuit basis.

One advantage is that a fault affecting one RCBO-protected circuit doesn't necessarily disconnect several unrelated circuits at the same time.

Whether an existing installation should be altered or upgraded needs to be determined based on the condition and design of the installation rather than RCD tripping alone.

Need a Replacement RCD?

At ReCircuit Resale, we stock new, new-other and used electrical protection equipment, including current and discontinued RCDs from manufacturers such as Wylex, Hager and Crabtree.

If testing has established that an RCD needs replacing and you're struggling to identify the correct device, send us:

A photograph of the consumer unit

and

A clear close-up of the existing RCD and model number

We can help identify the product and check whether we have a suitable replacement available.

Repeated RCD tripping can indicate an electrical fault. This guide is intended for general information and fault awareness rather than electrical diagnosis. Electrical faults and work within consumer units should be investigated by a suitably competent person using appropriate test equipment and in accordance with BS 7671 and the manufacturer's instructions.