RCD Keeps Tripping. Intermittent Fault-Finding Tips

1) Why does the RCD keep tripping intermittently?

There is no one answer for why this happens to an RCD but there are several possibilities including:

• RCD too sensitive
• Damage inside the consumer unit 
• Faulty RCD Trip Switch 
• Damaged Plug Sockets or Switches
• Appliance Faults
• Damaged Wiring
• Water In Electrics 

2) What is an RCD?

An RCD is a device that monitors electrical circuits for missing electrical current. The most common use for an RCD is for additional protection against electric shock. Whilst there are many types and ratings of RCD the 30 Milli Amp RCD is the one that protects against electric shock in our homes. 

RCD is short for Residual Current Device. This device constantly monitors electrical circuits for any stray electrical currents and when it senses that there may be some electrical current missing it trips the circuit off to prevent electric shock. 

If your home has one of these devices, it is important that it is the right type and that it is operating correctly. The device should be rated to trip at or below 30 Milli Amps as this is the level where dangerous electric shock can occur. RCD ratings can vary so make sure yours is correct.

If you do not have an RCD, consult an electrician to have your consumer unit upgraded to a modern one. If you DO have an RCD then its important that you check it every 6 months by pressing the test button. The device should trip when the test button is pressed. If it doesn’t, the device likely needs replacing so call a professional electrician to come and check it for you.

Your electrical system and any RCD devices should be checked every ten years by a professional and an EICR report produced to show the condition of the wiring installation. 

3) What steps can homeowners take to rectify the problem themselves?

We have produced some information for you to assist you in some basic and safe fault finding. 

Beyond the basic checks contained in this help sheet there is not much else that can be done safely by anyone other than a licensed electrician. Do not attempt to carry out repairs on electrical systems without the adequate qualifications, training, knowledge of test equipment and experience. 

If you find that you still have issues after following the guidance in the help sheet then contact your local electrician for further advice or assistance. 

4) Are there any safety checks I can carry out myself?

Whilst electrical work should be left to the professionals there are many checks that can be safely carried out yourself without the need for an electrician. Checking for a faulty appliance and many other home checks are covered in this article here , these are home checks that you can do today to improve your electrical safety. 

Please ensure that when working around electrical appliances, electrical systems or wiring that all the power is turned off and verified dead. 

5) How can an RCD be too sensitive?

Most RCD devices in our homes will be manufactured and set to trip at around 30 Milli Amps or less. This is important because if any electrical fault currents are allowed to rise above this level, then it is possible that someone could receive a deadly shock.

The RCD can deteriorate with age and become too sensitive which means that the device will begin tripping at less than 30mA. Once the device begins tripping at 15mA or less it is TOO sensitive and will likely cause a NUISANCE TRIPPING situation. The sensitivity of this device can be checked by an electrician with the correct test equipment and knowledge to carry out a ramp test with the right RCD tester.

This can give the illusion that there is an electrical fault in your electrical system when, in fact, it is likely that the device is simply failing and tripping with small amounts of background current leakage. This background current leakage can be normal with various appliances and can build up especially if the RCD device is protecting several circuits together. 

This is often the case when there is a MAIN RCD in a consumer unit protecting all the circuits. The only solution is to replace the consumer unit with a modern one containing several RCD devices. 

6) Does Consumer unit Damage cause RCD tripping?

To understand the various components inside a consumer unit and their purpose I have written an article showing what each component is and its purpose. If you would like to know more about the insides of a consumer unit then have a read.

Damage occurring inside a consumer unit can cause an RCD to trip. The photograph below shows a slug that had crawled into a consumer unit and bridged the electrical terminals of the RCD. This was causing the RCD to trip!

If you look carefully, you can see the slug hanging out of the bottom left terminal of the RCD device.

7) What about Damaged Plug Sockets or Switches?

When a plug socket becomes damaged it can cause tripping of the electrical system. A common issue for plug sockets installed in outbuildings is the ingress of insects. As with the RCD photograph above, slugs can work their way into electrical sockets, especially if they are poorly installed.

When this happens, slugs tend to crawl across electrical terminals, shorting them out and causing a trip switch to activate.

If the slug survives its travels, then the slime left behind will dry out and the problems will disappear only to return when the slug once again crawls across the terminals.

If a socket or switch becomes damaged by overheating, melts or becomes burnt then it can short out or cause electrical current to leak from one part of the socket to another, again causing intermittent or even permanent tripping of the RCD device.

8) Can Faulty Appliances Cause Intermittent Tripping?

Any appliance that uses electricity can cause intermittent tripping of the RCD. When an appliance begins to go faulty the wiring inside can deteriorate and short out. The internal components of the appliance can begin to fail and break down.

Any of these things can cause electrical failures and these are often detected by the RCD. Intermittent faults are common with old appliances.

Any appliance with a heating element such as an immersion heater, electric oven, washing machine or dryer, will cause a residual current device to trip, especially when the element is either brand new and may form condensation when heating up causing water ingress.

There may not be an obvious reason for the RCD tripping when an appliance is at fault and some investigation may be necessary.

9) Can Damaged Wiring Cause an RCD to Trip?

Damaged wiring can definitely cause an RCD to trip. A loose wire can also cause this. Any cable that is damaged can cause earth leakage current to appear as earth touches Line or Neutral inside the now damaged cable.

Damaged wiring on ring mains will take some time to pinpoint as the ring has to be tested, split, tested again and so on until the faulty section and root cause is found.

A circuit fault such as this will require a qualified electrician with the correct test equipment (an insulation tester) to carry out an insulation resistance test on the electrical circuit to establish the condition of the electrical wiring.

Nuisance trips can often be caused be electrical wiring under the floor, buried in walls, in the loft space or in the basement. The wiring may be inaccessible such as is the case with underfloor heating. There are many common causes of earth faults and short circuits in wiring and amongst them is the ’Nail Through the Floorboard’ situation.

We can see from the photograph below that the person that replaced these floorboards did a great job of nailing through the cables. They had managed this in several locations along the landing of the property.

This resulted in many short circuits, earth faults and the risk of fire.

It’s a shame when bad things happen to good circuits, however, the electricians that carried out this rewire are partially to blame having installed the cables in notches rather than drilling through the joists!!

10) Intermittent Tripping because of Water?

Electrical faults that cause a tripping RCD can also occur when water enters the electrical system. This is common with outdoor equipment such as outdoor sockets, pond pumps, outside lights, power supplies to outdoor buildings and an electric gate power supply.

Electrical boxes designed to contain wiring junctions can be poorly installed, buried in the ground without sufficient water ingress protection or can simply have their seals fail over time resulting in failure of the circuit.

11) How many times can I reset an RCD?

These devices have a lifespan and there is no set number of trips that an RCD can withstand before it fails and a new RCD needs to be installed.

The failure of an RCD device will depend upon:

• How many times it has tripped before
• The level of fault current it disposes of each time
• The internal condition of the device
• The age of the device
• The quality of the original manufacturing of the device
• The installed conditions of the RCD/Electrical Panel

IF you have to reset an RCD more than once in a short period then an electrician should be consulted to check WHY and to see if there are any electrical faults in the system.