Get Your RCD Tripping Sorted In Five Steps

You already know an rcd tripping means partial, or total loss of power. That’s why you are here, right? Well, you’ve landed on the right page! Rcd switches usually trip because of faulty appliances or wiring.If your residual current device has tripped with no reason you are aware of; this article may help you switch it back on.

If there is no reason you are aware of; the best chance you have of resetting your residual device is to unplug as many appliances as you can. Showers, ovens and hobs can be switched off. So keep reading and get your rcd switched back on!

Shower isolators remove power from the unit for maintenance purposes. So, if your rcd won’t switch on and the shower circuit is being protected – switch it off and re-try. If the rcd resets; you know there is a problem with the shower (or its circuit).

Why Your rcd keeps tripping: five steps you can yourself for nothing

Step 1. Identify what the residual device is protecting.

A dual rcd consumer unit close up pictured below: (probably the most common modern type installed in 2020).

If your consumer unit looks like the one above: the residual current device (always look out for test button) protects everything to the left of it. The first one (from the right) is protecting the cooker, first floor sockets and first floor lights. The second device from the right is protecting the kitchen sockets, central heating, ground floor sockets and ground floor lights.

Both residual devices in the image above (made by British General) are in the on position (up). In the off position the toggle would be in the down position.

Important: As a professional electrician I should add there are occasions where you shouldn’t, or where further checks are necessary. Some scenarios i can think of include:

  • Someone has just drilled a hole in the wall
  • You have just replaced a light fitting or socket outlet
  • Part of the electrical installation has become damaged – wiring or accessories
  • Heavy rain (and you have outside lights/socket outlets)
  • An appliance no longer works

So, in the example above: if the rcd on the right has tripped (inside the yellow highlighted box); it could be circuit 1 (cooker), 2 (first floor sockets) or 3 (first floor lights) at fault. The easiest things to do in this example would be:

  • Unplug, (not just switch off) all the appliances on the first floor socket circuit. Also check for things connected to it – such as under floor heating in your bathroom and outside security lights. You also need to check some of the sockets elsewhere (like the loft) aren’t causing a problem.
  • Switch the cooker isolator to the off position.

For the lights on the first floor: You can turn the switches and any dimmers to the off position and remove the bulbs wherever possible.

For central heating systems: there is often fused connection units (highlighted in green below) to remove the power supply for boilers and water heaters.

Boiler controls (highlighted in green). Fused connection units will remove the power supply from the boiler and water heater in the same way removing a plug would for rcd tripping troubleshooting.

Split fuse board with single rcd (least common, although still about!)

Single rcd (protects the circuits within the green rectangle). Circuit 1-6 on the left are not protected by the rcd

If your consumer unit looks like the one above the residual current device is not protecting all the circuits. Circuits 1-6 (only 1-3 in use, with 4, 5 and 6 blank) are not protected in the example above. You can check what your rcd protects by pressing the test button. Any circuits still working are not protected by rcd. It often lights and cookers in older houses.

A single rcd consumer unit:

The consumer unit photographed above has one residual device protecting the whole installation. These are the hardest for customers to troubleshoot because it could be any of the circuits causing a fault. In the example photographed above the customer switched the shower isolator off and the rcd trip switch went back on. Power was restored giving them time to get the shower replaced the following day.

This is what a full rcbo consumer unit looks like:

I installed this full rcbo consumer unit in a domestic property in Leckwith. It has residual protection (called an rcbo) on each circuit (test button in yellow). A fault on the sockets will remove power on just the sockets. This is the best setup for reducing power cuts if earth faults arise and the quickest for troubleshooting. If your installation looks like this: whichever rcbo is tripping – something on that circuit is causing a problem. If its sockets, unplug everything you can access and try to reset. If its a shower, switch the isolator off – same with the cooker or hob. If its lights you can remove all the lamps.

Step 2. Turn all electrical equipment in the property off (to prevent damage to televisions, computers and other sensitive electronic devices). Switch the residual current device off by the lever, or by pressing the test button. Now make a list of what no longer works that should. The list will tell you what circuits and appliances could be causing the problem. If you have two residual devices: by switching one of them off at a time – it will help you make a list of what device protects what. When you know what each one protects, you have a list of the possible faults.

Step 3.If you believe a socket circuit is to blame; unplug all the appliances – not just the easy ones, or the old appliances. Everything. Sometimes customers say things like: “i didn’t unplug the washing machine because its difficult to move”.  Or, “i didn’t unplug the kettle because it is only a few months old.” Well, new things can be faulty. I’m happy to attend, but if i unplug your washing machine and the fault clears, you have a call out fee and the cost of a new washing machine! So unplug.  Yes, it can be a pain, but you want the power back on right? With as much unplugged as you can – see if the rcd will reset.  If  it will, connect the appliances back one at a time. If you believe to have found a faulty appliance, try it by itself. Two appliances with a high combined earth leak can be enough to trip a residual protective device although not when used individually.  And this can be a big red herring when customers are troubleshooting tripping faults. As a professional electrician I was hired to troubleshoot an rcd trip in Cardiff Bay recently. The customer purchased a new microwave because every time they switched it on the residual current device switched off.  Unfortunately they had the same problem with the new one and called me.  The problem was with the wiring inside the socket the microwave was plugged in to.

Time for a brew?

What you have done so far may be time consuming but a valuable exercise. Even if you don’t find the cause of the tripping – write down what you have done and show it to the electrician so they don’t waste time (and your money) doing the same.  Any suspected appliances that you can do without; leave disconnected for a few hours or days if necessary to help confirm.  Sometimes appliances unknowingly faulty lived in a home without residual protection move to a new one and cause tripping. Portable appliance testing should confirm the fault, but that’s with the help and test equipment from an electrician . Users of the equipment would understandably assume a problem with the wiring or electrical installation.

Step 4.If you think your electric shower is causing a problem; turn the isolator off.A shower isolator removes the power in the same way unplugging a faulty kettle from its socket would. If the residual device resets this would suggest a fault with the shower (or its wiring).

Step 5. If your device trips are infrequent (the trickiest to diagnose), make a note of when it happens. Could it be:

  • An extractor fan in a guest bathroom?
  • A security light that no longer works?
  • An oven that’s just been cleaned?
  • An outdoor light fitting affected by the weather?
  • A rarely used appliance?
  • If you wake up in the morning with the residual current device in the off position – think what might be happening when you are asleep.  Do you have an immersion heater that powers on at midnight and off at 6am? Do you have heating in a greenhouse that comes on?  Do you have security lights that may have become damaged and trying to come on?

Referred to as  ‘nuisance tripping’ although electricians in Cardiff City Centre will tell you most residual devices tested do work as designed. Residual current devices detect earth leakage (electrical current leaking somewhere it shouldn’t be). They remove the power if the live and neutral go out of balance protecting users from electrocution and buildings from fire. Most trip correctly under fault conditions (faster than you can blink – between 20 and 30 milliseconds) ‘Nuisance’ arose because re-wireable fuses didn’t trip at all! Designed to protect the cables if overload occurred. Fuses and circuit breakers offer no protection from a person coming into contact with a live conductor. Residual current devices trip to prevent electrical related injuries and fire. They are a big part of the wiring regulations electricians adhere to.

If you have tried everything listed in this article to no avail, don’t worry.  Perhaps the trip is too random (always tricky to find). Don’t despair, what you have done will have saved the electrician you do call out time and enable them to continue with more involved troubleshooting.

Get Thinking with a checklist: How to find the rcd circuit breaker tripping cause

1. The first time the tripping started.

2. If any work has been carried out on the property. New lights, sockets, shelves, flooring, kitchen units can all cause tripping if the wiring has been disturbed unknowingly by a screw, nail or not terminated correctly.

3. If you have fitted any additional electrical appliances or had any repaired.

4. Previous unresolved electrical problems.

5. If you have experienced power cuts.

6. If you have power supplying outdoor fixtures or buildings.

How I Can Help You Troubleshoot Your Tripping RCD Problem

Residual current devices are designed to prevent 30ma of current leaking somewhere it shouldn’t. Most trip and remove power closer to 25ma to ensure they disconnect in the necessary time frame. If no leak (or rather nothing near the tripping threshold) is present the residual device can be ramp tested. This is when I can check its tripping exactly like the manufacturer designed it to.

I’ve covered appliances throughout this article although that is only one aspect of residual current. Problems with wiring inside accessories (like light switches and socket outlets), cable buried inside the wall, above the ceiling, or inside plastic trunking can cause tripping . Have you fitted shelves, a picture frame or a mirror? Could a screw or nail have damaged the wires inside the wall? You can expect buried cables if an accessory is close-by (like a socket or light fitting). Cables can be present without any sign of an accessory and often damaged unintentionally when something is fitted to the wall.

If you ask any electrician in Cardiff they will tell you rats love chewing through cables. So if you have cabling clipped along an outside wall or under decking – is it possible they have become damaged by rodents? It’s not just outdoors cables are at risk unfortunately. Rats can climb and sometimes cables inside the loft space can become damaged if you have had a problem with them.  It was common practice at one time to get cables from one floor to another by taking a brick out at both levels. The cables passed down the cavity of the walls as a route from first floor to ground floor. We don’t install cables like this anymore, but that doesn’t mean you can rule it out until it has been checked.

When i am troubleshooting, I make a list of the circuit descriptions from within the consumer unit and measure the leakage across each one. With the amount of appliances in use today the amount of residual leakage can be close to the tripping threshold with not one particular fault.  Sometimes its a little leak on one circuit, a bit more on another, and a larger amount on the circuit supplying outdoor items.  When you add them all together it’s not far off the amount the device is designed to trip. Some appliances will leak small amounts of current through their design.  Its not dangerous to the user, but in large premises (or, and) with lots of appliances it can be a problem. It is for this reason, my usual advice when replacing a consumer unit, or troubleshooting problematic residual current device faults is to fit a full rcbo consumer unit.  With this configuration you are allowed the same amount of residual current per circuit opposed to half the installation on a dual rcd or the entire premises when one rcd is protecting everything.

I have listed the results of an installation experiencing random tripping I visited recently.  With everything disconnected from the residual device it passed test after test.  I had no doubt the device itself was not the problem (it rarely is).  It was an accumulation of residual current:

Circuit descriptionLeakage (in milliamps)
Upstairs Lights0.7
Downstairs Lights0.4
Sockets Ground floor2.2
Sockets First Floor2.9
Sockets Kitchen1.5
Kitchen Appliances1.9
Immersion Heater1.7
Central Heating1.3
Garden lighting and pond equipment2.4
Total Leakage18.4
From the installation tested above, the total leakage was 18.4 milliamps.

The total leak for the installation was 18.4 milliamps at the time of test.  Because there was only one residual current device protecting the whole installation it was getting close to the tripping threshold with not one particular problem that could have been (easily) removed on the day.  The easiest part of the installation to break down further with a high overall reading (2.9ma) was the socket circuit on the first floor.  This is what i found:

ApplianceLeakage (in milliamps)
Computer 10.4
Computer 20.5
Electric blanket0.4
Games room0.9
Total Leakage2.2

I found 2.9ma leak at the consumer unit and 2.2 whilst on the first floor.  The missing 0.7 could be due to the wiring supplying the socket outlets, something intermittent or something i could not find attached to the installation.  My point is this: the bigger the installation, often it means more appliances. More appliances equals more natural residual current leaking to earth. The purpose of residual current devices is to protect us from current leaking to places it shouldn’t.

If you have followed my advice and still unable to find the cause of your rcd tripping then get in touch so i can help you (if you live in the Cardiff and Vale area).  The cost to resolve it will depend on the amount of time to find the cause and what is involved to rectify it.