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It is usually dark when this happens. You hear a click, the fridge goes quiet, half the house goes off, and suddenly you are standing in the kitchen with your phone torch wondering what on earth just happened.
Your RCD has detected an electrical fault and cut the power to protect you. That is the short answer. The longer answer is that there are several reasons why it keeps tripping, some of which you can narrow down yourself tonight, and some of which need a qualified electrician.
This guide gives you a clear step-by-step process to safely get power back to most of your house while you wait for an electrician. Everything described here involves nothing more than operating the switches and buttons on the front of your consumer unit. You do not need any tools, any electrical knowledge, or any courage beyond opening a cupboard door. I will also explain what an RCD actually does, why some boards handle faults far better than others, and when you should stop touching the consumer unit altogether and pick up the phone.
I am an electrician based in North East Scotland. I do this job every day across Aberdeen and Aberdeenshire, and in my experience the people searching for this page are usually doing it in the dark, on their phone, with the fridge off. So let us get to it.
What Is an RCD and What Does It Do?
An RCD stands for Residual Current Device. The name sounds technical, but what it does is straightforward: it constantly compares the current flowing out of your consumer unit on the live wire with the current returning on the neutral wire. Under normal conditions, those two values are exactly equal. If they are not, it means current is leaking somewhere it should not be going.
That leaking current could be escaping through damaged cable insulation, through water that has got into a fitting, or through a person who has touched a live part. In any of those situations, the RCD trips within milliseconds to cut the power to every circuit it protects.
Without an RCD, a fault like that can cause a fire or a fatal electric shock before any fuse has time to blow. This is why an RCD tripping is not a nuisance, it is the system doing exactly what it is supposed to do. It is a sign of a fault that needs finding, not a mechanism to override.
An RCD is not the same as an MCB, and the difference matters. An MCB (Miniature Circuit Breaker) protects against overload and short circuits. It trips when too much current flows through a circuit. An MCB does not detect leakage current. An RCD does not protect against overloads. They do different jobs, and on a well-designed consumer unit you need both working correctly.
In your consumer unit, the RCD is usually the large switch, often labelled “RCD,” “Main Switch” or “Isolator.” There is also a small test button on or beside it, usually marked “T” or “Test” — that is separate and used only for monthly testing. The MCBs are the row of smaller switches beside it, each one controlling an individual circuit in your house. Everything in this guide is operated from those switches. You are not opening anything, removing any covers or going anywhere near any wiring.
RCD vs RCBO: What Is the Difference?
An RCBO (Residual Current Breaker with Overcurrent protection) combines the functions of both an RCD and an MCB into a single device. It provides both earth leakage protection and overload protection in one unit, fitted individually to a single circuit.
On a modern full RCBO board, every circuit in your house has its own individual RCBO. That means if your washing machine develops a fault, only the washing machine circuit trips. Every other circuit in the house carries on working. The lights stay on. The fridge stays cold. You know immediately which circuit is at fault, and the rest of the house is completely unaffected.
In my experience, customers on RCBO boards rarely search for this page because their situation never becomes an emergency. One thing trips, they identify it, and they call me when it is convenient. It is a fundamentally different experience from losing half the house in the dark.
On an older RCD board, a single RCD protects a group of circuits. One fault anywhere on that group trips the whole lot, which is why you can lose half your house from a single faulty appliance. It is the design that makes a problem much worse than it needs to be.
This distinction matters for the step-by-step process below, and it matters a lot if you are thinking about upgrading your consumer unit. If your whole house went dark when one thing tripped, you almost certainly do not have a full RCBO board. That is worth addressing with an electrician once the immediate fault is sorted. See our consumer unit replacement page for more detail.
Step-by-Step: How to Get Your Power Back On
STOP — Before you do anything else.
Do not open the consumer unit cover. Do not touch any wiring inside the unit. Do not remove any panels or use any tools.
If you can see exposed wiring, scorch marks or burn marks on the unit, or if you can smell burning anywhere in the house, do not touch anything. Call an emergency electrician immediately.
Everything in this guide is done using the switches on the front face of your consumer unit. You are not opening anything, removing any covers or touching any wiring. The switches and buttons on the front face are designed to be operated by the homeowner. That is exactly what they are there for.
Before you begin, check these three things from the outside:
- No smell of burning near the consumer unit or anywhere in the house
- No visible scorch marks on the front of the unit, on any sockets or on any switches
- The front of the consumer unit does not feel warm or hot to the touch
If any of those apply, do not touch the consumer unit. Call an emergency electrician immediately.
If everything looks, smells and feels normal, here is how to isolate the faulty circuit using only the switches on the front of your board.
Step 1: Go to your consumer unit and look at the switches on the front
Your consumer unit is your fusebox. It is usually located in a hallway, under the stairs, in a cupboard or in a utility room. You are looking at the front face only. There is a large switch, often labelled “RCD” — that is the main residual current device. Beside it is a row of smaller switches. Those are your MCBs, each one controlling an individual circuit in the house. You may see labels such as “Lights,” “Sockets,” “Cooker,” “Shower” and so on. Do not open any cover or panel. Everything you need is right there on the front.
Step 2: Switch off every individual MCB using the switches on the front
Flip each small MCB switch to the OFF position, one by one. Work your way along the row. Do not touch the large RCD switch yet. Simply use your finger to push each small switch to the off position, the same way you would turn off a light switch. Keep going until every MCB is in the off position.
Step 3: Push the RCD switch back up to the ON position
With every MCB switched off, push the large RCD switch firmly upwards to the ON position. There is no separate reset button — you simply push the switch back up. Give it a firm, deliberate push.
Step 4: See whether the RCD stays on
If the RCD stays on with all MCBs switched off, that is a good result. It confirms the fault is on one of those individual circuits, not in the RCD itself or in the main supply cables feeding the board.
If the RCD will not reset even with every MCB switched off, the fault may be in the main tails (the cables between your electricity meter and the consumer unit) or in the meter itself. Those are not things anyone should touch. Leave everything switched off and call a qualified electrician immediately. Do not attempt to access the meter or the main tails.
Step 5: Switch the MCBs back on one at a time
Start with the first MCB and push its switch to ON. Wait a few seconds. If the RCD stays on, move to the next MCB. Switch it on. Wait again. Continue through the row, switching each MCB on one at a time and pausing briefly between each one.
Step 6: When the RCD trips again, you have found the faulty circuit
At some point, switching on a particular MCB will cause the RCD to trip. That MCB controls your faulty circuit. Take note of which one it was, or the label above it if there is one.
Step 7: Switch the faulty MCB back to off and push the RCD switch back up
Using the switch on the front of the unit, push the faulty MCB back to OFF. Then push the RCD switch firmly back up to ON.
Step 8: Switch all the remaining MCBs back on
With the faulty MCB left in the off position, switch every other MCB back on using the switches on the front of the board. Your house should now have power to every circuit except the faulty one.
Step 9: Find out whether the fault is a cable or an appliance
If it tripped on a socket circuit: Unplug absolutely everything on that circuit — every socket, including anything hidden behind furniture or tucked behind the television. Then switch the MCB back on. If the RCD trips again with nothing plugged in, the fault is in the cable itself — switch the MCB back off and call an electrician. If the RCD stays on with nothing plugged in, plug appliances back in one at a time. The one that causes the RCD to trip is the problem. Do not use that appliance again until it has been checked or replaced.
If it tripped on a lighting circuit: Switch every light switch in the property to the OFF position, including any outdoor lights. Then switch the MCB back on. If the RCD stays on, try switching lights back on one at a time — the one that causes a trip is the faulty fitting. A common culprit is an outdoor light or a bathroom fitting where moisture has got in. If the RCD trips immediately even with every light switch off, the fault is in the circuit cable — switch the MCB back off and call an electrician.
If the RCD trips immediately every time: Stop pushing it back up. A persistent fault will not clear itself. Leave the faulty MCB off, restore power to everything else, and call an electrician.
Keeping essential appliances running while you wait: If a socket circuit has tripped and you have another socket circuit still working, run an extension lead from a working socket to keep your fridge freezer powered until the electrician arrives. One heavy appliance per lead. If a lighting circuit has tripped, a plug-in lamp or LED lamp plugged into a working socket gives you light in the affected rooms in the meantime. These are sensible temporary measures while you wait, not permanent solutions.
If you have a modern RCBO board: the process above is not something you will need. On a full RCBO board, each circuit has its own individual combined device on the front of the board. If a fault occurs, only that one RCBO trips to the off position. The rest of the house is completely unaffected. You can see the faulty circuit immediately because its switch is the only one pointing down.
If the RCD trips immediately every time you press the reset button: stop pressing it. Every time you force a reset against a live fault, you are working against the protection the device is trying to provide. Leave it tripped, switch all the MCBs off using the front switches, and call an electrician.
Why Does an RCD Keep Tripping? The Most Common Causes
Understanding why your RCD keeps tripping helps you give the electrician useful information when they arrive, and it helps you spot whether the same fault is recurring. Here are the causes I see most often on jobs across Aberdeen and Aberdeenshire.
Faulty appliance. This is the most common cause by a significant margin. A washing machine with a failing heating element, a dishwasher with a damaged pump seal, a kettle with a cracked element, a fridge with deteriorating internal wiring — any of these can develop an earth leakage fault that trips the RCD. Once you have identified the faulty circuit using the steps above, unplug every appliance on that circuit. Then plug them back in one at a time and see which one causes the RCD to trip. That is your culprit. Do not use it again until it has been checked or replaced.
Damaged wiring. Cable insulation does not last forever. In older Aberdeen and Aberdeenshire properties, particularly those built before the 1970s, you may still have rubber-insulated wiring. That rubber dries out and cracks over decades, creating paths for current to leak to earth. On jobs in some of the older granite properties around Aberdeen, I have found wiring where the rubber insulation crumbles to dust when you touch it. That is a genuine fire risk and an EICR will flag it before it becomes an emergency.
Water ingress. Water is one of the most consistent causes of RCD tripping in Scottish properties. A leaking bathroom pipe above a light fitting, condensation inside an outdoor socket, a flooded garage or shed socket, water working its way into a garden light fitting. Aberdeen’s older granite properties, with their solid walls and sometimes ageing leadwork and pointing, can develop slow water ingress that is hard to identify until it starts affecting the electrics. If your RCD trips after heavy rain, always suspect an outdoor fitting or an outbuilding circuit first.
Nuisance tripping. Not every RCD trip has a single obvious fault behind it. Older RCDs can become oversensitive over time. More commonly, nuisance tripping happens when multiple appliances on the same RCD each leak a tiny amount of current through normal operation. Individually, none of them crosses the trip threshold. Together, their combined leakage adds up past the point where the RCD trips. This is one of the strongest practical arguments for individual RCBO protection.
A failed RCD. An RCD that trips immediately on every reset attempt, even with nothing connected to the board, may itself be faulty. RCDs are electromechanical devices and they do wear out. A failed RCD needs replacing by a qualified electrician. Do not attempt to open the unit or interfere with the device.
An RCD that has never been tested. According to Electrical Safety First, RCDs should be tested monthly by pressing the test button on the front of the unit. An RCD that has been sitting in the closed position for years without being tested can develop a stuck contact. If your RCD trips the first time you have ever tested it and it will not reset, it needs to be replaced.
RCD Tripping at Night: Why Does It Always Happen Then?
This is one of the most commonly searched variations of this question, and there is a clear practical explanation.
Most nighttime trips are caused by appliances that run on timers or kick in automatically overnight. Washing machines and dishwashers are routinely set to run on overnight economy tariffs. Storage heaters charge overnight. Immersion heaters on timers fire up in the early hours. Fridge and freezer compressors cycle on and off throughout the night, and a compressor with a developing insulation fault may leak just enough current to trip the RCD when it starts its cycle.
The other factor is temperature. On cold nights, condensation forms inside outdoor sockets, garden lighting fittings, outbuilding electrics and any fitting that is not fully sealed against moisture. That condensation creates a brief conductive path to earth. The RCD trips, and by morning when the fitting has warmed up and dried out, there is no obvious evidence of the cause. This is particularly relevant in North East Scotland, where cold nights and damp air make outdoor wiring more vulnerable to condensation-related faults. If your RCD keeps tripping overnight but you cannot find anything wrong in the morning, suspect outdoor fittings or outbuilding circuits and tell the electrician that detail when you call.
What Kind of Consumer Unit Do You Have? It Matters More Than You Think
Not all consumer units give you the same level of protection or the same experience when a fault occurs. There are three broad types you might have in a Scottish property.
Old fusewire board. The oldest type provides no RCD protection at all. Individual circuits are protected by fuse wire that melts when too much current flows. If the fuse wire does not blow, or if the fault is a leakage fault rather than an overload, there is nothing stopping it from continuing. These boards cannot be upgraded by adding new devices. They need full replacement. I still occasionally come across them in older Aberdeen granite properties that have not had any electrical work done in decades. If your home has a fusewire board, please speak to an electrician about replacing it.
Older RCD board. These have one or two RCDs covering groups of circuits. They provide earth leakage protection, which is significantly better than no protection at all, but they have no individual circuit protection. One fault on any circuit on the protected group trips the whole RCD. When it goes, a large portion or all of your house loses power at once. This is the type of board most commonly involved in the scenario this guide exists to help with.
Full RCBO board (modern best practice). Every circuit has its own RCBO on the front of the board. Earth leakage protection and overcurrent protection on every circuit, individually. One fault, one switch trips. The rest of the house stays completely on. This is what Faithful Spark installs on every consumer unit replacement.
Consumer unit replacement in Aberdeen and Aberdeenshire typically starts from £550 + VAT. It reflects a full day’s work, all necessary materials, and the compliance testing and certification required under BS 7671 Amendment 4. It is a one-off cost that removes the single-point-of-failure problem permanently.
When to Call an Electrician
Some situations call for immediate action, not a step-by-step process. Call an electrician straight away if:
- You can smell burning near the consumer unit, from a socket or anywhere in the house
- You can see scorch marks on the front of the consumer unit, on a socket, on a switch or on any fitting
- The consumer unit feels warm or hot to the touch on the outside
- The RCD will not reset even with all MCBs switched off on the front of the board
- The RCD trips immediately every single time you try to reset it
- The fault keeps returning after you have isolated and reset the circuits
For non-emergency faults where you have successfully isolated the circuit and restored partial power, a same-day or next-day appointment is appropriate. But do not leave a faulty circuit uninvestigated. The fault does not resolve itself. Contact Faithful Spark Electricians to book a diagnostic visit across Aberdeen and Aberdeenshire.
EICR: What Would Have Caught This?
Most recurring RCD faults do not appear without warning. They develop over time, and a thorough Electrical Installation Condition Report (EICR) would typically flag the early signs before they become a midnight emergency.
Deteriorating cable insulation, failing earthing connections, water ingress at outdoor fittings, overloaded circuits, RCDs approaching the end of their service life — all of these show up during a proper EICR inspection. A C2 coding on a deteriorating cable gives you the information while you still have a choice about when to fix it, rather than finding out at 11pm when the fridge is off. On jobs across Aberdeenshire I have found C1 faults that the homeowner was completely unaware of, because there had been no inspection for fifteen years.
For Scottish landlords, an EICR is not optional. Under the Housing (Scotland) Act 2006 Repairing Standard, all private rented properties in Scotland must have a valid EICR carried out every five years by a competent electrician. Failure to comply is a legal breach.
For homeowners, there is no legal obligation, but BS 7671 recommends an EICR every ten years or when a property changes hands. I would recommend not going past ten years, and sooner for older Aberdeen granite properties with pre-1970s wiring.
EICR inspections start from £150 + VAT at Faithful Spark Electricians. See our EICR Aberdeen page for more detail on what is included and how to book.
Frequently Asked Questions
Is it safe to keep resetting an RCD?
No. An RCD trips because it has detected a fault. Resetting it repeatedly does not fix the fault. It simply restores power until the fault trips the device again. Follow the isolation process in this guide to identify the faulty circuit, then call an electrician to find and fix the root cause. If the RCD trips immediately on every reset attempt, stop resetting it altogether.
Can I reset my RCD myself?
Yes, you can attempt to reset your RCD by following the step-by-step process in this guide. The switches and buttons on the front face of a consumer unit are designed to be operated by the homeowner. The key is to isolate the faulty circuit first rather than just pushing the RCD back on with everything still connected. If you cannot identify the faulty circuit, or if the RCD will not reset with all MCBs switched off on the front of the board, stop and call an electrician.
Why does my RCD trip when it rains?
Rain and the condensation that follows gets into outdoor sockets, garden light fittings, external cables and outbuilding wiring. Water creates a conductive path to earth that your RCD detects as a leakage fault. The most common culprits are outdoor sockets without adequate weatherproof covers, garden lighting on surface-run or buried cable, and sockets or fittings in garages or sheds that are not properly sealed. In North East Scotland, where wet weather is consistent, outdoor fittings need to be correctly rated for external use.
Why does my RCD keep tripping in the middle of the night?
Appliances running on overnight timers are the most common cause. Washing machines and dishwashers on economy programmes, immersion heaters on off-peak tariffs, storage heaters charging overnight, and fridge or freezer compressors cycling on can all trip an RCD if they have a developing fault. Cold temperatures overnight also cause condensation in outdoor fittings, which can create intermittent earth leakage that is hard to trace in the morning once the fitting has dried out.
My RCD trips but I cannot find the fault. What now?
This is more common than people realise, particularly on older installations where nuisance tripping is happening or where multiple small leakage currents are adding up past the trip threshold. If you have followed the isolation process and cannot pin down the circuit, or if the fault returns repeatedly, you need an electrician with a multifunction tester. Proper RCD diagnostics involve a ramp test, a half-times test, and a full trip time test at rated current. These tests identify whether the RCD itself is faulty, oversensitive, or whether there is a genuine leakage fault on the installation. Get in touch with our Aberdeen team to book a diagnostic visit.
What is the difference between an RCD tripping and an MCB tripping?
When an MCB trips, only the one circuit it protects goes off. An MCB trips due to overload or short circuit on its own circuit. When an RCD trips, every circuit on that RCD goes off simultaneously, which is why a large portion of the house can go dark all at once. An RCD trips due to earth leakage current detected across all the circuits it monitors. Both are doing their jobs correctly, but they are protecting against different things. Read our guide on how to reset a tripped circuit breaker for more on MCBs and RCBOs.
How do I know if my RCD is faulty?
Signs of a faulty RCD include: the device trips immediately on every reset attempt even with all MCBs switched off on the front of the board; it trips randomly with no identifiable fault; or, more dangerously, it fails to trip when you press the test button on the front of the unit. That last one means the RCD has failed in the closed position and is no longer providing protection. If any of these apply, the RCD needs to be replaced by a qualified electrician. Do not attempt to open the unit or work on the device yourself.
Do I need to replace my consumer unit if my RCD keeps tripping?
Not necessarily, but it depends on the cause and the age of the board. If the RCD device itself is faulty, replacing that device may be sufficient. If your board is old and you are repeatedly losing half the house from a single fault, a full consumer unit upgrade to a modern RCBO board is worth serious consideration. An electrician can inspect the condition of your existing board and give you an honest assessment.
How often should I test my RCD?
Monthly, using the test button on the front of the consumer unit. Press it — the RCD should trip. Then reset it using the switch on the front. That is the entire process and it takes under ten seconds. It confirms the RCD mechanism is working and has not seized in the closed position. Many homeowners have never done this in the years they have lived in their property. If you test yours for the first time and it does not trip, or it trips and will not reset, it needs to be replaced.
About the Author
Steven Watt is the founder of Faithful Spark Electricians, an NICEIC Approved Contractor based in Peterhead, serving Aberdeen, Aberdeenshire and the wider North East of Scotland. He holds City and Guilds 2357, 2365, and 2391-52, an HNC in Engineering Systems, and is an AICO Expert Installer, OZEV-authorised EV charging installer, and approved installer for Ohme, Myenergi Zappi, Andersen EV and ICS.
Faithful Spark Electricians | NICEIC Approved Contractor | Peterhead, Aberdeen and Aberdeenshire
