A circuit that keeps tripping can turn a normal day into a guessing game, especially when the fault comes and goes. In Swansea homes and small businesses, the cause is often hidden behind a single appliance, a damp socket, or a circuit that is carrying more than it should.
If tripping RCDs and breakers keep happening, the fault is usually a leaking appliance, an overloaded circuit, a short, or moisture in wiring. The safest way to narrow it down is to isolate appliances, reset circuits one by one, and look for patterns under load. Repeated trips, burning smells, or visible moisture need a qualified electrician.
What to do first after a trip
A single trip often points to one bad item, not a full house problem. The fastest safe move is to switch off the affected circuit, unplug obvious appliances, and then reset only once.
The whole check usually takes 10 to 20 minutes if the fault is simple. If the same device trips again straight away, stop there. That pattern matters.
Check which device actually tripped
Look at the consumer unit and identify the device that dropped. An RCD protects against leakage to earth, while an MCB protects against overload and short circuit.
That difference saves time. A lot of people reset the wrong device and chase the wrong cause, which is where the confusion starts.
Switch off the load first
Turn off lights, unplug kettles, heaters, washing machines, chargers, and anything with a motor or heating element. These are the usual suspects because they pull the most current when they start.
A common mistake is leaving everything plugged in and just pushing the switch up again. It may work once, then it trips again and looks random.
Compare the RCD and MCB symptoms
An RCD trip usually means current is leaking somewhere it should not. An MCB trip usually means the circuit has too much load or a direct fault between live and neutral.
That sounds technical, but the practical clue is simple. If one breaker trips when several appliances run together, think overload. If one device trips even with very little on the circuit, think leakage or a short.
What an RCD trip feels like
An RCD often drops more suddenly than people expect. It can trip because of a kettle with damp inside, an outdoor socket with water ingress, or a cable with damaged insulation.
Electrical Safety First has long warned that water and damaged accessories are common triggers for residual current device testing failures, especially in kitchens, bathrooms, and outdoor areas. Electrical Safety First guidance on RCD testing
What an MCB trip feels like
An MCB often trips when too many things run at once. A kitchen circuit with a kettle, toaster, and microwave can push a breaker over the edge very quickly.
The trick is to notice timing. If it trips when something starts up, that points to the starting surge or a fault in that appliance. If it trips after a few minutes, heat and sustained load are more likely.
The error most people make here is blaming the RCD when the MCB has actually tripped first. That simple mix-up sends the diagnosis in the wrong direction.
Which clues point where?
Use this table to separate the two quickly. It is often clearer than guessing from memory after the power has gone off.
| Clue |
RCD |
MCB |
| Main cause |
Earth leakage |
Overload or short circuit |
| Common trigger |
Moisture, damaged appliance, insulation fault |
Too many appliances, faulty device, wiring fault |
| Best clue |
Trips with one appliance or damp area |
Trips under heavy use or when starting equipment |
| What to check first |
Sockets, outdoors, bathrooms, appliances |
Load on the circuit, start-up surges, damaged leads |
Find the fault one circuit at a time
The cleanest method is simple: turn everything off, reset the RCD, then bring circuits back one by one. This usually finds the bad circuit in under 15 minutes if the fault is obvious.
If the unit trips again while one circuit is on, that circuit is your suspect. If it stays up until one appliance is plugged in, that appliance or socket is the likely problem.
Turn circuits on in order
Switch all MCBs off first. Reset the RCD. Then turn one MCB on and wait.
Give each circuit 30 to 60 seconds. Some faults show at once. Others need a fridge, boiler pump, fan, or charger to start before they appear.
A case seen often: a downstairs socket circuit seems fine, then the breaker trips only when a dehumidifier starts. The fault was not the whole circuit. It was the appliance plus an already busy load.
A one-circuit-at-a-time test works best when you leave each appliance unplugged at first. That way, the circuit tells its own story before a device changes the result.
Watch for the pattern under load
If a circuit stays on with nothing plugged in, plug items back in one by one. Start with low-power items, then move to heaters, kettles, washing machines, and vacuum cleaners.
This works well in theory, but in practice the fault often appears only after five or ten minutes. Heat changes things. So does vibration from motors and pumps.
Stop when the same item
If one appliance trips the circuit twice, stop using it. Do not keep trying it “just once more”.
That repeated trigger is usually enough evidence. A faulty plug top, damaged flex, or internal leakage can turn a small issue into a bigger one very quickly.
⚠️ Do not test suspect appliances on other sockets just to see what happens. If the appliance is faulty, moving it can spread the problem instead of solving it.
1. Identify
Check whether the RCD or the MCB tripped.
2. Isolate
Switch off circuits and unplug obvious loads.
3. Reset once
Restore [power](https://swansea-electrician.co.uk/your-rcd-cannot-detect-every-arc-or-power-surge/) with everything still disconnected.
4. Rebuild the load
Reconnect appliances one by one until the trip returns.
A practical way to pinpoint the culprit is to work methodically from the consumer unit. First, note whether the residual current device or the miniature circuit breaker has tripped. Then switch off every MCB, reset the RCD once, and bring each circuit back individually. If the RCD holds until one circuit is energised, that circuit is the likely source of the earth leakage or electrical fault. From there, unplug everything on that circuit and reconnect items one at a time.
If a specific faulty appliance or damp socket makes the trip return, you have narrowed the problem without guessing. This step-by-step approach is especially useful when a fault appears only under load or after a few minutes, because it separates a circuit overload from a hidden leakage issue.
Track hidden causes that come and go
Intermittent trips are the ones that frustrate people most. They often happen because moisture, heat, or a loose connection only becomes a problem at certain times.
A wall socket can look fine and still fail under load. A cable in a loft or outside wall can also fault only when the weather changes.
Why damp causes random trips
Damp creates a path for current where it should not go. Think of it like a tiny wet bridge between wires or between a wire and earth.
Bathrooms, kitchens, outdoor sockets, garage circuits, and garden lights are the usual places to check first. Moisture in these spots can cause a clean reset and then another trip ten minutes later.
The data point worth remembering is this: repeated intermittent trips often come from environmental faults, not from the consumer unit itself. That is why checking locations matters more than guessing at the breaker.
How a bad socket behaves
A faulty socket can trip only when a plug sits in a certain position. Wiggle tests are unreliable for safety, but a pattern is useful if one plug works and another does not.
The most common sign is a socket that feels warm, smells faintly burnt, or has a loose faceplate. If that happens, stop using it.
When load is the real trigger
Trips under load are a clue, not a mystery. If the breaker only fails when the kettle and toaster run together, the circuit may simply be carrying too much at once.
BS 7671 and the IET Wiring Regulations expect circuits to be used within their rating. IET guidance on BS 7671
Some faults only show up in very specific conditions. A trip under load often points to a circuit overload, a weak connection, or an appliance that fails once it heats up. A socket that looks normal may still be defective and trip only when a plug is inserted fully or when a heavy appliance draws current. Hidden moisture can also be the cause: water ingress in an outdoor fitting, a loft junction box, or behind a wall can create earth leakage long after the rain has stopped.
That is why intermittent trips are so frustrating. The circuit may reset cleanly in the morning and fail again later when humidity rises, a washing machine starts, or a motor in a fridge or pump kicks in. In those cases, damaged insulation or a loose connection is often the real issue, not the consumer unit itself.
Call a qualified electrician straight away if the breaker trips repeatedly, if there is a burning smell, scorch marks, buzzing from the consumer unit, or if any socket, plug, or cable feels hot to the touch. The same applies if the RCD will not reset, if the fault returns immediately after load testing, or if you suspect water ingress in a bathroom, garage, loft, or outdoor circuit. Frequent trips can mean a developing short circuit, damaged insulation, or a fault that is getting worse each time it is energised.
A professional can carry out safe testing, locate the earth leakage source, and confirm whether the overload protection device or the wiring itself needs repair.
