Lumiel provides fast-response fault finding for homes across Sutton, South London and Surrey. Our certified electricians trace persistent tripping to its source, carry out the repair and test the installation to restore safe, stable power.
This is written for the moment you are standing at the board, resetting the same switch again. An RCD that trips once has done its job. An RCD that trips again and again is telling you a fault is still there and has not been found.
Most repeat tripping traces back to a single faulty appliance, and you can often find it yourself. The rest is worth a proper look, because an RCD is the one device standing between an electrical fault and a serious shock. What follows is what you can safely check before calling an electrician.
What an RCD Does
An RCD, or Residual Current Device, compares the current flowing out along the live conductor with the current returning along the neutral.
In a healthy circuit, the two match. If they do not, current is escaping somewhere it should not: through damaged insulation, through water, or through a person.
When the difference reaches thirty milliamps, the RCD disconnects the supply within a fraction of a second. That speed is the purpose of the device. It is fast enough to prevent a shock becoming a fatal one.
The distinction is worth stating plainly. An RCD is not there to protect your appliances. It is there to protect you.
Common Causes
A Faulty Appliance. The most common cause by a considerable margin. Kettles, washing machines, dishwashers, fridges and immersion heaters develop small leakage faults as heating elements age. Older extension leads and outdoor equipment are frequent contributors.
Accumulated Leakage. Every appliance leaks a small amount to earth. This is normal. However, enough appliances on one RCD can bring the combined total close to the trip threshold. Nothing is faulty. The board simply has no headroom, and switching on one more appliance is enough to disconnect it.
Water Ingress. An external socket after rain. A leak above a ceiling light. Damp reaching a cable in a bathroom or kitchen. Water bridges connections and the RCD responds exactly as designed.
Damaged Wiring. A nail or screw through a cable from previous work. Insulation degrading with age. Rodent damage in a loft. Less common, more serious, and it will not resolve itself.
A Failing RCD. These are mechanical devices with a service life. An RCD that disconnects with no load, or refuses to reset with all circuits off, may be reaching the end of it.
Which Switch Has Tripped?
Before anything else, look at which switch has moved. It tells you a good deal about the fault you are chasing.
A Single Small Switch. That is an MCB, or Miniature Circuit Breaker, and each one guards a single circuit against too much current. If one has flipped on its own, something on that circuit overloaded it, or a live conductor met a neutral. The fault sits on that one circuit, which makes it the simpler of the two to trace.
One Larger Switch, Several Circuits Dead. That is the RCD, and it has cut a whole group at once. This points to earth leakage somewhere in the group, and it is the more urgent case, because leakage means current is finding a path it should not have. The rest of this guide is aimed at this.
Newer consumer units often fit an RCBO on each circuit. An RCBO, or Residual Current Breaker with Overcurrent, does both jobs in one device: the earth-leakage protection of an RCD and the overload protection of an MCB. If your board is built this way, a trip already points to a single circuit, and much of the work below is done for you.
When to Stop and Call Us
Some of what follows is reasonable to try yourself. Some points straight to calling us instead.
Contact a certified electrician if:
- The RCD will not reset with all circuits off.
- It disconnects with nothing plugged in.
- It operates repeatedly over several days with no obvious cause.
- More than one RCD is involved.
- There is any smell, mark or noise at the board.
Nuisance tripping from accumulated leakage is a design matter rather than a fault, and it usually points toward a board that would benefit from RCBOs on individual circuits. We measure the leakage on each circuit and tell you which of the two you have.
Our electricians carry insulation resistance and earth leakage testers. We diagnose the fault, explain what we have found, quote a fixed price and carry out the repair. The circuit is tested and certified before we leave.
Finding the Circuit
Where your RCD protects several circuits, you can usually isolate the affected one yourself.
Switch off every MCB in the group the RCD protects. Reset the RCD. It should hold with no circuits live.
Now switch the MCBs back on one at a time. When the RCD disconnects, the circuit you have just restored is the one carrying the fault.
Leave that circuit switched off. Unplug everything on it, reset, then reconnect appliances one by one. If it disconnects as you reach the tumble dryer, the appliance is your cause.
If the RCD disconnects with the circuit live but nothing plugged in, the fault is in the fixed wiring. That requires an electrician with test equipment.
Resetting Safely
A few rules are worth holding to.
Reset once. If it holds, continue and investigate. If it disconnects immediately, please do not keep resetting. You are re-energising a known fault, and the device is refusing for a reason.
This is different from testing circuit by circuit, described above. Switching each MCB back on to trace a fault is a deliberate, one-off check. What the rule above guards against is resetting the same circuit again and again once you already know it trips straight back.
Please do not remove the cover of the consumer unit. The outer lid is designed to come away. The board is not, and live parts sit behind it.
If you notice a burning smell, scorching, buzzing or crackling at the board, leave it switched off. That is not nuisance tripping.
Electrical Safety First recommends testing the RCD every three months. Press the test button and the device should disconnect instantly. If it does not, it is not protecting anything and needs attention.
Book an RCD Fault Diagnosis
If your RCD keeps tripping and you have run out of appliances to unplug, the next step is testing.
Lumiel provides electrical fault finding across Sutton, South London and Surrey. We are an NICEIC-approved contractor, fully insured, working to the 18th Edition Wiring Regulations. Fixed price quotes, with no hidden fees.
Call Lumiel to book a diagnosis.
Frequently Asked Questions
Almost always an appliance on a timer. An immersion heater, a washing machine, a dishwasher or a freezer defrost cycle. Note what is running when it happens and you will usually have your answer within a day.
The tripping itself is protection working correctly. The danger lies in the fault behind it, and in the temptation to work around the symptom. If you are resetting the same device daily, something on that circuit needs to be found.
It depends on the board. If everything else is sound and the RCD has failed, it can be replaced. If the board is old, lacks protection on some circuits, or trips constantly through accumulated leakage, an upgrade to a modern consumer unit with RCBOs is usually the better answer. We test first and advise accordingly.
