Testing & safety
RCD keeps tripping: how to find the cause and what to do
A click in the hallway, then silence. What the residual current device has just measured, how to find the culprit in a few steps – and when it is better to keep your hands off.
TOKSEL Elektrotechnik editorial team Published on 5 min read
A click in the hallway, then silence. The fridge falls quiet, the router stops blinking, somewhere a battery-powered smoke alarm chirps. The first impulse: off to the fuse box, flick the lever back up, carry on as before. And sometimes that works. Often, though, the lever drops straight back down – and that is exactly the moment to pause. Because the residual current device (RCD, FI-Schutzschalter) has just done what it is there for: it has noticed current taking a path it was never meant to take.
What the RCD actually measures
The residual current device – FI for short in German, RCD in English – constantly compares how much current flows into a circuit and how much comes back out. When everything is in order, the two are equal. If part of the current leaks away along another path – via the protective conductor (Schutzleiter), through moisture or, in the worst case, through a person – a difference arises. Once it reaches the rated value – usually 30 mA in homes – the RCD switches off in a fraction of a second. That makes it one of the most important life-savers in your electrical installation.
Safety first
- Do not keep switching the RCD back on if it trips again immediately.
- If you smell burning, if water is involved or if you see scorch marks: leave the circuit off and call a qualified electrician (Elektrofachkraft).
- Never bypass an RCD, and do not open any covers in the distribution board.
Narrowing down the cause step by step
With this method, you can often work out for yourself which circuit and which appliance is tripping the RCD – without tools and without opening the cover of the distribution board:
- Switch off all miniature circuit breakers (“fuses”, Leitungsschutzschalter) downstream of the affected RCD.
- Switch the RCD back on. If it stays on, the fault lies in one of the circuits.
- Switch the circuit breakers back on one at a time. If the RCD trips, you have found the affected circuit.
- Unplug all appliances on this circuit, then switch the circuit breaker and the RCD back on.
- Plug the appliances back in one by one. If the RCD trips, the appliance you plugged in last is the culprit.
If the RCD trips even though nothing at all is plugged into the circuit any more, the fault lies in the fixed installation – and that is a job for a qualified electrician.
The usual suspects
| Appliance or location | Typical cause |
|---|---|
| Kettle, washing machine, dishwasher | moisture or an insulation fault in the heating element |
| Outdoor sockets, garden lighting, pond pump | rainwater or dew in boxes and light fittings |
| Old light fittings and fairy lights | brittle insulation, moisture ingress |
| Many power supplies on one RCD | the sum of small leakage currents from computers, TVs and chargers |
| Junction boxes in the cellar or garage | condensation, corrosion |
| One particular light trips the RCD | neutral conductors swapped or connected to the wrong circuit, often after alterations |
| Tripping during thunderstorms | overvoltage – see Surge protection |
When to call an electrician
Call a qualified electrician if the RCD trips with no appliances connected, if it trips sporadically with no recognisable pattern, or if it will not switch back on at all. With insulation resistance measurement, leakage current measurement and systematic fault location, the cause can then be tracked down – often within one to two hours. We explain how the cost of such a call-out is made up in our guide How much does an electrician cost?
Prevention rather than detective work
- Press the test button: many manufacturers recommend doing so every six months. If the RCD does not trip, it must be checked.
- Spread the circuits: if every circuit runs through a single RCD, any fault plunges the whole home into darkness. Several RCDs, or combined RCD/MCB devices (RCBOs, FI/LS-Schalter) for each circuit, keep the rest of the home on the grid.
- Look after outdoor areas: check the seals on outdoor sockets and light fittings, and keep the cover flaps closed.
You can read about the different RCD types and when arc fault detection devices (AFDDs, Brandschutzschalter) make sense in our guide RCDs and AFDDs.
Conclusion
A tripping RCD is not a defect but a message. With a little calm, you can often decode it yourself – and if not, we will find the fault. We help in Cologne, Hürth and the Rhein-Erft district: call or WhatsApp us on +49 172 7133110, or use our enquiry form. Find out more about inspections under Testing & maintenance.
Frequently asked questions
Why does my RCD trip at night?
At night, appliances are at work that you hardly notice during the day: the defrost heater in the fridge or freezer, circulation pumps, outdoor lighting. On top of that, dew collects in outdoor boxes. The step-by-step method will help you narrow down the trigger here, too.
Can an RCD be faulty?
Yes. RCDs age too. They can become oversensitive or fail to trip when it really matters. That is why regularly pressing the test button and having the device measured during an installation inspection are so important.
Am I allowed to bypass the RCD?
No, under no circumstances. A bypassed RCD no longer protects against fatal electric shocks. If it keeps tripping, the cause must be found – not the protection switched off.
How much does it cost to have an electrician find the fault?
That depends on the effort involved. Many faults can be narrowed down within one to two hours. Photos of the distribution board and a description of when the RCD trips help to keep the time on site short.
Related service
Electrical installation
Electrical installation for commercial and residential buildings – new builds and refurbishments, including meter boards and sub-distribution.
This article provides a general overview (as of October 2026) and does not replace an assessment or advice in the individual case. The applicable standards, laws and the requirements of your grid operator are decisive.
