Short answer
If you hit a cable, the breaker or the RCD usually trips. Let go of the drill, keep away from the drill bit and switch off the circuit before you touch anything. Repairing means locating the damaged spot, joining the cable in an accessible junction box or replacing the section. Wrapping a cable in tape and plastering over it is not a repair.
Who this article is for For the moment you have just drilled and the lights went out. Read this before you touch anything.
What to do straight away
- Let go of the drill and do not touch the drill bit or the drill.
- Go to the meter cupboard and switch off the circuit. If you do not know which one, switch off the main switch.
- Only then take the drill bit out.
- Check whether there are burn marks or whether it is smoking.
- Call.
The breaker or the RCD should trip when a drill hole hits a cable. That is the protection doing its job, and it is why an RCD is no luxury.
Why you should not just plaster over it
A damaged core that is wrapped in tape and disappears behind plaster is a problem that comes back in a few years: damp, heat and oxidation do the rest. And you no longer know where it is.
A repair should be done with a junction box that stays accessible, or by replacing the section of cable. That is the standard and it is also simply sensible.
How the repair goes
- locate the damaged spot and expose it
- assess whether only the sheath has been hit or the cores as well
- fit a junction box at that spot, or renew the cable from box to box
- test: insulation, continuity and the operation of the RCD
- record the spot on a photo, so you know later where it is
A junction box in a wall must stay accessible. That can be done with a blank cover you can open later, behind a small hatch or in a cupboard.
How to prevent it
- do not drill directly above or below a switch or socket: the cable runs vertically there
- nor horizontally at switch height, because a run often goes there
- use a cable detector, and test it first on a spot where you know for sure there is a cable
- if you have photos of the walls from before the plastering, look at those first
Stay out of these zones, or look at the photos from before the plastering first.
That last point is why I always hand over those photos. What else is recorded during a renovation is in concealed or surface-mounted wiring.
From my own work
A customer in Beek was drilling for a mirror and hit the cable to the bathroom dead on. The RCD tripped, which is exactly what it should do. He had left the drill bit in and switched off the circuit, which was right. A junction box was fitted at that spot, neatly accessible behind a small hatch, and the cable was joined. About an hour's work.
When to call an electrician
- You have hit a cable and the circuit trips
- There have been sparks or a bang
- You are not sure whether you hit something but a circuit is behaving strangely
Leave the circuit off until I get there. Call +31 43 204 18 26 or outside office hours use the fault service.
Frequently asked questions
Is it dangerous if I drill into a cable?
The most dangerous moment is the contact itself. That is why you let go of the drill, switch off the circuit and only then take the drill bit out.
Can I repair the cable myself with tape?
No. A repair should be done with a junction box that stays accessible or by replacing the section of cable. Tape behind plaster comes back years later as a fault.
What if the circuit simply works again?
Have it checked anyway. A core that has been drilled into can work for a while and then still cause problems, and at least you now know where it is.
Further reading
RCD keeps tripping: how to find the cause yourself
Usually it is one appliance and not your installation. In four steps you find out yourself which one, and you read exactly where it stops and you need to call.
Lights flickering or dimming: what it tells you
Flickering in one light is usually the bulb or the dimmer. Flickering throughout the house is a reason to measure.
The circuit breaker trips: overload or short circuit
A breaker that only trips after a while points to overload. If it trips straight away, it is a short circuit.
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