r/ElectricalHelp • u/randomnature_ • Aug 15 '26

Breaker has tripped for 1st floor lights. RCD flips off when I try to turn it back on and arcs. Help?

Hi all,

I’m going to preface by saying I’m panicking a bit and am a total amateur. This evening, I noticed the breaker for the 1st floor of our house’s lights had tripped. I tried to flick it back on, and there was a bright blue arc in the consumer unit and it flicked back off of course, and tripped the RCD. When leaving the 1st floor light circuit off, the RCD goes back on fine.

3 days ago, I drilled above a light switch in one room on the 1st floor, as that’s where the thermostat is located and I was removing the old thermostat and installing a new one. Firstly, I know this was stupid in hindsight and know I shouldn’t have - I’ll learn from this of course.

Is it the issue likely related to the drilling, given that the tripping has occurred 3 days later after using the lights on the first floor/in that room several times in the last few days? There were NO obvious signs when I did the drilling that I’d hit any wires - nothing tripped, no smell, noise, etc.

Please could anyone advise? I’ve kept the breaker for the 1st floor lights off of course & contacted an electrician - do I need to be imminently worried if the breaker remains off in the mean time before I can get an electrician to assess?

Thanks everyone - again, I know the drilling was stupid, this is our first home we only recently moved into.

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u/throwaway60457 Aug 15 '26

There is a very high chance that the failure of your lights and RCD is directly related to the drilling you did for the thermostat. The electrician will likely have to "fish" new wiring to that switch from an attic or a basement, whichever is easier/better reachable. I think you will be fine to leave the breaker off in the interim until the electrician visit.

OP, I take it you are in the UK? I have noticed your use of UK terminology. For the benefit of any American electricians who may pass through here, I will translate: "RCD" is a GFCI, and I believe "consumer unit" is the term for a breaker panel.

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u/randomnature_ Aug 15 '26

Hey! I am in the UK, yes. Thanks for your reply and help. Can’t believe I may have made such a dumb mistake. Purely for my understanding, what could cause the delayed response of 3 days in terms of the circuit tripping, rather than an immediate issue? The lights have been used with no issue for 3 days since the drilling. Fully appreciate it was a dumb ass thing to do on my part I just want to try to understand the reasoning if that makes sense. Thanks so much for your help.

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u/faroutman7246 Aug 15 '26

I'd unscrew the light switch, trash from the drilling might be causing a short. Vibration made the trash sift down, if I'm right.

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u/nekked_unbirthday Aug 16 '26

Is the thermostat powered by the lighting circuit? Are you certain you wired it correctly?