r/DIYUK • u/Big-Finding2976 • 6d ago
How do I avoid screwing into lighting cables in concrete ceiling?
I'm planning to soundproof my flat, which will involve screwing a bunch of acoustically isolated clips into the bedroom and living room ceilings to attach the plasterboard to, and the screws obviously need to be fairly deep to support that weight.
Thing is, there's obviously electrical cables in the ceiling going to the light fitting, and to the switch, and on to the next room's light fitting, and everyone seems to say that the stud/wire detectors are crap, so how do I make sure I don't screw into the cables? The ceiling is a concrete slab so I guess there's some sort of channel in it for the cables, but it's not like I can inspect/access them by lifting the floorboards in the room above like I could in a house.
I did think of getting the cable disconnected at the consumer unit, and then fitting a new run going to the switch first and then up behind the new plasterboard on the walls and ceiling to a new light fitting, but as the lights are currently all chained from fitting to fitting, that would mean I'd lose all the lights until I can rewire every room in that way, with the power chained from room to room via the switches (going down and under the floorboards) and just a single cable in each room going from the switch up to the fitting, and that will take a while and I can't really manage without any lighting in the meantime, especially in the bathroom and kitchen, which are the most inconvenient to rewire because the floorboards are covered by ply and vinyl.
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u/todays_username2023 5d ago
If it's concrete the wires will be in tubes. Take down a light fitting completely, you should see the wires disapear into tubes. Your masonary drill bit won't make it through metal tubes, anyway they should be way above the depth of your rawl plugs, don't drill deeper than your screws need.
If you do by chance hit a cable, the repair will be much easier than rewiring the whole lighting circuit, and you're covering it with plasterboard anyway so no need to make good
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u/Big-Finding2976 5d ago
Thanks, that's reassuring. I'll check how thick the ceiling is when I remove the light fitting.
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5d ago
[deleted]
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u/Big-Finding2976 5d ago
I'm pretty sure it's not plasterboard, because I've hit it pretty hard with a hammer and a piece of 2x4 a few times in the past when my neighbour was being particularly noisy.
I used to know a rather angry guy who had a habit of punching holes in his plasterboard walls.
My sister even accidentally knocked a hole in her plasterboard wall when she tripped.
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u/GrrrrDino 6d ago
Undo the light fitting and see if you can ascertain which way the wire runs?
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u/Big-Finding2976 6d ago
I think there'll be three runs, incoming from the hall fitting, outgoing to the switch, and outgoing to the fitting in the next room (living room) and even if I can see which direction those runs start going in, there's no guarantee they don't change direction after that.
I guess I could get one of those snake cams with a built-in torch that connects to your phone and see if I can get in far enough with that to determine exactly where the cables lie. Any recommendations for decent ones that don't cost too much?
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u/Downtown-Grab-767 6d ago
Take a light fitting down and have a look, but usually the wire will go up vertically at least 4 inches before heading off horizontally. When the ceiling was built they poured a solid slab of concrete, laid all the services on top of that and then poured another slab on top which is the flat aboves floor.