Locating mains wiring in external walls with foil-backed insulation behind plasterboa

googler

I want to put some deep wall fittings/fixings below the wall lights in one of my rooms. This is an external wall.

Logic suggests that since the room has ceiling lights too, that the electricians/builders would have run the cable in the pitched roof void above the ceiling, and dropped them down vertically to the wall lights, but I want to make sure of this. I have no access to the roof void, no hatch

I have a Draper stud/metal/voltage detector, but all it's responding to is the metal in the insulation. Run it over the wall on metal/volt setting, and it beeps between the studwork, where the insulation is, and goes quiet when I pass it over a stud (and beeps where there are plasterboard nails in the studwork). All I'm getting is the continuous tone which indicates metal, no intermittent tone, which should indicate live wires.

Run it over an internal wall (no foil) on metal/volt setting, and it only responds to live wiring and nails. Hold it next to a loose cable (vacuum cleaner) and I get live wire tone. So I'm happy the detector is working fine.

I can't get a reading off the ceiling for live wires, probably because the device has a depth limit, and the cables (if there) will be running atop the joists, out of range

How would you proceed?

(How do I know the insulation has foil? I saw the studwork in other external walls when bathrooms were being redone)

jk0

Could you unscrew the base of the wall lights, and see which way the cable enters them?

TheCyclingProgrammer

You should be able to see behind the light fitting which way the cable is coming from, you should see the conduit.

googler

Done now, I was trying to avoid taking the wall light off, but when that was done, the cable was clearly going upward. Thanks all.

cyclonebri1

You also need to remember the detector will only bleep intermittently if the light is switched on, other wise it just detects as metal.