I'm trying to add a whole house fan in the attic.

Currently there are many power cables in the attic and as far as I know, they all feed lights and bathroom fans - implying they are all switched.

To connect the fan, I think I need a non-switched wire that I can tap into.

Will my search for a non-switched wire in the attic prove to be futile ?

Any tips on how to find one ?

  • 1
    Is power always run to the switch box first then to the light, or is there anywhere where there's only one cable in the switch box? Jun 6, 2020 at 15:46
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    Just because they supply power to a switch or to a fixture that is switched does not mean they are switched. Are any wires originating from the breaker box or are you only talking about wires that go from switches to fixtures or vise versa ?
    – Alaska Man
    Jun 6, 2020 at 15:49
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    Get a non-contact tester and run around the attic while all the lights are off. You might find something. Now, whether that's a circuit that you should use, that's a different question. Jun 7, 2020 at 0:43
  • non-contact testes have been known to give wrong answers on switch loops.
    – Jasen
    Jun 7, 2020 at 3:25
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    You shouldn't just be tapping wires, though. Don't cut into a cable and try to attach additional wires to it. That is unsafe, sloppy, and is the kind of thing that starts fires. The best way to run it is to go from a switch or outlet that has hot and neutral. The second-best way is to cut the cable and place 2 junction boxes about 9" on either side of it, with a replacement cable between them. That gives enough wire length inside the boxes to properly splice. Jun 7, 2020 at 5:05

2 Answers 2


You should check the instructions for the fan, but I suspect it draws too much current to simply be tapped into an existing circuit. It may be best to hire an electrician to bring a new circuit from the panel to the fan location.


Look for a light fitting where there are two or more cables going to it and it is the only light on that switch. - there will be a live and a neutral in that box.

Else fish a second cable down to an existing light switch that feeds a light fitting that only has one cable there will be an always hot and a neutral in there (so long as it's not a multi-way switch)

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