I'm installing an air conditioner above a bedroom window, but there's no electric outlet nearby. I'm to avoid running wire along the wall, and I noticed that the light fixture receptacle has an empty conduit pointing in the direction of the window. If it reaches the window (or close enough to it) I could drill near the window and put an outlet there. However, I have no way of telling if the conduit continues straight ahead or curves to somewhere. I put a snake wire in it, and it goes in fairly easily more than the distance from the light fixture to the window.

Is there any way to trace the path of the empty conduit? It's embedded in a concrete ceiling, about two or three inches deep.


  • Embeded is tough because most toners won't locate through concrete. I have had some luck putting a snake in and having some one rattle it around while I use a piece of pipe like a stethoscope. I have crappy hearing but can usually find pipes using this method. An automotive stethoscope may work well for you I just use a piece of conduit scrap.
    – Ed Beal
    Commented Aug 24, 2017 at 17:57
  • I guess to where is only going to be so useful. You have to access it - ... somewhere, or nowhere? Do you have any other paths you can access it with? (floor for example). Not to mention, can the wiring circuit you would connect to in the light support the A/C? what else is on the circuit? Are you trying to supply this power permanently for this use? (I.e., why cannot you have wire in conduit?
    – noybman
    Commented Aug 25, 2017 at 0:09
  • @EdBeal It's in the ceiling so using a 'stethoscope' will be a real pain Commented Aug 25, 2017 at 8:00
  • Good luck embedded locations are a real pain. But the method I described works.
    – Ed Beal
    Commented Aug 25, 2017 at 11:49
  • Don't be fooled by the empty conduit. Many electricians install one to use as part of the hanger for the box. There is a good chance it simply runs a few inches or feet and runs out. That would be my guess but you could run a fish tape down it (see @EdBeal), and see if you can hear it in the ceiling or tapping at another box. Commented Aug 25, 2017 at 13:34

3 Answers 3


This is going to be slow, but see if you can affix a strong neodymium magnet to the end of your fish tape, and detect it with a well balanced compass.

Even better, use magnetic viewing paper, and have someone reciprocate the fish tape while you watch through the paper for a vibrating field. magnetic viewing paper

I'd personally try a toner tracer first, but a magnetic field will be harder to block than a toner. Toner Tracer

Perhaps you could use coaxial cable as your push wire. Attach the toner to the core on one end, strip back an inch of jacket on the other so most of the toner'e RF energy makes it down the cable to a point emanator on the far end. Then carefully follow that point as you push the coax down the conduit.


The conduit may end in a box in the wall that has been painted over. Carefully tap on the wall in general area where the fish tape seems to get caught and look for a hollow. If you find a round/square shape, pry it off and the fish tape just be there.

(This is what actually happened to me, the OP).


I had used dye at one of the exit points I could not trace. After a day or two the green dye seeped through the plastered wall and I knew that is where the conduit ended. Unfortunately for the conduits that go up to roof I am yet to discover where they exit but I am not giving up. Fortunately I was forced to install solar since I would not have been passed for inspection.

Barbados home owner

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