We have a house with a lot of 2-prong outlets I'd like to replace. They're all fed by conduits. Multiple people (in real life and online) have told me that replacing them is easy: "Just fish the new cable through the conduit," or, "tie the old cable to the new cable and pull it out."

However, I can't do either of these things if I don't know which conduit-openings belong to the same length of conduit. The conduit out of all of the electrical boxes simply go up or down, and I don't see any of it in the basement or attic (except out of the panel). To make matters worse, almost all of the outlets in the house are on a single circuit, so they could be tied together in almost any way.

So, how can I tell where the ends of the conduit are so I can rewire my house?

  • Tough one. Most tracers are intended to identify which circuit breaker is connected to which outlet. Wire tracers generate tones, but seem to work only with unshielded wires (not in conduit). If most outlets are on a single circuit, a full rewiring seems in order.
    – bib
    Aug 29, 2013 at 18:24
  • 1
    @bib: Well, yes, I'd like to do a full rewiring. But I'd also like to utilize the existing conduit if possible. That's the purpose of this question. Aug 29, 2013 at 18:36
  • Don't the conduits end up at the service panel?
    – bib
    Aug 29, 2013 at 18:42
  • @bib: Some of them go from the panel to a box somewhere, but some must also go from box to box. I can't just pull the wire at the service panel without unsplicing it first... Aug 29, 2013 at 18:48
  • I prefer the F-Ray images3.wikia.nocookie.net/__cb20071224020934/en.futurama/…
    – Jason
    Aug 29, 2013 at 20:36

3 Answers 3


Since you're talking about an electrical circuit with a line/load connection in each outlet, you can start disconnecting one side of the connection and then noting all the receptacles and fixtures that lose power, which will be on the load side of where you disconnected. You can go through a process of elimination. Typically, circuits are wired the shortest distance between outlets, so you can make some intelligent guesses at which junction to try disconnecting next. Of course only work on the wiring with the circuit powered off, use non-contact testers, and other appropriate safety procedures.

Another method you can try is sound. Pipe a small speaker into one end of the conduit, and then put a hose from your ear to the other end to see where the sound is loudest.

When trying to label cat5 that had been run around my home, I've shorted two wires together at each location, with a different colored pair at each place. Then from the other end I just checked for continuity between different pairs.


My dad worked in a telephone equipment switching office and a few times enlisted my aid in tracing a pair of wires.

The technique is simple: person B goes to where the probable other end of the wires and feels them while person A alternately gently tugs and relaxes on the wire pair under scrutiny.

At first, person B will feel indistinct vague movement—at least in a telephone office situation where there are thousands of wire pairs side-by-side. After some quick elimination, a few dozen will be the focus. Then, by holding them firmly and providing "pull" on them, one can quickly determine which one is the right pair. Confirmation must be made by tugging back in case the wire pairs are closely wrapped.

For a pair of 12 gauge wire in a conduit the possibilities can probably be counted on one hand. Have a "tugger" rattling the wires while the follower take a good guess based on which direction the conduit goes and listen. Once a probably outlet or j-box is determined, open it up and tug on the wires to affirm.


Use smoke to trace the other end of the conduit.

  • 1
    Shoot compressed air through empty conduits to find them.
    – Mazura
    Sep 23, 2014 at 5:38
  • Incense cone (or purpose-made smoke thing) in one junction box, then take a vacuum cleaner around to others? Guess you could do same thing with compressed air, but I have a battery-powered vacuum but no air compressor :(
    – Nick T
    Feb 15 at 17:29

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