I've recently purchased a house with several cat5 cables running through the attic. I'm trying to hook one of them up to an access point on the ceiling that is positioned in a place that is about mid-cable. How do I identify which cable is which without cutting them in the middle? Is there a tool that can detect a signal in a cable non-destructively?


2 Answers 2


You can purchase a cheap tone and probe at harbor freight for less then $25. I have one and it works great. Harbor freight calls it a cable tracker, fyi


if you can't figure it out from the markings

use a tone genrator.

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circulate an AC current one way through the cable use a clamp meter

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circulate a DC current and use a magenetic compass.

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these circulating currents will have to return to the source through some other path (not through the same cable) use a lamp or other load to limit the current.

  • 3
    Tone generator is the right answer. Homebrew solutions are fine too in general, but "circulate an AC current" could lead someone who doesn't know better to hooking up CAT5 to a standard 120V 15A receptacle, which is not a good idea. If you have a specific safe way to do such a thing, great, but there isn't enough information here to do it safely. Dec 20, 2020 at 4:48
  • 1
    You can't circulate enough AC current on super-fine Ethernet wire to be detectable by a clamp meter made for AC mains. Further, return current has to come back somehow. If you did the obvious/expected thing of using other wires in the cable for return current, then the two opposite currents would cancel each other out and be undetectable by a clamp meter or compass. Put one around an appliance cord and see what happens. So you really need to drape a separate wire through the house. Dec 20, 2020 at 19:11
  • @Harper READ TO THE END they will not cancel, because they will not be in the same cable. "Cat." cable can hadle 2A per conductor no problem, 1A should be easily detectable,
    – Jasen
    Dec 20, 2020 at 21:05
  • you could return the current through another cat cable if you don't care which one of the two you cut, (but with DC one will defelct the needle in the opposite direction)
    – Jasen
    Dec 20, 2020 at 21:11

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