Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Method to determine if 2 ends of a buried (non-energized) electrical cable are the same line?

  1. Oct 18, 2014 #1
    Hello all. I am not an electrical expert here, just know enough to wire basic things at home (i.e. switches, outlets, etc)....so please be kind.

    My situation is this. We recently bought a new house and have found a couple of mysteries. The biggest one is that there are several electrical cables coming up out of the ground that are not energized, appear to be properly run, but are not labeled or connected to a power source. I suspect these were run with the intention of hooking them up as an outside outlet (i.e. a remote lamppost or Christmas lights) in one case, and running power to an outbuilding (for an interior light) in another case. There are several of these "cable ends" (ground/hot/neutral bundle) at various locations. I have found some not-connected ends neatly bundled in my circuit breaker box, but again with no labels.

    My question is this.....is there a safe/reliable method to determine/match up which end correlates with the other end? The number of "ends" in the box doesn't equal the number of "ends" I have found in remote locations. So I don't want to simply install an outlet on the remote ends, and then connect the in-house ends to a circuit breaker, and then turn things on/off. Ideally I'd like to test one line at a time to identify both of the ends, and then repeat until I've figured them all out. Then I can decide whether to remove, properly hookup, or properly prepare to leave for future use.

    Sorry if this is a bit confusing, please ask any questions that might help clarify what my situation is and I'll give as much detail as I can. But if you can give some advice on what options I might have to sort all this out I would appreciate it. Thanks!
  2. jcsd
  3. Oct 18, 2014 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    The easiest way would be to use clip-lead wire to short one end of the cable, and use a DVM on Ohms setting to measure the resistance of the other end of the cables. You will measure some low resistance on the selected cable, and you will measure an open circuit on the other cables. Makes sense?
  4. Oct 18, 2014 #3
    Yes, that makes sense. I'll give it a try when I get a chance over the next few days, and let you know if any further questions come up along the way. Thanks!
  5. Oct 19, 2014 #4


    User Avatar
    Science Advisor
    Gold Member

    That's a good idea for safety reasons. Next safety thing, once you identify "which wire", is to make sure you have a safety ground and the wires are capable of handling what ever loads you attach. Protects you and your house investment.
  6. Oct 21, 2014 #5

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    I prefer to apply a low DC voltage from a transistor battery or lantern battery to one end and look for it at other end with an inexpensive voltmeter. That way you won't get fooled into thinking that an accidentally shorted wire you didn't know about is the one you intentionally shorted.
    A unique voltage gives unambiguous indication.
  7. Oct 22, 2014 #6
    Using the method suggested by berkeman I have identified both ends of one mystery cable, but several other ones are still unmatched up so I'll continue my search.

    dlgoff....understood and I agree 100%.

    Jim Hardy...I like that idea, takes that last bit of doubt out of the equation. Would a standard 9V battery work for this purpose?
  8. Oct 22, 2014 #7


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    When you find a length of wire that's unused, you have to consider that it may be unused because there was a problem with it. (Boring old health and safety rears its head.) You should really check it for insulation between conductors and to Earth if you did't actually take it off a reel yourself - or if you can check with someone about its history. Buried cables can have been subjected to all kinds of abuse which nice clean ends would not give a clue about. Line testers are a bit more expensive than simple DMMs but perhaps you could borrow or hire one. . . . .?
    Sorry to be a pain but that had to be said - being PF and all.
  9. Oct 22, 2014 #8

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Sure ! Cheap little alligator clip test leads from a hobby site belong in your toolkit.

    old jim
  10. Oct 24, 2014 #9
    Not a pain at all sophiecentaur, I appreciate the comments. That is largely why I am doing this....hate having random wires around and not knowing why/where they go/come from. My first concern was to make sure they weren't live, and now move onto the identification challenge. If there is no reason for them to be there, or they are "bad" for whatever reason, then my goal would be to remove them or at the very least label and safely consolidate them. If I ever decided to actually use one, I like the idea of using a line tester....pretty sure someone I know must have one!

    And your suggestion worked great Jim Hardy. The one line I tentatively identified both ends previously was 100% confirmed with the 9V battery setup. Of course no of the other unknown lines are matching up with the ends I've found so far....so either I haven't found them all yet, or they are severed/etc underground. A good challenge for me either way...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook