There's a subpanel on a shed on my property that is fed by two cables. One is live, giving me 120 volt power. I'd like to be able to use both cables and have 240 volt power as well, but the second cable is dead.

Both cables are underground, making it impractical to trace them physically, and my contractor has been unable to figure out where the other cable goes. There are several other subpanels around the property, but my contractor inspected all of them and didn't find a place where the unpowered cable ends up. (Obviously it should come out the same place as the live one. Obviously that's the first place my contractor looked. No joy.)

Is there a practical way to trace this cable? It seems to me that if someone applies alternating current to it, it should radiate EMF, which could be detected. Depending on how far underground it is, though, that might be impractical.