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Power-User

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Sorting Wires

11/06/2017 4:31 AM

I promised to help a friend tomorrow. His problem is he has five or more cables running underground between two buildings . He remembers that there was a spare pair buried at the time against future use. Is there an easy way to find the unused cable. As far as I could get from him was that the others were connected but not in use. He wants to tap into this line to put power to a shed being built between the two existing buildings. I was going to trace a signal through each cable but he was a bit hesitant to admit that access to either end of the line was, well, difficult. Untill I see the set up I really cannot give more information. As they are not in use no current will be present Has anyone struck a situation like this before and how was it handled. Of course once I see it the situation might be easier than I thought. Any advice on this would be appreciated.

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Guru

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#1

Re: Sorting wires

11/06/2017 5:55 AM

Well a metal detector would probably do the job....

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Guru

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#2

Re: Sorting wires

11/06/2017 6:31 AM

If access to the unused end is difficult? How does power get applied when needed?

Don't do anything unless you view, hold, and splice the wire inside the building.

Why any wire would be difficult to get to at both ends is the only mystery.

.. report back!

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Guru

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#3

Re: Sorting wires

11/06/2017 8:17 AM

If the "spare" cable was taken out of the ground at its ends, it should be evident. If it was buried next to the other cables, a metal detector will not localise it.

Presumably, if it was for future use, digging at the building ends of existing known cables should find it.

If the ends were not brought into a building and ends were not totally sealed, water may have got in, making it useless.

If you can find the cables at the place where you want to tap-in, I would pass a DC current [as big as practical] through one core of the desired cable returning by one core of a different cable and discriminate by direction of alignment/movement of a compass (the currents in the two cables must be in opposite directions). Obviously, you will have to get the cables physically apart, since go-return currents close together have little external field. If you are lucky, the desired cable is a different diameter to the others!

Where cables are buried in walls or ceilings of a building, I have had to resort to looping 1 kHz through the two cores (live & neutral) from an audio amp via a step-down transfo to increase the current and a telephone pickup coil detector to the sound input of a laptop computer or an amp/headset. If the cables are well away from surface, the wire alignment (twist of cable) obviously unknown, even this could only show which side of a wall a cable was hidden or where it sneaked away from other cables.

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#4

Re: Sorting wires

11/06/2017 8:33 AM

Now we see the benefit of keeping the "as built" drawing up to date, don't we?

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#13
In reply to #4

Re: Sorting wires

11/07/2017 3:32 PM

Ah, good to hear your voice again, Captain.

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#5

Re: Sorting Wires

11/06/2017 10:55 AM

After you dig amd expose he wires make the four that are terminated hot. They make a probe that when put beside the the wire will let you know if its hot.

The one thats not is your spare.

What I don't understand is why the spare was not run from panel to panel. From the statement that the ends are difficult to get to. As that would make it a spare.

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#6

Re: Sorting Wires

11/06/2017 2:00 PM

Be careful, (1) don't get hurt, and (2) don't do anything not up to code.

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Power-User

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#9
In reply to #6

Re: Sorting Wires

11/06/2017 5:25 PM

Definitely, three good repeatable directives.

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Guru

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#7

Re: Sorting Wires

11/06/2017 4:27 PM

Do these other buildings belong to your friend? You might not want to be an accomplice to electricity theft.

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Power-User

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#8
In reply to #7

Re: Sorting Wires

11/06/2017 5:22 PM

Yes, they are all his own property. Part of the exercise is to eventually separate the two so he can sell the far building.

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#10

Re: Sorting Wires

11/06/2017 9:03 PM

Thanks everyone for all your help and advice. Panic over, the wires were not power wires but telephone extension, speaker wires (he is very keen on music) and a spare pair of speaker wires. He wants to pipe music into the new shed. All aspects of shed construction are under contract. How we got our wires crossed (groan and giggle) I do not know. I was still able to help him by doing a small machining job for him. All is well.

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Guru

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#11
In reply to #10

Re: Sorting Wires

11/07/2017 5:51 AM

Ok, thanks for telling us the "end-story" - mostly posters do not write to say if comments helped to sort their problem.

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#12
In reply to #10

Re: Sorting Wires

11/07/2017 8:48 AM

Cheers, glad it turned out as stated. Good luck helping your friend and neighbor.

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