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Tracing Electric Line

Post in 'DIY and General non-hearth advice' started by fraxinus, Apr 14, 2008.

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  1. fraxinus

    fraxinus Feeling the Heat

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    I have to replace an old brick walkway that runs from the front porch to the woodshed/aka garage. There is an electric line that runs from the cellar to the garage and crosses under the walkway at some point. I would like to a) avoid electrocuting myself and b) avoid severing the line. I know there must be some device that can trace the current so I can mark and take extra care where the line crosses, but I have no idea what it's called or where to find one. Any help would be much appreciated.

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  2. sylvestermcmonkey

    sylvestermcmonkey Member

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    They're called buried electric cable locators, and range in price from a few hundred to a few thousand. Tempo makes an inexpensive one which may work for you: http://www.tempo-textron.com/prod_detail.cfm?cat=800&subcat=802&pid=10442

    You might try an electric supply distributor near you to see if they have anything more appropriate, or check with a local electrician who may be able to mark its location for less than it would cost you to buy the Tempo instrument. Good luck!
  3. Highbeam

    Highbeam Minister of Fire

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    My local rental place rents out something similar. I would just hand dig it to expose the line (breaker off of course) and then carefully avoid hurting it during the job. Especially if it is in conduit, really hard to hurt a wire in conduit with a shovel. The soil used to backfill the old powerline trench should be easy to dig and was required to be no more than 24" deep.
  4. sylvestermcmonkey

    sylvestermcmonkey Member

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    When you locate and unearth the cable you should inspect it and consider its suitability for your present and future needs. If all you ever plan to have in your woodshed / garage is a couple of incandescent lights so what, but if you ever plan to use the circuit for powered machinery - a compressor for instance, even a garage door opener - consider increasing the conductor size to minimize voltage drop. Excessive voltage drop will cause motors to draw more current, dissipate more heat, and reduce their lifespan.

    Also be sure the existing cable is the appropriate type. It should be marked UF (water and sunlight resistant underground feeder and branch circuit cable). It's highly unlikely that it's in conduit as it's not usually required and most homeowners do things on the cheap. Don't be surprised if it's only buried a few inches too.

    If you replace the cable putting it in appropriate conduit is highly desirable. Also consider laying a marker tape, available from electric supply dealers or perhaps HD / Lowes. It's buried 6" or so above the cable and is intended to warn future excavators of the presence of buried electric lines.
  5. fraxinus

    fraxinus Feeling the Heat

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    Thanks very much for your excellent information and advice.
  6. jebatty

    jebatty Minister of Fire

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    Really weird but actually works. Get some heavy steel wire, a straightened out coat hangar or #10 steel wire, about 24" long. You need two of them. Bend each into an L, the vertical portion being about 18" and horizontal portion being about 6". Hold both wires by the horizontal section, with the long section sticking out straight and parallel to the ground. Walk back and forth over the area where you think the buried wire is, and when you cross the buried cable the wires in your hands will bend down towards the ground. You can trace the whole path of hte buried cable doing this.

    A master electrician showed me this method of locating a buried cable, I tried it in several locations where I knew the approximate cable location, and was amazed by how well I could locate the cables.
  7. reaperman

    reaperman Member

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    Call your power company, they can trace underground lines or else they have sub contractors who trace for them. They will always trace the main lines running to your home for free. And will also trace secondary or private lines for a small fee. If you are digging, I would recommend calling your local gopher one for a free underground locate, its also the law. They come and locate your lines free of charge, then you can talk to the locater about locating the line you have in question.
  8. granpajohn

    granpajohn Minister of Fire

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    If it's after the meter, they aren't required to trace & paint it, but they often do it anyway. The new number is 811. Visit www.call811.com for info specific to your state/area. Be prepared with a description of where you intend to dig, even if it's wrong. They just want to get out there and trace it as quickly as possible, and if they go too far, they don't mind.
  9. sylvestermcmonkey

    sylvestermcmonkey Member

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    I don't question your personal experience jebatty but I do question how this could possibly work. Some force would be required to move the coat hanger wires but there can be none from this buried cable. First, the conductors would have to be energized for any electric or magnetic field to be developed. Second, the current would have to be substantial to affect a steel wire some distance away. Third, since it's alternating current the force could only cause the wires to vibrate, not move or rotate in a consistent direction. Finally, the electromagnetic fields generated by a pair of conductors housed within the cable would exactly cancel each other leaving nothing to be detected anyway.

    Having said all that I'm still open to a theory that would explain this phenomenon. All the scientific knowledge we have today will be considered seriously deficient centuries from now and my skepticism will appear closed-minded if not dimwitted. At one time everything was made of earth, air, fire, and water and that was good enough to explain the mysteries of the universe. I have no doubt my understanding of electrons and how we make them behave may one day seem quaint, but it's good enough for the time being.

    Besides, everyone knows the technique you described is how you find water. For that I used a rusty old pair of pliers. Worked great.
  10. fraxinus

    fraxinus Feeling the Heat

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    Sylvester & Jebabatty: I've actually seen the two wire technique work to find water pipes below ground. Slightly different technique. Wires were held with the long ends crossing. They would swing away from each other when over the buried pipe. It was also not too very long ago that no one would think of drilling or digging a well without having a dowser check out the property for the best site - probably still happens. I've no idea how these things can or could work either, but there are a few centuries worth of folk wisdom behind them.
  11. jebatty

    jebatty Minister of Fire

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    You've got it right, I mis-remembered. Cross the wires and they swing apart. I puzzled over the theory just long enough to find where the buried cable was, and then I dug and learning the theory became irrelevant.
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