Help locate a cable short

Discussion in 'General Electronics Chat' started by hhhunzai, Feb 10, 2012.

  1. hhhunzai

    Thread Starter Member

    Nov 14, 2011
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    Hello Everyone!
    Refer to the subject, please guide me in a situation, there is a power cable 25sq. mm, 4 core pvc/pvc non swa buried directly in ground and in some ducts.The cable has damaged anywhere and it shows short circuit between every conductor. I have tested with a uni-T multimeter, it shows almost 2 to 3M Ω resistance between each conductor.The operating voltage is 3 phase, 415volt, 50Hz

    Please suggest me a technique to sort this short circuit out, without digging the all area and ducts underground about 2.5 feet beneath .Is it possible to locate the exact location of the leakage area?

    Can we built an circuit Electronic circuit for it with Wheatstone Bridge?

    Your opinions are requested in this regard
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    "it shows short circuit between every conductor." and "it shows almost 2 to 3M Ω resistance between each conductor"

    Are you saying that 2-3MΩ is a short?

    Ken
     
  3. hhhunzai

    Thread Starter Member

    Nov 14, 2011
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    Yes, actually I have mentioned that, I have checked it with a multimeter but not with a high voltage Megger or cable tester.
    I am pretty sure that, a slight leakage is existing between these conductors.
    There is an other cable with this cable it shows infinity during check with a multimeter.
    I have performed such tests before too, and the ultimate problem was shortcircuit with a slight leakage and conductivity due to underground moistures.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Well, your measurement does sound like moisture infiltration. Dead shorts and opens are do-able, but high resistance leakage paths are beyond me. Perhaps others can help.

    Ken
     
    Last edited: Feb 10, 2012
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  6. DickCappels

    Moderator

    Aug 21, 2008
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    Just to eliminate some possible confusion: Is that really 25 mm square millimeters? If it is, that's a pretty good size cable, designed to carry a lot of current.

    (nearly) Regardless of the conductor size, depending upon the properties of the insulation, length of the run, and the way the conductors are laid with respect to one-another, that amount of leakage might be "normal".

    Is the leakage causing a problem, or is it that you are just concerned about the fact that your meter does not read "infinity"?

    By the way, most people would not consider 2 to 3 meghoms to be a short.
     
  7. Mark_T

    Member

    Feb 7, 2012
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    If the cable is long, old or hasn't been used for a while this would be a normal reading associated with moisture. Its not a short.
     
  8. hhhunzai

    Thread Starter Member

    Nov 14, 2011
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    0
    After all the problem has been sorted out by digging some area from load end about 20 feet.
    The issue was as i said, cable was short.
    And the short was not a slight but it was a bad enough, two of the conductors were melted badly due to sparking and the others were leaking too.
    The measured resistance was due moisture between these conductors.
    I will show you the pictures if I will get a camera with its cable.

    I would request you to please continue this topic to collect more information about the cable fault locators, as Mr. KMoffett has contributed some data by searching on Google.
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  10. hhhunzai

    Thread Starter Member

    Nov 14, 2011
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    This was the cable damaged due to short circuit.
    Some of the pictures I have added.
     
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  11. Lundwall_Paul

    Member

    Oct 18, 2011
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    One thing I would suggest would be replacing the entire length of cable selecting a cable that is rated to be buried directly underground. Don’t stretch the cable to make it reach as you will need slack for earth movement. Lay the cable on crushed rock to improve drainage. I don’t know how long your run is but you should allow for line loss.

    As far as testing the cable to calculate breaks or shorts I do not have any suggestions. I would strongly lean to replacing the entire length with a properly rated for undergroud cable burial an one with a larger gauge.
     
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