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Thread: Stray voltage on ground wire in townhouse

  1. #1
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    Stray voltage on ground wire in townhouse

    My accountant called me to help troubleshoot a issue he is having at his townhouse. Here is what happened so far, coax cable burnt clean off of his receiver box at the main tv and in the master bedroom the ground wire in tv power supply cord heated up only on the ground wire and melted it a little bit. So now there is a spiral all along the cord from plug to tv. His range was off and randomly started smoking so it was shut off at the breaker. I come over to try and start looking into this, what I have found so far is there is a voltage difference of approx 10-12 volts between ground and neutral at every receptacle and also on the panel mains. Between a grounded outlet and coax ground in a room there is the same voltage difference. I go to the garage and open the panel and also the tel/cable supply panel, disconnect all coax lines running up the rooms and measure them, 0 volts difference. I measure the coax line leaving the townhouse to the main ground in the panel and same voltage difference of 10-12 volts. I've never encountered this before but only heard of guys trying to troubleshoot it. Where would be the best place to begin looking at it?
    Thanks for any insight

    Forgot to mention, tightened all neutral and ground connections in the panel. Some were quite loose
    Last edited by WestCascadesElec; 08-31-17 at 02:11 AM.

  2. #2
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    Turn off the main before anything else burns up and then start looking where the lost neutral is. It may be on the homeowner side or the utility side.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  3. #3
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    Welcome. Definitely a lost neutral, and probably an illegal parallel bond/connection or several between neutral and ground before the main. Lost neutrals on the service typically only burn up coax from the first splitter to the pole or pedestal.

    See this article:

    https://www.electrical-forensics.com...n-Neutral.html
    Electricians do it until it Hertz!

  4. #4
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    170831-0612 EDT

    WestCascadesElec:

    In your main panel the EGC bus bar (what I believe you are calling ground) must be bonded (very low resistance connection) to the neutral bus bar. Thus, within the main panel the voltage difference between the EGC bus bar and the neutral bus bar must be very low (millivolts). If not, then fix this bond. Usually the bond is via screws from said bus bars to the main panel enclosure.

    If the voltage between said bus bars is low, then create a long test lead (an extension cord can be used). Connect this test lead to the EGC bus bar. Go to an outlet where you saw a difference between EGC and neutral, and relative to the test lead measure the voltage between the test lead and the outlet EGC, and the test lead and the neutral. This will tell you which path has an open somewhere.

    .

  5. #5
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    I agree with the crowd here. You are looking for an open neutral _somewhere_ combined with a neutral-ground connection somewhere else.

    Neutral current is trying to get back to the transformer, and is using the egc and grounded cable shield as the path.

    The fault _may_ be in another house. A neighbor's open neutral could put current on shared grounded metal, eg the cable tv system.

    The fault may involve bootleg grounds or ground to neutral connections in branch circuits.

    You may need to add a galvanic isolator to the incoming cable to break the ground path.

    -Jon

  6. #6
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    Not only is there an open neutral issue someplace (as mentioned may even be at a neighbors's house) but seems to be no bond between neutral and EGC at the service either.

  7. #7
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    170831-0923 EDT

    Within my Sq-D main panel there appear to be two substantial cross members (bars) between the EGC bus bar and the neutral bus bar. Their total cross sectional area may be as large as one of the hot bus bars.

    I don't know my present neutral current, but the voltage drop between the EGC and neutral bus bars is prrsently 0.3 millivolts. Some of this voltage may be inductive coupling to my one tutrn loop formed by the meter test leads.

    .

  8. #8
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    Quote Originally Posted by gar View Post
    170831-0923 EDT

    Within my Sq-D main panel there appear to be two substantial cross members (bars) between the EGC bus bar and the neutral bus bar. Their total cross sectional area may be as large as one of the hot bus bars.

    I don't know my present neutral current, but the voltage drop between the EGC and neutral bus bars is prrsently 0.3 millivolts. Some of this voltage may be inductive coupling to my one tutrn loop formed by the meter test leads.

    .
    With Square D loadcenters made for the past 25 or so years, that cross member is considered a part of the neutral assembly and both terminal bars are considered neutral buses. They aren't even designed to be easily separated to make one a neutral and one a EGC bus - the intent for a separate EGC is to add a separate bar that is bolted to select position(s) on the cabinet itself.

  9. #9
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    170831-1329 EDT

    kwired:

    On my 52 year old QO main panel it is truely one neutral bus used for both neuttal and EGC. Of the three actual neutral bars there is no way to separate one from the group.

    There is no obvious designed place for a separate EGC bus.

    .

  10. #10
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    Quote Originally Posted by gar View Post
    170831-1329 EDT

    kwired:

    On my 52 year old QO main panel it is truely one neutral bus used for both neuttal and EGC. Of the three actual neutral bars there is no way to separate one from the group.

    There is no obvious designed place for a separate EGC bus.

    .
    That type of panel is often referred to as SOSE (Suitable ONLY for use as Service Equipment) as different from SUSE (Suitable for Use as Service Equipment.)

    If you needed to use it as a sub panel for any reason you would have to add one or more insulated neutral bars, possibly creating a configuration that was not UL Listed.

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