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  • lost neutral

    have a barn that is subfed from main house with 100 amp breaker. under no load read 125 volts on both legs, however, when i flip a light on i go to about 70 volts on the powered leg and 190 or so on the dormant leg in the panel. i assume this is a lost neutral so i bonded the ground with the neutral at the sub-panel, same problem. do i have a bad neutral somewhere in the barn, past the sub panel? how can i trace this? why is it only happening under a load? also swapped out breaker at main house panel and no difference. thanks in advance.

  • #2
    Re: lost neutral

    since no one else has responded to this I will give my two cents,

    on 240/120 single phase, the transformer is built in such a way that the winding is for 240, and is center tap, for the neutral, the neural is bonded to the ground, but when

    a load is applied and no continuous neutral exists, the load will travel from the hot leg through the item being used, to the neural, and instead of back to the transformer, since the neutral is loose or broke, it can not travel back to the transformer, so it travels through some other item that is connected on the other side of the panel and back through the transformer if both items carried the same load (amps)the volts would be the same,
    but when one is different the voltage will change depending on how much the difference is,

    for example if you turned on two switches and they were on opposite legs with equal loads, (say each a 100 watt light bulb), your voltage would be the same leg to neutral to leg again, but if the bulbs were say a 100 watt and 150 watt bulb the 100 watt would burn brighter and the 150 watt dimmer as it has more resistance,
    the picture below show a balanced load,



    SHUT OFF POWER, before working in any electrical box,

    as far as tracing it goes, is I would first check for tightness all the neutral lugs in the boxes, at both ends, and possibly even in the house and out to the pole, (especially if the wire is aluminum) but that is where I would start,

    if the wire is burnt in two in the ground, one may be able to us the ground wire (if one is ran to the sub panel), and check for continuity, or string out a second wire to make a complete path, and check for continuity, if it is broke one may be able to check ohms Resistance, to ground and do that from both ends, and may get a idea where it broke/burnt or deteriorated at.(if it direct bury),

    from your first statement, you say your only turn on the light, and it comes on, but the voltage drops and rises on the legs, if there is no other electrical items being used in the barn and the loose or broken wire is in the barn side, then you should have an open circuit, (no light), as there would be no return path for the power, to cross over to the other hot power leg on, if I am understanding you correctly, so if there are no other loads, in the barn on then It would make me think that the break or loose connection may be back in the main panel, and it is possible that if the loads are properly balanced that one may not see much voltage fluctuation in the main panel if it in the main panel the light in the building where it is located should be brighting and dimming as well if that is where the break/ loose connections is, if there solid voltage in the main panel I would look between the main and in the sub panel and in the sub panel,,

    here is a power point that shows by the numbers what is happening,
    http://code-elec.com/userimages/Lost%20Neutral.ppt
    found on this web site, http://www.electriciantalk.com/f2/12...-neutral-1318/


    other discussions that are similar to yours situation,
    http://www.electricalknowledge.com/f...rchives/30.asp
    Last edited by BHD; 10-31-2010, 04:00 PM.
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    • #3
      Re: lost neutral

      so you are getting 190v on one leg at the sub panel with load ??? im just wanting to know if im reading your post right. and some advice. YOU SHOULD NEVER BOND A NEUTRAL WITH THE GROUND IN A SUB PANEL. ANYTHING METAL THATS GROUNDED IN THE BARN COULD BECOME ENERGIZED.

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      • #4
        Re: lost neutral

        Originally posted by ronnie1231 View Post
        so you are getting 190v on one leg at the sub panel with load ??? im just wanting to know if im reading your post right.
        Are you aware that you are replying to a six month old post?

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        • #5
          Re: lost neutral

          If he connected the nuetral to bond(ground) as a test to see if he lost a nuetral, that is OK just for testing. he said he still has the same problem. I'll bet that his problem is that he lost one leg of one phase. if he has a hot water heater or some 240v device, the good leg passes through the water heater element and you read a voltage on the dead leg. He needs to check to see if he has both legs at the source.

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          • #6
            Re: lost neutral

            Originally posted by QROKING View Post
            If he connected the nuetral to bond(ground) as a test to see if he lost a nuetral, that is OK just for testing. he said he still has the same problem. I'll bet that his problem is that he lost one leg of one phase. if he has a hot water heater or some 240v device, the good leg passes through the water heater element and you read a voltage on the dead leg. He needs to check to see if he has both legs at the source.
            Are you ALSO aware that you are replying to a six month old post?

            Comment


            • #7
              Re: lost neutral

              Originally posted by Speedy Petey View Post
              Are you ALSO aware that you are replying to a six month old post?
              oh yeah? your responding to a response to a 6 month old post!! Heh, this is a slow moving board, you can easily (accidentally) bring up something from two pages ago and it be a year old!
              We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

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              • #8
                Re: lost neutral

                To set ppl straight with the bonding of the neutral in a subpanel, for testing it is allright. That will NOT energize metal in the barn. But it cannot be left that way.

                Bonding must be done at the first point of disconnect, and how could that ever be a subpanel?

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                • #9
                  Re: lost neutral

                  Originally posted by masterbeavis View Post
                  oh yeah? your responding to a response to a 6 month old post!! Heh, this is a slow moving board, you can easily (accidentally) bring up something from two pages ago and it be a year old!
                  Accidentially??? He replied to the OP, near the top of the front page, as if it were the day of the original post (ie: "He needs to check to see if he has both legs at the source."), a half hour after I made the first "six month old" comment.

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