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Thread: Voltage drop at panel in one phase only

  1. #1

    Default Voltage drop at panel in one phase only

    Really like this forum, and this is my first post.

    I'm a new homeowner of a two-family Victorian, and I've been sorting through some electrical issues with our first floor rental unit.

    We had some circuits that were not getting power so I checked voltage at the circuit breakers in the designated 100A single phase panel for the first floor. All breakers were on. I noticed that there was either low (20 to 40V) or no voltage at certain breakers. Then I discovered that these "certain" breakers were all connected to the same phase. Breakers connected to the other phase were fine.

    I disconnected a wire entering one of these troubled breakers and tested for voltage again. With no load attached, this breaker read 112V. This was consistent over several breakers tested. Again, these breakers are all on the same phase.

    I tested different breakers, and swapped out for some new breakers, with the same results: Low voltage under load, more normal voltage without load. I also popped out the breakers, tested them for continuity, and they tested OK.

    For a short term solution, I connected all breakers to the stable phase in the box until I can get an electrician over here. When I called my electrician-friend, he mentioned that there could be an issue with the neutral, which freaked me out.

    Anyone experience a problem like this? Thanks.

    The other (quicker) question is that I'm measuring 109V on one phase and 112V on the other. These voltages seem a little low to me, especially since the first floor is currently vacant with barely any power being used at all. 2nd floor panel reads around 115V and 116V, which seems OK to me. Should I be concerned?

  2. #2
    Join Date
    Nov 2005
    Location
    SC
    Posts
    593

    Default

    I would agree with your electrician... You probably have a neutral problem. This could be at the meter, the panel, the service drop, or the transformer. Contact your utility and tell them you have a loose neutral. They usually respond quickly.

  3. #3

    Smile

    I too would waste no time calling the utility Co. If you have one or any No. of what's called multi-wire circuits then a loose neutral (depending on where it's located) can cause any range of voltages, say from 30v to over 200v to appear on your 120v receptacles, even those you may consider to be on the non-faulty side of your incoming power. This will burn up circuit boards in computers, micro-waves etc. very quickly. If you find that after your Neutral problem has been resolved and your M/wave doesn't work, that's what probably happened. Good luck I am a novice in residential wiring but I believe I am correct in my understanding of what the effect of a loose neutral has on multi-wire circuits. So yeah call the utility Co. yesterday
    Last edited by sidecutter; August 20th, 2007 at 07:15 PM.

  4. #4

    Default Will call them!

    Thanks for the input. I will call the utility company ASAP. I wasn't sure if the problem was their jurisdiction or not.

  5. #5
    Join Date
    Aug 2004
    Location
    Kansas
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    1,645

    Default

    Sorry I'm not following..... how could you have a feeder or service neutral problem if one leg is operating fine? Op says outlets on some circuits have no power. He discovers that these outlets that don't work are on the same leg. I am assuming here that the op is stating that loads don't work when plugged into these outlets. He tests 20v to 40v at the breakers connected to the leg in question with the breakers on. With a wire removed from one breaker on the leg in question he reads 112 volts. I dont see where we have proved much. I assume he is testing to the common neutral bar with the current from all the other loads flowing on it.
    It sounds more like he has lost a hot leg to the 100 amp panel. The other panel in the house is having no issues. I would like to see a line side voltage test at the mains for this panel with the main off and on or all breakers of both legs off and on. Each leg to neutral and leg to leg with a solenoid tester not a digital. Also a test of a branch circuit at a receptacle box hot to neutral and hot to ground would be nice. The key thing here IMO is nothing works on the one leg but does on the other leg. He probably hasn't noticed that the 220 volt items arent working either.

    Roger
    Last edited by Roger; August 22nd, 2007 at 02:02 AM.

  6. #6
    Join Date
    Dec 2003
    Location
    Welland Ontario
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    4,782

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    Quote Originally Posted by Roger View Post
    Sorry I'm not following..... how could you have a feeder or service neutral problem if one leg is operating fine? Op says outlets on some circuits have no power. He discovers that these outlets that don't work are on the same leg. I am assuming here that the op is stating that loads don't work when plugged into these outlets. He tests 20v to 40v at the breakers connected to the leg in question with the breakers on. With a wire removed from one breaker on the leg in question he reads 112 volts. I dont see where we have proved much. I assume he is testing to the common neutral bar with the current from all the other loads flowing on it.
    It sounds more like he has lost a hot leg to the 100 amp panel. The other panel in the house is having no issues. I would like to see a line side voltage test at the mains for this panel with the main off and on or all breakers of both legs off and on. Each leg to neutral and leg to leg with a solenoid tester not a digital. Also a test of a branch circuit at a receptacle box hot to neutral and hot to ground would be nice. The key thing here IMO is nothing works on the one leg but does on the other leg. He probably hasn't noticed that the 220 volt items arent working either.

    Roger
    I was thinking the same thing until I read the last paragragh where he has 109v on one leg and 112v on the other. It's not much difference but uneven voltage between the legs is the classic symptom of a loose or broken neutral. We could be getting confused by how the readings are being taken. This definitely requires further testing to determine the exact problem. Either way it sounds like the POCO should be called to check it out.

  7. #7

    Default

    I believe you have a loose connection in a hot wire on that phase service conductor. When you read a partial voltage on a phase but not full voltage from hot to neutral most often the phase in question is picking up voltage through a 240 volt circuit such as a water heater element carrying line one hot through the element partially energizing the second phase. Then again often times you have a loose connection on the service conductor or service drop where it will test 120 volt till put under load thus killing the voltaged due to the load through a bad connection failing while under load. I believe Roger is correct in his diagnosis.

    Just my opinion

    Wg

  8. #8

    Default voltage problem

    I'm new at this forums also first day. You do need a good quailfied electrician, you could have back feed where somebody tied two circuits together some where in the house. You could have a open ground causeing all kids of funny voltage going different places and the neutral could be loose or open some place.

  9. #9
    Join Date
    Aug 2004
    Location
    Kansas
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    1,645

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    Thanks Joe for bringing that to my attention. I'll put that into my memory banks.
    This is what I like about this forum. We all share our knowledge for the good of the poster. Very rarely does anybody jump in and say you don't know what your talking about.... but expresses their thought process for the problem without being insulting to yours. This wasn't an easy post to diagnose based on the testing but I agree the poco should be called.

    Roger

  10. #10

    Smile

    Just curious about something. I'm a novice in residential wiring, so I just know some basics from reading these posts. I'm wondering wether it could be, not impossible, shall we say if a loose main neutral could could cause the phenomena being discussed to be the result of say a number of multi-wire circuits that "also" had individual neutral wires a little loose (or not loose) at the neutral bar?? If the load on these multi-wire circuits were a mixture of inductive and resistive loads, could the voltage from the breaker on LINE I let's say show normal voltage if perhaps most of the loads on LINE 1 are resistive loads and show a different voltages on LINE 2 if that side had a number of Inductive loads. Just curious If I need to get back to the basement with my books soon (lol) Come to think about it these tests, would have to be made under load Well maybe I will go to the basement. Critical comments welcome

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