25v on my neutrals

Discussion in 'Electrical Forum discussion & Blog' started by docaudio, Dec 1, 2008.

  1. docaudio

    docaudio New Member

    Messages:
    9
    Location:
    North Tustin, CA
    I'm trying to sort out an intermittent issue with a bedroom and bathroom feed.
    The home was built in '84 - Big Bear Lake, CA. Two downstairs bedrooms and a small bath are feed from one 20A run. One bedroom is fine, receptacles test OK.
    Second bedroom and bathroom receptacles show 25v neutral to ground, 90v neutral to hot, and 120v hot to ground. I also have lighting in a hall and the bathroom that is not working (bulbs are good) The problem comes and goes, but have not found any pattern. It's a vacation home, so my time is a bit limited to troubleshoot.
    I thinking I have a neutral that is floating, but I'm not sure.
    Thanks for any ideas!
    -Bill
  2. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    The circuits need to be verified with a megohmeter or "megger". That is the better and safer course of action for diagnosing a potential problem.
  3. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    If the grounded (neutral) was open then the circuit would not work at all.
    Without being there to actually see and test everything there is no way that proper advice could be given on how to find the problem.

    My most sincere advice is to hire someone to fix the problem. Chances are that you could stumble on the problem and even cure the problem but without more information such as the lay out of the circuit anything said would be only guess work.

    Start with what you think is the last junction be it a light or receptacle that is working properly and work downstream from that point if everything is on the same circuit.
  4. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    JW,
    for the benefit of those of us who don't have formal electrician's education, what should we expect to see on a properly wired 120v circuit?
    this would be my (un)educated guess - please correct as needed.
    hot to neutral - 120v
    hot to ground - 120v
    neutral to ground - 120v (for a receptacle) or 0v (if hot is switched off up-line)
    or if i'm way off, please clarify.
    Thanks
    BeekerC

    in general, what can you say about potential causes for a voltage drop on any of the three wires?
  5. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    There is cable capacitance, from each conductor to each other conductor. The 90/25 represents the ratio of capacitance reactance, at 60 Hz, from N to H and from N to G (but, I'd be more comfortable with these measurements if the N measured 60v to H and 60v to G).

    Assuming you used a high input impedance meter (what make and model is your meter?) to measure these, I think the neutral wire to this outlet is floating.

    To confirm, if you switch on the non-working bulbs the N should then read 120v w/respect to G. Alternately you could connect an incandescent lamp from N to G and have the 25v go to 0v.
    If this doesn't happen, more testing is req'd with a known good outlet and an extension cord.
    Last edited: Dec 1, 2008
  6. Cookie

    Cookie .

    Messages:
    5,658
    Location:
    .
    Thank you for replying to the OP, I hope with that information the OP will be able to solve his problem.
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    The votlage drop across the entire circuit will equal the applied voltage.
    In the problem above there are several reasons that he is getting the voltage readings he is getting. It would take the rest of the day to cover each and every one of them here which I do not have the time for.

    For ease in answering your question I answered each one beside each using red font
  8. docaudio

    docaudio New Member

    Messages:
    9
    Location:
    North Tustin, CA
    Hey 'Thatguy', that makes a lot of sense. BTW, the meter is a Triplett 9000.
    I have most of the walls opened up (drywall replacement) so I'll try to find the problem neutral and trace the run where it goes bad. I know it's not enough info to know exactly, but it seemed to me that it was a flaky neutral somewhere.
    Thanks to all for the responses!
    -Bill
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    Would not the capacitance between two insulated conductors be different than between one insulated conductor and one uninsulated conductor?
    If it is capacitance between the conductor that he might be reading with a digital meter it would all go away with a analog or solenoid meter would it not?

    If he is reading 120 volts between the grounded (neutral) and the equipment grounding conductor on a non working light then there would be a wire lose somewhere in the circuit is that not true. Remember that the grounded and the equipment grounding are bonded together in the service equipment assuming that the system is installed correctly. If this is the case then it wouldn’t work at all would it?

    I agree with your last statement, “more testing is required.â€
  10. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Couldn't find an input impedance spec for the meter

    but since it's a digital meter I assume it's at least 10 MΩ.

    I think the fact that there is more than 2v or so between N and G (see page 5 of the link below)
    http://www.idealindustries.com/media/pdfs/products/instructions/61-164-165_instructions_v4.pdf
    means the neutral is not connected, for starters. Hopefully that is the only problem.
    Usually I put a non-neon test lamp between H and N and H and G (and H and a cold water pipe if available). The lamp should light in all cases. It will trip upstream GFIs, though.
    If this test gives me answers that don't correspond to my mental image of how the wiring should work, I look for a good ground to measure with respect to.

    Cookie, it is my pleasure.
    The taxpayers paid for some of my education, and they might as well get something for it.:p
    Last edited: Dec 1, 2008
  11. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Would a standard plug-in circuit tester also point out the problem? I don't usually use a meter to check outlets.

    Steve
  12. docaudio

    docaudio New Member

    Messages:
    9
    Location:
    North Tustin, CA
    Actually, that's what I started with and noticed that the center green light was dim when checking the problem receptacles.
    -Bill
  13. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Yeah, I just don't own one.
    They can correctly check about 1/3 of the problems resulting from the ~30 wrong ways to connect or not connect one, two or three wires to one, two or three terminals.
  14. docaudio

    docaudio New Member

    Messages:
    9
    Location:
    North Tustin, CA
    Problem solved!

    I went up yesterday to have another look at things and found a suspect receptacle with a loose neutral. Of course, it was nowhere near the problem area (upstairs, on a living room wall, instead of downstairs where the problem was) So, I have to now re-label the breaker panel with the correct circuit info. Actually, the breakers are much better divided throughout the house than the labeling would suggest.
    Anyway, thanks for all your info and help!
    -Bill
  15. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Ahh. So there is still a use for my Fluke!
  16. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Yes, but for household use you have to load it down with an incandescent lamp so phantom voltages don't register at all.

    But with the lamp, you have to know if you're looking at 120v or 240v.

    Try two 120v 4w or 7-1/2w lamps in series for all cases. Probably neither lamp will light on 120v but it still gets rid of phantom voltages.

    I have a cardboard sleeve around mine so the other tools don't crush the glass envelope.
    Last edited: Dec 3, 2008
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