A really stupid question from a dummy!

Discussion in 'General Electronics Chat' started by speter42, Jun 19, 2014.

  1. speter42

    Thread Starter New Member

    Jun 19, 2014
    I have, (had), a working 100A underground wire to my garage. All of a sudden, I have 30volts comming from a 120v source... WTF!
    All seems to be tight and secure.
    PS...(have had a lot of rain lately)
  2. wayneh


    Sep 9, 2010
    And the question? I think you already know the answer.

    How was that wire protected?

    BTW, this is potentially a VERY dangerous situation. Turn off that circuit at the breaker box (it IS on a breaker, right?) before getting anywhere near it.
  3. matty204359


    Apr 6, 2011
    I have had similar strange voltage readings coming from an improperly grounded GFCI. But I doubt this is the case since its a 100A service to an external structure. but if you do have a GFCI you might wanna check it out.
  4. MaxHeadRoom


    Jul 18, 2013
    Is this a 240v/120v supply or just 120?
    When you say 120v, is this from each 120v conductor to neutral?
    What do you measure to ground conductor from each 120v line?
    Is this a remote building or attached to the house?
  5. #12


    Nov 30, 2010
    C'mon. Be reasonable. You know that can't be the truth.
    There must be a defect someplace, and your job, should you decide to accept it, is to find the fault.

    Good education and a good meter will find the problem. Lack of understanding and a good meter will get you killed.

    At this point in the conversation, I am worried that you're just smart enough to be dangerous.

    You're talking to people that do this for a living. We can figure it out, but asking you to stand on wet ground and look for a fault in a 100 amp power line is a scary proposition.
    KJ6EAD and atferrari like this.
  6. Lestraveled

    Well-Known Member

    May 19, 2014
    Ditto what #12 said.

    When you open the cover of a 120/220V breaker box you are entering into a dangerous area. If you do not have the skills and understanding to SAFELY work in the box, then don't do it. Let someone else do it or seek assistance from someone who is experienced.

    Take a moment and think about it. Electrical shocks are extremely painful, even when they are fatal.

  7. speter42

    Thread Starter New Member

    Jun 19, 2014
    From the source, there's a 100A breaker going to the garage. Each 120v leg
    measures 121 volts from the source.
    At the receiving end, (garage), each leg measures about 30 volts...(somewhere between the source and the garage I lose 90 volts from each leg)...Yesterday all worked well, as it has for the last 15 years.
  8. inwo

    Well-Known Member

    Nov 7, 2013
    See if you still have 240 leg to leg.

    If you have open neutral keep the main breaker off to prevent frying things.
  9. MaxHeadRoom


    Jul 18, 2013
    If you measure 120v from line to neutral, but line to ground is 30v, then this indicates an open or ungrounded situation?
    If you measure 30v to both neutral and ground then they both have a problem.
    You need to do a test of both neutral and ground continuity with power off.
    Preferably with a megger, both high voltage insulation and continuity version.
    KJ6EAD likes this.