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Electrical - stray voltage

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  • Electrical - stray voltage

    I was across the way helping a neighbor out with a pool pump yesterday. When I finished, I found myself back down at the breaker box. She tells me that she had to run an extension cord to another room because her new flat screen tv is getting a bit fuzzy. I hate extension cords as a permanent solution. A fellow told her that it was a grounding issue. She asked me to take a look.

    I grab my stupid plug (you know, the one that you plug in to an outlet and it tells you a few issues with lights) and check it. It tells me open ground. Ok, that could be easy enough. I pull the cover and find that the romex is hooked up correctly. Strange. I check line to neutral, 120 volts, then line to ground, 120v, THEN I check neutral to ground, 40volts ac. ?????

    This is an old house. I see three different wiring styles running through it. It was built before it was wired. Then it was wired later with wire and posts. Next there was armored wire and then romex ('70s) and then newer romex '80 sumthin. Also, it has crawlspaces that I cant get into but there are wires stapled in there.

    So, I unplugged everything except the stove which is new (installed 2 days ago) but the problem was there before the install. Still 40v neu to grnd. Some things are hardwired in and cant be easily pulled off the circuit. The circuit is 15 amp and runs 1/2 the house!

    I put everything back and told her that I would have to do some research. Short of replacing the receptacle, which may or may not be the issue, Im doubtful this will do much of anything.

    I would trace everything back in my house if I were here. But there it is an electrical mess. Wire everywhere. Some used some cut off and left.

    So where is a good place to start? Just re-pull that room and be done?

    Civil engineers build targets, Mechanical engineers build weapons.

  • #2
    Pulling new wire is what I would term the "right" solution. Better to have a real ground and appropriately sized wire. Old armored cable can be dangerous and the old tar covered romex is a bit of a fire hazard when it's ancient.

    The outlet is the cheap easy thing to check so spend 1.00 and get a new one. If it doesn't fix it, get yourself some romex and fix the problem.



    • #3
      Start at the beginning

      It would probably be best to start where power comes in and see if it is the same at the main breaker. It's not unheard of that the power company could have issues outside the house. It's also possible that the ground rod driven at the house is bad, or you may need additional ground rods.

      I once lived in the first house in Corvallis, Oregon to have electric power. It had the same issues: Bare wire on ceramic, cloth wrapped individual wires, cloth and tar covered wires, romex, etc. We had one stereo connected for power to two icepicks stuck in the wall about six inches apart.

      If things look good at the main breaker, repulling is the easiest way to go given all the copper buried in the walls.


      • #4
        First, check for aluminum wiring. If you find any advise that the house be professionally rewired completely. Best place to look is at the main service box.

        If no aluminum is found you have a poor connection on the neutral. Go to the main box and check there for a neutral to ground problem while running a significant load on the circuit at the outlet in question. There must be a load to cause a sufficient ground current to flow to create a drop on the neutral to ground.

        Measure from the box shell to the neutral bar. If you have a voltage there then check the bonding of the neutral bar to the box. There should be no measurable resistance or voltage drop from box shell to neutral. If that is good then the problem lies between the load and the box. Since safety ground and neutral must be bonded at the box the presence or quality of the earth ground don't play a part in producing a neutral to ground differential.

        If you have a differential at the box between neutral and ground then ground the neutral to the box using bare wire of an ampacity equal to the service.

        Then go measure the neutral to ground voltage back at the outlet. It should be less than 5 vac under maximum load.

        If the problem is in the wiring as shown by no drop at the box then it's up to you how far you want to go looking for the bad connection. The bad connection will be in the neutral somewhere, probably a pair of wires twisted together with some tape around them instead of a wire nut or a Marrette.

        As for system earth ground, that is worth checking too just for safety. It is most likely grounded to the plumbing system so check to be sure that hasn't been isolated by the installation of plastic plumbing somewhere.
        Free software for calculating bolt circles and similar: Click Here


        • #5
          Check all the plug-in devices on the same buss bar too (multiple circuits). It could be a mis-wired appliance back feeding to neutral. An old fan, lamp, etc. Might even be a mis-wired 3-way switch. There may be a lurking hazzard somewhere in the house.


          • #6
            All good information so far, thanks. The comments are noting what I was thinking. Which is, this could be hours of work tracking down the real issue.

            I did look at the grounding at the box and it looked good. I was planning to go outside and see if the grounding rod was a true grounding rod or an old pipe jammed into the ground. I found that my house was grounded to an old led pipe that was dug into the ground about 1.5 foot. That was the first thing that I changed when I moved in.

            The more little things that I do for the neighbors around here the more I see that the whole place resembles its beginnings. This area was an old fishing camp. Shacks were thrown together for summer weekend getaways from the booming metropolis of the teens and 20's. When houses like mine were built, the workers mimicked some of the poor practices of the previous shacks on many things. Yet the fellow that built my house, even with all of his faults in some of the construction, put an extra two courses of block in the basement. I have a good ceiling height down there and a large open area. I bet a pool table might fit down there nicely.

            Thanks again for the thoughts.
            Civil engineers build targets, Mechanical engineers build weapons.


            • #7
              For those who are knowledgeable about electrical power distribution systems....

              Following Evan's good advice, connections in power distribution panels loosen with time. Every once in a while it can be a good idea to tighten all the wiring connection screws to maintain a properly operating, safe power supply system, especially connections on ground/neutral bus bars.


              • #8
                Could you be picking up a 'phantom' or spurious voltage due to the use of a modern, high impedence voltmeter. See

                Using a $4 HF digital multimeter, I once encountered a 50 volt voltage on some rough-in wiring for new lights with the circuit switch off. I rechecked all my digital meter measurements then progressively switched to smaller ranges on an old analog meter and, sure enough, the indicated voltage progressively dropped to as low as 5 volts on the 0-10 volt range.

                David Merrill


                • #9
                  Most likely the earth ground (grounding conductor) is not connected to the nuetral, (grounded conductor). NEC mandates it be connected in one spot only in the distribution panel. In the newer panels it is the one green screw the is between the neutral buss on one side and the grounding buss on the other. It is there to be removed if the panel is to be used as a sub panel. this lack of connection somewhere is what I'd be on the lookout for.



                  • #10
                    Earth ground has nothing to do with a neutral to safety ground voltage differential.
                    Free software for calculating bolt circles and similar: Click Here


                    • #11
                      Originally posted by Evan
                      Earth ground has nothing to do with a neutral to safety ground voltage differential.
                      Evan, he is talking about the bonding between the neutral and the earth (safety ground, equipment grounding conductor).

                      I would kindly and gently suggest to you that if there is a voltage difference between safety ground and neutral, the VERY FIRST place to look for it is at the place where the two are supposed to be connected.... but may NOT actually BE connected.

                      If they are not, then the only "connection" is between the ground rod/ground system and the ground rods at the poles, the "connection" being actually through the earth.

                      A very significant difference of potential can exist in that condition.
                      Last edited by J Tiers; 05-22-2009, 12:34 AM.

                      Keep eye on ball.
                      Hashim Khan


                      • #12
                        I would kindly and gently suggest to you that if there is a voltage difference between safety ground and neutral, the VERY FIRST place to look for it is at the place where the two are supposed to be connected.... but may NOT actually BE connected.
                        How perceptive of you. Obviously you didn't read what I already posted.

                        I somehow misread what hoof posted although I did read it. Perhaps you should go back and read my first post. Perhaps you did but misread it?
                        Free software for calculating bolt circles and similar: Click Here


                        • #13
                          Years ago, my grandfather had a house that started out with gas lighting and was later wired. He always thought his electric bill was too high.

                          Well one day he was cutting out old gas pipe when his hacksaw bridged a gas pipe and a water pipe and and arced and glowed nicely. During the years of wiring changes, one electrician had used the gas pipe for grounding and grounded the hot side rather than the neutral. Easy to do giving some of the wiring was knob and tube.



                          • #14
                            I don't want to be the prophet or doom here, but doing electrical work on a neighbor or friend's house could be a mistake. This house sounds like it may be ripe for an electrical incident/accident and even if it is completely unrelated to any work you may do there, it is possible that you may be held responsible for the consequences. I know you want to help, but it may be better to leave this to a licensed electrician.
                            Paul A.
                            SE Texas

                            Make it fit.
                            You can't win and there IS a penalty for trying!


                            • #15
                              look for switched neutrals in electrical devices. This combined with no grounding can result in a hot ground, especially in devices with a motor in them.