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Stray voltage?

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  • Stray voltage?


    Is this normal or something I should pursue further:

    I was replacing a light fixture with a ceiling fan today in my home. I had the fixture wired to the wall switches (2 sets in the room, one light and one fan switch on each box) and the 14/3 wire run by the contractor when the house was built (3 years ago).
    After ensuring the 2 way switches for both the fan and light circuits were off, I checked the lines for voltage. The black wire (original light circuit) gave a reading of 45 vac to ground and to neutral. The red wire (fan circuit) read 0 to neutral and ground, and the neutral wire read 0 to ground. I turned off the breaker and the 45 reading on the black wire went to 0.
    By the way, with switches on, the red and black read 120 vac to neutral and ground as is normal).
    The light circuit also has other lights including a flourescent kitchen fixture, and I believe it also feeds the doorbell transformer. The light switches for the light circuit wire that showed the 45 vac reading when off are one normal toggle switch and one rheostat switch. The rheostat switch is the push in on/off and voltage increases when turned clockwise. Could this be the culprit?
    What would be the cause of the 45 vac reading?
    By the way, the fan is now installed and lights and fan appear to work fine (all work done with the breaker off).
    The only other abnormal event was that the clock reset on the microwave when I shut off the breaker (Like there was a momentary outage). The microwave is an over the stove type with its own dedicated circuit and breaker. The breakers on the light and microwave circuit are on opposite legs in the breaker box and separated by almost the full height of the box.

    I am not a licensed electrician. I have assisted a couple in the past and have successfully passed the 2005 NEC code course at the local community college.

    Any insight would be appreciated.

    Practicing at practical wood working

  • #2
    Re: Stray voltage?

    I've seen the voltage as high as 92 volts with the breaker on, and both switches in the off position. Two things people tend to forget: 1. The neutral wire is still a current carrying wire -- it is NOT a ground.
    and 2. Wall switches are prone to current leakage -- not enough to light the bulb, but enough to set one on his a$$. That's why one must always turn off a breaker before working on any electrical circuit. And make sure to test the circuit with a meter or Wiggy that you've tested on a working circuit to ensure it is working properly. And yes, that rheostat switch is probably the culprit with some voltage leaking past it. I wouldn't worry, seen this many times. For the tripping of the microwave, I'd take a close look at the panel. Check to make sure that all the screw terminals are tight. Sounds like you might have a loose terminal for a neutral wire. But check them all, ground bar, neutral bar, and screw terminals for the breaker. Also, is there No-Ox on the braided wires for the two bars and any 30, 40 or 50-amp breakers in the panel. Even the braided copper wires should have no-ox on them to keep from working loose from the effects of heating, cooling, etc. Check this out and let us know, and post again if it doesn't take care of the problem. If the panel doesn't show anything, you might want to check the outlet the microwave is on and see if the screws are tight, recept. is grounded, box is grounded, screw terminals have a couple wraps of elec. tape on them, etc.
    Jim Don
    Last edited by JimDon; 06-13-2008, 09:36 PM. Reason: Added somemore verbage


    • #3
      Re: Stray voltage?

      Once again Jim did a great post.

      I will add that you want to be sure you don't have a broken or poor neutral connection somewhere. If you have a good way to do so, please...

      1. Shut off the main breaker to your house.

      2. Drive a good ground rod in the ground outside and water the earth well.

      3. Connect a 100 foot length of #12 stranded copper wire that's insulated to the ground rod.

      4. Using a good VOM like a Simpson 260 or Triplett 630, measure the resistance using the R x1 range from the earth ground wire to all questionable electrical ground points. If you read over 20 Ohms, stop and try to fix it fast. Aim for under 10 Ohms.

      You connect the meter in series with the grounded test wire and any electrical ground.

      I personally did this at my place and almost fainted at the findings. Needless to say, I got to work fast upgrading the grounding here.

      Please tell all you can about measurements and findings. As Jim stated, NEVER trust a switch other than a good quality knife blade type to really open a circuit. Many low cost wall mounted toggle switches open the contacts less than 0.010 inches and actually arc over leakage. This is why in my place I only have spec grade Hubbell switches, receptacles and other wiring devices and why I keep a good AC Voltmeter ( 0-300 range ) with test leads handy.

      Woussko no likka gettings zapped.

      My old saying comes to mind but may not actually apply in your case.
      "Quality only costs more until it is put into use. Then it actually costs far less. Remember the PITA factor.


      • #4
        Re: Stray voltage?

        Thank you for the info. I will update you when I have a chance to check the box and the grounds. It may be a few days as I will have to find a good time to power down the house. It is hot here, and LOML doesn't do the "no A/C" thing very cheerfully. If it was an impending disaster, that would be different, but as it is, I'll wait until she is spending the day with her Momma (she's 92 years old and everyone calls her 'Momma").
        I'll check with my nephew (licensed Sparky) to borrow a good ohm-meter. I'll probably clamp to the service entrance ground rod for the ground/neutral check unless you think it would be better to drive another.
        I installed another fan today, and I could tell the person who installed this light fixture took pride in his work. Seeing the difference in the two installations, I will definitely be doing the checks. In this state, a licensed electrician does not have to actually be on site during all the work, but must be available if needed. Altho he is responsible for checking all the work, life has a way of diverting attention sometimes. I do not have much faith in the local code inspectors, as I found an open 4 square box under the kitchen sink with wires hanging out when I moved in, not to mention several other non-electrical issues.

        Thank you again

        Last edited by Gofor; 06-14-2008, 06:02 PM.
        Practicing at practical wood working


        • #5
          Re: Stray voltage?


          If you have iron or copper pipe for your water service where there's a long length of it underground, that makes a very good ground. You can connect the wire to that. The same with any good 5/8 or 3/4 by 8-10 foot ground rods driven into the ground. You just want to be sure you have a really good earth ground for your reference point. I have a way to force current from a good ground through the electrical circuit and back, but it's dangerous unless one really understands. For safety the use of a good Ohm Meter and having the main shut off is how the testing really should be done. Check the mounting screws of switches and receptacles. Be sure they all give a low resistance reading. Also, check that the round or U hole of all receptacles really are connected to ground.

          Something I find in older homes and commercial buildings is that they connect the neutral to grounding screws. This is a very bad practice and should always be corrected. You need to remove receptacles on suspected circuits and look at the connections. Another thing is to not trust conduit or BX jackets to really provide a good ground. Threaded galv pipe with all joints good and tight and with lock nuts on both sides where connected to a wiring box makes a good ground, but just to be sure, use a copper ground wire. You can't over do it when safety is involved. In this case it's fine to go a bit apeus.

          Example: #6 copper ground wire on a 20 Amp circuit where all other conductors are #12 copper. Yes it is overkill, but you'll have a great ground. I like to be sure all connections are super good too. Nope, I didn't go that far here at The Woussko Hut but sometimes on long runs, I think it would be a wise thing to do when I save up the $$$ and have time.


          • #6
            Re: Stray voltage?

            This is something wild that can happen. If you have a ground fault where there is a good bit of current flowing to ground, the ground conductors are actually at several Volts AC above a true earth ground. This is where I like to also use the good earth ground wire and a good VOM meter like a Simpson 260 or Triplett 630 and take both AC and DC Voltage readings. If you get an reading, then you may well have a serious fault where there is serious current flowing in the ground wire. This requires fixing right there and then. No putting it off. If you must, open the circuit breaker for that circuit and tape it off. Then as needed have a good electrician come and help out.

            Everyone please remember that you can't go trying to save some $$$ when your life and/or home are on the line.

            I need to get busy and do some pictures showing how to do the tests but if people don't understand what to do, then it really is best to have someone in the know help. Anyone that's a good electronics tech or serious HAM radio type should be able to help.

            Warning: Do not use a Digital Multimeter for such tests. You really want a good analog Multimeter like the Simpson 160, 260, 270 or Triplett 310 or 630 type. There are other similar brands and models that work fine. An older Amprobe with a pointer movement and Ohms range can be used. Even a 6 Volt lantern battery and a PR13 bulb properly connected up, works.
            Last edited by Woussko; 06-14-2008, 07:43 PM.


            • #7
              Re: Stray voltage?

              The meter I use most is the old Amprobe Model A, and I also have a A.W.Sperry Snap 9 (also fairly old, but both are in good condition). Both are analogue. My BIL gave me a Craftsman digital multimeter, but it has given me faulty readings too many times so I don't trust it for critical measurements. Will these work?
              House was built in 2005, so metal in the plumbing is not even a choice. In a past life, where I worked on a crew that also did Cathodic Protection work, I would have had access tro some coke-breeze to ensure a good ground field, but, alas, no longer. We also did soil conductivity test (driving pins in the ground out to 100', etc), but again, I no longer have access to that equipment.

              If the foxes hadn't killed the moles, I could have used them and a few pins in the ground to check out the soil resistance!! (Sorry 'bout that, but couldn't resist!!).

              Last edited by Gofor; 06-14-2008, 09:06 PM.
              Practicing at practical wood working


              • #8
                Re: Stray voltage?

                Originally posted by Woussko View Post
                Many low cost wall mounted toggle switches open the contacts less than 0.010 inches and actually arc over leakage.
                This is probably a corona leak over the switch gap... might also be "proxied" from an adjacent wire not related to the circuit, too. Not at all uncommon, mostly the voltage drops under load.

                A switch that only opens for 0,25 millimeters isn't probably even allowed here... 230V country and rather strict code even for one... they aren't so sucked up in the eastern block though. In the deepest darkest eastern Yurup they sometimes wire entire houses with floor lamp cord from a transformer, no main switch, no fuses... you know, it works 'til it quirks.


                • #9
                  Re: Stray voltage?

                  Sorry for the long delay

                  DummyLoad has some good thoughts on this. It really could be leakage from anywhere and anything. I would first try hard to be sure all grounds are good and then look for anything that looks like it may be leaking. You could try shutting off power to one device or circuit at a time and keep taking measurements. Sooner or later you'll find the trouble maker. You old Amprobe or the Snap-9 should work. I like to rig up a test lamp socket with a 10 Watt light bulb. I connect it to a good known ground and then probe things. If there's enough fault current to make the 10 Watt light bulb glow or light up bright, WHAM. I have to look hard and fix it fast. In older houses insulation on wiring can start to arc slightly and for a long time before it gets bad enough so you can find it easy. This is where shutting off power on a circuit and disconnecting one item at a time can help. Start at the far end and work back to the breaker or fuse. You may find a poorly done wiring job in a junction box.

                  As for receptacles and switches, any that seem junky, just replace them. Reasonable quality ones aren't that much $$$ and save you on grief later.
                  Last edited by Woussko; 07-08-2008, 10:53 PM.


                  • #10
                    Re: Stray voltage?

                    We get a lot of this phenomenon @ 230V and in most cases it is harmless... it will show on the contact voltage indicator with the little orange light in it, but seldom on the non-contact indicator... also digital meters will register it (they don't load the measured wire remarkably), analogue not so much... if it gives a remarkable reading on an analogue meter, it can also take some load and can be of real concern.

                    Note that a flimsy short gapped switch controlling an inductive load will arc over whenever breaking the circuit... this will eventually pit the contacts and possibly create protrusions on them. they later on contribute to the corona effect and the switch can suddenly decide to maintain the arc, which is no good.