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Thread: odd wiring results

  1. #1
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    odd wiring results

    I am having some problems figuring out the shop lights. There is one central junction box in the middle of the garage ceiling. It has one cable for power in and one for the wall switch. I was using a lighted switch.
    From the hot lead in to either of the switch conductors I read 20 volts. About 10 volts to my aluminum ladder on a dry concrete floor.
    I first tried to use a wago connector to tie the incoming hot lead to the switch. I did it with the power on so I could measure voltages and make sure I had it correct. I saw arcing and it got hot enough to melt. So there is more then just stray voltage. Once it was connected it cooled off and did not melt anymore. I had to let it cool a little while while I ran and got pliers since it had burned my fingers connecting.
    I think the switch ground is also good, 120 volts. This is modern plastic insulated romex , 1969. There is no conductivity between any of the three wires to the switch box.
    Maybe if I did this with the power off I would have never known?
    Bill D

  2. #2
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    Try a different multimeter.

    What problem are you trying to solve?

  3. #3
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    1969, if there is a white wire connected to one or more black wires in that ceiling box, one of those black wires is hot coming in. That white carries hot to the switch and the single black wire is hot coming back from the switch when the switch is on. Most lighted switches require a neutral wire which you don't have to a switch wired like that. Probably the majority of lighting circuits in 1969 and well later are wired like that.

    Some digital multimeters can give some odd low voltage readouts sometimes that don't really mean anything.

  4. #4
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    I was standing in the shop and the lights went out after they had been on for five minutes or more. No noise,smell or smoke. I went to the breakers and found one was tripped off, reset it, got an instant trip. took off the dead front and reset to see an instant trip and flash. Took off the wire from the breaker and it is a dead short to ground.
    Turns out that breaker is not the shop lights. I find nothing that is powered off.
    I think a wire nut connection jumped loose in the ceiling box and turned out the lights. So two seperate problems that breaker may have been tripped off for three years or more. The electrician who did the wiring used the shortest possible wire length. They are too short to come out of the box and be easy to measure. I would have made them at least one inch longer. Probably under some physical pull for decades and slowly pulled out. A proper job the wires would be relaxed and not pulling apart. connected and tucked back down so no tension is on the join.
    I had two cables I added for my lights running out of this junction box. I disconnected everything so I am only measuring hot to switch wires floating in the walls. No connection to neutral or ground busses. So it is not a bad neutral. I think it is just stray voltage and a wiggie type tester may show nothing.

    Bill D
    Last edited by Bill Dufour; 05-14-2024 at 11:36 PM.

  5. #5
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    Most lighted switches require a neutral wire which you don't have to a switch wired like that.
    Some of the older lighted switches had a neon bulb and a resistor in series with the load when the switch was in the off position the neon light would glow. If the light burnt out or was removed from the socket, the switch wouldn't glow.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  6. #6
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    Some digital multimeters can give some odd low voltage readouts sometimes that don't really mean anything.[/QUOTE]

    THIS!!!!

    The long story short is I was pulled in to a job someone else did the troubleshooting on. This machine is a Plasser track stabilizer. (90,000 lb railroad track vibrator) I was told to change the transmission. Two day job. Reman transmission $26,000. Guess what? Still no 2nd gear. So then I trouble shot it. Broken wire on the output from the controller. Digital multimeter showed voltage. Old fashioned test light showed nothing. I made it a habit to always start at the beginning and see everything with my own eyes.

  7. #7
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    Quote Originally Posted by Jim Koepke View Post
    Some of the older lighted switches had a neon bulb and a resistor in series with the load when the switch was in the off position the neon light would glow. If the light burnt out or was removed from the socket, the switch wouldn't glow.

    jtk
    THis is the way mine works. AFAIK the neutral is only needed for a pilot light type switch not an illuminated one.
    Bill D

  8. #8
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    I have had an illuminated when off switch act funny and another not work at all when the bulbs or light fixtures were switched to LED. I assume the capacitors in the LEDs charge and discharge causing the switch illumination to be weak and flickering or not work at all. Regarding the OP's problem I am confused but suspect a short somewhere.

  9. #9
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    The illuminated switch lights rely on a current path through the lamp filament when the switch is open. A tungsten filament has very low resistance when cold. The construction of the LED bulb driver circuits does not provide a path for enough current to power the switch's lamp.

  10. #10
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    I switched the ones in the rental house to these. They work with LED lights and no neutral needed.

    Regardless of the hundreds of dollars you have invested in digital multimeters, it's good to have a 20 buck analog one to keep things honest sometimes.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

  11. #11
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    Quote Originally Posted by Tom M King View Post

    Some digital multimeters can give some odd low voltage readouts sometimes that don't really mean anything.
    Quote Originally Posted by Tom M King View Post

    Regardless of the hundreds of dollars you have invested in digital multimeters, it's good to have a 20 buck analog one to keep things honest sometimes.
    The old analog, swing needle, meters on the good ones might have a resistance of 10,000 Ω per volt. Back in the day that was a very light load. Compared to a digital meter, it is huge. A digital meter has such a light load on a circuit it seems a fly going between the test leads disturbs the earth's magnetic field enough to cause a reading.

    I have a problem with a 220v circuit that may be caused by a 2-pole breaker having one pole not working. At the end of the circuit when hot, across the two wires it measures 0V. To neutral or ground, one wire measures at 120V. The other side measures 119V to ground but not neutral. That is how a digital meter measures the effect of induction from the two wires being in a conduit together.

    The electrician who did the wiring used the shortest possible wire length.
    That is not a very good electrician. There should always be an inch or two of a service loop at both ends. There is always some vibration from many different sources. Wires pulled tight in a conduit can be a problem over time.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  12. #12
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    The input impedance of a digital multimeter is constant across the ranges. With the old analog meter, dropping the range down reduces the input impedance (ohms/volt) so if you have some high impedance leakage that measures say 70V on the 250V scale, dropping the scale down to say 125V range, will not show the leakage at 70V but at a lower voltage because of the loading by the lower meter scale. This is a an indication of a high impedance leakage source such as through some degraded insulation.

  13. #13
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    I can see the thought about leakage but, leakage to where? I get no conductivity from any of the three switch wires to the hot lead. AFAIK the switch cable is only connected at the switchbox. I suppose a staple may have nicked one wire of the switch cable and also the hot lead ground but impedance is too high to measure. If it was connected somehow why 20 volts and not 120. It is a full 120 volt to ground or neutral on the hot cable and around 5-10 volts to my ungrounded fingers and the aluminum step ladder.
    I do not own a megger.
    BillD

  14. #14
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    I'm certainly not clear on what is happening.
    You got arcing and it was hot enough to melt and burn your fingers? Was there a load on the circuit like a incandescent lamp?
    Unrelated breaker tripped or was it always tripped?
    Voltage to ladder is strange but I don't know how you did the measurement and it could just be stray since your fingers and ladder are not well grounded.
    Is this all working now?

  15. #15
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    There should have been no load. The wiring to the switch was floating at the non switch end. It was just acting as an antenna. the switch was off. Voltage to ladder was just touch one meter lead to ungrounded aluminum ladder on rubber feet on dry concrete floor. Other lead to incoming hot lead. I suppose the neon lamp could be a current draw but one side is tied to the neutral wire was not connected at the far end.
    Bill D
    Bill D

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