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Thread: Why are these voltage readings normal?

  1. #1

    Default Why are these voltage readings normal?

    I've removed a Lutron dimmer switch with the goal of installing a regular light switch. There are two romex sets of wires coming into the box. One set reads a normal 118VAC between black and white. But the other set reads nothing between the black and white wires but on that set, there is 118 VAC between the black wire and ground AND between the white wire and ground.

    Why do the readings on the second romex set make sense? Where would they be getting power from? The power goes away from all of the wires when the breaker is opened.

    Appreciate your explaination on these readings.

    Ron

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by scubar View Post
    But the other set reads nothing between the black and white wires but on that set, there is 118 VAC between the black wire and ground AND between the white wire and ground.
    The black and white are connected together (maybe by an incand. lamp filament)?

  3. #3

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    Quote Originally Posted by scubar View Post
    Why do the readings on the second romex set make sense?
    Who said they did? Cheap digital DMMs are notorious for picking up stray voltages.

    Quote Originally Posted by scubar View Post
    Where would they be getting power from?
    Its induced voltage it picks up off other wires it runs next to in the ceiling/ wall/etc.

    Quote Originally Posted by scubar View Post
    The power goes away from all of the wires when the breaker is opened.
    Because you shut off the wire inducing the voltage.

    Ok now before you go blowing your fingers off check if I'm right. Connect a test light between the ground and the white wire in the second set. Did it light up? If yes then I'm wrong and something else is going on. Otherwise its safe to say that the first pair is power and the second pair is from the fixture. Connect the whites from each pair together and wire the switch between the blacks.

    rick

  4. #4
    Homeowner Thatguy's Avatar
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    An incand. test light; no neons.
    http://en.wikipedia.org/wiki/Phantom_voltage

  5. #5

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    Thanks for your responses. The switch works fine and the voltage was likely feed through another lamp.

    Ron

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