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Thread: Why do I have voltage when switch is off?

  1. #1

    Default Why do I have voltage when switch is off?

    Can anyone tell me what is going on with this circuit? This is a circuit with two 3-way switches and one 4-way switch controlling a ceiling fan with light. In the dining room it is the same with two 3-way switches. With lights off I'm getting varying voltages of 34 to 60 volts. However, the fan and lights work normally as they should. I've check every way I know how. The previous owner had all the wiring done by a supposedly licensed electrician and as far as I can tell all wiring appears to be correct. The only thing I can think of is stray currents feeding in through the earth ground being connected to the neutral some way. This is a very old house with no ground on most circuits, only a neutral and hot wire.

  2. #2
    Jack of all trades DonL's Avatar
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    Hello Randyj,

    What kind of meter are you using ?

    Where are you reading that voltage ?

    DonL

  3. #3

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    I bet your using a digital volt meter right? Its called stray voltage. Its capacitively coupled causing a voltage reading on a digital meter.Electricians will have a different type meter. Are you having a problem of some sort?

  4. #4

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    I'm using a Fluke digital meter. I don't have the model number with me but it is definitely not a cheap one and is one that I got from a electrical supply house, not a box store or Walmart...
    Not really having problems, just noticed the unusual voltage readings and got concerned.

  5. #5

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    I got the voltage readings from the lead wires that are connected to the light/fan... before installing them. I also got weird readings such as about 17 volts across the terminals of the 3 way and 4 way switches. Of course, when I disconnected the hot wire the voltages disappeared.

  6. #6

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    You are in series with the light. There is voltage drop across the bulb. Or you are reading between the hot leg and an open neutral therefore the meter has no idea what 0 volts is and you will end up with unpredictable results.

  7. #7

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    You must take your readings between the black wire and the white or ground wire OR between the red wire and the white or ground wire. Any reading other than 0 or approx 120 is useless. Make sure the meter is set to measure AC and not DC

  8. #8
    Jack of all trades DonL's Avatar
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    Hello Group,

    I hope you all are having a good day.

    There should not be a voltage drop across the light bulb, If no current is flowing, when it is off.

    The best Digital Meters have a very high input capacitance as Jacob pointed out, That is normal. As to not load down the circuit under test.

    But if You put a digital meter lead close to a florescent lamp, You will see a reading. That is normal.

    I like using an old school analog meter for household voltages, And use the digital for TV repair and OP amp work, where a high input capacitance meter has less chance to load the circuit down, and give bad readings.

    Some of the best new digital meters, go nuts when you even try to read the voltage on the battery of a car with electronic ignition. To much stray RF on the electrical system.

    No replacement for the old school Simpson Meters.

    You all have a great day.

    DonL

  9. #9

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    Quote Originally Posted by drick View Post
    You are in series with the light. There is voltage drop across the bulb. Or you are reading between the hot leg and an open neutral therefore the meter has no idea what 0 volts is and you will end up with unpredictable results.
    If you read my reply above you'll see that I was taking the readings directly from the neutral & hot wire (black & white) without the fixture even being connected.... However, I was getting all kinds of crazy readings across the terminals of the switches. IMO, there should never be anything other than 0 or 120 volt readings anywhere in the circuit.

  10. #10
    Jack of all trades DonL's Avatar
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    Randy,

    Put a 1 meg resistor across the input on the meter, To kill stray readings, then measure the voltage. I would think it will read 0 volts.

    When the switch is off, the only way it would be zero, is if the switch shorted the inputs together. (I doubt it does, unless you wired it that way)

    Be careful when measuring , or the Voltage and Current police will get you. lol.

    DonL

  11. #11
    Electrician ActionDave's Avatar
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    Very common to have these readings when checking a three-way or four-way circuit wired in romex using a digital meter.

    Go buy a cheap analog meter, or an expensive one if you wish, and do the same tests; report back.

    Don't forget your PPE.

  12. #12
    Electrical Contractor/Instructor jwelectric's Avatar
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    As has been pointed out, a DVM when testing voltages in a multi-wire cable or raceway will read a ghost voltage due to reactance between the conductors.

    One thing to keep in mind is just because a meter has a voltage range on the dial does not mean that it can handle that much voltage in a fault situation. Case in point, although an eight dollar analog meter from an electronics store might just blow up in your hand if used incorrectly.
    Although the meter is fused it is not rated for flash over. There is documentation of these type meters failing and the user being hurt.

    Take special care in checking your meter settings and then recheck the setting. Once you have checked and rechecked then check the meter to insure it is properly set. Yes make it a habit to check your meter for proper settings constantly.

    I always turn my meters off after each use which forces me to be aware of the setting of the meter before each use.
    To check a voltage of 120 to ensure it is off before beginning work on the circuit I will first turn the meter to its highest voltage setting and then check a know voltage source. Then check the spot that needs attention returning to the known source for one more check. Then I turn the meter off.
    After de-energizing the circuit to be worked on I once again set the meter to its highest voltage setting and check the known voltage, check the de-energized circuit and once again check the known voltage once again turning the meter off.

    Doing this procedure each and every time insures that the meter is not set on resistance and loaded by live circuits which will surly damage the meter and possibly me.

  13. #13
    Moderator & Master Plumber hj's Avatar
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    quote; To check a voltage of 120 to ensure it is off before beginning work on the circuit I will first turn the meter to its highest voltage setting and then check a know voltage source. Then check the spot that needs attention returning to the known source for one more check. Then I turn the meter off.
    After de-energizing the circuit to be worked on I once again set the meter to its highest voltage setting and check the known voltage, check the de-energized circuit and once again check the known voltage once again turning the meter off.

    How do you have time to get anything done, if you are spending that much time just checking your meter and the lines?

  14. #14
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by hj View Post
    How do you have time to get anything done, if you are spending that much time just checking your meter and the lines?
    By ensuring that I am not wasting time laying around recouping from an accident.

  15. #15
    Jack of all trades DonL's Avatar
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    Hello all,

    The comment ;
    "Case in point, although an eight dollar analog meter from an electronics store might just blow up in your hand if used incorrectly.
    Although the meter is fused it is not rated for flash over."

    First off You should not be holding a meter in your hand when taking measurements, Bad Idea even if it is called a hand-held meter.

    Flash over is normally a mater of lead spacing, and good meter leads.

    Any Cat II rated meter will be safe for Household use. But I make a habit of not holding one in my hand while measuring.
    That may not be in any book, Just command sense.

    That will "ensuring that I am not wasting time laying around recouping from an accident"

    If You have a problem with putting your meter on the wrong range or setting , It is best not to be using it.

    All Randyj needs is a Neon Bulb Built into an Electricians Screwdriver. Works Good Last a Long Time.


    Have a great day all.

    DonL

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