Why do I have voltage when switch is off?

Discussion in 'Electrical Forum discussion & Blog' started by Randyj, Apr 26, 2011.

  1. Randyj

    Randyj Master Plumber

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    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. DonL

    DonL Jack of all trades Master of one

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    Hello Randyj,

    What kind of meter are you using ?

    Where are you reading that voltage ?

    DonL
  3. jacobsond

    jacobsond DIY Junior Member

    Messages:
    59
    Location:
    ND
    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. Randyj

    Randyj Master Plumber

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    Location:
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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. Randyj

    Randyj Master Plumber

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    Location:
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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. drick

    drick In the Trades

    Messages:
    392
    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. drick

    drick In the Trades

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    392
    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. DonL

    DonL Jack of all trades Master of one

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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. Randyj

    Randyj Master Plumber

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    Location:
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    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. DonL

    DonL Jack of all trades Master of one

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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. ActionDave

    ActionDave Electrician

    Messages:
    346
    Location:
    Colorado
    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. jwelectric

    jwelectric Electrical Contractor/Instructor

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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. hj

    hj Moderator & Master Plumber Staff Member

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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. jwelectric

    jwelectric Electrical Contractor/Instructor

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    By ensuring that I am not wasting time laying around recouping from an accident.
  15. DonL

    DonL Jack of all trades Master of one

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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
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    and there are going to be cases where there is no other choice but to hold the meter while testing such as the use of an ammeter.
    or the blowing of a SFE fuse in the meter where arcing occurs between the blown portions of the fuse
    In most cases a Cat II meter would be alright for testing but the closer you are to the supplying transformer the higher the Cat rating needs to be. It is possible to have more available calories per square centimeter on a single phase 240 volt panel than on a 480 volt three phase panel.

    Having a safe procedure that is followed time and time again will ensure that the wrong setting is not used. Just simply picking up the meter and using it creates bad habits and bad habits result in accidents.

    I know these are used daily but I highly recommend they not be used. Ever be around one during an arc and you will throw yours away.
  17. DonL

    DonL Jack of all trades Master of one

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    Hello JW and all.

    The use of a ammeter on AC and holding it in your hand is different than Connecting it into the circuit.
    You are just reading the Current going threw the wire. Unless you are reading DC current, you need no direct connection.

    Cat II is rated at 600 Volt. If You have more than that in your house, Then the Transformer Is on the wrong tap, Wont come close to 600.

    The Fuse on the meter is to protect the meter for operator error, Not for the users protection, Just protects the meter.

    Using the Proper rated leads is more protection than any fuse will proved. Fuses blow slower than flesh.

    JW, Have You ever heard of keeping 1 hand in your pocket ?

    If you work on 3 phase systems then of coarse you need at least a CAT III meter.

    CAT II is fine for working around the house, and is considered Low voltage. It depends what you compare it to.

    You mix Apples and Oranges when you say a ammeter is the same as a voltmeter, as far as safe use.
    Same applies to hand held Non Contact Devices, Thay are safer, but not as accurate.

    Direct connection to a unknown voltage is always a risk.

    I guess I am not hearing where you are coming from.

    We are talking about working around the house, not bench or factory work. Single Phase System.
    Unless a factory is your home.

    A neon Bulb is better that the touch test. The old timers used the touch test, But I do not recommend it.

    I will not throw my Neon tester away, The screwdriver still works, lol.


    Enjoy your day.


    DonL
    Last edited: Apr 27, 2011
  18. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
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    Location:
    North Carolina
    It is not the voltage rating that is the problem. The category rating on meters is the ability of the meter to stand up to transient voltages from such things as surges from lightning, grid switching, large capacitors and so forth.

    As I have said a category II or III in most cases will be fine for checking voltages around most residential branch circuits, but the closer you get to the supply source the more likely to run into voltages transients and the higher the category rating of meter will need to be used.

    Voltage transients are a very common occurrence in AC utility furnished power.

    Checking the amperage of a conductor is just as dangerous if not more so than taking a voltage reading. When taking an amperage reading most people get a false sense of safety due to the fact that they are not coming in contact with a live terminal such as doing a voltage reading.

    During an amperage test the meter can be subject to more voltage than doing a voltage reading simply due to the makeup of the meter. The jaw of an amp probe is a simple transformer winding that opens and the closes around the conductor. It is again opened to remove. In both cases bare metal is exposed to the live circuit. Arc flashes have occurred during amp readings.


    The fuse internal to a meter is not a rated fuse. Most are simple AGC/SFE type fuses and these will arc over if they get started. The ionization of the air around the fuse will conduct current. This I have witnessed myself. Having a DVM set for an amperage or resistance test and touching the leads to a live circuit can result in a very enlighten experience and with shocking results. Did you catch the pun in that sentence? ;)

    Make it a practice to always be checking the setting of you meter to remain safe while using the meter is not bad advice no matter the person making the statement.
    Knowing the limitations of a meter is good advice no matter who is giving it.
    Understanding the dangers involved with the use and maintenance of electrical circuits is good advice for anyone to listen too. Now you either agree with this or you disagree, which is it?
  19. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX
    Hello all.

    To answer JW;
    "Understanding the dangers involved with the use and maintenance of electrical circuits is good advice for anyone to listen too. Now you either agree with this or you disagree, which is it? "

    I agree with You for the most part.

    The Amp Meter that own and use most has no Exposed Metal, and is Double Insulated.
    I very rarely check UN-insulated wires, other than checking for current on the ground wire.

    Like I said before, If a person does not no what they are doing, They should not be using any electrical testers.

    People get hurt every day sticking a knife into a toaster.

    How many people do you think disconnect their car battery before changing their motor oil ?
    Not many, even if the owners manual says to do so. (I sure don't, waste of my time)

    It is hard to protect against stupitdy.

    Have a great day.

    DonL
  20. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX
    Where did You go Randyj ?

    Sorry Your Thread got blown out, but you stir and run, lol.

    Get back in an tell us your outcome. I know You are over there laughing.

    Tell us about your shocking experience.

    Sometimes the best meters give false readings, if there is stray stuff flying around.

    Just think about all the RF bombarding you at this very moment.
    You can Rectify the RF in the air using PIN Diodes and charge batteries. I kid You not.

    Have a Great day.


    DonL

    "Books tell how it should be, Experience tells how it is"

    P.S. Make sure to use your PPE when talking on your cell phone.
    Last edited: Apr 28, 2011
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