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Thread: Testing 220V with multimeter. What should the meter read?

  1. #1
    DIY Junior Member TXTom's Avatar
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    Default Testing 220V with multimeter. What should the meter read?

    I am troubleshooting problems with a new booster pump that I installed at my house. Here is my post from the "Pump/Well Board":
    I just installed a storage tank and booster pump at my house. The booster pump won't run. I need some wiring help. I am using a standard pressure switch to control the booster. There is no pressure on the system so the contacts on the switch are closed. I have a 20amp double pole breaker that I am using to power the pump. The pressure switch is connected to the breaker with a red and black wire and ground. The pump is wired to the pressure switch with a red and black wire and ground. The terminals on the switch are wired so that the contacts complete the red/red and black/black connections. The booster pump is a Goulds GB. It is wired for high voltage from the factory. I connected the red and black wires to terminals 1 and 4 as shown on the motor's diagram. The ground is connected to the green terminal. Why won't my pump start?

    More: http://www.terrylove.com/forums/showthread.php?t=16322

    Thanks,

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by TXTom View Post
    I checked the voltage from ground to the terminals and I get 125V on each terminal. I have a feeling one of the Legs is not working, but I thought that maybe each would add together to make 250V. Am I wrong?

    Tom
    Not if you are using a two pole breaker. Could be wrong if using two single pole breakers.

  3. #3
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by TXTom View Post
    Testing 220V with multimeter. What should the meter read?
    Not meaning to sound harsh or like a smarty but if you are testing for voltage on a 22o volt circuit you should read 220 volts when checking leg to leg.

    Check for voltage on both the load and line side of the pressure switch and at motor.
    Make sure that if the motor has an internal overload that the reset button is set.
    Last edited by jwelectric; 10-31-2007 at 09:12 PM.

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    DIY Senior Member BrianJohn's Avatar
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    L1 to L2 220 nominal,
    L1 to ground 110 nominal
    L2 to ground 110 nominal

    Check this at the circuit breaker load terminals.
    Check this at the line terminals of the pressure switch
    Check this at the load terminals of the pressure switch
    Check this at the motor terminals.
    Check voltage across the contacts (L1 line to L1 load, L2 line to L2 load) of the pressure switch you should have "0" volts, if the contacts are closed.

    If you have 110 and 220 as noted above then you have a wiring issue at the pump or a defective pump or you smoked the pump.

  5. #5
    DIY Junior Member TXTom's Avatar
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    Thanks for the info. I am using a double pole 20A breaker. I will check my readings again. I believe I was reading 0 volts across L1/L2. I will check it again.

    Thanks,

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    The only other thing I can think of is a poor connection somewhere. In that case a sensitive voltmeter would show the proper voltage, but the actual voltage would drop to zero under load. In your case, though, there's always a load on the circuit because the switch is closed (assuming the motor is actually wired properly and connected). Be sure to let us know what you eventually find.

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    Moderator & Master Plumber hj's Avatar
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    Default voltage

    IF the pump is in the "run" position when you check voltage at the circuit breaker, one leg could be dead but you would still have 120v backfeed from the leg that is working. Unless you have 220/240 across the breaker, you do not have any power.

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    DIY Junior Member TXTom's Avatar
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    It was a bad breaker. The breaker was new, but one leg was dead. Thanks for the tips. Knowing what the voltage readings should be for the 220 was very helpful.

    Tom

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    DIY Senior Member BrianJohn's Avatar
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    It may be possible depending on the type of panel and CB style that you are not on two separate lines, with some of the old SLIM LINE styles it was possible to have both poles on L1 or L2.

  10. #10

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    Quote Originally Posted by BrianJohn View Post
    It may be possible depending on the type of panel and CB style that you are not on two separate lines, with some of the old SLIM LINE styles it was possible to have both poles on L1 or L2.
    Sounds that way.... they're called piggy-back, half-inch, half-size, tandem breakers. But they don't give you 240volts as they only sttach to one (120v) buss bar in the panel. You will get 120volts to ground on each wire, but not 240 between them as it is the same 120 volt source.
    Just my 2 worth.

  11. #11
    DIY Junior Member TXTom's Avatar
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    Thanks- But it was a bad breaker. I replaced the breaker in the exact same slots and everything is peachy...... Voltage at the bad breaker was 125V to ground on one pole, and 17V to ground on the other. Voltage across the poles was 107V. New Breaker voltage is 250V across the poles.

    Thanks,

  12. #12
    DIY Senior Member BrianJohn's Avatar
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    GE and several others (I THINK) made slim 2 pole.

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