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Thread: GFI Testing w/ Multimeter

  1. #1
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    GFI Testing w/ Multimeter

    I've wired six 20 amp/110volt outlets to a blank face GFI, and when I turn on power and try and click the reset button, the GFI keeps clicking off. I've double and triple checked that I have the line and load connections correct, I've swapped it with another new GFI, same problem persists. I bypassed the GFI just to see if the breaker would pop, and it didnt. Rather than pulling each outlet out of its box and checking the connections, is there a quick way to test each outlet with the multimeter to see where the problem is? If so, what should I be looking for?

  2. #2
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    Quote Originally Posted by Thundermasmacho View Post
    I've wired six 20 amp/110volt outlets to a blank face GFI, and when I turn on power and try and click the reset button, the GFI keeps clicking off. I've double and triple checked that I have the line and load connections correct, I've swapped it with another new GFI, same problem persists. I bypassed the GFI just to see if the breaker would pop, and it didnt. Rather than pulling each outlet out of its box and checking the connections, is there a quick way to test each outlet with the multimeter to see where the problem is? If so, what should I be looking for?
    The problem is most likely an unintended connection between the neutral wire and the EGC or other grounded surface somewhere on the load side of the GFCI.
    Unfortunately a meter will just measure that continuity exists and not tell you where unless you get a very low ohm (less than 1 ohm) reading between neutral and EGC and can measure carefully enough to detect a fractional ohm difference in the reading from one place to another. The lower the reading, the closer you are to the problem.

    NOTE: I am assuming that you are allowed to perform this sort of electrical work on your premises. Otherwise I would just recommend that you bring in a licensed electrician.

  3. #3
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    Is anything plugged into these outlets yet?

  4. #4
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    Since these are Blank Face what is connected to the load side?
    Curt Swartz
    Electrical Contractor

  5. #5
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    Quote Originally Posted by curt swartz View Post
    Since these are Blank Face what is connected to the load side?
    The OP said six 120V 20A outlets
    Probably actually receptacles.

    Sent from my XT1585 using Tapatalk

  6. #6
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    Quote Originally Posted by GoldDigger View Post
    The OP said six 120V 20A outlets
    Probably actually receptacles.

    Sent from my XT1585 using Tapatalk
    The OCD part of me convulses when the term 'outlet' is used where 'receptacle' should be. Especially by those who should know the difference.

  7. #7
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    There is a plug-in module that has LEDs to indicate improper and proper wiring at the U ground receptacle. This may be quicker than removing each receptacle.

    https://www.google.com/search?source...k1.7PjIZl0xijM
    Am I in shape?? I get plenty of exercise pushing my luck!!

  8. #8
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    Quote Originally Posted by GoldDigger View Post
    The problem is most likely an unintended connection between the neutral wire and the EGC or other grounded surface somewhere on the load side of the GFCI.
    Unfortunately a meter will just measure that continuity exists and not tell you where unless you get a very low ohm (less than 1 ohm) reading between neutral and EGC and can measure carefully enough to detect a fractional ohm difference in the reading from one place to another. The lower the reading, the closer you are to the problem.

    NOTE: I am assuming that you are allowed to perform this sort of electrical work on your premises. Otherwise I would just recommend that you bring in a licensed electrician.
    I agree this is the most likely cause.

    Presumably these receptacles are daisy chained to the load side of the GFI. I'd be inclined to start at the first receptacle and disconnect the wiring going to the rest of the receptacles one at a time and see where the problem is.
    Bob

  9. #9
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    Quote Originally Posted by petersonra View Post
    I agree this is the most likely cause.

    Presumably these receptacles are daisy chained to the load side of the GFI. I'd be inclined to start at the first receptacle and disconnect the wiring going to the rest of the receptacles one at a time and see where the problem is.
    The computer science jocks will tell you that the most efficient search for this type of problem is to start by disconnecting at the middle receptacle to see which half the problem is in, then keep dividing in half. It is called a binary search.
    Since the OP installed the wiring, he knows where the middle is. In an existing building, you would have to guess at the routing, so the search would be less efficient.

  10. #10
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    Quote Originally Posted by ATSman View Post
    There is a plug-in module that has LEDs to indicate improper and proper wiring at the U ground receptacle. This may be quicker than removing each receptacle.

    https://www.google.com/search?source...k1.7PjIZl0xijM
    OP can't even get power to the receptacle(s), so those aren't going to indicate anything. If he bypassed the GFCI and has neutral to ground fault or even neutral and ground reversed they will still indicate "correct" wiring.

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