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Thread: testing integrity of buried egc?

  1. #1
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    testing integrity of buried egc?

    Power goes to garage underground with galvanized rmc. Its 50+ years old and also serves as the egc and I fear it might be shot.

    Do I need special equipment to test the integrity of the egc?

    I tested impendence from where it exits my main panel and to an outlet in the garage and it was jumping all over the place... 100-200 ohm. Im assuming its compromised but I also suspect I am unable to test in this manner accurately with a standard dmm.

  2. #2
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    Quote Originally Posted by ricry View Post
    Power goes to garage underground with galvanized rmc. Its 50+ years old and also serves as the egc and I fear it might be shot.

    Do I need special equipment to test the integrity of the egc?

    I tested impendence from where it exits my main panel and to an outlet in the garage and it was jumping all over the place... 100-200 ohm. Im assuming its compromised but I also suspect I am unable to test in this manner accurately with a standard dmm.
    What procedure did you use to perform this impedance test? Temp wire back to beginning of circuit and test continuity? Turn loads off and use the feeder neutral for said temp wire is an easy way, but make sure there is no N-G bonding beyond beginning of the feeder, which is hopefully service panel if bonding is done there.
    I live for today, I'm just a day behind.

  3. #3
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    I tested between garage outlet ground prong and main panel with extension cord.

  4. #4
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    Quote Originally Posted by ricry View Post
    I tested between garage outlet ground prong and main panel with extension cord.
    Not sounding so good then. Can try to see if the EGC will carry any significant load - but be careful. If it can't carry say a 1000 watt heater, it will never trip on a ground fault.
    I live for today, I'm just a day behind.

  5. #5
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    I always pull an EGC in underground runs, even when in metal.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #6
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    Quote Originally Posted by LarryFine View Post
    I always pull an EGC in underground runs, even when in metal.
    Around here RGC buried for 50 years would be a trace of rust in the earth. The TW might still be good. Chance of salting? Make it less.

    Dig down and look at it.
    Tom
    TBLO

  7. #7
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    Would it not be possible to run some #14 thhn from the ground bar in the main panel out to the garage and test continuity between the rmc and the thhn?

    Should be able to test off the existing neutral too, that is ran out to the garage, assuming it's in good shape.

  8. #8
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    Quote Originally Posted by Cow View Post
    Would it not be possible to run some #14 thhn from the ground bar in the main panel out to the garage and test continuity between the rmc and the thhn?

    Should be able to test off the existing neutral too, that is ran out to the garage, assuming it's in good shape.
    He said he used an extension cord, have to assume but maybe remind him to make sure the cord used was in good condition.
    I live for today, I'm just a day behind.

  9. #9
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    Quote Originally Posted by LarryFine View Post
    I always pull an EGC in underground runs, even when in metal.
    But you were 50 years too late for the one in the OP, what do you do when you run into something existing and it is questionable?
    I live for today, I'm just a day behind.

  10. #10
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    Quote Originally Posted by kwired View Post
    But you were 50 years too late for the one in the OP, what do you do when you run into something existing and it is questionable?
    If you can't push a fishtape through the tube of rust, you have to use the neutral and re-ground it.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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