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Thread: Subpanel ground/neutral

  1. #1
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    Subpanel ground/neutral

    I was tripping AFCIs. After an investigation, I found that the ground and neutral in my subpanel were reversed (in other words, the ground from the main went to the neutral bar and the neutral from the main went to the ground bar). After reversing them, AFCIs do not trip.

    Questions: Was that a real issue (given that the two are tied together at the main)? Should the neutral and ground in the subpanel be tied together like in the main?

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    Yes, that would cause AFCI and GFCI trips. The problem here is that the neutral from the load side of the AFCI and/or GFCI should never touch another circuit or ground. There are special circuits that detect neutral-to-ground leakage and trip.

    The only place in most situations that the ground and neutral should EVER be connected together is at the service disconnect (commonly, the "main" panel).

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    Reply

    Quote Originally Posted by rnatalie View Post
    Yes, that would cause AFCI and GFCI trips. The problem here is that the neutral from the load side of the AFCI and/or GFCI should never touch another circuit or ground. There are special circuits that detect neutral-to-ground leakage and trip.

    The only place in most situations that the ground and neutral should EVER be connected together is at the service disconnect (commonly, the "main" panel).

    Thank you - That is what I thought. Mistakes happen. This is why these forums are so important.

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    While it's hard to argue with success, I'm.having difficulty determining how the AFCI how the AFCI knew it was connected to the Green vs White wire.
    Tom
    TBLO

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    Quote Originally Posted by ptonsparky View Post
    While it's hard to argue with success, I'm.having difficulty determining how the AFCI how the AFCI knew it was connected to the Green vs White wire.
    I sent it a message when nobody was looking.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by ESolar View Post
    I was tripping AFCIs. After an investigation, I found that the ground and neutral in my subpanel were reversed (in other words, the ground from the main went to the neutral bar and the neutral from the main went to the ground bar). After reversing them, AFCIs do not trip.

    Questions: Was that a real issue (given that the two are tied together at the main)? Should the neutral and ground in the subpanel be tied together like in the main?
    No, Neutrals and ground can not be tied together at sub-panels

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    My question is, how did the AFCI know that it’s white pigtail was connected to the ‘green’ wire vs the ‘white’ wire? Both went back to the same location. It doesn’t matter that they were swapped accidentally.

    A detail is missing.
    Tom
    TBLO

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    Quote Originally Posted by ptonsparky View Post
    My question is, how did the AFCI know that it’s white pigtail was connected to the ‘green’ wire vs the ‘white’ wire? Both went back to the same location. It doesn’t matter that they were swapped accidentally.

    A detail is missing.
    I was wondering too. Perhaps it was indirectly making it trip by putting current on the EGC system which then made it sense a N-G bond in the branch circuit that it didnt quite pick up before? Thats all I got.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    I'm assuming that this was in conduit and the equipment grounding conductor buss was mounted directly to the panel. My guess is you were getting parallel paths between the EGC conductor and the conduit causing your trip.

    I should add that this was happening at the receptacle itself between the ground strap and the neutral..
    Last edited by rlundsrud; 05-17-19 at 12:32 PM.
    The world is round, you will get there no matter what path you take.

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    It's somewhat puzzling to me that the AFCI was tripping with the neutral and ground bar connections reversed. Nothing apparently changed on the load side of the breaker (either hot or neutral), just where the neutral pigtail on the line side was tied. Either way any voltage on the neutral pigtail must be very small and I don't know why the breaker would trip even if there were a few volts AC on the neutral line going into the breaker.
    However, because all of the neutral current on the subpanel was going through equipment grounds perhaps there are some marginal connections (like through painted knockouts, bonding screw, etc.) that cause fluctuations if not actual arcing in the conduction path, causing the AFCI to trip. Kind of reaching for straws here but that's all I've got.

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