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Thread: GFCI wiring question

  1. #1
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    Default GFCI wiring question

    I want to save a little on wire if possible on two circuits and run one 12-3 instead of 2 12-2 inside the house, through the wall and to an outside outlet. I plan on putting the 2 GFCI outlets in the basement to protect them better. My question is can I share the netural wire AFTER it leaves the GFCI?
    The other question is do I even want to share the netural up to the GFCI or should each run be dedicated. This will be 20 amps and I expect to have them near capacity.

    - Michael

  2. #2
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    No, you can't.

    GFCI works by comparing the current in the hot wire against the current in the neutral wire. If the current isn't the same, some current is finding its way back through some other path, and the breaker trips.

    I would be very wary of sharing a neutral to the GFCI. I can't put my finger on why, so it may just be superstition on my part, but it's a risk I wouldn't take (even though I have no idea what the risk is.)
    There sure as hell *are* user-serviceable parts inside!

  3. #3
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    Default Re: GFCI wiring question

    Quote Originally Posted by Michael
    I want to save a little on wire if possible on two circuits and run one 12-3 instead of 2 12-2 inside the house, through the wall and to an outside outlet. I plan on putting the 2 GFCI outlets in the basement to protect them better. My question is can I share the netural wire AFTER it leaves the GFCI?
    The other question is do I even want to share the netural up to the GFCI or should each run be dedicated. This will be 20 amps and I expect to have them near capacity.

    - Michael
    I disagree with Noginboink:

    If your GFI's are downstream from the panel, they wont detect a difference in neutral/black downstream of them.

    However you still should NOT do this because lets say you put a 20Amp breaker on each black wire)... that means up to 40Amps could flow through the single white wire.
    Go out and buy enough 12/2 do make two runs.

    Which is fine, if you understand that, and the gauge of the single neutral wire is enough to handle all the current from both breakers.

    But I still wouldn't do it that way, just get two wires and do it with care


    Thanks,
    Dave

  4. #4
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    Default Re: GFCI wiring question

    Quote Originally Posted by xmus
    Quote Originally Posted by Michael
    I want to save a little on wire if possible on two circuits and run one 12-3 instead of 2 12-2 inside the house, through the wall and to an outside outlet. I plan on putting the 2 GFCI outlets in the basement to protect them better. My question is can I share the netural wire AFTER it leaves the GFCI?
    The other question is do I even want to share the netural up to the GFCI or should each run be dedicated. This will be 20 amps and I expect to have them near capacity.

    - Michael
    I disagree with Noginboink:

    If your GFI's are downstream from the panel, they wont detect a difference in neutral/black downstream of them.

    However you still should NOT do this because lets say you put a 20Amp breaker on each black wire)... that means up to 40Amps could flow through the single white wire.
    Go out and buy enough 12/2 do make two runs.

    Which is fine, if you understand that, and the gauge of the single neutral wire is enough to handle all the current from both breakers.

    But I still wouldn't do it that way, just get two wires and do it with care


    Thanks,
    Dave
    I agree with both statements.

    If you put the GFI's in the yard and ran a shared neutral that was capable of carrying that load then you'd be ok, if you put the GFI's in you basement and ran 2 hot wires and 1 neutral wire from the GFI's to your SSR's this could get flaky.

    For the sake of safety I would run 2 cables.

  5. #5
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    sharing neutrals can safely be done. The only thing to keep in mind is that you MUST, I repeat MUST feed ea circuit from different phases on the breaker panel. In doing so the amperage loads will not add up and overload the neutral.

  6. #6
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    Thanks for the replies.
    I think I will go with the extra $40 and run 2 wires all the way. They were going to be on different phases/legs in the breaker panel, but I would probably sleep easier at night with the extra wire.
    Outside in the yard, let it smoke and burn the snow - Inside, smoke is not allowed.
    - Michael

  7. #7
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    Quote Originally Posted by Michael
    Outside in the yard, let it smoke and burn the snow - Inside, smoke is not allowed. - Michael
    Well put

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