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Old 10-10-2012, 02:49 PM   #1
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Question on GFCI with shared neutral


A few years ago, I ran 12/3 to 2 20A outlets using a shared neutral. I'd like to change these outlets to be GFCI, but was wondering if GFCI would work on a shared neutral, or if I could only install a single one and just cap off the other line.

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Old 10-10-2012, 04:08 PM   #2
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Question on GFCI with shared neutral


I dont believe GFCIs work on shared neutrals. I ahve tried it and failed.

Maybe a real electrician can chime in though, and offer a solution.

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Old 10-10-2012, 04:16 PM   #3
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Question on GFCI with shared neutral


GFCIs will work on a shared neutral, but you have to keep line neutral and load neutral seperate
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Old 10-10-2012, 04:22 PM   #4
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Question on GFCI with shared neutral


You can put ground fault circuit interrupter units on a multiwire branch circuit wherever you wish to.

But if you want to continue protection from one GFCI receptacle to additional plain receptacles, you need a separate 2 wire cable off of the load terminals of the GFCI receptacle.
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Old 10-10-2012, 04:31 PM   #5
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Question on GFCI with shared neutral


Actually, now I remember what I was trying to do was install a GFCI breaker on a shared neutral circuit. <---- This did not work for me.
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Old 10-10-2012, 04:50 PM   #6
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Question on GFCI with shared neutral


I've had trouble with GFCI breakers, as well - especially when the actual load is a long ways away. Not sure why... For instance, an outlet on a lamppost 100-feet from the house never worked.

Thanks for the other responses. I'll put two GFCI's at the end of the 12/3 and then run 12/2 to any other outlets beyond that.
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Old 10-10-2012, 06:06 PM   #7
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Question on GFCI with shared neutral


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Originally Posted by dmmanning View Post
I've had trouble with GFCI breakers, as well - especially when the actual load is a long ways away. Not sure why... For instance, an outlet on a lamppost 100-feet from the house never worked.
Then you had a neutral to ground short, or another neutral related issue. I can assure you right now, the issue was not with the GFCI breaker.
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Old 10-10-2012, 07:09 PM   #8
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Question on GFCI with shared neutral


For very long runs beyond a ground fault circuit interrupter, induced currents (due to capacitance) between hot and ground could be sufficient to trip the GFCI.
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Old 10-10-2012, 07:17 PM   #9
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For very long runs beyond a ground fault circuit interrupter, induced currents (due to capacitance) between hot and ground could be sufficient to trip the GFCI.
Not that I don't agree with you... But seriously. You want to give me the exact length that this occurs at? The reason I bring it up, is because I've never witnessed this in the field... I use a meggar and always find an insulation break down.
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Old 10-10-2012, 07:48 PM   #10
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Question on GFCI with shared neutral


I've seen it.

We did a pool installation with a rather long feeder conduit. Instead of using several GFCI breakers, we installed a big one on the feeder, protecting the entire pool panel from the source.

Nuisance tripping occurred, even with all the loads turned off.

This was a new installation, with THWN wires installed in PVC conduit.

Ended up having to scrap the idea of Ground-fault protection on the feeder, and used individual breakers on each piece of equipment.

Never had another problem after that.
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Old 10-11-2012, 06:43 AM   #11
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If you put the single large GFCI unit out at the pool house rather than at/in the main panel then I would not expect nuisance tripping.
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Old 10-12-2012, 05:32 AM   #12
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Question on GFCI with shared neutral


There was no "pool house" -- DUH ...

Besides, you can NOT back-feed a GFCI breaker and use it as a main in a panel

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