Is it possible to have two GFIs on 12/3 cable (to create two appliance circuits) where the neutral is shared between two circuits, each GFI is at the beginning of each circuit in a 2 gang box? I figured this was totally fine, and inspector approved. However, when I reset one GFI and attempt to reset the other they both trip right away. Never did a circuit this way before, but have to since I”m close to a sink. Sounds like it should work fine but that is why I called my inspector first to ask and he was fine with it.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Learn more about the benefits and compliance details for the DOE's new water heater energy-efficiency standards.
Featured Video
How to Install Cable Rail Around Wood-Post CornersHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Not sure if this will help but I had a similar problem--one 12/2 cable feeding a box with a GFCI and a 3-way switch. A 12/3 cable from that box to the second switch and then from there 12/2 on to the lights. Operating the three way switches would trip the GFCI. Someone here had an explanation for it a few months ago when I posted the problem.
Edited 5/27/2004 3:09 am ET by davidmeiland
Probably won't work. A GFCI measures the unbalanced current between hot and neutral as well as the potential between neutral and ground. If the neutral current is not exactly equal to the hot current, it assumes the difference is going someplace it shouldn't, and it trips. Also, if the ground and neutral are too far apart in voltage, it assumes you have a bad ground or neutral and it trips. If you draw much current on the shared neutral it may trip. Different brands of GFCI may might give different results. Try a different brand if you have any.
Gfi must have it's own neutral. There's probably some leakage or an inbalance surging from the other device which may be your problem.
You can do it, but you have to keep the neutral separate AFTER the GFCI.
You have two options.
1. Install GFCI's at least receptacle.
2. Split the circuit. At the first box install 2 GFCI and connect the neutral on the LINE side of each one along with the 12/3 neutral. Then run SEPARATE 12/2 from the LOAD side of each GFCI to the receptacles for that half of the circuit.
If you've got the neutrals bonded together where they exit the GFIs, then the GFIs will trip.
A GFI must have it's neutral totally unconnected to any other circuit or ground.
Pretty sound advice so far IMHO. You might want to also, in addition to making the checks so far recommended, double check the neutral connections back to the box. One or more weak neutral connections could allow the voltages between the two 120v circuits to vary enough to throw off or, worse case, destroy the small integrated circuit that controls the GFIs.
I'm not a big fan of shared neutral circuits in residential settings. They IMO offer little in the way of savings in terms of material costs or time while significantly increasing the risk of harm or property damage.
Had my elec inspection today. Passed with flying colors. Based on the advice here, and his explanation also, I have a pretty good understand of what I did wrong. What I did will work as long as I don't try to put any receptacles on the Load terminals. But since I had downstream receptacles, sharing the neutral just won't work with GFIs, period. Ya gotta run 12/2. So lesson learned. Inspector said he made the same mistake once, his was a bigger issue to fix whereas mine was easy due to accessability to pull new wire.
I agree with you about shared neutrals. Why did I do it? Using up what I had, I don't use much of it at all so was tired of having the stuff lay around.