Wiring GFCI plugs on 12-3 cable


Old 08-16-05, 05:00 AM
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Wiring GFCI plugs on 12-3 cable

I am in the process of rewiring the GFCI circuit in my kithchen and I'm having a small problem. I ran the new circuit using 12-3 cable so that 2 plugs could share the black wire and 2 could share the red wire. The first plug on the black circuit is a GFCI plug, with a second 'regular' plug branching off of it. Same goes for the red circuit -- total of 4 plugs altogether. The circuit uses a double-pole 20 amp breaker, with the red wire leading to one and the black to the other.

Both black and red circuits share the white wire, which is pigtailed at each plug and attached to only one of the 'white' screws on each plug.

When I plug a lamp into either of the GFCI plugs, everything works fine. But when I plug the lamp into either of the non-GFCI plugs, the corresponding GFCI plug that is upstream trips.

Anybody know off-hand what the issue is? COuld it be the way the neutral wires are connected?

Thanks in advance for any help!
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Old 08-16-05, 05:13 AM
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You cannot use GFCI receptacles in this manner. With a multi-wire circuit you either need to provide GFCI protection with a GFCI double pole breaker or you need to provide GFCI protection at each receptacle, using only the line side of the devices. Your other option is to switch to using 12-2 after the GFCI receptacles.

The problem you are running into is that the current on the neutral wire does not equal the current on the hot wires. This is how a multi-wire circuit works, and one reason why multi-wire circuits are tricky to use.
Old 08-16-05, 07:00 AM
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As Bob says, GFCI and multiwire circuits don't get along well. It's just one of the reasons on my list that I don't really care for multiwire circuits.

You can of course install the double-pole 20-amp 120/240 GFCI breaker, but these are expensive. You can also just buy four GFCI receptacles, connect only the line side of each, and be done with it. Actually, you may only need three depending on exactly how you routed the cable and which outlet is on which hot wire. Or, if the walls are still open, you can split the 12/3 into two 12/2s at the first box, and then you only need two GFCI receptacles.

Bottom line is that you cannot connect a shared neutral to the load side of a GFCI receptacle.
Old 08-16-05, 09:46 AM
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I figured it had something to do with the shared neutral wire. I think I will just buy 2 more GFCI receptacles and be done with it. Thanks for the helpful info!

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