GFCI Neutrals


Old 02-10-16, 09:07 PM
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GFCI Neutrals

I was going to wire a GFI today but wanted to check something:

The GFI is in the box where a MWBC splits. I was going to hook the black from the 12-3 to the line. The 12-3 red is connected to a 12-2 cable and I left that as is.

There are 2 more 12-2 cables in the box (besides the 12-2 that the red is connected to)

I was going to connect those to load.


What to do with the neutral from the cable that is connected to the source red?

I think it should be attached to the line along with the shared neutral from the 14-3??
Old 02-11-16, 04:17 AM
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I think you need to start over.

This GFI, is it a 120 volt GFCI receptacle or is it a 120 volt (single pole) GFCI circuit breaker? Or perhaps a 240 volt (two-pole) circuit breaker?

Or is the "box" simply a junction & pull box with an extended cover for a receptacle? Are you changing the standard receptacle for a GFCI receptacle and then ground fault protection for a circuit beyond the receptacle?

You mention a 12-3 cable that appears to be the supply of a multi-wire branch circuit. Then you mention three 12-2 cables, one of which is powered from the red lead of the 12-3.

In your last sentence you mention a 14-3. Was that typo and you meant the 12-3 cable supplying power?
Old 02-11-16, 05:32 AM
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What do the other 12-2 cables go to?

A 2 conductor cable continuing downstream and originally fed by half of a multiwire branch circuit may be readily connected (both hot and neutral) to the load terminals of a ground fault circuit interrupter unit.

The neutral from the source cable with a hot wire connected to the line side of the GFCI would also be connected to the line side of the GFCI.

If two wire ends want to go under one screw, cut a pigtail (jumper) of the same color (you can mix and substitute red and black) and connect that to the screw. Connect the other end of the pigtail to the two wire ends in question.

There must be no path, using pigtails or otherwise, between the line side neutral and the load side neutral of the GFCI unit. This will limit some of the connection combinations you are allowed to use and limit what you can attach to the load terminals. If both halves of a MWBC continue downstream in the same 3 conductor cable, then neither half may be connected to the load terminals of a GFCI receptacle.

Last edited by AllanJ; 02-11-16 at 05:55 AM.
Old 02-11-16, 07:29 AM
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Let me clarify.
I want to install a GFI on a MWBC, 12-3 is the feed and it's on a double pole 20amp breaker. The box where the GFI will go is where the split occurs.

I only want to connect the black wire to the GFI line and leave the red wire powering the fridge, non-protected.

Besides the 12-2 going out to the fridge, there are two other 12-2 cables in the box that I want to connect to the load. (I'm not concerned with those).

I don't know why I got confused. I know that in a box where a MWBC is split, the neutrals must be pigtailed.

Can I get confirmation... The neutral from source (12-3) will be pigtailed to the neutral going to fridge (red non-protected wire) and connected to line side of GFI?
Old 02-11-16, 07:46 AM
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Yes, that's correct. All the neutrals, including the one from the line side of the GFCI get pigtailed.

If you are protecting anything downstream of the GFCI by connecting to the load terminals, *that* neutral connects only to the load side neutral connection on the GFCI.
Old 02-11-16, 08:02 AM
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Your description sounds good to me.
Old 02-11-16, 08:18 AM
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Thanks guys, I'm good to go.

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