gfi receptacles sharing the same neutral

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Stevenfyeager

Senior Member
Location
United States, Indiana
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electrical contractor
On an older home, three kitchen outlets are wired on a 12-3 (sharing neutral.) (Top of duplexes is one cirucit, bottoms is the other circuit.) I have been asked to replace the duplex receptacles with gfi's. I always avoid sharing neutrals with gfi's. But no choice here. Will they work if I use only the line side on the gfi's? Thank you
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
On an older home, three kitchen outlets are wired on a 12-3 (sharing neutral.) (Top of duplexes is one cirucit, bottoms is the other circuit.) I have been asked to replace the duplex receptacles with gfi's. I always avoid sharing neutrals with gfi's. But no choice here. Will they work if I use only the line side on the gfi's? Thank you
In a word, yes.

In more words, you cannot use the continuation terminals of the GFCI receptacle to protect (or even feed) downstream receptacles. And, of course, you can no longer have each duplex receptacle split between two sides of the MWBC.
 

John120/240

Senior Member
Location
Olathe, Kansas
You state top is one circuit, bottom is other circuit, a total of three receptacles ? Correct. In this case I would make the first GFCI receptacle all on the black, second GFCI on the red, third on the black. With a 12-3 HR I don't see any other choice.
 

kwired

Electron manager
Location
NE Nebraska
You state top is one circuit, bottom is other circuit, a total of three receptacles ? Correct. In this case I would make the first GFCI receptacle all on the black, second GFCI on the red, third on the black. With a 12-3 HR I don't see any other choice.
You could put first receptacle on the black, second on the red, and feed thru to the third receptacle from the second. Still effectively two 120 volt circuits but one less GFCI.
 

480sparky

Senior Member
Location
Iowegia
This will not work:

2cirgfirecepMWBC.jpg


The only way to line/load protect the downstream receps is to rewire them to separate neutrals:

2cirgfirecep.jpg


Or, you could just install a 2-pole GFCi breaker:

2cirgfibrker.jpg


Or just use the Line only side of a passel of GFCIs.
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
On an older home, three kitchen outlets are wired on a 12-3 (sharing neutral.) (Top of duplexes is one cirucit, bottoms is the other circuit.) I have been asked to replace the duplex receptacles with gfi's. I always avoid sharing neutrals with gfi's. But no choice here. Will they work if I use only the line side on the gfi's? Thank you
You can use a two pole gfci breaker or you can do what kwired said. Either will work fine.

I used gfci recpts to protect my counter top circuits. They are on a MWBC and have zero troubles. I could have used a two pole gfci breaker but the recpts were cheaper. In your case it might be more cost effective to slap in a breaker.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
This was very common practice before GFCIs became a requirement in kitchens. It's actually very efficient and balanced way to wire a home, especially on the countertop where many high-wattage devices may be plugged in simultaneously. The should come up with a split GFCI receptacle as a replacement that can also protect downstream outlets. Would be nice to have a direct retrofit device.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
You can use a two pole gfci breaker or you can do what kwired said. Either will work fine.

I used gfci recpts to protect my counter top circuits. They are on a MWBC and have zero troubles. I could have used a two pole gfci breaker but the recpts were cheaper. In your case it might be more cost effective to slap in a breaker.

Excellent point. That would be both code compliant and efficient and balanced... but expensive, perhaps moreso than the cost of the individual GFCI receps.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
You could put first receptacle on the black, second on the red, and feed thru to the third receptacle from the second. Still effectively two 120 volt circuits but one less GFCI.

But wouldn't the inbalance of monitored neutral current trip the GFCIs on the other leg?
 

Little Bill

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Tennessee NEC:2017
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But wouldn't the inbalance of monitored neutral current trip the GFCIs on the other leg?

If you split the circuits before hitting the 1st GFCI then it will work. Take the 12-3 to a junction box (or the box for the first recep), pigtail the neutral into two and carry on.
 

user 100

Senior Member
Location
texas
If you split the circuits before hitting the 1st GFCI then it will work. Take the 12-3 to a junction box (or the box for the first recep), pigtail the neutral into two and carry on.

The 12/3 splitting into a couple of 12/2s was done quite a bit years back to supply the required 2 sabcs, and yes, you can retrofit this setup with gfci recs.
 

kwired

Electron manager
Location
NE Nebraska
This was very common practice before GFCIs became a requirement in kitchens. It's actually very efficient and balanced way to wire a home, especially on the countertop where many high-wattage devices may be plugged in simultaneously. The should come up with a split GFCI receptacle as a replacement that can also protect downstream outlets. Would be nice to have a direct retrofit device.
I even done that to the first outlet, and GFCI's were required (at least within six feet of sink) when I first started in the trade. You could always split into two wire only circuits after that first outlet. If you want two circuits at each duplex, nothing prohibits it, but just isn't so practical when it comes to meeting the other codes that apply. If they made a so called "split circuit GFCI receptacle" it probably would cost as much or more then a two pole GFCI breaker, why not just go with the breaker if that is how you want it? Now we need AFCI on top of that so that presents another challenge, 2 pole AFCI may be out there but certainly are not common as of yet.

But wouldn't the inbalance of monitored neutral current trip the GFCIs on the other leg?
Three wire cable to the last outlet in my description there was only using black and white and was connected to the "feed thru" terminals of the second outlet. You still have two 120 volt circuits but this way can use two GFCI's instead of three. You still only have one 120 volt circuit that is usable at any one receptacle outlet location no matter which way you do it with receptacle type GFCI's.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
If you split the circuits before hitting the 1st GFCI then it will work. Take the 12-3 to a junction box (or the box for the first recep), pigtail the neutral into two and carry on.

Oh sure. You bet. I do this all the time for kitchen appliance circuits. I run a 12-3 to the first box and then split it off.
 

handy10

Senior Member
(Top of duplexes is one cirucit, bottoms is the other circuit.) I have been asked to replace the duplex receptacles with gfi's. Thank you

I cannot decide whether I don't understand the question or I don't understand the answers. It is certainly possible to use a GFI on a MWBC, but is it possible to split the duplex receptacle so that one of the receptacles is on one side of the MWBC and the other side is on the other side of the MWBC? The GFIs that I have seen have terminals for the incoming hot and neutral and terminals to continue the wiring to the next load, but the entire duplex receptacle is on one portion of the MWBC.
 

kwired

Electron manager
Location
NE Nebraska
Oh sure. You bet. I do this all the time for kitchen appliance circuits. I run a 12-3 to the first box and then split it off.
Unless AFCI rules were amended out if you are still on 2011 NEC or earlier where you are, you don't run 12-3 to the first box for kitchen outlets anymore.;)

I cannot decide whether I don't understand the question or I don't understand the answers. It is certainly possible to use a GFI on a MWBC, but is it possible to split the duplex receptacle so that one of the receptacles is on one side of the MWBC and the other side is on the other side of the MWBC? The GFIs that I have seen have terminals for the incoming hot and neutral and terminals to continue the wiring to the next load, but the entire duplex receptacle is on one portion of the MWBC.

If using "feed thru" terminals of a GFCI receptacle - you can not supply MWBC wiring on load side of that GFCI.

If you have "three wire cable" running from outlet box to outlet box, you can put a GFCI receptacle in every box, but you can not have both 120 volt halves of the MWBC available at any individual duplex GFCI receptacle like you can with a standard receptacle.

I suppose you could run one GFCI load wire to the top of a standard duplex and the bottom of that duplex could be supplied via the load side of a second GFCI that is supplied from the other half of the MWBC. But you can not do this with only a 12-2 cable as the feed to the load side receptacle, sharing the neutral will not work with the GFCI's.

Otherwise a 2 pole GFCI breaker at the origin of the source gives you the same flexibility of which receptacle or half of receptacle is on which half of the MWBC there once was before GFCI protection was a requirement. It also is likley more expensive, and does leave user having to find the breaker should the GFCI trip, where the receptacle has the reset right at the outlet location. Feed through protected outlets can sometimes have you hunting for the GFCI though.
 

John120/240

Senior Member
Location
Olathe, Kansas
I cannot decide whether I don't understand the question or I don't understand the answers. It is certainly possible to use a GFI on a MWBC, but is it possible to split the duplex receptacle so that one of the receptacles is on one side of the MWBC and the other side is on the other side of the MWBC? The GFIs that I have seen have terminals for the incoming hot and neutral and terminals to continue the wiring to the next load, but the entire duplex receptacle is on one portion of the MWBC.

You could make each half of the receptacle on its own circuit & GFCI protected. It would not be practical IMHO.
One way would be to have a GFCI device for each circuit , then from Load side of each GFCI to your receptacle. In this case break the tabs on both Hot & Neutral side of receptacle.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Unless AFCI rules were amended out if you are still on 2011 NEC or earlier where you are, you don't run 12-3 to the first box for kitchen outlets anymore.;)



If using "feed thru" terminals of a GFCI receptacle - you can not supply MWBC wiring on load side of that GFCI.

If you have "three wire cable" running from outlet box to outlet box, you can put a GFCI receptacle in every box, but you can not have both 120 volt halves of the MWBC available at any individual duplex GFCI receptacle like you can with a standard receptacle.

I suppose you could run one GFCI load wire to the top of a standard duplex and the bottom of that duplex could be supplied via the load side of a second GFCI that is supplied from the other half of the MWBC. But you can not do this with only a 12-2 cable as the feed to the load side receptacle, sharing the neutral will not work with the GFCI's.

Otherwise a 2 pole GFCI breaker at the origin of the source gives you the same flexibility of which receptacle or half of receptacle is on which half of the MWBC there once was before GFCI protection was a requirement. It also is likley more expensive, and does leave user having to find the breaker should the GFCI trip, where the receptacle has the reset right at the outlet location. Feed through protected outlets can sometimes have you hunting for the GFCI though.

Wisconsin has not yet adopted 2014. But yeah, I don't look forward to more AFCIs :/
 
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