GFI on multiwire circuit.

[arnettda]

I need to replace some Kitchen outlets with GFIS. They are wired from outlet to outlet with a multiwire circuit.(12-3 Nm) Can I put a GFI in every outlet opening or will I have problems with nusience trippings since all the GFIs share the same neutral? Line and Load will not work. I can make all the outlets one circuit. The red wire would feed all the way through to the Microwave outlet. Or could I use a two pole GFI breaker in the panel?
Thanks

 

[sandking]

Why not just install a GFI in the first box then use standard recepts down stream from the load side of the GFI? You dont need to have a GFI at each opening, but they can all be protected from the first one as long as they are daisy chained on the same circuit.

 

[sandking]

I just re-read your question. The load of the GFI will not work since the micro is on the same nuetral. Yes, you can wire each GFI on the line side without an issue.

 

[Little Bill]

I need to replace some Kitchen outlets with GFIS. They are wired from outlet to outlet with a multiwire circuit.(12-3 Nm) Can I put a GFI in every outlet opening or will I have problems with nusience trippings since all the GFIs share the same neutral? Line and Load will not work. I can make all the outlets one circuit. The red wire would feed all the way through to the Microwave outlet. Or could I use a two pole GFI breaker in the panel?
Thanks

You can use GFCIs on a MWBC and shouldn't have any nuisance trips as long as you wire them correctly.

 

[jumper]

You can use GFCIs on a MWBC and shouldn't have any nuisance trips as long as you wire them correctly.

Yeppers.:thumbsup:

 

[kwired]

How many GFCI receptacles are we going to need. A two pole GFCI breaker is not cheap but several receptacles add up fast. The breaker only takes minutes to install - usually.

 

[thunder15j]

How many GFCI receptacles are we going to need. A two pole GFCI breaker is not cheap but several receptacles add up fast. The breaker only takes minutes to install - usually.

This would surely save a bunch of labor, but probably would lead to a future homeowner headache since a ground fault on any one of several receptalces on the two circuits would cause a a major outage in the kitchen. Also an overload on one circuit is going to take out the other circuit.

 

[ActionDave]

You can use GFCIs on a MWBC and shouldn't have any nuisance trips as long as you wire them correctly.

But in the OP's case he cannot because the neutral is shared from box to box.

 

[Dennis Alwon]

But in the OP's case he cannot because the neutral is shared from box to box.

I disagree. THe op has a 12/3 going from box to box. If he uses a gfci in every box it will work fine or he can use a dp GFCI. I would use the former.

 

[kwired]

This would surely save a bunch of labor, but probably would lead to a future homeowner headache since a ground fault on any one of several receptalces on the two circuits would cause a a major outage in the kitchen. Also an overload on one circuit is going to take out the other circuit.

Overload on one circuit will take out the other anyway if using a two pole breaker for the MWBC.

How many people have much trouble with 'nuisance tripping' of GFCI's on a kitchen circuit? I don't know that I ever see it. Most of the nuisance trip calls I get are usually outdoor receptacles, or construction site GFCI protected receptacles, and usually involve either moisture in a cord or connected load, improperly connected device or appliance, or damaged insulation on some equipment, all good reasons for the GFCI to trip. Kitchen appliances just don't give any trouble unless they have been tampered with or misused, then it is good that they do trip.

 

[ptonsparky]

One of my first learning experiences with GFCIs way back when the world would come to an end because of all this new fangled stuff. Pigtail out at each box to the line side of each GFCI. Used to make for a really crowded bevel backed metal box but with a big enough hammer handle it would all fit.

 

[ActionDave]

I disagree. THe op has a 12/3 going from box to box. If he uses a gfci in every box it will work fine or he can use a dp GFCI. I would use the former.

You're right. I meant he can't go line and load.

 

[Little Bill]

For those who might not understand, please explain why you can't go line-load. If you go line-line or tap/pigtail at each box, or go line-load you are still sharing the neutral.

 

[jumper]

For those who might not understand, please explain why you can't go line-load. If you go line-line or tap/pigtail at each box, or go line-load you are still sharing the neutral.

Bill, we missed the fact that it is only one cable box to box. You can not line-load here. You can share the neutral, but not through the GFCI receptacles.

 

[480sparky]

This wiring method will not work:

You either need to install 2-cond. cables downstream from the GFCIs:

Or use a 2-pole GFCI breaker:

Or else put GFCI receps in every box.

 

[Dennis Alwon]

For those who might not understand, please explain why you can't go line-load. If you go line-line or tap/pigtail at each box, or go line-load you are still sharing the neutral.

You are sharing a neutral but that neutral is not going thru the GFCI so it will not measure the discrepancy in the neutral current. If it were on the load side then the GFCI will notice that the difference in neutral current.

 

[Little Bill]

Bill, we missed the fact that it is only one cable box to box. You can not line-load here. You can share the neutral, but not through the GFCI receptacles.

I reckon so. I was thinking the way 480 shows in the 2nd drawing.

You are sharing a neutral but that neutral is not going thru the GFCI so it will not measure the discrepancy in the neutral current. If it were on the load side then the GFCI will notice that the difference in neutral current.

Thanks, I understand but am not as good at explaining (without talking and pointing) as you and others are.

 

[jmellc]

Split the ckts at the 1st box. Use black for that GFCI recep & the ones downline of it. Use the red to feed a 12-2 direct to microwave. Pigtail main neutral to feed 1st GFI & over to microwave. I used to do that all the time for kitchen ckts. But the guys are right that if you use a DP breaker, as required, 1 ckt will trip the other.

Another wonderful result of someone at the NEC. While I don't like common neutrals, DP breakers defeat the whole purpose of spreading the loads.

I may try to locate some 12-2-2 if I get more kitchen work. That solves both problems.

 

[cadpoint]

It's the problem that it's a kitchen, my question is, is this the full-fillment of the 2 circuit requirement or happens to be one of the two, that happens to have more wires?

... I can make all the outlets one circuit. The red wire would feed all the way through to the Microwave outlet...

MO, no can not go to one circuit, IE or making a dedicated circuit that for the microwave. See first question.
(disclaimer of no book in sight ... )

Is that what the manufacturer is asking for?

 

[kwired]

Split the ckts at the 1st box. Use black for that GFCI recep & the ones downline of it. Use the red to feed a 12-2 direct to microwave. Pigtail main neutral to feed 1st GFI & over to microwave. I used to do that all the time for kitchen ckts. But the guys are right that if you use a DP breaker, as required, 1 ckt will trip the other.

Another wonderful result of someone at the NEC. While I don't like common neutrals, DP breakers defeat the whole purpose of spreading the loads.

I may try to locate some 12-2-2 if I get more kitchen work. That solves both problems.

You can use handle ties, then both poles do not trip when there is a fault only on one.

One other problem that comes up with using 12-2-2 is box fill. Sure you can use larger boxes but they will not be the basic 25-50 cent plastic nail on boxes we usually see.