GFCI on Shared Neutral

[Strombea]

I know that this has been discussed before, but i am having trouble on a service call. The run from panel is 100 ft, and it is a 3 wire circuit supplying 2 different GFCIs and nothing else. (outdoor kitchen) So the GFCI 1 goes out every 2 or 3 months and GFCI 2 seams to be fine. I know that GFCIs can share a neutral, personally i would have ran 2 neutrals. so the question is why does the first one go bad?

I think that when the GFCI 2 has an appliance plugged in, then the current on the neutral is going through the neutral line screw on GFCI 1 and the hot side of GFCI 1 has nothing thus wearing on the GFCI?

My options are to figure the basic principal of this out and fix it, or to simply pull a new neutral through the conduit, and completely separating the circuits.

Another thought is:

Does the length of the "sharing point" matter for the GFCI neutrals? If i was to take the neutrals off the GFCI and simply wire nut them 12" back with a pigtail, would path of least resistance totally bypass GFCI 1? because technicall all neutrals are connected, so at some point the actual connection or "splitting point" matters

Not a big deal, just wondering, I will be pulling a second Neutral.

 

[kwired]

I think you will not see much any difference in performance between either wiring diagram posted. Running an additional neutral would probably not make any difference either. None of the concerns mentioned really have much to do with why the GFCI may trip.

 

[Strombea]

I think you will not see much any difference in performance between either wiring diagram posted. Running an additional neutral would probably not make any difference either. None of the concerns mentioned really have much to do with why the GFCI may trip.

The GFCI actually goes bad and doesnt work, it doesnt trip.

 

[GoldDigger]

When you say that #1goes out, do you just mean that it trips or that it fails and has to be replaced?
Most likely cause for a trip is the wiring itself or something plugged in at or downstream of #1.

 

[Strombea]

IF GFCI 2 has current running the GFCI 1 has that current on the neutral screw(line), and i know that GFCIs don't care what is coming in but that could be a part of it, if the neutral side of the GFCI winding has current and the hot side doesnt? I have litterally replaced GFCI 1 3 times with brand new GFCI's, and they just quit working all together.

 

[Strombea]

When you say that #1goes out, do you just mean that it trips or that it fails and has to be replaced?
Most likely cause for a trip is the wiring itself or something plugged in at or downstream of #1.

It has to be replaced, maybe bad luck with new GFCIs?

 

[mjf]

The GFCI actually goes bad and doesnt work, it doesnt trip.

IF GFCI 2 has current running the GFCI 1 has that current on the neutral screw(line), and i know that GFCIs don't care what is coming in but that could be a part of it, if the neutral side of the GFCI winding has current and the hot side doesnt? I have litterally replaced GFCI 1 3 times with brand new GFCI's, and they just quit working all together.

Something is wired wrong. GFCI receptacles DO care what is coming in. If you're getting current on the neutral of #1 it is "reading" reverse polarity and won't operate (reset). Have you taken a "bad" GFCI and tried wiring it on a different circuit?

Maybe the problem actually lies in GFCI #2......why is it backfeeding current on the neutral?

 

[flatlander]

What brand are you using.
Or is there a possible loose connection somewhere with the shared neutral. The loose connection will fry anything.

 

[Strombea]

Something is wired wrong. GFCI receptacles DO care what is coming in. If you're getting current on the neutral of #1 it is "reading" reverse polarity and won't operate (reset). Have you taken a "bad" GFCI and tried wiring it on a different circuit?

Maybe the problem actually lies in GFCI #2......why is it backfeeding current on the neutral?

What brand are you using.
Or is there a possible loose connection somewhere with the shared neutral. The loose connection will fry anything.

I use Leviton

and the "current back feeding" is simply only when an appliance is being used on GFCI 2, thus when an appliance is used in GFCI 2 there is Current on the neutral line side Of GFCI 1, this is why i dont under stand why just pulling a seperate neutral won't fix it. It seems that with a separate neutral and hot wire on each recep, that the GFCI can't get "confused" or fry?

 

[Sierrasparky]

Current on the nuetral is the unbalanced load - not a backfeed.
If each GFCI is using 5 amps you will see zero amps on the nuetral home run. However break the nuetral and you will fry the GFCI. I would take bets you have a loose nuetral some place.

 

[ActionDave]

Current on the nuetral is the unbalanced load - not a backfeed.
If each GFCI is using 5 amps you will see zero amps on the nuetral home run. However break the nuetral and you will fry the GFCI. I would take bets you have a loose nuetral some place.

:thumbsup:

 

[guschash]

I think you need to use a connector on the neutrals instance of taking them to the screw terminal. Taking then to the screw terminal takes them thought the first GFIC , you don't want to do that.

 

[kingpb]

Using the screw or wire nut just changes the node location, but in electrical flow, its the same point.

A separate neutral will change the circuit. I have seen problems before with shared neutrals on GFI circuits, and as a practice do not advocate it being done.

 

[kwired]

Actually you should change things to the way they are in the diagram on the right. Since this is a multiwire branch circuit, you would violate 300.13(B) the way drawn in the left diagram, but besides the code violation I don't see any significant reason to cause failure of the first GFCI, and would guess it is because of some other condition then the wiring connections that has caused failures. I believe the main goal of 300.13(B) is to prevent removal of a device from interrupting continuity of the neutral conductor, if the conductor is otherwise securely connected it shouldn't cause any normal operating problems.

 

[ActionDave]

Using the screw or wire nut just changes the node location, but in electrical flow, its the same point.

A separate neutral will change the circuit. I have seen problems before with shared neutrals on GFI circuits, and as a practice do not advocate it being done.

It is the way I have my kitchen wired. I have used them dozens of other times. No problems.

 

[kwired]

Using the screw or wire nut just changes the node location, but in electrical flow, its the same point.

A separate neutral will change the circuit. I have seen problems before with shared neutrals on GFI circuits, and as a practice do not advocate it being done.

Sharing neutrals with the GFCI's is only a problem with the GFCI's if the protected side gets mixed up with the non protected side causing current imbalance in the monitored current through the GFCI itself. Otherwise as drawn in OP sharing a supply side neutral is not a problem with the function of a GFCI. If it were we are in trouble because once you get above the branch circuit level (feeders and services) we are dealing with a multiwire circuit most of the time.