Renovating an old house and electrician didn’t want to run 2 sets of 12-2 wire from the panel to the kitchen. He instead ran a 12-3 wire to a junction box and then 2 seperate 12-2 wires to the kitchen. Circuits protected by 2 20A breakers.
Is this legal? I understand that the two hot wires are OK, but if both circuits are pulling close to 20A, are you overloading the neutral?
Any feedback will be appreciated.
Unfortunately, the electrician has already been paid.
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Replies
If he did it correctly, w/ a shared neutral like that, he used both legs of the 240 coming into your house. They are 180 out of phase, so at max load on both, the net current in neutral is zero. Did he put a pair of breakers in box connected together w/ a bar? Are the two breakers adjacent? Bar means that you turn off both ckts at same time to keep from having a live ckt in a box w/ one turned off.
Don
The Glass Masterworks
"If it scratches, I etch it!"
Perfectly legal; although the use of a JB is a bit questionable IMO. I would have just run the three conductor wire through all outlets.
Around here the code requires three conductor wire for kitchen outlets; one hot powers one half of duplex receptacles the other powers the other. I think this is different from the NEC.
Scott.
Perfectly legal, with a couple of caveats. The two breakers must be on opposite legs of the 240V line, and, depending on who you ask, should be ganged together with their levers tied.
the neutral would carry any unbalanced portion of the two loads. not the sum of them
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Technically, it carries the sum of the signed quantities. But one is positive when the other's negative, so they tend to cancel out.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Thanks to all for sorting this out for me. The two breakers are next to eachother and therefore on different legs of the 240V. The breakers are not ganged together with a bar. What is the thought process for deciding if the breakers should be ganged together, or if it is OK to leave them as is.Thanks,
They keep changing if the 2 breakers needs to be tied or not.I think that what you have is legal until the 2008 NEC. So it depends on which version of the code that your local area as adopted and any local amendments.With a setup like yours the only concern is that if you are working that junction box then you need to be sure that both breakers are off. It would not hurt to put a label by the 2 breakers and mark SHARED NEUTRAL in red marker.Also it would not hurt to leave a note in the junction box about how this is wired and also one in the first receptacle in each box.Last month I spent 6 hours trying to find a bad connection master bedroom and bath that was feed by a shared neutral circuit and then the one leg branched and went in 2 direction. I know what the problem was in 5 minutes. But spend the rest of the time trying to figure out which way power feed. .
William the Geezer, the sequel to Billy the Kid - Shoe
I had a similar situation in that I had a now-unused 10ga 3 wire line that was for a wall oven that I wanted to use to power two new circuits for the fridge and the new microwave.I had two electricians tell me that it was ok to share a neutral, but that the breakers had to both be on the SAME bar or side in the panel box.This advice given to me by two separate electricians is conflicting with the advice given here - can someone else chime in as to the correct way it is supposed to be?JT
I think what it comes down to is what Bill said there is no right answer.It depends on the the code that is being followed in your area and what the inspector has to say about it whether there is a bar or not and what the correct way is. Last time I ran into this the inspectors locally where not liking shared neutrals for the reasons Bill stated. The sparky wired it with 12-2-2 does not cost that much more then 12-3 just last month it was the same price as 12-3 at HD. For those wondering 12-2-2 is a black, white, red, white with red stripe and bare ground. I am not an electrician and if Bill or any one wants to correct me that is fine, But when you wire it with 12-3 ( shared neutral) it has been explained to me that problems with over heating could arise if the neutral is lost (in theory).Wallyo
Edited 4/16/2009 12:01 pm by wallyo
If the neutral is lost, a 110v circuit using a shared neutral can become a 220v circuit. In my mind, the main arguement against shared residential circuits are that they are advanced, and can be difficult when remodelling or doing maintainance. This applies to contractors, homeowners, and electricians. I just came back from a job where three (!) seperate "residential electricians" could not diagnose a slight problem in a commercial lighting circuit. Of course, it is the customers fault, because they asked the kids pulling romex at their new house to come over after work, and help out at their restaurant. So it really depends on who or what a electrician is. But the point is, recognizing a residential shared neutral circuit can be difficult
Thank Mark that is what I remember hearing.Wallyo
"If the neutral is lost, a 110v circuit using a shared neutral can become a 220v circuit. In my mind, the main arguement against shared residential circuits are that they are advanced, and can be difficult when remodelling or doing maintainance. "That is true. And it is why a lot of people don't like them in residential. But a number of electricans don't feel that they are a problem.And don't forget that the residential service is a shared neutral system..
William the Geezer, the sequel to Billy the Kid - Shoe
And don't forget that the residential service is a shared neutral system.
Don't almost all multi-pole systems share a neutral at some point during the distribution? 480/277 certainly do, at the minimum, from the panel to the pole.
The key to a shared neutral system is that it be recognizable as such. I think that it is actually easier in a commercial setting to recognize a shared system, because everything is in conduit and j-boxes, often up in the air and easily traceable. Residential systems are generally difficult to trace out, and people diagnosing problems are likely to not be as familiar with such a system as commercial electricians. And a residential setting is much more likely to have a contractor or homeowner with a modicum of electrical knowledge messing with the system. So it is not the electricians one has to worry about with a shared neutral system, but the "electricians"
You're all still missing the point -
If these circuits are for the kitchen, how are you going to do GCFI if there is a shared neutral?
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Not all jurisdictions require GFCI protection for kitchen counters. My area insists on three conductor wire for split receptacles, hence GFCI isn't an option.Scott.
You're all still missing the point -
If these circuits are for the kitchen, how are you going to do GCFI if there is a shared neutral?
GFCI outlets will work fine, not breakers
Ahhhh, maybe that's what I was thinking of!
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
> GFCI outlets will work fine, not breakersA 240V GCFI breaker will work.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
GFCI outlets will work fine, not breakers
A 240V GCFI breaker will work.
You're right, I'm wrong. GE makes 20A 120/240 two pole/three wire GFCI breakers
Still cheaper using a GFI outlet and standard breaker probably, 7 for the breaker, 10 or so for the GFI outlets. 34 gets the job done 2 of each.Wallyo
Edited 4/16/2009 8:02 pm by wallyo
Several times I have been hired by a seller to add GFCI to a kitchen becaue the buyer wants them.While I have never found one in my area with a shared neutral you know know what is downstream at any local so I always in install one at each receptacle location and don't use it to feed anything else..
William the Geezer, the sequel to Billy the Kid - Shoe
"While I have never found one in my area with a shared neutral you know know what is downstream at any local so I always in install one at each receptacle location and don't use it to feed anything else."I don't quite get what you're saying here. If you install a GFCI on a circuit at the first Kitchen outlet, then everything downstream is protected. How can a shared neutral appear downstream in an outlet circuit?
BruceT
Well my main concern is refrigerators that might be downstream. Also possible DW and GD on older homes. While they are not a concern, they can be a nuisance.And who knows if there might be a neutral grounded or neutral from 2 circuits tied together in like a box that might have a receptacle and the switch for a sink like or the GD.For the multiwire at any one box you might have the red wire on the incomeing and outgoing cables wire nutted in t he back of the box.And the black and whites junction at the switch. Yes that is not legal under current code. Have no idea if it was 30 years ago.Now if I realize that is what is going on I will pigtail it.Other wise in all of the other cases where I see a receptacle that has is used to join the income and down stream wires I just replace it with a the GFCI using the LINE terminals to join them.Many of the other boxes are very tight on space. So I don't pigtail by default.The whole idea is to get the GFCI protection and get out. Not to analyze the kitchens electrical system and see if needs improvement..
William the Geezer, the sequel to Billy the Kid - Shoe
I usually remove the first outlet and then check to see what else that disconnected downstream, but I had not thought of the fridge possibly being on the same circuit or a neutral touching ground downstream somewhere or a or the neutral tied in with a lighting circuit in a common box somewhere.Your way is also more convenient for the user if a GFCI trips, since he doesn't have to look elsewhere for the source of the problem. I once was called to fix a "dead" GFCI receptacle in a bathroom only to find out after a great deal of tracing time that there was a garage GFCI ahead of it in the circuit.
BruceT
Yeah, when we redid our kitchen I was planning to put all the outlets on GFCIs and bought two units, one for each side. But when I got the boxes open they were a mess, so I just installed a GFCI on each side of the sink and called it good -- it simply wasn't worth it to spend several hours trying to sort out the wires.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
I ran 12-3 a few times on the Tahoe house last year. Good reasons:
some of the pulls were quite difficult and getting past the choke points only once was really worth it;
dishwasher and disposal were in the same cabinet;
hoping to use a 220 tool or appliance at some time in the future but having 110 circuits now is a useful way to wait;
ran out of 12-2 but had the 12-3 left over so I could finish the day's work safely;
copper was really expensive at that time so I saved a fair amount.
All wires were clearly marked in the breaker box and used adjacent opposite phase breakers (but not tied together). In the kitchen, I went through the refrigerator plug (no GFI) first. The boxes were all nice and big so pigtails were easy.
As an owner/electrical sub (not a pro but I refered to Rex Cauldwell's book a lot), the inspector scrutinized my work pretty carefully. He was satisfied with all the 12-3 circuits.
Eric
> How can a shared neutral appear downstream in an outlet circuit?FU by sparky or (more likely) jackleg.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
This is the way you would do it 12-3 only to the first box after that it is two 12-2's. See attachment.But if you ran 12-2-2 You run it to the first box with GFI i#1 wired to black and white
then to the second box GFI #2 wired to red and white with red stripeAfter that you can split all the outlets (breaking the tab on hot and neutral) down stream top to BLK and WH bottom to Red and white with red stripe one wire to pull.
Edited 4/16/2009 5:53 pm by wallyo
Have you actually done this? Others with more GFI knowledge than I (BH comes to mind) will hopefully jump in, but it seems to me that there will be different levels of current on the main neutral versus hots, and the GFI will trip.Scott.
His diagram should work fine. The important thing is that the current AT THE GFCI be balanced between hot and neutral. Doesn't matter if there is an imbalance elsewhere so long as things are balanced at the GFCI.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
By "Have you actually done this?" I assuming you mean the 12-3 then split two 12-2's.I think it is the way I did it, It was so long ago I can not remember exactly, it was my sisters house yes it was inspected. I would have to stop over there and trip the GFI outlets in the kitchen and see what down stream goes off. I remembering using 12-3But I did not draw out the attachment, I found that online.I don't think it would trip you see each GFI is monitoring the current down steam from it on the load side, it is not monitoring current on the line side. And when it comes down to it all neutrals are shared. All the GFI #1 knows is what the neutral is carrying that second it does not know what current GFI #2 is carrying on the neutral at the same time. At least my rambling sounds good?But as always I welcome and look forward to Bill,s input on this.WallyoWallyo
>>Have you actually done this?<<This came up when I was wiring a kitchen remodel last year. The advice I got from Bill at the time was that you can wire to the first outlet on the A/B circuit with 12/3, and split to (2) 12/2 lines from the the GFI's to the downstream outlets, and the downstream outlets will be protected. I did so, and tested, and everything works fine.Steve
Cool, good to know. Thanks to both of you.Scott.
That said, I didn't do it that way on the one I'm doing now. It's simpler just to keep the circuits separate from the start. No need for contiguous tied-together breakers, and it's easer for future would-be electricians to figure out what's what. Wire is cheap enough.Steve
One place that using multi-wire can save you butt is in remodeling where you might run conduit or the cables might be "tightly bundled".The way that derating works is it is a lot for effective to use multiwire circuit rather than circuits with individual neutrals..
William the Geezer, the sequel to Billy the Kid - Shoe
To GFCI a shared neutral circuit you pretty much need to use a 240V GFCI breaker, unless you split the shared neutral circuit into two independent neutral circuits at some point and then GCFI them separately.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
> I am not an electrician and if Bill or any one wants to correct me that is fine, But when you wire it with 12-3 ( shared neutral) it has been explained to me that problems with over heating could arise if the neutral is lost (in theory).If the neutral is lost, and you have a large load (like a toaster) on one side of the circuit and a small load (say, a radio) on the other side then you will essentially end up applying 240V to the smaller load. This could obviously cause something like a radio to malfunction in a destructive fashion.The wiring itself will not overheat.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
"the breakers had to both be on the SAME bar or side in the panel box"
The bars alternate in the box. In other words, if you put a breaker in a slot, and a breaker in the slot directly below it, they will each be on a different leg. Same side of the box, but different power legs.
Mike HennessyPittsburgh, PA
Good pick up Mike missed that thought Julian was talking tie bar across the breakers, read too fast.
"I had two electricians tell me that it was ok to share a neutral, but that the breakers had to both be on the SAME bar or side in the panel box."That is wrong.Now panels have changed over the years and some different. The 2 breakers must be on different busses. Thus you have 240 between the 2 hots and the neutral only carries the difference in currents.But most panels, when using normal size breakers any 2 ADJACENT breakers are on different legs. I would have to look at the panels to be sure, but I *think* that breakers directly across from each other are on different legs. But even where legal I would STRONGLY advise between any installation where the 2 breakers are not adjacent, even when a tie bar is not needed. Just too confusing for anyone that works on the panel or any wiring associated with that circuit in the furture.Now there are some variations. For example some GE panels have a 240 breaker will fit in one standard size slot..
William the Geezer, the sequel to Billy the Kid - Shoe
The two breakers should definitely NOT be on the same "bar" -- they must be on opposite legs of the 240V line or the neutral can be overloaded. But in most panels adjacent full-sized breakers are on opposite bars, so using two adjacent breakers is OK.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
So, aside from only having to run one wire from the panel to the first box instead of two, is there a real advantage to this setup in a residential application?'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb
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There is an advantage to the shared neutral setup -- less voltage drop.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Thanks. I think I can understand the usefulness of that in a commercial setting, but what's the practical value in a residential one? And I'm assuming a 2500 sf house here, not a place where you're a 500' wire run away from the panel.Is that a 'best practice' or more a 'in a perfect world' suggestion on ways to avoid voltage drop.'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb
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Roman I tend to agree with you in a basic house not much use, if it is a Mac Mansion and you have very long runs 100' feet or more there is a use. Wallyo
All good, just as long as both of them are GCFI at the ends...
... because you need GCFI in the kitchen...
...But you can't do GCFI when you share a neutral, unless the main breaker for both of them is a special GCFI at the breaker box... which is much more expensive and a PITA than two 12-2 wires and two GCFI outlets
Tu stultus es
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.