I will be running three new circuits to a kitchen. Two will serve two double duplex above countertopo outlets each with a GFCI outlet, and the third will be to a simplex outlet to power just the refrigerator. Can I safely and properly run one neutral for these three circuits?

I will also be running a new circuit to the bathroom with one GFCI duplex outlet on it. Can I safely and properly use that same neutral above? =TB=

>Can I safely and properly run one neutral for these three circuits?
No way! A "neutral" is a current-carrying grounded conductor.

>Can I safely and properly use that same neutral above?
No. And frankly, this question shows that you know enough to be very dangerous.
I strongly caution you against doing whatever you have planned... especially as it pertains to taking senseless shortcuts.

You have scared me.

Dennis,
you don't suppose Tom has 3 ph ???

No way any one should even consider doing what tom is thinking about. Even with 3 phase.

Mr. Brooklyn,

The reason everyone is so upset is because the common neutral conductor will be overloaded, and that's not good!

Running the circuits as you have described them will result in as much as 40 amps flowing in the common neutral during peak usage. If they were all on the same Line [AKA "Phase"], that would result in as much as 80 amp load on the common neutral during peak use. That would fry a #12 cu conductor, which is good for only about 30 amps max [fused or breaker size is 20 amps max in most conditions].

What you should do in your case is to run a 3 wire circuit for the Kitchen appliance circuits, place the "Hots" on opposite "Phases" [so that if you checked the voltage between the two hots, there will be 240 volts]. If you do not read 240 volts across the two hots, or if you read no voltage, chances are they are not on opposite lines. Using a two pole circuit breaker could assist in this goal [full space 2 pole units, not just simply a "Stacked" 1 pole breaker]. The type of panel used will determine the exact arrangement. If this is not possible, use two separate 12-2 NM cables - one per 4 plex receptacle / circuit.

For the other two circuits [the refrigerator and the bathroom circuits], use separate 2 wire runs for those circuits. One 12-2 NM cable for the refrigerator circuit, one 12-2 NM cable for the bathroom circuit.

As with the others, I also suggest that you seek the assistance of a Qualified Electrical Installer for this installation. The results of wiring the installation the way you first planned would easily result in a fire!!!
This is not an insult, rather it's a very helpful and serious suggestion!

Scott SET

Scott:

Good Advice! I would like to add the following:

NM Cables are required to be identified as NM-B to comply with rules in Section 110-3(b) and Article 336.

I know that's what you meant, but if the installer used Type NM (pre 1984 cable) it would be a violation.

are we in a 'dwelling' using NM-B ??

Mr. Brooklyn,
I don't recommend your doing what I suggest here, I'm just throwing it in to see the other guy's thoughts, as I've wondered. I haven't and wouldn't do this myself.

What if the run was in conduit, properly phased, and had a #8 neut? (Is that compliant?)

Hi Guys:
Thanks for the concerned replies. I see that I raised some eyebrows to say the least on this one; it looks like I better re-read my Wiring 1-2-3 book. I'll do as Scott35 said using a 2 pole breaker on the two kitchen circuit and use seperate 12-2s on the two others. I would be using the common type of BX, I'm not sure what NM-B is. My house is from 1907 and I generally, but not in all cases, have been replacing the old cloth covered wire cable as I renovate from room to room.

I'm not sure what your NEC says about it, but in the U.K. our "code" specifies that each individual branch circuit leaving a distribution panel must have its own neutral.
One large neutral to two or three branches might be OK from the ampacity point of view, but if someone shut off one breaker to work on an outlet they could unwittingly break into a neutral - believed dead - which is still carrying current on the other circuits. Not good.

Joe: NM is Romex, right? What exactly is the difference between NM and NM-B?


[This message has been edited by pauluk (edited 09-26-2001).]

electure,
There are very few places where the code permits oversized neutrals for multiple circuits and this is not one of them. 215-4 and 225-7 are two places that I can think of, there may be one or two more.
Don(resqcapt19)

[This message has been edited by resqcapt19 (edited 09-26-2001).]

pauluk,

Prior to 1985, NM cables had conductors rated for 60 deg. c.(or was it 75?). Romex made since then is rated 90 c. and is called NM-B. This poses problems when customers in homes built prior to 1985 want a new fixture installed, as most new fixtures require 90 c. supply wires.

Romex made since then is rated 90 c. and is called NM-B. This poses problems when customers in homes built prior to 1985 want a new fixture installed, as most new fixtures require 90 c. supply wires.

[/B][/QUOTE]

NM-B ampacity is based upon 60 deg. C per article 336-26. 90 deg. C is used for derating purposes as long as the final derated ampacity does not exceed the 60 deg. C rating. The 90 deg. C rating is for withstanding temperatures (heat transfer)from light fixtures, etc. My 1969 home has the old 60 deg C. NM romex and it's a real bear dealing with the overly baked and cracked conductor insulation.

it's a romex job, go with Scott T's post. If it had been 208Y120 we could talk...


Scott W; http://www.afcweb.com/table2.html
Scroll down to the super-noodle stuff. It's marketed for that 'harmonic' hype we all recently lived thru.
So your post got me to thinking, the code allows generally for no more nuetral load than the ungrounded conductor, are third , fifth, ninth orders exempt??

Joe,
Thanks for the kind words! And also for picking up on the NM-B mistake I made
I so rarely work with Romex, that I neglected that important temperature ID !!!

Mr. Brooklyn,
Glad we all could help out here! If you are using AC or MC [AKA "BX"], the same goes - 2 or 3 wire with ground.
All the MC cable I have worked with lately uses THHN cu conductors, and of course have an insulated grounding conductor [sized per NEC 250].

Steve,

I know that you know what's up with the oversized common grounded conductor in the MC cables you speak of. This would be the few places where inbalanced and excessive load currents would be accepted, as Don [resqcapt19] mentioned.
The triplen harmonic currents would only be in the common grounded conductor, so the best thing to do is increase the ampacity / size of said conductor.

I have no idea where, or if, an increased size common / neutral could be used on multiwire circuits per the NEC - such as using a #8 THHN common neutral with two multiwire hots [2 Line A, 2 Line B, 1 phase 3 wire system].
This would be where Scott W is going with his message.
It would work, but it sure looks suckee!!! [in my mind, that is].
It would work on simple Linear and balancable loads, but what a nightmare if there was any high level THD!!! Seems that even Squirrel Cage Split Phase Induction Motors on these circuits, running at varying loads, would reflect some high levels of double frequency pulsation and resultant harmonics!
Just my opinion only! Please be kind in flamed responses just tossing out some ideas and stuff to discuss.

Scott SET

P.S. edited some bad spelling

[This message has been edited by Scott35 (edited 09-27-2001).]

Scott,
If you have a handbook, 225-7 has a good explanation of using a single neutral sized for the maximum unbalanced possible. ie. If you run (6) 20 a. ckts, off a single phase panel (3 each bus) you could run a neutral sized for 60 a.
Maybe it would help in keeping the mess minimal if running all ckts. through a lighting contactor. Anyone ever do this?

Tom,

I hope that it is clear to you that much of this discussion has nothing to do with your original question. I strongly second the suggestion that you seek help before doing anything.

This latest discussion about the oversized neutral would only work with individual wires within a special cable, raceway or enclosure. Right Guys?

Bill

It is, and I will Bill, thanks. =TB=

Multi-wire branch circuits are allowed by NEC 210-4.

hmmm,
ok now, just what size noodle would 215-4(a)'s have serving 3 sets of 3-wire feeders??

Anyone ever do this?

I see it..no i have not done it...but i can be taught!

I sure didn't mean to abruptly change the subject. Glad Tom B. got his answer.

I thought about mounting a neutral bar in a lighting control cabinet (once while I was looking like a meatball in a bowl of spaghetti). Cabinet was connected by a 2' nipple to the panelboard, and I was going to extend the neutral feeder up to the neutral bar. I didn't, but never could think of a reason that I couldn't.
I'd be glad to hear of a reason why not.
Scott T - You're right, it would look really stupid

Not unless its 3 phase. 2 ckts on the same phase will draw twice the current on the neutral

Probably the wiring rule is this regard could be stated that any circuit breaker should be able to be replaced with a GFCI or AFCI. If you have several CBs for the UGCs, then you can't do that with a shared neutral.

And if your sleeping area is wired with three phase, you'll need three-pole AFCIs.

Aldav 53,
Under the conditions stated, Tom B would have to have "4 phase" for 1 common neutral of the same size as the phase conductors to supply 4 circuits.(including bathroom GFCI)

What exactly is the difference between NM and NM-B?

NM was manufactured with 60 degree insulation and NM-B is manufactured with 90 degree insulation. The NEC Article 336, Part C. Construction Specifications

See Section 336-30 in the NEC

[This message has been edited by Joe Tedesco (edited 10-15-2001).]

Listen to these guys! "Sharing" neutrals can be tricky, especially if something goes wrong, there is an "open" neutral created, you need to troubleshoot something, or GFI's are involved. The simplest, surest, safest way is to run a separate neutral for each circuit- then make sure that the circuits stay separate!
Sometimes, if you know enough to ask a question, you already know you're in over your head. That's why even the best new journeyman recognises that his education is just beginning!

The important issue to remember when running multiple circuits on the same neutral is to phase them properly. There is nothing wrong in running 12-3 to say, the refrigerator and branching off of it to a small appliance circuit provided you pigtail the neutrals at the refrigerator outlet and say, use the red for the refrigerator and the black (jointed in the box) to the other circuit. The neutral, being on different phases, will never draw more than the highest amperage of any particular phase. The overcurrent protection can be put on either a double pole 20 with a common trip or two single pole 20's with a "trip bar" that will trip both breakers if one trips.

C.
A "trip-bar" or handle tie will not always trip the second breaker if the first one trips. Only a common trip breaker will do this every time. While the use of a double pole breaker or handle ties is a good idea, it is not required by the NEC unless both circuits are on the same device yoke.
Don(resqcapt19)

Yes,
very evident in the use of nails to accomplish this...

Aah, the old 6 penny 2 pole (or 3 pole).
Why do the holes run all the way through the handles, anyway? The factory usually only uses the first 1/8" or so.

As for the oversize neutral idea (I've already said I don't do this), isn't that doing the same thing that you're doing running to the neutral bar in a subpanel?

[This message has been edited by electure (edited 10-17-2001).]