I'm glad I was not the only one confused by that post.

Whew. Me too! Thanks.

And, while on the subject, it may be that you can put 16 #12s in 3/4" conduit, but that pertains only to maximum fill requirements and ignores the issue of derating which kicks in, if memory serves me, at 8 current carrying conductors under these circumstances. When dealing with derating, neutrals count as current carrying conductors so, in that sense anyway, the neutrals do get you.

When all is said and done, the answer to the OP is: Yes, you can run two independent circuits (4 conductors) OR a multiwire circuit (3 conductors) in 3/4" EMT with room to spare. No?

A quick comment on derating.

For 14, 12 & 10 the magic number is 9. With more than nine CCCs (current carrying conductors) you need to worry about derating. Under nine there is NO concern.

For the purposes of what is a CCC. BOTH neutrals and "hots" carry current. With multi-wire circuits, where the neutral only carries the current imbalance, that neutral is not counted as a CCC.

For 14, 12 & 10 the magic number is 9.

Yep, it's over 9 and I should have double-checked that first. You're 100% right on, Petey, and thanks for that.

If he used a DP breaker and shared the neutral as common won't this possibly cause induction heating?

I'm Understanding that Greenmile wants to run 2 120 volt circuits in his shop. Yes you can put those 2 circuits in a 3/4 pipe easily with room to spare. By stating you want to run 12 wire I'm guessing the circuits are 20 amp. That means a total power draw of 40 amps with 2 separate circuits. If you use a 2 pole breaker you are limiting yourself to just 20 amps. The proper installation if sharing neutral or not is to have two separate 20 amp single pole breakers. If sharing a neutral make sure to use A & B Phase for hots. Otherwise you will overload the neutral. Since this installation is for your shop, spend the extra money and use separate neutral you want as much power as possible.

W....W....WHAT?!???

"If you use a 2 pole breaker you are limiting yourself to just 20 amps."
Not true.

"The proper installation if sharing neutral or not is to have two separate 20 amp single pole breakers."
Again, not true. You can deliver 20A + 20A = 40A total using a DP breaker on opposite legs.

Please don't offer advice on this forum unless you know what you're talking about. Either you know what you're talking about and you just can't verbalize and explain it properly or you know very little about basic house wiring. Which is it? I'm saying that nicely. Others may not be so nice.

Pudge, somewhere in the middle of Dave's dribble, we lost your question. I can't answer that one for you. What I can say is a MWC sharing a neutral is very common. And using a DP breaker has no bearing on a MWC other than to ensure both sides of the circuit are shut down for safety's sake. It also ensures the circuits will be on opposite phases and not be accidently moved around in the panel. It sounds like NEC 2008 will require this anyway. I'm not sure how far along you are in school, but when using a MWC, the neutral carries the DIFFERENCE between the two legs...not the SUM. (Providing each leg is on a seperate phase) Therefore, the max the neutral could ever see is the limit provided by the over protection device. When both circuits are pulling current, it could conceivably see zero. (I hope your instructor is better at explaining stuff than I am!)

greenmiles question has nothing to do with a mwc. He clearly states he wants to run 2 circuits with 12 wire. If those are 2 separate receptacle circuits you do not want to protect those circuits with a 2 pole breaker, they should be on there own singlepole 20 amp breaker. I admit I made a wrong statement concerning the power drop I relize they are 180 degrees out of phase. As for overloading the neutral that is why it is important to be sure that when you are sharing a neutral, the hots are on different phases. Other factors like harmonics can cause heating of the neutral and they are sizing the neutral bigger than the hots and calling it a super neutral.

ps. Merry Christmas to you too Bigbird.

"That means a total power draw of 40 amps with 2 separate circuits. If you use a 2 pole breaker you are limiting yourself to just 20 amps."

That is plain old WRONG.
A multi wire circuit will deliver 20 amps on each side, exactly the same as two separate 20 amp circuits.

"The proper installation if sharing neutral or not is to have two separate 20 amp single pole breakers."

Again, not always correct.
Under the present code if you have a single yoke (most commonly a duplex receptacle) fed by each leg of a multi wire you are REQUIRED to use a double pole breaker.

"Other factors like harmonics can cause heating of the neutral and they are sizing the neutral bigger than the hots and calling it a super neutral."

Harmonics? Harmonics are found in RF transmission. Inductance maybe. Super neutral? Never heard of over-rating a neutral wire and calling it a super neutral. Unless that's a commercial or 3 phase thing I've never read about it, heard about it, or seen it until your posting. Does anyone else with a big clue (Petey, Brick, Normel, Bus Driver) know more about this? If it's true I'm eager to learn.

Greenmile states he wants to run 2 circuits, not a mwc to a single yoke. As For the super neutral http://www.alliedeg.com/SuperNeutralCable_1591.asp
Do any of my critics actually have any field experience,or are we simply trying to interpret code and theory. . The truth comes out now.

Self employed Licensed Master Electrican.
Almost 20 years total in the trade.
Seven years prior in a related field.
Satisfied?

I have to say, I am getting the impression that you might have a clue, just you have a terrible way of putting it in words.

Yes, I have heard of Super Neutral cable. Have I seen it used? No.
It has never been spec'd on any commercial jobs I have done and I doubt you'll EVER see it in a residential setting.

It is used on jobs with high harmonics like hundreds of fluorescent fixtures.

The OP has the option of running one or two neutrals. He also has the option of using two single pole breakers on different hot legs or a double pole breaker when using the single neutral. If using two neutrals the only difference is that the two single pole breakers can both be on the same hot leg, but don't have to be. The total circuit capacity either way is the same - two 20 AMP circuits.

As suspected, the "Superneutral" appears to be the trade name of a product line designed for commercial and and industrial environments where the sheer quantity of electrical discharge lighting and switching power supplies present does cause problematic harmonics. Unless a McMansion type house like those found in the local ski areas and wired with 3 phase, it wouldn't ever even begin apply to residential wiring, and most of the time doesn't even to the target market - where the most often used solution is to use a full sized neutral rather than a reduced one.

Since the 2008 NEC will require all multiwire circuits to be on a multipole breaker, it is purely preference whether someone does that now or not, given Brick's exception.

Since single phase means exactly that, it is somewhat difficult to understand how you put hot wires on different phases. The neutral on this type of circuit is simply the center tap of a transformer that happens to be grounded, and can't ever carry more than the unbalance between the two hot wires.

If a "wannabe" electrician wants to argue 3 phase stuff there's a couple of other more appropriate places to do so. Just make sure you wear a barrel to cover your backside.

"If you ran a 12/3 conductor to j box then split the circuit"

You cannot split (divide) the circuit in a J-box, that has already been done at the circuit breakers, hence, the use of the 12/3 wire.

...a residential single phase service has 2 phases...

Gotcha. I guess that's why they call it a single-phase system, eh? Think about it.

Let's see now. A lot of single guys in a bar are actually married. Yeah, that works. The logic is impeccable.

Dave: Have you actually checked the 2008 code to determine if dp breakers will be required in this case? Nah, you're probably right: All the folks on this forum have conspired to make up this hoax just so they can jerk you around.

Think about that, too.

Dave has worked under folks his whole life and ONLY knows what he has been told.
His boss told him to make sure he puts those two breaker on different "phases"so that's all he know.
Yes, it can be a common term to use, BUT IT IS NOT CORRECT. There are NOT two "phases" in a single phase system.

THIS is SINGLE phase.
Dave, you show me two "phases":

Man, after that last post I feel embarrassed for Dave as well. Calling someone a moron when you are the one who is wrong is pretty funny.

Dave, there is such a thing as two-phase systems, but are rare and they aren't used in this context. Single phase residential systems are very different from a 2-phase system. If you want to know more I can probably find you some literature.

I am still a student so I dont always know what I am talking about, but, IF I'M NOT SURE ABOUT WHAT I AM TALKING ABOUT I WILL EITHER SAY SO OR NOT POST IT AT ALL. IF I AM WRONedG AND SOMEONE CORRECTS ME I WILL NOT TELL THEM THAT THEY DONT KNOW WHAT THEY ARE TALKING ABOUT. PRETTT MUCH ALL OF THE PEOPLE HERE KNOW ALOT MORE THEN YOU OR ME DAVE.

Pudge wipe off your nose you got something on it.

Question.
I got an e-mail "warning" sent to me regarding a post I made in this thread. Basically this e-mail said that is I had a problem with another member to e-mail Gardenweb about it. Sorry, I take care of my own dirty work.

I have NO CLUE which post this could be referencing. In fact, I did not even know you could report posts in this forum.
So far, I have been pretty tame I think. I guess someone wants to take this thread to a whole new level.

How about the clown that reported this say so in a PUBLIC forum instead of running to the teacher? Afraid you might be called on it???

Not me, but i have noticed some of the posts have been removed. I too can take care of my own Business. As far as I'm concerned we are having a debate about electrical issues. I have taken nothing personal. In my 20 years of using computers i have never chatted or blogged and find this addictive and am enjoying this discussion. While were back on the subject answer this if you can. Greenmile question was for two circuits. He doesn't state what the circuits are for but since they are 12 gauge I think it's fair to say they are 20 amp circuits . Maybe one is for power and other for lighting. Why would you want his lights to go out when he trips the power circuit? That is why I stand by my statement of using 2 separate 20amp single pole breakers. In addition I know in North America we use a single phase service for residential. How do you identify the two hots. I have always called them A & B phase Black & Red which you say is common terminology. You asked about my credentials. 15 Years in commercial and industrial. From the service truck to $300 million data center. One thing for sure I don't care who you are, you never will know all there is to know about Electricity. Best wishes and look forward to future discussions.

At the load end I refer to them as Line-1 & Line-2, at the service I refer to them as Leg A and Leg B. But that's just the way I learned.

I never liked using a two pole breaker for a multiwire circuit, however we are going to have to get used to it in 08.

The funny thing about some of these threads that trigger long debates is that, half the time, I suspect the OP is long gone.

But there's still some benefits to resolving disputed issues, IMO, until the "thread gets it right". Not only does robust discussion provide for a kind of continuing education, but it's always possible that someone else will read a thread and come away with an erroneous conclusion.

That's why I threw in a comment about derating (see above), even though it wasn't exactly on point in terms of the OP scenario. I didn't want someone else reading the thread to take Dave's comment as carte blanche for putting 16 #12s in a 3/4" conduit without also understanding the effects of potential heat and the code requirement to derate.

Then, when Petey followed up and noted that the rule of thumb was 9, not 8, I didn't take that as nit-picking or insulting in the least. On the contrary, it demonstrated a self-monitoring and self-correcting system at work. That's all goodness IMHO and I think it is what distinguishes this forum from most of the other DIY sites I've seen.

There's a lot of pride in accuracy among the core regular sparkies here and I appreciate that. Thumbs up, Petey, and when you think I'm wrong or misleading, take this as a sincere standing invitation to take issue with what I've posted. Any time.

[If it isn't already obvious, it certainly wasn't I who complained.]

joe notes that he did/does not like using a double-pole breaker for MWBC. My preference was always for the double-pole breaker as it was the safer way. Disconnecting any part of the circuit disconnects all of it. In addition, any such circuit that also served a 240 volt load has always required a double-pole breaker. I encountered one MWBC installed by a relative of mine, serving 120 volt loads only at time of installation. Used two circuit breakers. Some other person later used that circuit for a 240 volt load. I discovered it while doing some repair work at that location. It is my strong conviction that the double-pole has always been the best choice.

The last spools of wire I purchased ran ~$70 for 500 feet of #12 (THHN/THWN). If you purchase cut wire expect to pay about double that.

I guess trying to save the OP a few dollars by pointing out he could easily run a multi wire circuit was just to kind.

"I too can take care of my own Business. As far as I'm concerned we are having a debate about electrical issues. I have taken nothing personal."

Oh really Dave? Then why did you tell me to go f myself as you put it? I see it's deleted by the moderator now, which is good. But remember Dave, some of us here don't forget.

Bigbird I still wished you a Merry Christmas. I think it was the comment about saying it nicely. But hey thats in the past this is a whole new begining. Now come here and give me a hug. Just Kidding.

"But hey thats in the past this is a whole new begining. "

Sounds good to me. Enjoy the forum. My motto is share when you can and learn when you can't.

"My motto is share when you can and learn when you can't"

Perfect 'Bird. Couldn't have said it better.

Like petey racer I also got a "freindly reminder" to one of my posts and I wasnt even hotile in any of them. I was just telling dave my philosophy but guess he cant take constructive critisism.

I have nothing useful to add here, but I've thoroughly enjoyed this thread. Seems it's always the simple questions that bring the heat.

This is as close as I come for this problem. Am trying to retrofit the plugs in an old kitchen. The current duplex receptacles are wired with 14/3 wire from two circuit breakers. They are on different lugs. Are there double pole GFCI circuit breakers available to protect these kitchen circuits? I am an amateur trying to do my own work, could be over my head, and need your experience for advisary purposes. Enjoyed the discussion..hope I can be humble when I am corrected..

Although I can't say that I understand what is meant by "retrofit", the short answer is: Yes, there are 2-pole, 15-amp circuit breakers available for most boxes.

(Short comments: If you want to bring those circuits fully up to code, they should be 20-amp circuits on #12-3, but you'd have to pull new wire. Also, since two-pole GFCI breakers tend to be on the pricey side, you might save money by using GFCI outlets.)

WOW, I had no idea that such a simple question could result in such a dick measuring contest.

You are fairly new here - and it's really a shame that the classics have rolled off the saved posts. People really used to get educated here................

I know this thread is old but after reading all of it, noone ever asked the OP if this "shop" was attached or detached. This would change things dramatically.

"I know this thread is old but after reading all of it, noone ever asked the OP if this "shop" was attached or detached. This would change things dramatically."

The only thing would be if he had a separate structure and did NOT have a panel in the separate structure.

He would then be limited to a single circuit at 20 A with GFCI protection, but a multiwire is still only one circuit.

With No indication of a separate structure it would appear the shop is in a basement.

It's a simple question. The answer is Yes. period. No need to draw extravigant drawings or try to show how much you know or don't know. Do all electricians have huge egos? How did 3 phase circuits, power factors, ELI the ICE man and trigonometry get into this?

J-man, what is your problem?

This Dave guy made some very erroneous statements and was called on them. That's it. It has nothing do do with the size of our d**ks thank you very much.

If this thread bothers you so much why read it?

If this thread bothered me , I wouldn't read it. I just get a kick out of it and had to add my 2 cents worth. But I have a question for you petey - Does NY even require a state lisence for electricians? No ill feelings to you, just a question.

No, NY, just like it's neighbor Pa, have NO statewide licensing. Only certain local areas have their own licensing requirements and a few counties have county wide licensing.

I personally DO NOT agree with this and am in strong favor of a statewide license and continuing ed to renew.
I seriously doubt NY will EVER see this.

Petey, Maybe you should write to Hillary. The state would make money, the electricians would be more educated and houses would be safer.Also more jobs would be created for continuing ed instructors.

Those few of us who care are already trying.

Then there are some (a) counties trying to get a county wide license with certain "requirements" that can ONLY be met by union shops, such as a (mandatory) certain kind of classroom education. I won't go into detail, but this is fact.
They also want $500/yr for this license (with NO reciprocation), when most others in the general area are in the $100-$200 range. They purposely want to keep out smaller one man shops.

This IS NY don't you know.

I'm back.. After the daisy chain discussion, I came to the conclusion that their is a huge difference between Commercial/industrial and residential. Being that this site is geared for residential, i just read the posts now. I stand by my statement though, jobs are engineered all the time with multiple circuits sharing a neutral on single pole breakers. If thats a new code change then we will adjust. Greenmile never stated what his circuits were for, and like i said before why do you want the lights to go out when you trip a receptacle circuit? If your concerned with the safety of not having a two pole breaker then just run the extra neutral. Simple as that. Journeyman i think you are right. there is a big clues bunch who have ego problems and just wait for people to slip up on their code and then they have to prove how much code they know ( Proud of you ) Like to see them with their tools though. I think very electrician out there can be taught a thing or two. There are many ways to skin a cat. Petey i don't think my statements are so erroneous. You took a couple of mispoken statements and tried to hang me over them. I'd love to work with you on a job to see your skills. I think you would get schooled. With that said, i will continue to read this site because i do enjoy reading about the different methods guys use to get jobs done.

"I'd love to work with you on a job to see your skills. I think you would get schooled."

And only an idiot would actually put something like this in writing.
I know I am good, but I don't go around saying it. I let others tell me, but I truly do NOT need YOUR approval.

Knowing the code is one thing. Knowing how to put it to practical use is another thing entirely.
I'll leave it at that.

my dad could beat up your dad

"I know I am good, but I don't go around saying it." You just did. Your right you don't need my approval but your seeking someone's..

I've read many of petey racer's posts and I have a great deal of respect for his knowledge and pratical application.

I'd love to work with Petey for awhile, think I could learn a thing or two. But he'd have to come south. :)