# multiwire branch circuit



## Magnettica (Dec 19, 2006)

Thanks for the clarity, Speedy. 

From that wording, I would assume yes, yes to a requirement for a 3-pole breaker for 3 individual circuits sharing the same neutral.

I have the NEC on CD. I rarely use it though. I mostly refer to the 2005 NEC handbook for discussion.


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## wayni (Nov 12, 2007)

Speedy Petey said:


> Then I get your point. Finding the answer is actually the key. As we get older knowing a lot from memory becomes the key. Or at least knowing a baseline and all of the basics.
> I also learned how to use the code book early on and also self taught. So many guys called me Mr. Code because none of them knew it very well and I always had my nose in the book. Everyone always just did what the boss told them to do. I was always a "Why?" person.
> Since computers and the internet I realized how much I was misinterpreting. This was almost ten years ago.


Plan. Build. Use. 

Union guys will know this, we call it Codeology. A great method to finding answers and utilizing the code.

I once had a journeyman who told me to make a habit of referencing pertinent NEC sections whenever I do, or use, something new. Best advice ever. I apply Codeology and current events and pretty soon I can recite code sections.

My journeyman has nicknamed me "NEC." I think he is joking.


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## frenchelectrica (Sep 26, 2003)

JohnJ0906 said:


> I admit I'm not a big fan of the '08 210.4(B) (handle ties for MWBCs) but I DO like the '08 210.4(D) - MWBC grounded and ungrounded conductors have to be grouped by wireties or similar means. PITA to try to identify which neutral goes with which circuits when there is 2 or more in the same conduit.


Tell me about it ugh i have same sisuation too with tons of MWBC with mixed bags of netural run in the conduct.

only thing i wish they do make the netural with specal stripe so you can pinpoint the group fast like white with red stripe for one group of MWBC and other white with bleu stripe for second set of MWBC it will really speed up pinpointing which batch it is.

normally with that many full boaters [MWBC] only way i can be safe is kill all the breakers feed that conduct homerun it kinda annoy with me but once a while i will hit it right with clamp on ampmeter to ring it to verify the current is zero but i still rather kill the breaker first before i touch the dammed netural wire :cursing:

Merci, Marc


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## Speedy Petey (Sep 30, 2003)

wayni said:


> I once had a journeyman who told me to make a habit of referencing pertinent NEC sections whenever I do, or use, something new. Best advice ever.


This is something I tell my "apprentice" all the time. He just doesn't get it.


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## voltamp (Nov 30, 2004)

*Same yoke, 2 pole breaker*

What is extremely surprising is that this is a trade page and those at times are asking questions that would embarrass any tradesman in the field.


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## BigMikeB (Aug 1, 2007)

voltamp said:


> What is extremely surprising is that this is a trade page and those at times are asking questions that would embarrass any tradesman in the field.


The fact its a trade page means little, some places you dont need more than a business card to do electrical work, take some time and read some of these posts. You'll learn.


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## JohnJ0906 (Jan 7, 2007)

voltamp said:


> What is extremely surprising is that this is a trade page and those at times are asking questions that would embarrass any tradesman in the field.


Would you rather they ask the question or keep quiet and do something unsafe in the field?

Not everyone here is an EC, we do get some younger/newer guys here trying to improve their knowledge of the trade. For that matter, it's why I'm here too. :shifty:


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## gregnc (Dec 2, 2007)

i do mostly residential and havnt ran into any MWBC in a dwelling. are there other advantages to doing this besides 1 less home run and 2 less wires to land in the panel?do any of you use this method for the 2 small appliance circuits?


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## Celtic (May 23, 2007)

gregnc said:


> are there other advantages to doing this besides 1 less home run and 2 less wires to land in the panel?


The main advantage is money....less wire to install, less wires to terminate, less labor = money savings for the EC.




gregnc said:


> do any of you use this method for the 2 small appliance circuits?


yup.


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## Speedy Petey (Sep 30, 2003)

Celtic said:


> The main advantage is money....less wire to install, less wires to terminate, less labor = money savings for the EC.


On a personal note I must say the use of the word "main" in this statement is NOT true.
Yes, the other reasons are true and my main reasons for using MWBCs. 
The fact that it saves me money is incidental and is not a deciding factor. There are other things I that I do for similar reasons that cost more so it is a wash.


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## macmikeman (Sep 12, 2005)

Over the years I have pretty much eliminated installing mwbc's into dwellings I wire except for the dw and disposal combo setup using a three wire with ground home run. Not so for commercial installations, where in my humble opinion, they are in fact much better suited, and not as liable to getting buggered up by common jack of all trades guys foolin around where they don't belong for the most part.


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## AustinDB (Sep 11, 2006)

I've read the thread and not sure if I understand fully. If you're running two circuits for lights on single phase, it IS ok to use the two hots in a 12-3 in a double wide breaker b/c one circuit is 180 out from the other, therefore maximum current will never be more then 20A's? If above is accurate, does it matter the end use for the circuit (lights, receptacle, or something else)? 

Another question regarding multiwire circuits, is it common place to wire new construction using this method? I commonly see 14/2 and 12/2 in new construction-does it only make sense when the wire terminates in a common jb?


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## Mark Twenhafel (Dec 23, 2006)

Just a couple of nit-picks first: 120/240 residential service is single-phase. The two ungrounded conductors differ in polarity, not phase. They are 180 degrees different in polarity, not phase. But, for most people, that's a kinda', sorta' thing.

Your reasoning is correct, though, on why you can use the same neutral to return two circuits without overloading the neutral--because the two hots are 180 degrees different in polarity.

I pull romex in new stick-frame homes, and we still use 12/3 and 14/3 -- we do it to save homeruns. For instance, we recently pulled a 12/3 homerun into a laundry room and used one hot for a dedicated for the washer and the other for the GFCI wall receptacles. Also, pull 14/3 up to the paddle fan--one for the fan, the other for the light kit. And, I've pulled 1x/3 (can't remember which) up to a bathroom exhaust fan from the switch--used one conductor for the exhaust fan and carried the other conductor to the switched, recessed light.

So, yea--it doesn't matter, as far as I know. (But, I'm still pretty new.)

But, all of this changes in the 2008 NEC, because the 2008 requires arc fault circuit interrupters nearly everywhere, except where GFCI's have to go.


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## Speedy Petey (Sep 30, 2003)

Mark Twenhafel said:


> But, all of this changes in the 2008 NEC, because the 2008 requires arc fault circuit interrupters nearly everywhere, except where GFCI's have to go.


Why will this change? They DO make two-pole AFCIs as well as two-pole GFCBs. 

Also, (I don't have a copy yet) as far as I have seen ALL residential 125v, 15 & 20 amp circuits will require AFCI under the 2008 code, regardless of the GFI requirement. 

I'd wait and see though. I suspect we will see a few local amendments to this little rule.


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## zesone (Jul 19, 2007)

*Riding on Long Island*

Hey Speedy,

You go riding on Long Island or do you trek upstate or PA?


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## AustinDB (Sep 11, 2006)

thanks for the clarification Mark.


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## Speedy Petey (Sep 30, 2003)

Zesone, I live upstate. About 100 miles north of the city.

There are several local MX tracks within an hour of me and trails ALL over.


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## Mark Twenhafel (Dec 23, 2006)

Speedy Petey said:


> Why will this change? They DO make two-pole AFCIs as well as two-pole GFCBs.
> 
> Also, (I don't have a copy yet) as far as I have seen ALL residential 125v, 15 & 20 amp circuits will require AFCI under the 2008 code, regardless of the GFI requirement.
> 
> I'd wait and see though. I suspect we will see a few local amendments to this little rule.


My bad--thanks for catching that, Speedy. Yea, I'm totally green and shouldn't be giving advice. Sorry if I gave anyone bad information. I'm only up to Ch. 3 on the code -- hope to finish Ch.3 today and start Ch 4. 

Um, yea, everything that Speedy said.


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## Speedy Petey (Sep 30, 2003)

It's cool Mark. We all learn here every day. :thumbsup:


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## jrclen (Jul 10, 2007)

Mark Twenhafel said:


> My bad--thanks for catching that, Speedy. Yea, I'm totally green and shouldn't be giving advice. Sorry if I gave anyone bad information. I'm only up to Ch. 3 on the code -- hope to finish Ch.3 today and start Ch 4.
> 
> Um, yea, everything that Speedy said.


Your post on where you pull 3 conductor romex was a great post. We all get tripped on occasion, don't let that stop you from jumping in. We are all learning. Even after years of being in the trade. That's one of the main things I like about this work.


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