# Using 14-3 wire for two 15A circuits



## InPhase277 (Feb 9, 2008)

david.plymouth said:


> I am currently adding circuits to my basement and noticed that the original wiring of the sump pump and furnace is done using a common 14-3 wire instead of individual 14-2 wires. The 14-3 wire runs from the service panel to a junction box where 14-2 wires then feed the sump pump outlet and the furnace. Is this common practice? The only benefit I can see in doing this is that only one wire has to be run the majority of the distance, about 40 feet in my case. It still uses the same amount of circuit breakers as running individual wires. The electrician has also used this technique for the dishwasher and the garbage disposal.


I wouldn't say that it is very common, but it is legal. It is called a multiwire branch circuit. The only rub is that the two hot conductors must be on different phases of the panel, otherwise the neutral could be overloaded. In areas following the 2008 code, the two hots must be on a double pole breaker. Also, make sure the breaker(s) that feed your equipment are 15 A, and no higher.


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## joed (Mar 13, 2005)

I don't know how common it is but I would do it that way. One 14/3 is cheaper than two 14/2 cables.
It's legal. Any electrician would know what is right away. It might confuse an inexperienced home owner, but that is not really a concern.


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## 220/221 (Oct 9, 2007)

It's called a multi wire branch circuit and _here_ it is very common. I avoid it just to avoid the potential issues related to it. It's hard not to use it with the DW/disposal and kit counter top circuit because it is going to the same box in many cases.

The 2 hot wires must be on seperate phases/legs and your neutral connections had better be *bulletproof*. If you lose the neutral path back to the panel you may end up with 240V at your 120V circuits.

THey also must be on a 2 pole breaker as of 2008 code.


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## CowboyAndy (Feb 19, 2008)

MWBC's are pretty common around here. They can save on materials and labor.


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## duckdown (Dec 30, 2008)

Instead of pulling 14/3, I would pull 12/3 to be safe. The difference in price is minor...


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## jbfan (Jul 1, 2004)

duckdown said:


> Instead of pulling 14/3, I would pull 12/3 to be safe. The difference in price is minor...


Why would you be safer?


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## Gigs (Oct 26, 2008)

I think he means safer from having to do it over if your ampacity needs grow.


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## handyman78 (Dec 29, 2007)

duckdown said:


> Instead of pulling 14/3, I would pull 12/3 to be safe. The difference in price is minor...


If it is already installed and connecting a permanent item like furnace and sump, I wouldn't change it. I would consider upgrading if it supplied receptacles which could be used heavily at times.


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## david.plymouth (Dec 26, 2008)

*Whirlpool bath wiring*

I'm installing a whirlpool bath in the basement which requires two separate 15 amp circuits, one for the pump and one for the heater. Is it okay to use a 12-3 wire for these two circuits or should I go with separate 14-2 circuits (or 12-2)?


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## joed (Mar 13, 2005)

It only needs 14/3 for 15 amp circuits. I would NOT use two 14/2s or two 12/2.


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## ACB Electric (Nov 29, 2008)

absolutly nothing wrong with it proding it is circuited aproapriatly in the panel, customers allways want the lowest price, so whereever time and materials can be saved legally most of us end up doing it. I personaly would not go to the extent of a seperate junction box to split it, nor will I use a connection to a device as a splitting point for the neutral, it is seperatly marreted and tagged, and make note on the panel of the spliting point, and that it is a mwbc.


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## cambruzzi (Dec 30, 2008)

I saw this for the first time in a home I was working on yesterday. Almost one whole side of 100amp sub panel was wired this way. Kinda freaked me out for a second but figured it out quick and its good to know now that its legal. Thanks guys!


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## jerryh3 (Dec 10, 2007)

cambruzzi said:


> I saw this for the first time in a home I was working on yesterday. Almost one whole side of 100amp sub panel was wired this way. Kinda freaked me out for a second but figured it out quick and its good to know now that its legal. Thanks guys!


What were you doing in the panel?


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## williswires (Jul 21, 2008)

Whirlpool baths, a.k.a. "hydromassage tubs" in the 2008 NEC, require GFCI protection, and that GFCI must be readily accessible.

So, you have a choice of GFCI receptacles under the tub that must be readily accessible, or GFCI breakers at your panel.

(680.71 NEC)


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## cambruzzi (Dec 30, 2008)

my electrician was installing a phase coupler for my customer and I pulled the cover off for him before he got there.


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## cambruzzi (Dec 30, 2008)

Just trying to save time. Not doing anything wrong buddy! 


I'm a low volt guy!!


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## jerryh3 (Dec 10, 2007)

cambruzzi said:


> my electrician was installing a phase coupler for my customer and I pulled the cover off for him before he got there.


Phase coupler? X10 system?


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## chris75 (Aug 25, 2007)

jerryh3 said:


> Phase coupler? X10 system?


 That would be my guess.


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## CowboyAndy (Feb 19, 2008)

williswires said:


> Whirlpool baths, a.k.a. "hydromassage tubs" in the 2008 NEC, require GFCI protection, and that GFCI must be readily accessible.
> 
> So, you have a choice of GFCI receptacles under the tub that must be readily accessible, or GFCI breakers at your panel.
> 
> (680.71 NEC)


 
Also note that a traditional gfci breaker will not work in a MWBC setup. A 2-pole gfci breaker has to be used.


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## Gigs (Oct 26, 2008)

CowboyAndy said:


> Also note that a traditional gfci breaker will not work in a MWBC setup. A 2-pole gfci breaker has to be used.


For me that's a good enough reason to avoid them, you'll regret it later if you ever upgrade into a code cycle that requires AFCI/GFCI and double pole MWBC breakers.


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## chris75 (Aug 25, 2007)

Gigs said:


> For me that's a good enough reason to avoid them, you'll regret it later if you ever upgrade into a code cycle that requires AFCI/GFCI and double pole MWBC breakers.


ITs not rectroactive, meaning you dont have to change things becuse the codes change. I have no AFCI's in my own home, and I doubt I ever will. :thumbup:


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## PirateKatz (Sep 10, 2008)

Please excuse my ignorance on the subject but...

If I'm picturing things correctly, wouldn't this require two separate circuits to share the same neutral?


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## cambruzzi (Dec 30, 2008)

jerryh3 said:


> Phase coupler? X10 system?


X10 is outdated technology. The signals are weak and the systems fail quite frequently. Ive found the UPB system to work much better. The signal is 20 times stronger and each system has its own id along with each device which makes interference rare. the coupler joins the 2 phases in the house together so the signals can travel to devices on both phases.


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## CowboyAndy (Feb 19, 2008)

PirateKatz said:


> Please excuse my ignorance on the subject but...
> 
> If I'm picturing things correctly, wouldn't this require two separate circuits to share the same neutral?


Yes, thats exactly how it works.


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