Using 12/3 To Power Two Circuits

robertc65

I would like to run two additional 20 AMP circuits to my second floor. One for each bath room. I'm no electrician but from what I have seen some electricians would run a length of 12/3 from the breaker panel to a junction box and then 12/2 to each outlet. Of course in doing so one circuit would use the black wire while the other circuit uses the red wire for the hot side. This leaves just one wire for the neutral to be shared by both circuits. Is it OK to use one length of 12/3 from the breaker panel instead of two lengths of 12/2 allowing for a separate neutral on each circuit. Is it ok to have a shared neutral. Wouldn't the current from both circuits flow though the shared neutral. What is the correct way to do this. I don't mind running two lengths of 12/2 from the breaker panel but saving wire would be nice also.

Thanks in advance

Rob

Dave Y Crockett

I have never heard of it and would not reccomend doing it . When it comes to wiring bathrooms play it safe and don't try to copy other sparkys . Just meet the code .....good luck!

Dave Y Crockett

Also Rob , In my house ,all bathrooms are on one 20 amp GFI breaker for the outlets . The lights and fans are linked from undesignated HRs from hallway lights or outlets . Thats what the state inspector required.

Ken@K&R

I would not recomend shared neutrals for bathrooms since they need to be GFCI protected. A GFCI senses and compairs current between the Hot and Neutral side. If it senses a differnce of 5 milliamps it trips. This means the current needs to return about the same as it leaves. With shared neutrals this wont happen and will cause tripping. I have been told you can run 12-3 to the first bathroom and then pig tail off of it with 12-2 for the second. I have never tried this out though.

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Ken

bigjay

It is possible to run your bathroom circuits this way and still meet the intent of the code as far as GFI protection. You can run a 12/3 from the panel to the first bathroom outlet, and branch from there to the other bathroom with a 12/2. You would then have to install a GFI receptacle in each bathroom and tie to the line side only on each. Also, any additional outlets in either
bathroom would have to have their own GFI receptacle, fed only on the line
side. If done in this manner all receptacles will be GFI protected and the shared neutral does not matter. You can also use a 2 pole GFI breaker with
standard receptacles.Tie down the black and red wires on your 12/3 homerun at the panel on seperate phases so you do not risk overloading the neutral, if you go with the receptacle option.

Speedy Petey

I am surprised at the misinformation given in this thread.
Bigjay's is the only post that is correct and concise.

If we are not sure of a certain subject maybe we should not post replies that are simply conjecture.

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stars13bars2

Yes this is "Contractor Talk", where you can have a painter tell you how to do your wiring.

mdshunk

Amen, brother.

When a home is laid off with back to back bathrooms sharing a common wet wall (think main bath and master bath on other side), I normally run a 12-3 home run for both bath recs. Stop at first bath rec box with 12-3, and 12-2 out of that box to second bath. Point of use GFCI receptacle in each box.

All homes that I wire make liberal use of multiwire circuits whenever humanly possible. It's a cost effective, efficient, compliant, and safe way to wire. It will not effect GFCI receptacles in the least. At present, unless you're using Cutler Hammer service equipment, we still need to run 2 wire home runs for the AFCI circuits.

Dave Y Crockett

Yeah ,I can see some certain redoubt in suggesting things that are uncertain . I only know one direction , forward . The wholesale scam is chasing do -it yourselfers off the street and rouses like this proves it .Try burning books brothers. Avoid schools though as they might make you more stupid .God bless America!

Ken@K&R

Im not sure if this was directed to me or not. The reply I left was basically the same as everyone elses from what I see though.

A GFCI senses and compairs current between the Hot and Neutral side. If it senses a differnce of 5 milliamps it trips. This means the current needs to return about the same as it leaves. With shared neutrals this wont happen and will cause tripping. I have been told you can run 12-3 to the first bathroom and then pig tail off of it with 12-2 for the second. I have never tried this out though.

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Ken

robertc65

Bigjay Are you saying that by having the red on one phase and the Black on the other I will not over load the neutral. Is this due to the phase difference?

Speedy Petey

Ok. I'm not sure what you are getting at. Yes a single pole GFCB does as you say.
A two pole measures both legs AND the neutral. If you want to use GFI breakers at all with shared neutrals a two-pole GFCB is required.

Using GFI devices it doesn't matter at all once the circuit is split. If you are talking about a shared neutral circuit throughout, such as split wired receptacles, then again, a two-pole GFCB is required.


You have been told? By whom.


Hey, I don't mean to be so critical but your profile says you are an electrician. This is pretty basic stuff for an electrician.

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Speedy Petey

That is exactly what he is saying. If the current draw is equal on both legs the current on the neutral is 0.
With a multi-wire circuit, just as a feeder, the neutral only carries the current imbalance.

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mdshunk

Holy smokes, Ken. I like you and all, but I almost fell out of my chair when I read what you wrote. Like Speedy says, this is pretty much electrician 101 stuff here. Maybe a picture would help?

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Ken@K&R

Ok unless im missinformed I have been told you can run 12-3 to say the first box then pig tail 12-2 to the 12-3 and hook up a GFCI outlet to the pig tail. Then run the 12-2 off to the next box useing the same method. This means the neutral is not shared off the load side and will not cause tripping. You just have to use a normal dp breaker this way to draw from 2 seperate legs.

"The neutral can be shared prior to the line side connection of a gfci receptacle, not on the load side." Direct quote by Mike Holt

Yes I am licensed with 15 years as a commercial electrician.

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Ken

Ken@K&R

MD,

LMAO thats exactly what I was trying to say. So whats wrong with doing it that way? Where did my explination go wrong? Sounded good when I was writing it. I could picture it just like that in my head.

OOP's I see what I did now. That line about neusance tripping kind of snuck in there and screwed up what I was auctually saying a bit. I was thinking one thing and typeing something else.

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Ken

mdshunk

Ah, yes. It's the 'work all day and try to type at night' syndrome. It sneeks up on you like that. I'm presently working 10 hours, getting a few winks, then doing another 8 during the overnight doing lighting retrofit, then getting a few more winks. About another week of that project left.

Ken@K&R

MD,

Man I feel sorry for you. I can barley handle 8-10 hours a day since I got diabeties. Kind of weired sugar goes up brain functions go down. Last time I did what your talking it was for a company named TRI-M. I specilized in service changes for them for 2 years. It was come in Friday after the factory closed and leave Monday morning when it reopened. I wish my body could still handle 36 hours of straight 500 - 2000 MCM pulls and terminations. Id be making a killing instead of the company.

On a good note at least they paid for my left and right igunal hernia surgerys, the 2 broken toes, and the broken hand. lol

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Ken

mdshunk

No need to feel sorry for me. After all, I scheduled it that way. I could have turned down the after hours work, and in hind sight I probably should have. I will make a profit, but not the usual margin. Lighting retrofit work is pretty popular stuff that lots of guys like to bid on. You have to whore yourself out a little bit to get any of it. I happened to notice that the bid specs didn't call for a warranty, so I'm installing maximium amount of crap (ie- cheap) material possible. Needless to say, I was awarded the work.