# 12-3 for outlets?



## PARENOS (Nov 24, 2008)

I am doing a attic conversion and have ran into a 12-3 that was run by an electrician that started the job but is to booked up and she can not get back. Being that i thought everything was hooked up and all it would be was some outlets and lights, I told her that I could handle that. The electrician ran a 12-3 upstairs for the outlets, I believe he did this so he could branch out with the other live wire for any future outlets, however the panel box is 100 and there is only one more circuit open to wire in this 12-3. Is is bad practice to just wire in one of the hots on a single pole and leave the other hot in the box, I really do not want to go this way. I would appreciate any ideas


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## rselectric1 (Sep 20, 2009)

He or she probably intended to share a neutral to run 2 circuits to the addition. This is OK as long as they are on opposite legs at the service panel. It sounds like you need someone who is qualified to check this out.

I have come in "second hand" on jobs and it took me awhile to figure out what the original sparky was planning.

No offense to you, but you need help here.


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## JumboJack (Aug 14, 2007)

It could also be for a half hot switched outlet....Call a sparkie...


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## 480sparky (Feb 1, 2009)

My vote is the red is a spare.


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## Tinstaafl (Jan 6, 2008)

PARENOS said:


> Is is bad practice to just wire in one of the hots on a single pole and leave the other hot in the box, I really do not want to go this way.


It wouldn't hurt anything as long as you cap off the extra hot wire. But if it bothers you, just disconnect the other end from its breaker... if it's actually connected already. Not entirely clear from your description.

ETA: It could be as simple as he just ran out of 12/2, and had enough 12/3 to get the job done, never intending to use the extra conductor. It happens...


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## Winchester (Jun 29, 2008)

Just do a split receptacle and you won't be doing what you didn't want to do.

Break off the little tab, put the red on one outlet and the black on the other.

:laughing:

p.s. whenever fishing wires to remote spots on the home we usually bring a spare anyway. doesn't hurt anything and sure makes things easier if someone changes their mind about something after you're done fishing and pulling for wires...


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## 480sparky (Feb 1, 2009)

I don't this this is for split (half-hot) receps. By the OP, this is the feed from the panel to the attic.


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## paintr56 (Feb 4, 2005)

PARENOS said:


> I am doing a attic conversion and have ran into a 12-3 that was run by an electrician that started the job but is to booked up and she can not get back. Being that i thought everything was hooked up and all it would be was some outlets and lights, I told her that I could handle that. The electrician ran a 12-3 upstairs for the outlets, I believe he did this so he could branch out with the other live wire for any future outlets, however the panel box is 100 and there is only one more circuit open to wire in this 12-3. Is is bad practice to just wire in one of the hots on a single pole and leave the other hot in the box, I really do not want to go this way. I would appreciate any ideas


I would call the original electrician and see what they had in mind.

Jim


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## Ben of Hyde (Jan 3, 2010)

I wouldn't.


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## mrmike (Dec 9, 2008)

PARENOS said:


> I am doing a attic conversion and have ran into a 12-3 that was run by an electrician that started the job but is to booked up and she can not get back. Being that i thought everything was hooked up and all it would be was some outlets and lights, I told her that I could handle that. The electrician ran a 12-3 upstairs for the outlets, I believe he did this so he could branch out with the other live wire for any future outlets, however the panel box is 100 and there is only one more circuit open to wire in this 12-3. Is is bad practice to just wire in one of the hots on a single pole and leave the other hot in the box, I really do not want to go this way. I would appreciate any ideas


 Why would the second one "red wire" be hot ? Just leave each end unhooked & capped off............


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## jarhead0531 (Mar 5, 2008)

Hire a sparky unless you have an electrical license.

I have seen 12-3 used to feed outlets off two breakers with a shared neutral and always felt like that was wrong. Lets say they use space heaters/window ac units in a couple spots fed by this split 12-3, even if they are on the the two seperate circuits they still share the same neutral, and the combined load could very easily exceed the 20A current carrying capacity of a single 12 thhn. 

Now since there is no current limiting device on the neutral over time the extra amps(aka heat) would eventually cause a insulation failure. Am I completely off base here, if so please enlighten me. It just seems like its a shortcut to avoid having to fish two wires instead of one.


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## Anti-wingnut (Mar 12, 2009)

jarhead0531 said:


> Hire a sparky unless you have an electrical license


Because you said this, you are absolved for your other error!




jarhead0531 said:


> I have seen 12-3 used to feed outlets off two breakers with a shared neutral and always felt like that was wrong. Lets say they use space heaters/window ac units in a couple spots fed by this split 12-3, even if they are on the the two seperate circuits they still share the same neutral, and the combined load could very easily exceed the 20A current carrying capacity of a single 12 thhn.
> 
> Now since there is no current limiting device on the neutral over time the extra amps(aka heat) would eventually cause a insulation failure. Am I completely off base here, if so please enlighten me. It just seems like its a shortcut to avoid having to fish two wires instead of one.


When two hots (or three in the case of a three-phase system) from *seperate poles* feed a shared neutral, the loads "cancell out", and the neutral only carries a small unshared load. *Done properly*, there is no danger in overloading the neutral.

Done improperly, the whole house could burn down


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## 480sparky (Feb 1, 2009)

jarhead0531 said:


> ............ and the combined load could very easily exceed the 20A current carrying capacity of a single 12 thhn. ............


 
1. Who wires attics with 12 THHN?
2. The ampacity of 12 THHN is 30, not 20.


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## woodchuck2 (Feb 27, 2008)

The 12-3 from the panel to the first recepticle would be the feed, the Electrician most likely ran 3 wire for a second feed if needed. If the 12-3 is ran from recepticle to recepticle then i would believe it is for switched recepticles, black being the full time feed and the red being switched. I run 3-wire to hard to get locations in a home when pulling circuits such as an attic space or a basement/crawl space and there are one or two finished living spaces in between.


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## Zinsco (Oct 14, 2009)

jarhead0531 said:


> Hire a sparky unless you have an electrical license.
> 
> I have seen 12-3 used to feed outlets off two breakers with a shared neutral and always felt like that was wrong. Lets say they use space heaters/window ac units in a couple spots fed by this split 12-3,* even if they are on the the two seperate circuits they still share the same neutral, and the combined load could very easily exceed the 20A current carrying capacity of a single 12 thhn. *
> 
> Now since there is no current limiting device on the neutral over time the extra amps(aka heat) would eventually cause a insulation failure. Am I completely off base here, if so please enlighten me. It just seems like its a shortcut to avoid having to fish two wires instead of one.


No, the load on the neutral is not the sum of the hots, but the difference between the hots. Each leg is 180 degrees out of phase with the other.


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## KennMacMoragh (Sep 16, 2008)

Did you check it with a volt meter to see what was going on? A 12-3 would indicate they are planning a 240V outlet wouldn't it? Does the homeowner plan on putting a sauna or something in the room?


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## nolatigabait (Aug 14, 2008)

Not necessarily. I agree with 480, it sounds like he ran it as a spare. I do it all the time.


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## 480sparky (Feb 1, 2009)

nolatigabait said:


> Not necessarily. I agree with 480, it sounds like he ran it as a spare. I do it all the time.


I was unaware you always agree with me. :laughing:


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## boman47k (Oct 13, 2006)

480sparky said:


> 1. Who wires attics with 12 THHN?
> 2. *The ampacity of 12 THHN is 30, not 20*.


Just curious, are you serious? 

I thought it was more:
14awg - 15 amps
12awg - 20/21 amps
10awg - 30/33 amps

Of course, I don't even know what THHN means. :laughing:


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## rselectric1 (Sep 20, 2009)

boman47k said:


> Just curious, are you serious?
> 
> I thought it was more:
> 14awg - 15 amps
> ...


THHN is the type of covering (insulation) on the wire.

If you have a code book, check out table 310.16. There are lot's of variables.


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## macmikeman (Sep 12, 2005)

Magnettica said:


> *240(D) Small Conductors.* Unless speci?cally permitted in
> 240.4(E) or 240.4(G), the overcurrent protection shall not
> exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,
> and 30 amperes for 10 AWG copper; or 15 amperes for
> ...


Not quite right young padawan. If you did that in conduit with thhn-2 conductors ok. Since you used romex, see 334.80 first paragraph.


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## EES (Jan 4, 2010)

macmikeman said:


> Not quite right young padawan. If you did that in conduit with thhn-2 conductors ok. Since you used romex, see 334.80 first paragraph.


Is that the one that says you have to use the 60* column for nm?


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## EES (Jan 4, 2010)

PS Is it safe to assume that those who think it's a good idea are those primarily involved with residential?


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## stars13bars2 (Feb 13, 2005)

The red tag would be for 300.9.


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## Magnettica (Dec 19, 2006)

stars13bars2 said:


> Unless those condensing units were inside, they were not wired legally. :no:


Oh, please explain. 


Nameplate rating:

Minimum ampacity: 24 amps
Maximum Overcurrent protection: 40 amps

My install indoors or outdoors is code compliant. Read 440.6 (A)


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## Magnettica (Dec 19, 2006)

macmikeman said:


> Not quite right young padawan. If you did that in conduit with thhn-2 conductors ok. Since you used romex, see 334.80 first paragraph.


NM-B:thumbsup:


60º column, 25 amps.


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## Zinsco (Oct 14, 2009)

.
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................................................I love to backstab.
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## boman47k (Oct 13, 2006)

*general purpose rec's*

***


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## househelper (Mar 20, 2007)

Magnettica said:


> NM-B:thumbsup:
> 
> 
> 60º column, 25 amps.


 If you used the NM-B from the disconnect to the condenser, whether in conduit or not, you are in violation... NM-B is not allowed in a wet location.
And I can't believe this thread has gone on for 4 pages....


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## Magnettica (Dec 19, 2006)

househelper said:


> If you used the NM-B from the disconnect to the condenser, whether in conduit or not, you are in violation... NM-B is not allowed in a wet location.
> And I can't believe this thread has gone on for 4 pages....


Who would run romex from the disconnect to the C/U?


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## stars13bars2 (Feb 13, 2005)

Magnettica said:


> *
> Sure, I've wired air conditioning condensing units with #12 romex (NM for you code junkies ), and even wired it to a double pole 40 amp circuit breaker. Legal as hell. 440.6 (A).
> 
> The ampacity of the conductor depends on the insulation. :thumbsup:*


*

You bragged about doing it and how legal it was. *


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## macmikeman (Sep 12, 2005)

Hey Magnettica, Sorry. I even quoted your post but somehow I got #14 nm into my brain and flagged the ampacity of 14 romex. You were quite clear on #12 though and I just misread it. Bad macmikeman....go into the corner and think about what you did....:no:


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## Magnettica (Dec 19, 2006)

Yeah, my bad too.... I was speaking of the line side of the A/C disconnect. 

Yes, 300.9 (a new code for the 08' by the way), makes it clear that romex is not permissible in exterior raceways.


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## Magnettica (Dec 19, 2006)

macmikeman said:


> Hey Magnettica, Sorry. I even quoted your post but somehow I got #14 nm into my brain and flagged the ampacity of 14 romex. You were quite clear on #12 though and I just misread it. Bad macmikeman....go into the corner and think about what you did....:no:


No problem, I have much respect for you as an electrical contractor. :thumbsup:


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## Bubbles (Sep 27, 2007)

*#12*

I know it's code, but I would never use it for a high total powered item like that because of P=I^2R . It's generally peanuts to run #10 compared to job cost. I have a chart somewhere on the heat losses and shortening of motor life. That's just my opinion though, I know nothing.


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