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Electrical 12-3 question Stormin Mormon 05-27-2006
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Posted by Stormin Mormon on May 27, 2006, 11:20 pm
I've got a customer who needs some lights, and an electrical socket
installed. He has a roll of 12-3 WG Romex.

Can that (safely and legally) be used to run two 20 amp circuits a
distance away from the circuit panel?

Seems like if the red and black legs were out of phase, the most the
neutral would carry would be 20 amps. If red and black were both
drawing 20 amps, it would act like a 220 VAC circuit.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
.



Posted by Jennifer Duquesne on May 27, 2006, 11:34 pm
Safely? Yes. As long as each wire is in fact on a different leg.

Indeed, the neutral load is most often considerably reduced--assuming diff.
phases. Neutral mains are allowed (NEC) to be considerably smaller than hot
wires, altho this is not applied to local runs.

Legally? Depends. Some places rate #12 wire for only 15 A.
Imo, #12 is good for at least 30A, altho you might have to be more careful
about run lengths, wire-nutting, etc.

Old-time house wiring was in fact soldered AND wire-nutted--a very safe,
albeit more time consuming, construction method.



> I've got a customer who needs some lights, and an electrical socket
> installed. He has a roll of 12-3 WG Romex.
>
> Can that (safely and legally) be used to run two 20 amp circuits a
> distance away from the circuit panel?
>
> Seems like if the red and black legs were out of phase, the most the
> neutral would carry would be 20 amps. If red and black were both
> drawing 20 amps, it would act like a 220 VAC circuit.
>
> --
>
> Christopher A. Young
> You can't shout down a troll.
> You have to starve them.
> .
>
>



Posted by Doug Miller on May 28, 2006, 9:18 am
wrote:
>Safely? Yes. As long as each wire is in fact on a different leg.
>
>Indeed, the neutral load is most often considerably reduced--assuming diff.
>phases. Neutral mains are allowed (NEC) to be considerably smaller than hot
>wires, altho this is not applied to local runs.
>
>Legally? Depends. Some places rate #12 wire for only 15 A.

12ga aluminum, sure. I never heard of anyplace limiting 12ga copper to 15A.

>Imo, #12 is good for at least 30A, altho you might have to be more careful
>about run lengths, wire-nutting, etc.

Your opinion is not relevant. The National Electrical Code limits 12ga copper
to 20 amps. Period.

>
>> I've got a customer who needs some lights, and an electrical socket
>> installed. He has a roll of 12-3 WG Romex.
>>
>> Can that (safely and legally) be used to run two 20 amp circuits a
>> distance away from the circuit panel?
>>
>> Seems like if the red and black legs were out of phase, the most the
>> neutral would carry would be 20 amps. If red and black were both
>> drawing 20 amps, it would act like a 220 VAC circuit.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Posted by Mark Lloyd on May 28, 2006, 11:43 am
On Sun, 28 May 2006 13:18:41 GMT, spambait@milmac.com (Doug Miller)
wrote:

wrote:
>>Safely? Yes. As long as each wire is in fact on a different leg.
>>
>>Indeed, the neutral load is most often considerably reduced--assuming diff.
>>phases. Neutral mains are allowed (NEC) to be considerably smaller than hot
>>wires, altho this is not applied to local runs.
>>
>>Legally? Depends. Some places rate #12 wire for only 15 A.
>
>12ga aluminum, sure. I never heard of anyplace limiting 12ga copper to 15A.
>
>>Imo, #12 is good for at least 30A, altho you might have to be more careful
>>about run lengths, wire-nutting, etc.
>
>Your opinion is not relevant. The National Electrical Code limits 12ga copper
>to 20 amps. Period.
>

I found the paper I had in college, copied from the 1951 NEC. It
mentions up to 40A for #12, but that is with specific types of
insulation. The normal limit is 20A.

>>
>>> I've got a customer who needs some lights, and an electrical socket
>>> installed. He has a roll of 12-3 WG Romex.
>>>
>>> Can that (safely and legally) be used to run two 20 amp circuits a
>>> distance away from the circuit panel?
>>>
>>> Seems like if the red and black legs were out of phase, the most the
>>> neutral would carry would be 20 amps. If red and black were both
>>> drawing 20 amps, it would act like a 220 VAC circuit.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Posted by Doug Miller on May 28, 2006, 3:16 pm
>On Sun, 28 May 2006 13:18:41 GMT, spambait@milmac.com (Doug Miller)
>wrote:
>
>I found the paper I had in college, copied from the 1951 NEC. It
>mentions up to 40A for #12, but that is with specific types of
>insulation. The normal limit is 20A.

To clarify: various conditions of installation and/or insulation provide
varying ampacities for 12ga copper, often in excess of 20A -- but it still
gets a maximum overcurrent protection of 20A regardless of the ampacity.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

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