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.
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.
12ga aluminum, sure. I never heard of anyplace limiting 12ga copper to 15A.
Your opinion is not relevant. The National Electrical Code limits 12ga copper to 20 amps. Period.
Never heard of that.
So years of accepted practice and the NEC are flawed?
So are you suggesting he should get the soldering iron out?
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.
The NEC table value is 30A (or higher) which can be used for temperature and other derating. As others have said, the NEC then limits #12 to 20A breakers/fuses.
Old wiring was soldered and taped. Not likely any was soldered and wire-nutted.
bud--
Yes and No.
Just to cover what you said, good have the red and black on different phases, so you don't overload the neutral. nuff said there.
IMHO:
Back to the Yes and No part. If seems 'legal' if no outlet(light, receptacle, etc) is in a bedroom. If any outlet is in a bedroom, you need to have AFCI per 2005NEC. Since ARCI breakers aren't designed to work on a shared neutral circuit, you need a seperate neutral per circuit.
I suggest you speak with your local code enforcer, and he/she can really provide the final word, on what you are planning is ok.
Good luck, and remember, only qualified personnel can work on electrial circuits per the NEC. ;)
Tom @
I've been told this by electricians from the NYC area.
IMHO: NYC codes run wild to over regulate, maximizing code enforcement fees/fines, and electrician profits.
:p
later,
tom @
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.
So it can handle more than 20A, but with a maximum of 20A?
12ga copper wire is capable of handling more than 20A, but the NEC does not permit use of breakers or fuses greater than 20A.
Stormin Mormon posted for all of us... I don't top post - see either inline or at bottom.
Remember this clown purports himself to be an HVAC tech!
Agreed. And what you want to ask your local code guy about is a "split neutral", since that's what you're proposing.
In my area, split neutrals are legal, and we did our computer room that way, rather than pulling two separate circuits. It would be a good idea (not sure if required by code or not, but still a good idea) to put the two halves of your split neutral on a double pole breaker with a handle tie, since both hots are going to go into the outlet boxes. Good protection for someone who might pop the cover from one of these outlet boxes later, not realizing there are two separate hot feeds inside. Also ensures that you've got the two halves of the split neutral on opposite legs.
Our biggest aggravation with split neutrals was box fill issues. Do check your box fill calculations before you start running wire, as two extra volumes (for the extra hot going in and out of the box) may be enough to push you over the limit for some smaller boxes.
Here we call them 'shared neutrals'
later,
tom @
Have to add a correction to my post.
I was told that a double pole Arc Fault breaker existed, and you can have a shared neutral. Not that they exist on the shelf, but might be able to special order them for doing bedroom circuits on a shared neutral.
later,
tom
You can do legally do it, at least in most places. As a safety matter, I personally would not do it, unless there was no easy other option. It leaves the possibility of a homeowner later doing repairs and not realizing the wiring in an outlet, for example, is fed by two seperate breakers. They could turn one off and be in for a surprise. And there is the possibility of someone later moving one half of the circuit back to the same phase, in which case the neutral becomes overloaded. Or if you wanted to use a GFCI/AFCI on the circuit. Lots of good reasons to avoid it where possible.
Tell me. Do you install box dividers between switches on different circuits installed in the same box? Dividers are only required by the US NEC if the voltage between adjacent devices will exceed 300 volts such as the switches on the 480/277 volt lighting circuits very commonly used in larger buildings but there are slots in most multi ganged raised covers to facilitate the use of box dividers. Isn't it a logical extension of your line of reasoning that ganged switches on different circuits should be separated by box divider barriers.
There are many ways for a box to end up having multiple circuits in it multiwire branch circuits are only one of the ways that comes about. Multiwire branch circuits are a completely safe and very cost effective method of supplying circuits to distant parts of homes as long as they are installed and maintained by persons who have taken the time to fully understand the dangers of the energy that they are working with. Such circuits lend themselves very nicely to loads such as the dishwasher and the food waste disposer, refrigerator and microwave, bathroom basin receptacle and the rest of the bathroom including heat lamps; kitchen counter top receptacles and the list goes on.
Any one who would assume that one breaker would deenergize everything in a box is too careless to be doing electrical work of any kind. If a person does not have the wit or wisdom to work safely with electricity they should keep their hands out of wiring. It is simply not possible to idiot proof the entire world.
Which is why such installations should always be done with a double-pole breaker: the common disconnect makes it impossible to have one side of the circuit energized and not the other.
Which is why such installations should always be done with a double-pole breaker: it guarantees that the two sides of the circuit will always be on the same leg.
Double-pole versions of both exist.
No, not really.
Here's what Square D, a very respected major manufacturer which everyone is familiar, with, has to say about shared neutrals:
"This document explains why the practice of sharing neutrals in wiring is not a good general wiring practice and why it is incompatible with the use of AFCI's:"
They go on to list all the disadvantages, which make it undesirable, especially if it's being done only to save the cost of a wire run, which isn't that much.
In that diagram, the receptacle on the left appears to be miswired, with the hot (red) connected where neutral should be.
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