For a variety of reasons I am re-wiring my partially rebuilt shop with conduit rather than in the wall. I plan to use EMT concerning which I have the following questions: Can I use two sets of #12 THHN conductors in a 1/2 in. conduit in order provide 2 20A circuits around the shop (it is small)? If so do I need 2 ground wires or can I use one to service both circuits? Can I run a 115V and a 230V set in the same tube?
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You can fit four 12 ga wires in 1/2" EMT.
When you say
"do I need 2 ground wires or can I use one to service both circuits?"
Are you referring to the neutral? If so yes, but don't. A shared neutral isn't worth the savings of a piece of wire.
Bill Hartnman will be along soon.
The OP was asking if he needs two sets of ground wires. The answer is no, you actually do not need any. If done correctly, the EMT can be used as your ground path.
It is up to the OP whether he uses two neutrals or share a neutral. Having independent neutrals can alleviate a bunch of trouble that can surface in the future. But given that EMT is being used and wires can be added at a later date, if done coorectly and with the proper understanding of the system, shared neutrals are not to be avoided
Edited 11/11/2009 9:52 am ET by McMark
As McMark says, you don't really need a ground at all but it is still a good idea. If that pipe gets banged around you can loosen it up and lose your ground if the pipe is the only path.
I would also use compression fittings, made up wrench tight, not the set screw fitting if I really was using the EMT as the ground path.
A wire is better.
As for fill, you can actually put up to 9 in a 1/2" EMT but that can be quite a tug and the box on each end will have to be huge.
Yes you can mix 240 and 120 in the same pipe.
OK so what are the thoughts on this: for two circuits in a 1/2 in. EMT I will use two hot conductors, two neutrals and one common ground. I have always felt that it is better to use a wire rather than relying on the pipe for the ground path. I will use the compression connectors as much for appearances as anything else
You're good.Don't forget to de burr your conduit on the cut ends.
220/240= 2 hots and a ground(some machines require a neutral if they have lights,etc, as in ovens)
110/120=1 hot, 1 neutral, and 1 ground
you need:
3 hots, one neutral and one ground(I have also been told that two seperate ciruits require 2 grounds, but I have never been called on it by th AHJ/inspector) I don't have a NEC book around right now.
or
3 hots and one neuntral and used the conduit for you ground. Just make sure everything is securely tight and you don't use any plastic pipe/fitting/boxes. I'd do this . Easier to pull and less money. BTW, I hate 1/2". I always used 3/4"+ in shop situations because of murph'y law of more power.
Oh yeah, I always run #8 or larger for a single line, just in case you have a compressor(constant load)
Edited 11/12/2009 11:27 am by migraine
Edited 11/12/2009 11:29 am by migraine
You only need one ground, sized to the largest circuit in the conduit. That can be the conduit if it is metal.
I'Knew" that, but, as a precaution, because of past things that i'vve been told, I put in the disclaimer.
mY response was more for the #of hots and neutrals.