How many wires in pipe

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Old 08-04-11, 06:30 AM
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How many wires in pipe

Hello and good day to all.
Is it still acceptable in single phase residential wiring, for two (15 or 20 amp) circuits to share one neutral wire? Is it better not to do that? How many 12 gauge wires would be allowed to run in a 1/2" versus 3/4" EMT? The conduit(s) length will only be about 10 feet.
 

Last edited by old dude; 08-04-11 at 09:28 AM.
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Old 08-04-11, 08:51 AM
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Is it still acceptable in single phase residential wiring, for two (15 or 20 amp) circuits to share one neutral wire?
Yes. You just have to usa a double pole breaker.
How many 12 gauge wires would be allowed to run in a 1/2" versus 3/4" EMT?
9 before you have to derate.
 
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Old 08-04-11, 09:32 AM
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Thank you much Justin for reply!
So I can only run 9 conductors in either 1/2 or 3/4.
So then there is no reason to buy 3/4 inch that I can see.
Is that correct?
Also, if my math is right, I can run 5 hots, 3 neutrals and one ground.
Does that sound ok?
 
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Old 08-04-11, 09:45 AM
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So I can only run 9 conductors in either 1/2 or 3/4.
So then there is no reason to buy 3/4 inch that I can see.
Is that correct?
3/4'' is easier to pull, plus you can pull more non-current carrying conductors.

You do not need a ground wire if you are running conduit and it is continuous to the breaker panel.
 
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Old 08-04-11, 10:01 AM
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The maximum amount of wires you may put in a 1/2" EMT pipe is nine. You must start derateing the wires at four or more. (80% 4-6, 70% 7-9, etc) But when using THHN wires the ampacity starts at 30 amps for #12. So if you do the math, 70% of 30 amps is 21 amps. The max you can fuse #12 is 20 amps so the derateing in affect does nothing.

3/4" EMT you can put 16 #12 in the pipe but then derateing has much more effect so if you have more than 9 wires to pull I suggest running two pipes.

1/2" EMT pulls just fine as long as you don't have too many bends in it.
EMT is rated for grounding as long as you install metal boxes and use the correct fittings rated for EMT.
 
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Old 08-04-11, 10:07 AM
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Originally Posted by old dude View Post
to share one neutral wire?
In addition to the double-pole breaker requirement you also need to use mechanical fasteners (wirenuts) on the neutral wire splices. It cannot use the feed-through screws on a receptacle for example.

if my math is right, I can run 5 hots, 3 neutrals and one ground.
Yes or 6 hots, 3 neutrals and use the pipe as ground. If you don't need the sixth hot I would use the copper ground wire just for good measure.
 
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Old 08-04-11, 02:15 PM
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Many many thanks to you all!
Your help is very much appreciated!

old dude
 
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