Multiple circuits in same conduit options

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Old 09-02-09, 09:08 AM
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Multiple circuits in same conduit options

Probably a few ways to do this but I would like to hear your expert thoughts on this. I have already run the 3/4" emt and the one way distance is approximately 30 feet. I have to run 1 15amp circuit at 240V and 2 circuits 20 amp at 120V thru this conduit. I was going to run a separate ground for the 240V and another ground to be shared with the 2-120v circuits. Should I share the neutral or just go ahead and run 2 of them? That is 4 current carrying conductors plus the return neutral if I do it that way. If I use 2 neutrals does that count as 1 more current carrying conductor for a total of 6 current carrying conductors? I just need to derate for the current carrying conductors over 3.
Thanks,
Grumple
 
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Old 09-02-09, 09:22 AM
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Since you are running EMT you do not need a separate ground. The steel pipe is your ground. Just wire nut your grounds to your metal box using a grounding lead and a green grounding screw.

Are you sure your 240 volt machine needs a neutral? Most cases they do not, since you need 120 volts for your control panel, although I have some machines that do. You should double check.

Yes, I would share the neutral (IE: use a multiwire circuit) between your 2 - 20 amp circuits. You will need to use a 2 pole breaker for this circuit if you are in the 2008 code.

Grounds are not counted for derateing nor are neutrals that only carry the imbalance (multiwire) unless you are on a 3 phase system. I only count 4 current carrying conductors.
 
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Old 09-02-09, 09:26 AM
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Originally Posted by Grumple View Post
I was going to run a separate ground for the 240V and another ground to be shared with the 2-120v circuits.
You can use the metal conduit as a ground or one #12 ground can be shared by all three circuits.

Should I share the neutral or just go ahead and run 2 of them?
Either plan is fine, but there are some additional requirements when the neutral is shared. You must use a double-pole 20A breaker, and the neutrals must be connected with wirenuts instead of the feed-through terminals on a receptacle.

I just need to derate for the current carrying conductors over 3.
You will have up to 6 CCC, but it doesn't matter until 10 CCC when dealing with #14 and #12 wire; larger wires are different.
 
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Old 09-02-09, 09:34 AM
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Originally Posted by Tolyn Ironhand View Post
Since you are running EMT you do not need a separate ground. Just wire nut your grounds to your metal box using a grounding lead and a green grounding screw.

Are you sure your 240 volt machine needs a neutral? Most cases they do not, since you need 120 volts for your control panel, although I have some machines that do. You should double check.

Yes, I would share the neutral (IE: use a multiwire circuit) between your 2 - 20 amp circuits. You will need to use a 2 pole breaker for this circuit if you are in the 2008 code.

Grounds are not counted for derateing nor are neutrals that only carry the imbalance (multiwire) unless you are on a 3 phase system. I only count 4 current carrying conductors.
I do not need nor am using a neutral to my 240V motor on the mill. The neutrals I mentioned were for the 2 120v circuits. The mill does not have a control panel (although I could add one and put everything in there) but will be fed by a twistlock drop. I am glad I asked as I have separate breakers available for the 2 120V circuits so I would have been in error if I tried to use 1 neutral and 2 breakers.
Thanks,
Grumple
 
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Old 09-02-09, 09:37 AM
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Originally Posted by ibpooks View Post
You can use the metal conduit as a ground or one #12 ground can be shared by all three circuits.

*** Ok, I will run the one #12 ground as I feel better that way and get to use my added ground bar as my other one was full.


Either plan is fine, but there are some additional requirements when the neutral is shared. You must use a double-pole 20A breaker, and the neutrals must be connected with wirenuts instead of the feed-through terminals on a receptacle.

***I may run separates as I have the wire and the breakers are just waiting to be used (spares).



You will have up to 6 CCC, but it doesn't matter until 10 CCC when dealing with #14 and #12 wire; larger wires are different.
Thanks for clearing that up. I always go overkill on the wire so I am always good there but sometimes I have to save some $$ to pay for strain reliefs etc

Thanks,
Grump
 
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