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#100315 - 11/09/06 10:49 PM Ground wire  
louigy35  Offline
Junior Member
Joined: Nov 2006
Posts: 2
How many grounds do I need to pull in a 2"inch conduit emt with 28 circuits in it(38 wires total),to feed 120v 20 amp receptacles and one 208v 30amp receptacle? All circuits are run with #10awg from the panel to a gutter 150 feet apart.
Looking in table 5 says that the approximate area for THHN #10 is 0.0211 x 39 =0.8229 and then in table 4 for 2" EMT over 2 wires 40% is 1.342 so is that 2" conduit the right size? or I missing something?

[This message has been edited by louigy35 (edited 11-09-2006).]

[This message has been edited by louigy35 (edited 11-11-2006).]

[This message has been edited by louigy35 (edited 11-11-2006).]

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#100316 - 11/09/06 11:03 PM Re: Ground wire  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
I say one #10.

(I posted that without thinking it through. I even -for some silly reason- was thinking "PVC" rather than "EMT." Electure is right on.... this job seems a bit, uh, unusual... maybe you should re-consider your plan?)

[This message has been edited by renosteinke (edited 11-10-2006).]

#100317 - 11/09/06 11:12 PM Re: Ground wire  
Celtic  Offline
Joined: Feb 2005
Posts: 361

...but that isn't what I would do.

~~ CELTIC ~~
...-= NJ =-...

#100318 - 11/10/06 07:26 AM Re: Ground wire  
electure  Offline

Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
You need to pull 0 grounds in your EMT, the EMT is acceptable as an equipment grounding conductor.

You have another couple of issues, though.
If you have more than 30 (31-40) conductors in any cross-section of your gutter(wireway), as well as in the 2" EMT, your conductors must be derated to 40% of their ampacity.
Check out Table 310.15(B)(2)(a), and 376.22

The #10s are too small.

Like Celtic, I would find a different way to do it.

#100319 - 11/10/06 11:04 AM Re: Ground wire  
Zapped  Offline
Joined: Oct 2002
Posts: 482
Huntington Beach, CA, USA
Although the EMT is acceptable as electure indicates, I am anal enough about grounding to run an "insurance" ground, i.e., a single #10 or #8 THHN stranded. I've seen mechanical grounds fail too often from damage or future servie or modifications.

Not to second-guess your work, but I'm with everybody else on this about your design.

If you're running 24 X 120V 20A circuits, and have individual neutrals (?), then add the 208V circuit, you've got 50 #10's in that pipe (plus a back-up ground, if you so choose). That's one heck of a pull physically, and quite a bit sorting-out to be done by the installer - not to mention anyone with the misfortune of servicing the work later. If you do it, please as least number the wires and related nuetrals for the sake of everyone involved.

Just my opinion. I could be that next guy...

#100320 - 11/10/06 05:54 PM Re: Ground wire  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
I think it's worse that that- Just doing the raceway fill calc for 50 wires and assuming THHN he only has a wire worth 14a. Now if he has a wet location or high ambient or he is feeding 120v. receptacles he is in even worse shape.

George Little

#100321 - 11/11/06 11:12 AM Re: Ground wire  
louigy35  Offline
Junior Member
Joined: Nov 2006
Posts: 2
Thanks everyone for your info.By the way the drawings in this proyect (school} calls for #10 for all home runs ,even though the fardest class room is 260ft appart from the panel.

#100322 - 11/11/06 11:20 AM Re: Ground wire  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
The distance may be fine on 10 AWG depending on the actual load.

However if the EC decides to stuff them all in one raceway they will be creating an NEC violation.

Bob Badger
Construction & Maintenance Electrician

#100323 - 11/20/06 10:28 AM Re: Ground wire  
Almost Fried  Offline
Joined: Sep 2006
Posts: 98
Madison County, Ark. USA
I have always considered that it's cheaper to pull a few big wires than a bunch of little ones...The engineers that sometimes design this stuff we're supposed to install intelligently, often don't have a clue, the kinds of clues that callouses on your hands give you over the years. Think about a sub panel at the location of the gutter, rather than remoting all those circuits. MNSHO :{)

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