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#100315 - 11/09/06 07:49 PM Ground wire
louigy35 Offline
Junior Member

Registered: 11/09/06
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 08:03 PM Re: Ground wire
renosteinke Offline
Cat Servant

Registered: 01/22/05
Posts: 5305
Loc: 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 08:12 PM Re: Ground wire
Celtic Offline

Registered: 02/26/05
Posts: 367
Loc: NJ

...but that isn't what I would do.
~~ CELTIC ~~
...-= NJ =-...

#100318 - 11/10/06 04:26 AM Re: Ground wire
electure Offline


Registered: 12/24/00
Posts: 4229
Loc: 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 08:04 AM Re: Ground wire
Zapped Offline

Registered: 10/01/02
Posts: 481
Loc: 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 02:54 PM Re: Ground wire
George Little Offline

Registered: 01/18/04
Posts: 1492
Loc: 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 08:12 AM Re: Ground wire
louigy35 Offline
Junior Member

Registered: 11/09/06
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 08:20 AM Re: Ground wire
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: 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 07:28 AM Re: Ground wire
Almost Fried Offline

Registered: 09/04/06
Posts: 104
Loc: 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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