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#208139 12/29/12 03:36 PM
Joined: Oct 2012
Posts: 13
B
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I'm installing overhead raceway for aproximately 50 machines in a machine shop.Most will be on 20 amp three pole breakers.I'm going to be running 2" EMT from the panel to the raceways.I'm thinking about running a #6 ground wire from the panel ground bar to the raceway,and installing(bonding) a terminal ground bar inside the raceway.From the ground bar in the raceway I would run a #12 ground wire to each machine saving me time and wire.I'm thinking this is legal

Any and all comments are appreciated.

Joined: Oct 2012
Posts: 13
B
Member
I should add that I'll be running 1/2" emt from the raceway to each machine.

Joined: Jul 2004
Posts: 9,672
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G
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Legally you could run a single #12 all the way to where you start splitting them out. The problem is the splice in the raceway. If there is adequate space, you can splice in a conduit body.
This is really a gray area since all grounding conductors only count as one.

You are also going to have some serious derating problems with that many conductors in a single raceway so we are not even talking about #12s. All of the wires, including the ground, have to start getting bigger when you go over three 3 phase circuits in a pipe. (9 current carrying THHN)
In the 10-20 wire range you will need #10.

At a certain point more raceways ends up being cheaper.


Greg Fretwell
Joined: Apr 2002
Posts: 7,283
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Bossanove5:

Heed these words...

"You are also going to have some serious derating problems with that many conductors in a single raceway so we are not even talking about #12s. All of the wires, including the ground, have to start getting bigger when you go over three 3 phase circuits in a pipe. (9 current carrying THHN)
In the 10-20 wire range you will need #10.

At a certain point more raceways ends up being cheaper."

I have seen what Greg is saying happen in the field a few times...results were downright ugly, expensive, and one cost a young guy an unwanted 'vacation.'

As to your question on the EGC...yes it is no issue to install a ground block within a wireway/troff/gutter and run a single EGC to the source panel. Common practice is to size the EGC from the panel to the block to the largest OCP of the circuits, although that is not an NEC requirement.




John
Joined: Jul 2004
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Quote
within a raceway


Really?

How is that accessible? It is OK in a condolet tho.

Quote
300.13 Mechanical and Electrical Continuity Conductors.
(A) General. Conductors in raceways shall be continuous between outlets, boxes, devices, and so forth. There shall be no splice or tap within a raceway unless permitted by 300.15; 368.56(A); 376.56; 378.56; 384.56; 386.56; 388.56; or 390.6.


Each of those "unlesses" refers to a removable cover.


Greg Fretwell
Joined: Apr 2002
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gREG:
i FEEL THAT THE op IS REFERING TO WIREWAY, TROFFS, NOT CONDUIT.


John
Joined: Jul 2004
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OK my fault, I was confused by the 2" EMT thing.


Greg Fretwell
Joined: Apr 2002
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Not as confused as my pittiful typing job above.!!!!!


John
Joined: Oct 2012
Posts: 13
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Let me clear up the confusion:

The first 14 set of machines will have there own 6x6 square raceway.This raceway will be fed by a 2" conduit so the maximum #12 wires including the ground inside the raceway will equal 43 (Counting all the ground wires as one)

The second set of 19 machines will be fed the same way by (58 #12 wires) their own 6"x6" gutter and 2" pipe.

I know section 310.15(b)(a) calls for derating which permits only 10.5 amps for each #12 wire for the amount of wires I'm using.

The machines pull about 15.3 amps each.So I would have to use #8's which is kinda crazy.

Any more thoughts on this?

Thanks


Joined: Jul 2004
Posts: 9,672
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G
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Just to be clear, grounds count as one for box fill but they are all counted in pipe. Again tho, you really only need one.

If you ran 3 raceways with the wires split up you would avoid the derating problem. Even 2 would be better, even if not legal.


Greg Fretwell
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