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Joined: Apr 2002
Posts: 7,381
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RE-thinking the one conduit, maybe??

2" is legal for 36-#8 (fill) but you need 43. 2x2" drop you to 22 conductors each, but still 45% derate leaves you at #8.
3 conduits, 14 circuits (5-5-4)16 conductors, 50% derate, back to #10. 1/2" or 3/4" for each machine, panel to machine...back to #12 unless there is a VD issue for length.

Other options? Bus Duct? There are 'small amperage' bus ducts available. Cost effective??

Like I said above....this can get really ugly, depending on when that 'number of conductors' rears its ugly head!!


John
Joined: Oct 2000
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Bossanova;

The Project, as described, is going to require several different Derating Methods, as the Wiring Methods will be a combination of Two different Raceways:
EMT and Metallic Wireways (AKA "Gutters").

Suggest reviewing Article 376 prior to any choice of installation.

With the Wireways, there are Two things for consideration, per Section 376.22 - Number of Conductors and Ampacity:

376.22(A): Cross Sectional Fill.
This limits the Wireway to a Maximum 20% Conductor fill.
Equipment Grounding Conductors _ARE_ included.
Although there may be 541 #12 THHN CU. in a 6"x6" Gutter, without exceeding 20% fill, the next part kills that idea instantly...

376.22(B): Adjustment Factors.
Where the Total Current Carrying Conductors does not exceed 30, no Derating is required.
Equipment Grounding Conductors _ARE NOT_ counted.

Having 31 or more CCC's will require Derating Factors, per Table 310.15(B)(2)(a), as follows:

a. 31 to 40 Conductors: Adjustment Factor = 40% (Imax x 0.4),
b. >40 Conductors: Adjustment Factor = 35% (Imax x 0.35).

As you can see, there is a point where either (A) or (B) will influence the Wireways.

Along with the Wireway issues, feeding them with Raceways, such as EMT, has an altogether new Conductor Fill and Derating concept to figure in.
Using Section 310.15(B)(2)(a), exception #3, if the Segment of EMT between the Panelboard and the Wireway, does not exceed 24", the Conductors may be installed without Derating Factors applied, so there is a little give-way in that situation.

Good luck!

--Scott (EE)


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jul 2007
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The intent of the derating/conduit fill is to limit heat buildup from so many conductors in a race way. I've dealt with lighting panels that had only two 2" conduits coming out of the panel. One had the feeders and the other had all of the circuits in the panel. The feeder conduit was cool to the touch while the other conduit dang nearly burnt my hand


"Live Awesome!" - Kevin Carosa
Joined: Jun 2004
Posts: 1,273
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You should seriously look at cable tray.

With it you can massively cut down on wire make-up.

http://www.legrand.us/cablofil.aspx#.UOCs4vnQTso

It's also going to be quicker and easier.

Expect that your loads will actually need at least #10 THWN-2 conductors -- just because of voltage drop at start-up.

Distant machines may warrant up-sizing to #8.

Cable tray also makes for very smooth changes and additions.


Last edited by Tesla; 12/30/12 07:10 PM.

Tesla
Joined: Oct 2012
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Thanks everyone for your valued input.I have some re-engineering to do.

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