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#193839 04/22/10 01:42 PM
Joined: Dec 2002
Posts: 59
Hello everybody. I left my NEC at home and need to size a pull box ASAP. I will have 12(twelve) 3 1/2 inch emt's in and 12 out. Each will have 4 500mcm and 1 1/0. All conductors will make a 90 degree turn in this box. Thanks in advance, Richard

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sparky806 #193840 04/22/10 06:28 PM
Joined: Mar 2003
Posts: 849
2008 NEC 314.28 (2)
6x3.5 = 21
11 x 3.5 = 38.5

21 + 38.5 = (59.5 x 59.5 X 6 Min.)
figured that there all in a row both walls.

Last edited by Yoopersup; 04/22/10 06:29 PM.
Yoopersup #193844 04/22/10 11:29 PM
Joined: Jan 2004
Posts: 1,507
Adding to what Yooper said, make sure that the raceways containing the same conductors ie; Raceway "A" has conductors coming into the pull box and Raceway "B" has these conductors going out are at least 21 inches apart.

George Little
George Little #193847 04/23/10 12:34 AM
Joined: Mar 2003
Posts: 849
Yep 6 x 3.5 = 21 inches .

Yoopersup #193850 04/23/10 06:00 AM
Joined: Jun 2004
Posts: 1,273
12 in and 12 out...

Where do you get 6 x 3.5" ?

Right off the bat the bonding run is too small...IF this is one load.

It must be sized to handle the fault current for ALL hot conductors at the SAME INSTANT.

Are you really running 12 x 500kCMIL x 3 hots and 1 neutral?

Or is this a bank of runs to dependent panels off of a bank of independent breakers?

BTW your neutral seems massively oversized -- IF you're driving mainly 3-phase loads.

What does the EE have on his 1-line? Sounds like he goofed.

At these power levels bus-duct or cable-bus (MPHusky) is normally used.

Is this a high-rise building?...

Can you use cable-tray and MC?...

Too many unknowns to take a stab at.

I can say, twelve feeders flat across is a monster rack and ordinary strut is going to sag. You'll need double deeps.

Further, during the pull operations -- don't spare the lube.

Last edited by Tesla; 04/23/10 06:08 AM.

Tesla #193851 04/23/10 09:51 AM
Joined: Mar 2003
Posts: 849
the six comes from 314.28 (2) Angle ,U pills, Or splices.
The distance between raceways enclosing the conductors shall not be less then SIX TIMES the metric designator (Trade size) of the larger raceway.
I don't recall a Question about the ampacity ??? This could be 12 - 400 amp feeders for all we know.

Yoopersup #193861 04/23/10 10:41 PM
Joined: Dec 2002
Posts: 59
First of all I want to say thanks for everyones input. What I am doing is refeeding a 475' piece of 3000amp busduct. The Ideal way would be to extend the duct, however it was installed in 1951 and I have not been able to find matching duct.
I wouldn't really call this a high rise. It's 5 stories, 1.5 million square feet. Complete rehab. All switch gear and bus duct is original. We have redone the risers and panels on parts of 3 floors. The building had it's own generators when built. We removed those and tied it into POCO's grid last year. If anyone knows where to get about 100 feet of 50 year old Westinghouse 3000amp bus duct, then I won't need that pull box.

sparky806 #193862 04/24/10 12:15 AM
Joined: Mar 2003
Posts: 849
Just Curious how you came up needing 12- sets of 500Kcmil??
& the 1/0 in each pipe ain't gonna do it? (250.122(C)
& Teslas Right Neutral seems kinda Big?? (prally mostly 3 phase loads).

Yoopersup #193863 04/24/10 03:19 AM
Joined: Sep 2004
Posts: 68
One way of solving your problem is to install any type of new 3000 amp busway from the source to a point close to the terminal cabinet of the old busway. Install a terminal cabinet on the new busway and a set of short conduit nipples to the old busway terminal cabinet. Install 500kcmil (or smaller parallel) jumpers from new to old. You will be tens of thousands of dollars ahead of the game. Materials may be more expensive, labor will be way less!!!

homer #193864 04/24/10 03:47 AM
Joined: Jun 2004
Posts: 1,273
Google Salinger, they have an amazing amount of old bus-duct.


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