Conduit Fill Discrepancy: Southwire vs NEC

[viaPipeline]

So have a bit of an issue at the job I'm on. There are 8, 4" EMT runs entering a box.

However, there are only 3, 4" EMT exiting it at the back (opposite the cover) and going up through the ceiling about 2.5ft to another box, then to the switchgear. These holes were drilled in the concrete (x-rayed for PT cables) months ago.

In each of the 8 incoming 4" conduits are 4 350kcmil aluminum THHN conductors and a #2 (I think) ground.

The individual who had the holes drilled saw the table in NEC that said 4" EMT could hold 11 350kcmil conductors and assumed because 11 x 3 = 33, this should be enough.

Since 11 isn't a multiple of 4, however, that means that not all of the circuits will be able to stay together.

My Southwire Conduit Fill app says 4" EMT can hold 12 conductors before hitting 40% Fill.

1) Why the discrepancy between NEC and Southern and who go believe?

2) How screwed are we? What other problems might there be? The feeders have been pulled and if we have to remove the box, we have to pull them out.

 

[Seven-Delta-FortyOne]

I just did the Calc and the southwire app is saying it’s a violation.

 

[Seven-Delta-FortyOne]

 

[viaPipeline]

I just did the Calc and the southwire app is saying it’s a violation.

Huh. I've done it a few times. Also found another table that references "compact" (which supposedly includes aluminum) conductors that gives 12 instead of 11.

My Southwire app says 4, 350kcmil thhn aluminum conductors and 4 #2 grounds occupy a little over 39% fill

Edit: looks like you have copper

 

[Seven-Delta-FortyOne]

As far as removing the box, when I’ve had to remove a box with conductors, I’ll tie a pull cord to the conductors, pull them out far enough to remove the box, and just let the box hang while I do my thing.

 

[Seven-Delta-FortyOne]

Missed the aluminum part.

 

[Seven-Delta-FortyOne]

Huh. I've done it a few times. Also found another table that references "compact" (which supposedly includes aluminum) conductors that gives 12 instead of 11.

My Southwire app says 4, 350kcmil thhn aluminum conductors and 4 #2 grounds occupy a little over 39% fill

Edit: looks like you have copper

I believe that is the discrepancy.

Some (most?) AL wire is or can be gotten as compact wire. So when AL is entered on the Southwire app, it coincides with the compact wire table in annex C

 

[Tulsa Electrician]

Little more info and we can help.

An example would be change the 2.5' long raceway to 2' and use the nipple rule, 60% fill and no adjustment.

4" EMT@60%=8.852
350 mcm THHN= .5242
8.852/.5242=16.886
16 per nipple.
3-4" nipples.
8*4=32 conductors
So you only need 2- 4" or put 12,12 and 8 in your 3-4" nipples.
Then factor in your proper sized EGC. Which with a couple of terminal bars in each j box should not be an issue with fill.

The EGC may need a change depending on the feeder or feeders OCPD. A one line or clarity on what you have would help.

If a single feeder to the switch board your EGC is undersized.
Qty 8*350 al @250 amps= 2000
Assume 2000 amp OCPD #2cu would be good for 500 amp OCPD.

Since you used term ground (#2) , I assumed EGC for feeder(s).

So move or get larger box and change to nipples.

 

[Tulsa Electrician]

I meant to say you could move or.
Did not want to imply do it.
Sorry.