Calculations size of wireway

[fc]

Need to calculate the size trough needed for 16-500kcmil (line and load from ATS) 10 foot distance.
376.22 tells me that the sum of the cross sectional area of all contained conductors at any cross section of a wireway shall not exceed 20% of the interior cross-sectional area of the wireway.
My calculations for 16- 500kcmil (.7073 x 16) = 11.30 total if I divide that by 20% I come up with a cross sectional area of 56.60
How do I calculate the cross section of the trough size I would need?

 

[steve66]

I'm probably not understanding the question right, because it seems like you are 99% of the way to your answer.

Since you need a 56.6 sq inch area (lets call it 60" for simplicity), pick a width. Say you pick a 10" width. So you need a 6" height since 6x10=60. Or if you pick a 12" width, you need a 5" height. Is that what you are asking?

Also, are you sure 376 applies, and not cable trays? Have you checked derating to see if it applies (I don't know offhand if it does or not, but (16) 500KCM cables in one tray sounds like a lot.)

Steve

 

[cpal]

additionally if you solve for the square root of the total sq area, you will come up with a dimension of one side of a sq troft.

 

[fc]

Also, are you sure 376 applies, and not cable trays? Have you checked derating to see if it applies (I don't know offhand if it does or not, but (16) 500KCM cables in one tray sounds like a lot.)

Steve

I think a metal trough from ATS to main CB would be Article 376. In the trough is the line and load. There both paralled runs.

 

[ramsy]

Re: 376.22 ..My calculations for 16- 500kcmil (.7073 x 16) = 11.30 total if I divide that by 20% I come up with a cross sectional (wireway) area of 56.60

With your parallel install, I guess your EGC's are part of the 16 total, included as #500's. And, I supose your wireway is above ground, which permits you to avoid wet locations (THWN) class insulation?

 

[iwire]

In the trough is the line and load. There both paralled runs.

fc if this is an Article 700 installation be careful what conductors you 'mix' in the troughs.

I would not even figure this, it would be 12" x 12" wireway, you will need the room to bend the condutors.....assuming you have to exit a side of the wireway.

If you size wireways to NEC minimums make sure you have plenty of band-aids around to patch up your cut hands.


FWIW You will not have to worry about derating at all.

 

[fc]

With your parallel install, I guess your EGC's are part of the 16 total, included as #500's. And, I supose your wireway is above ground, which permits you to avoid wet locations (THWN) class insulation?

EGC are #1/0 copper and I need to add them into the calculation also.
The installation is above ground. I think a 12" x 12" x 10' trough will be above the calculated cross section that it requires.

 

[fc]

fc if this is an Article 700 installation be careful what conductors you 'mix' in the troughs.



If you size wireways to NEC minimums make sure you have plenty of band-aids around to patch up your cut hands.


FWIW You will not have to worry about derating at all.

Thanks---- I will tell my men I will supply the band-aids and may even buy them lunch. (what a guy) lol.
I would love to pitch in on this one but when you reach a certain age the 500's look like they may bite a little. I leave it to the young ones.
The system is for commercial office computer room.

 

[infinity]

I agree with Bob. Sometimes you need to throw away the code minimum size (20%) and go with something that makes the installation practical. I would consider the 12X12 to be a decent size to try and shape in 16-500's.