Cable tray and 392.80 calcs waste of time

[dm9289]

I was going thru some calculations on cable tray ampacity and got kicked back and forth in code.

My feeling on waste of time anyone who has worked in a factory knows if there is a tray there it will get filled, so in my practical opinion all the info about special spacing to gain ampacity is likely to be ignored, such as 2.15 x diameter of cable spacing in a triangular fashion or multi conductor cables not stacked and 1 cable distance in between.

Enough of my whining and getting to what I think the math is from 392.80(A)(2)(b) assume 75C cable singles
310.15(B)(16) 310.15(B)(17) x 65% for tray

1/0 150a 230x.65= 149.5
2/0 175a 265x.65=172.5
3/0 200a 310x.65=201.5
4/0 230a 360x.65=234
250 255a 405x.65=263.2

It really seemed to kick me around and redirect for little or no gain.
Did i do the calcs wrong?

 

[Tulsa Electrician]

I would look at this way. use 90c @ 65%310.15- b-17 then look at 90c 310.15b-16. for adjustment than use 75c termination if applicable.

1/0 @90 c (17) 260 x .65=169
1/0 @ 90 c (16) =170
and so on.

 

[dm9289]

I would look at this way. use 90c @ 65%310.15- b-17 then look at 90c 310.15b-16. for adjustment than use 75c termination if applicable.

1/0 @90 c (17) 260 x .65=169
1/0 @ 90 c (16) =170
and so on.

yes so little to no difference the length and calculations in code to just get back to an answer that is very close to using 310.15(B)(16) seems a bit much