cable tray

[derick hoffpauir]

I am trying to calculate the cable ampacity of 4 500kcmil 3/c w/g 600v tray cable. I have some questions about section 318 in the 1999 code. Table B-310-3 in Appendix B has the ampacity at 416A, if not less than one cable diameter spacing is maintained. This is fine for new installations, but what about when new cables are added to old tray and the spacing is thrown out the window. What adjustment factors must be used?

 

[rbalex]

Re: cable tray

The first question that must be answered is."Are you permitted to add 4-3/c 500kcmil to the tray in the first place?" Will it exceed the fill permitted by 318-9? The fill limitations are more restrictive than many folks recognize.

If you do meet the fill requirements of 318-9 then determining the ampacity is fairly straight forward from direct application of 318-11.

 

[derick hoffpauir]

Re: cable tray

If I follow 318-9(a)(1), this allows me to put the cables in without spacing, and I can use Table 310-16 for ampacity. If spacing is maintained then 318-11(a)(3) allows the use of Table B-310-3 which has a higher ampacity. Does 318-9(a)(1) mean that everywhere in my facility that has cables stacked in tray and the cables are 4/0 or larger, then I am in violation.

 

[rbalex]

Re: cable tray

Originally posted by derick hoffpauir:
...Does 318-9(a)(1) mean that everywhere in my facility that has cables stacked in tray and the cables are 4/0 or larger, then I am in violation.

Since I don't know what else is in the tray I can't answer directly; however, both 318-9(a) (1) & (3) prohibit stacking where #4/0 and larger conductors are involved.

[ October 05, 2004, 03:10 PM: Message edited by: rbalex ]