Optimal conductor choice for cable tray

[rotmgbetter]

Hi.

For a 480/277V 2500 amp service conductors in a cable tray, what would be the optimal cable choice be? For a wye system, seems like 750 MCM-4 conductor MC cables are 3 inches thick and look impossible to install. Are single conductors the correct choice? I'm having trouble finding tray rated single conductor wire but seems like other people are preferentially using them.

What is normally the most economical way to spec this system?

 

[Julius Right]

According to NEC Art 392 for Ladder or Ventilated Trough Cable Trays if the cables are installed as per 392.22(B) then 750 MCM single core cable ampacity shall be 785*0.75=588.75 A
If the load will be 2500 A then 2500/4=625 A then you need 800 MCM.
However, for solid bottom, in my opinion, we have to take ANSI/NEMA WC 51 ICEA P-54-440 AMPACITIES OF CABLES INSTALLED IN CABLE TRAYS. If we take two feet width cable tray and the 750 MCM copper 1.348” cable diameter, according to NEC Chapter 9 Table 5, the depth [according to ANSI/Nema WC51] for 3*4 single-core cables it is 12*1.348^2/24=0.9 and according to table 5.2 ampacity is 653 A. A factor of 1.348/1.22 is to be applied so 721A ampacity it is for 90oC conductor temperature.
However, since the conductor temperature is limited to 75oC, according to NEC ,a 0.86 factor will be applied so, finally, the ampacity is only 620 A.
So, you need 4 x750 mcm copper parallel cables. If the tray width is only 12” you need 1250 mcm for 4 parallel cables.

 

[don_resqcapt19]

Hi.

For a 480/277V 2500 amp service conductors in a cable tray, what would be the optimal cable choice be? For a wye system, seems like 750 MCM-4 conductor MC cables are 3 inches thick and look impossible to install. Are single conductors the correct choice? I'm having trouble finding tray rated single conductor wire but seems like other people are preferentially using them.

What is normally the most economical way to spec this system?

I just looked at the spec sheets for a couple of manufacturers and all of there conductors 1/0 through 750kcmil are listed and marked for use in cable tray. I think that is true for most if not all conductor manufacturers.