Example - NEC® Section 392.9(A)(1)
Width selection for cable tray containing 600 volt multiconductor cables, sizes #4/0 AWG and larger only. Cable installation is limited to a single layer. The sum of the cable diameters (Sd) must be equal to or less than the usable cable tray width.
30" Usable Cable Tray Width
29.82" = Equals Cable Sd
3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 2 | 2 | 2 | 1 | 1 | 1 | 1 |
|
|
|
|
Cross Section Of The Cables And The Cable Tray
Cable tray width is obtained as follows:
|
| (D) | (N) | Multiply (D) x (N) |
Item | List | List Cable | List Number | Subtotal of the |
Number | Cable Sizes | Outside | of Cables | Sum of the Cables |
|
| Diameter |
| Diameters (Sd) |
1. | 3/C - #500 kcmil | 2.26 inches | 4 | 9.04 inches |
2. | 3/C - #250 kcmil | 1.76 inches | 3 | 5.28 inches |
3. | 3/C - #4/0 AWG | 1.55 inches | 10 | 15.50 inches |
The sum of the diameters (Sd) of all cables (Add Sds for items 1, 2, & 3.)
9.04inches + 5.28 inches + 15.50 inches = 29.82 inches (Sd) A cable tray with a usable width of 30 inches is required. For
a 10% increase in cost a 36 inch wide cable tray could be purchased which would provide for some future cable additions.
Notes:
1.The cable sizes used in this example are a random selection.
2.Cables - copper conductors with cross linked polyethylene insulation and a PVC jacket. (These cables could be ordered with or without an equipment grounding conductor.)
3.Total cable weight per foot for this installation.
61.4 lbs./ft. (without equipment grounding conductors)
69.9 lbs./ft. (with equipment grounding conductors)
This load can be supported by a load symbol "B" cable tray - 75 lbs./ft.
| Appendix Sheet 3 |
Cable Tray Manual | Cooper |
47
