Example - NEC® Section 392.9(A)(2)
Width selection for cable tray containing 600 volt multiconductor cables, sizes #3/0 AWG and smaller. Cable tray allowable fill areas are listed in Column 1 of Table 392.9.
30" Usable Cable Tray Width
Cross Section Of The Cables And The Cable Tray
Cable tray width is obtained as follows:
|
| (A) | (N) | Multiply (A) x (N) |
Item | List | List Cable | List | Total of the |
Number | Cable Sizes | Cross Sectional | Number | Cross Sectional |
|
| Areas | of Cables | Area for Each Item |
1. | 3/C #12 AWG | 0.17 sq. in. | 20 | 3.40 sq. in. |
2. | 4/C #12 AWG | 0.19 sq. in. | 16 | 3.04 sq. in. |
3. | 3/C #6 AWG | 0.43 sq. in. | 14 | 6.02 sq. in. |
4. | 3/C #2 AWG | 0.80 sq. in. | 20 | 16.00 sq. in. |
Method 1.
The sum of the total areas for items 1, 2, 3, & 4:
3.40 sq. in. + 3.04 sq. in. + 6.02 sq. in. + 16.00 sq. in. = 28.46 sq. inches
From Table 392.9 Column 1 a 30 inch wide tray with an allowable fill area of 35 sq. in. must be used. The 30 inch cable tray has the capacity for additional future cables (6.54 sq. in. additional allowable fill area can be used.)
Method 2.
The sum of the total areas for items 1, 2, 3, & 4 multiplied by
( | 6 in. |
| ) = cable tray width required | |
7 sq. in. |
| |||
|
|
|
| |
3.40 sq. in. + 3.04 sq. in. + 6.02 sq. in. + 16.00 sq. in. = 28 46 sq. in. | ||||
( | 28.46 sq. in. x 6 in. | ) = 24.39 inch cable tray width required | ||
| ||||
| 7 sq. in. | |||
Use a 30 inch wide cable tray.
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.
31.9 lbs./ft. (Cables in this example do not contain equipment grounding conductors.) This load can be supported by a load symbol "A" cable tray - 50 lbs./ft.
| Appendix Sheet 4 |
Cooper | Cable Tray Manual |
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