Example - NEC® Section 392.9(A)(3)
Width selection for cable tray containing 600 volt multiconductor cables, sizes #4/0 AWG and larger (single layer required) and #3/0 AWG and smaller. These two groups of cables must have dedicated areas in the cable tray.
24" Usable Cable Tray Width
9.09"1.93"12.98"
2 | 2 | 2 | 2 | 1 | 1 | 1 |
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Cross Section Of The Cables And The Cable Tray
Cable tray width is obtained as follows:
A - Width required for #4/0 AWG and larger multiconductor cables -
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| (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 |
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| Diameter |
| Diameters (Sd) |
1. | 3/C - #500 kcmil | 2.26 inches | 3 | 6.78 inches |
2. | 3/C - #4/0 AWG | 1.55 inches | 4 | 6.20 inches |
Total cable tray width required for items 1 & 2 = 6.78 inches + 6.20 inches = 12.98 inches
B - Width required for #3/0 AWG and smaller multiconductor cables -
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| (A) |
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| (N) | Multiply (A) x (N) | ||||
Item | List | List Cable | List Number |
| Total of the | ||||||
Number | Cable Sizes | Cross Sectional | of Cables | Cross Sectional Area | |||||||
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| Area |
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| For Each Item | |||
3. | 3/C #12 AWG | 0.17 sq. in. | 20 |
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| 3.40 sq. in. | |||||
4. | 3/C #10 AWG | 0.20 sq. in. | 20 |
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| 4.00 sq. in. | |||||
5. | 3/C #2 AWG | 0.80 sq. in. | 4 |
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| 3.20 sq. in. | |||||
| Total cable tray width required for items 3, 4, & 5 |
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| 6 in. | 1 |
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| 6 in. |
| 1 | ||
(3.40 sq. in. + 4.00 sq. in. + 3.20 sq. in.) ( |
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| ) = 9.09 inches | |||||
7 sq. in. |
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| 7 sq. in. |
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Actual cable tray width is A - Width (12.98 in.) + B - Width (9.09 in.) = 22.07 inches
A 24 inch wide cable tray is required. The 24 inch cable tray has the capacity for additional future cables (1.93 inches or 2.25 sq. inches allowable fill can be used).
Notes:
1.This ratio is the inside width of the cable tray in inches divided by its maximum fill area in sq. inches from Column 1 Table 392.9.
2.The cable sizes used in this example are a random selection.
3.Cables - copper conductors with cross linked polyethylene insulation and a PVC jacket.
4.Total cable weight per foot for this installation.
40.2 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 5 |
Cable Tray Manual | Cooper |
49