CSLB C-10 Electrical ContractorWiring Methods and MaterialsHard
A ladder-type cable tray is 18 inches wide and will contain multiple single-conductor Type XHHW cables sized 1000 kcmil, each 1.2 inches in diameter. Per NEC 392.22(A)(1), for single conductors sized 1000 kcmil and larger, the sum of the cable diameters must not exceed the tray width. What is the maximum number of these cables permitted in the tray?
- A21
- B12
- C15
- D18
Show answer & explanationAnswer & explanation
Correct answer: C. 15
The sum of cable diameters cannot exceed the tray width: 18 in ÷ 1.2 in per cable = 15 cables. Any additional cable would cause the total diameter sum to exceed the 18-inch tray width, violating the rule for large single-conductor cables in cable tray.
Why the other options are wrong
- A. 21 cables would far exceed the 18-inch tray width.
- B. 12 cables underutilizes the allowed tray width.
- D. 18 cables would require 21.6 inches of width, exceeding the tray.
Cable Tray Fill for Large Single Conductors
For single-conductor cables 1000 kcmil and larger, NEC 392.22(A)(1) requires the sum of cable diameters not exceed the cable tray width.
- Rule applies to conductors 1000 kcmil and larger
- Sum of diameters ≤ tray width (not area-based)
- Divide tray width by individual cable diameter to find max count
Memory trick: Big cables line up side by side, never wider than the tray.