Cable Tray Sizing Question From Mike Holt's Electrical Exam Prep Book

[blake1008205]

Hello everyone, I'm working through the Electrical Exam Prep Book and have a question about the answers for two of the questions in the prep book about cable tray sizing and can't come to the same answer as they have it for the life of me. They do not specify what type of tray.

Question 1: What is the minimum inside width cable tray needed to accommodate ten 2/0 THWN-2 conductors?
Question 2: What is the minimum inside width cable tray needed to accommodate ten 1/0 THWN-2 conductors?

Their answers are 12in for Q1 and 8in for Q2

 

[Julius Right]

From NEC Art.392.80 Ampacity of Conductors
(A) Ampacity of Cables, Rated 2000 Volts or Less, in Cable Trays
(2) Single-Conductor Cables.
(c)Where single conductors are installed in a single layer in uncovered cable trays, with a maintained space of not less than one cable diameter between individual conductors, the ampacity of l/0 AWG and larger cables shall not exceed the ampacities in Table 310.17 and Table 310.19.
So, you'll get the maximum ampacity.
In this case you have to double the number of cables to 20.
For 1/0 diameter of 0.532" the tray width is 10.64" and for 2/0 diameter 0.578” tray width 11.64".
However, not for solid bottom tray where the ampacity has to be calculated [310.14B]
For cable diameter see Chapter 9 Tables- Table 5 [Continued]