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NEC 2017_392.22(B)(1)(b)_What's the smallest width of the Ladder Cable Tray?

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    NEC 2017_392.22(B)(1)(b)_What's the smallest width of the Ladder Cable Tray?

    Hello,

    I have this question, "For a ladder tray; with ten single 500 KCM THHN conductors , ( diameter of .949 from table 5 page 685) what is the smallest width of tray?"
    The answer given is, "12 392.22.B.1.B"

    I determined it to be 10.55" using 90%. ((0.949 x 10) / 90%) but missed using table 392.22(B)(1) because I only referenced 392.20(D) and missed 392.22(B)(1)(b). So I was wrong with a fill in answer, but might have gotten multiple choice.

    Once I looked at the answer, I read the code in 392.22(B)(1)(b) which needs the conductor cross-sectional area, which brings in A=πR².
    That math leads me to 7.85524" using 90% (((3.14*(.949/2)²)*10)/90%)
    Using the table 392.22(B)(1), that leads to 8" width.

    But the answer given was 12". So Why is the answer using diameter but the code requires cross-sectional area?
    What am I missing here?
    Which is the correct way to determine the smallest width for a Ladder Cable Tray?

    Thanks,
    Phil

    #2
    Anyone??

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      #3
      http://www.cooperindustries.com/cont...s/CTManual.pdf

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