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Thread: Free air or not free air

  1. #1
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    Free air or not free air

    We have some existing wire we are evaluating. It is a jacketed cable with 3 pieces of 500kcm
    .It is hanging in building rafters so I guess it is in free air. But I thought free air rating was individual conductors separated from one another so they can vent. Does anyone know the true definition of free air for conductor ampacity

  2. #2
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    If it is a cable Table 310.15(B)(16) applies.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  3. #3
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    I just never seen a clear definition. Do you believe this cause of the header. Or is there anywhere that defines conditions for free air

  4. #4
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    IMO tables that apply to conductors in "free air" would be something hung from insulators and only contact with other items would be at the insulators, or some assemblies that have a messenger wire as part of the assembly. If it is laying on rafters it would need to be in raceways or use a recognized cable method from chapter 3.
    I live for today, I'm just a day behind.

  5. #5
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    Quote Originally Posted by dm9289 View Post
    I just never seen a clear definition. Do you believe this cause of the header. Or is there anywhere that defines conditions for free air
    Yes, the headers of the ampacity tables tell you that a cable is always 310.15(B)(16) and that Table 310.15(B)17 only applies to single conductors.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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