For NEC Table 310-17, what is the definition of "free air"? A major manufacturer of motor control equipment has sized conductors to motor starters inside enclosures (such as a Hoffman NEMA 4 enclosure) based upon Table 310-17, ampacities in free air. I have always used this table for overhead conductors, such as festooning or other article 225 applications, not for wiring inside of an enclosure. The difference in ampacities is tremendous. For 75C wire, 350kcmil has an ampacity of 310A in a raceway (Table 310-16) and 505A in free air (Table 310-17). Is Table 310-17 the correct table for conductors in an enclosure?
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