APPLYING CORRECTION FACTORS
310.14(A)(3), IN AND TABLE 310.15(B)(1)
Conductors routed through ambient temperatures exceeding 86°F are required to be derated according to the correction factors of Table 310.15(B)(1). The ampacity correction factors are also based on the insulation and the size of the conductors utilized.
Tip: A raceway is more than 24 in. (600 mm) in length, otherwise, it is considered a nipple.
Example Problem: What is the ampacity of 4 - 10 AWG THHN copper conductors routed through an ambient temperature of 120°F?
Step 1: Finding amperage of conductors
Table 310.16
10 AWG THHN cu. = 40 A
Step 2: Finding correction factors
Table 310.15(B)(1)
120°F requires a multiplier of 82%
Step 3: Finding amperage
Table 310.15(B)(1)
40 A x 82% = 32.8 A
Solution: The ampacity is limited to 32.8 amps for each conductor.
Remember 240.4(D) small conductor rule.
