Code Q&A: Ampacity Adjustment Factors ― Metal Wireways

Q. What ampacity adjustment factors apply to conductors installed in metal wireways?


See the answer below.









This answer is based on the 2017 NEC.

A. When more than 30 current‑carrying conductors are installed in any cross‑sectional area of the wireway, the conductor ampacity, as listed in Table 310.15(B)(16), must be adjusted per Table 310.15(B)(3)(a) [376.22(B)]. Signaling and motor‑control conductors between a motor and its starter used only for starting duty aren’t considered current carrying for conductor ampacity adjustment.


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