A 100-foot, 480-volt industrial circuit has an established required conductor ampacity of 100 amperes. Use copper THWN-2 conductors in a raceway, not more than three current-carrying conductors, 30°C ambient and the specified 75°C termination ampacity limit. No correction or adjustment applies, and the separate voltage-drop check is satisfied. Under 2026 NEC Table 310.16, what is the smallest conductor meeting this ampacity requirement?

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why C is correct

At 75°C, 4 AWG copper is rated 85 A and fails; 3 AWG is rated 100 A and meets the requirement. The 100-foot run does not by itself make 250 kcmil the minimum: voltage drop must be evaluated separately, as stated here. The stated required ampacity and conditions govern this selection; they are not universal wire sizes for every circuit in that location. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, first printing January 2026, public sample pages 370–379, especially Table 310.16 on page 379. https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf