In a raceway containing 30 current-carrying conductors, the ampacity of each conductor is reduced to ___ percent of that for a single conductor?

• A. 80
• B. 70
• C. 45
• D. 50

Answer: (C)

Heat buildup from many current-carrying conductors in the same raceway means each one can carry less current safely. The NEC specifies derating factors depending on how many current-carrying conductors are in the raceway. For 21 to 30 current-carrying conductors, the ampacity is reduced to 45% of what a single conductor would carry. So each conductor’s usable ampacity is 45% of its single-conductor rating. That’s why the correct choice is 45.