Where service-entrance conductors are installed in parallel in two or more raceways or cables, the size of the grounded conductor in each raceway or cable shall be based on the total circular mil area of the parallel ungrounded service-entrance conductors in the raceway or cable, sized in accordance with 250.24(C)(1), but not smaller than _____ AWG.

• A. 1/0
• B. 3/0
• C. 2/0
• D. 4/0

Answer: (A)

When service conductors are paralleled, the grounded (neutral) conductor in each raceway or cable must be sized based on the total circular mil area of the parallel ungrounded conductors, as called out in 250.24(C)(1). This ties the neutral’s capacity to the combined capacity of the live conductors feeding the load, ensuring the neutral can carry the unbalanced current without overheating. In addition, the NEC sets a minimum size for the grounded conductor in such parallel service installations to guarantee adequate current-carrying capacity regardless of the calculated size. For copper conductors, the minimum not smaller than is 1/0 AWG (and for aluminum, the equivalent minimum is 4/0 AWG). Therefore, the smallest acceptable grounded conductor in this scenario is 1/0 AWG copper, which is why that option is the correct minimum.