What is the calculated ampacity for three 8 AWG THHN copper current-carrying conductors in a nonmetallic wire way with six 4 AWG conductors at 35°C?

To determine the calculated ampacity for three 8 AWG THHN copper current-carrying conductors under the given conditions, it is essential to consider both the ampacity rating from the National Electrical Code (NEC) and the effects of having additional conductors in the same conduit or wireway.

For 8 AWG THHN copper conductors, the base ampacity at 30°C is typically around 40 amps, but this can be adjusted based on factors such as temperature and the number of conductors. The temperature correction factor for 35°C would slightly adjust this value. The NEC also specifies a derating factor when multiple conductors are grouped together. Specifically, with a total of nine conductors (three 8 AWG and six 4 AWG), the ampacity for each conductor is derated to avoid overheating due to the lack of airflow between them.

Taking into account these adjustments, the calculated ampacity for three 8 AWG THHN conductors in the specified environment would be about 36.96 amps after applying the necessary derating from the NEC tables. This reflects an appropriate accounting for both the temperature rise and conductor grouping effect, aligning perfectly with answer B. This illustrates a key concept in electrical design