What is the ampacity of three 8 AWG THHN copper conductors in a nonmetallic wireway at 35°C?

To determine the ampacity of three 8 AWG THHN copper conductors in a nonmetallic wireway at 35°C, it's essential to refer to the National Electrical Code (NEC) and associated tables that provide ampacity ratings based on wire gauge, conductor material, insulation type, and ambient temperature.

For 8 AWG THHN insulation, the normal ampacity at 30°C (as per NEC Table 310.16) is generally around 40 A. However, when calculating ampacity in conditions that differ from standard, you have to consider the temperature adjustment factors.

At 35°C, it's critical to apply the ampacity correction factors to account for the slight increase in ambient temperature. The key is that a temperature adjustment factor generally permits a slight adjustment (in this case, very minor) over the range being considered.

Given that you have three conductors in a wireway, it's also important to note that if they are installed in a manner that doesn't permit heat dissipation (such as bundled too closely or in conduit), this could necessitate further ampacity derating according to NEC guidelines.

Taking into consideration all these factors and the calculation approach, the estimated ampacity leading to the correct answer of