What is the ampacity of each of the nine 8 AWG THHN copper conductors supplying three 3-phase motors in RMC at 30°C?

To determine the ampacity of the 8 AWG THHN copper conductors, it's essential to refer to the National Electrical Code (NEC) table for wire ampacities, specifically focusing on the ratings at a temperature of 30°C.

For 8 AWG copper conductors, the ampacity can vary based on several factors, including the operating temperature and how the conductors are installed (whether they are in conduit, in free air, etc.). At 30°C, THHN copper conductors typically have an ampacity of about 50 A under standard conditions. However, if there are multiple conductors bundled together or installed in a way that heat dissipation is affected (as might be the case with nine conductors supplying three-phase motors), derating may apply.

Derating is necessary to prevent overheating of the conductors when they are carrying current close to their maximum capacity, especially in conditions where heat cannot adequately escape. In this scenario, with nine conductors, the NEC requires a derating factor due to the number of conductors which would lower the ampacity from the nominal value.

Calculating the new ampacity would involve applying the appropriate derating factors to the baseline ampacity of 50 A for an