What is the ampacity of six 8 AWG THW copper conductors installed in EMT when the ambient temperature is 30°C?

To determine the correct ampacity of six 8 AWG THW copper conductors installed in EMT at an ambient temperature of 30°C, it is essential to reference the National Electrical Code (NEC) tables, specifically Table 310.16, which provides ampacity ratings based on wire size, insulation type, and installation conditions.

For 8 AWG copper conductors with THW insulation, the base ampacity at 30°C is about 50 amps (based on standard tables). However, the number of conductors being installed together significantly impacts the overall ampacity due to the adjustments required for multiple conductors in a raceway. When more than three conductors are installed together, derating factors come into play to prevent overheating.

In this case, with six conductors, the NEC requires that the ampacity be derated. According to the NEC, when three to six conductors are bundled together, a derating factor of 70% is applied to the base ampacity. Therefore, the adjusted ampacity would be calculated as follows:

1. Start with the base ampacity for 8 AWG copper THW at 30°C: approximately 50 A.

2. Apply the derating factor: 50 A