What is the ampacity of three 8 AWG THWN copper conductors installed in EMT at an ambient temperature of 40°C?

To determine the ampacity of three 8 AWG THWN copper conductors installed in EMT (Electrical Metallic Tubing) at an ambient temperature of 40°C, it is important to refer to the National Electrical Code (NEC) tables, particularly Table 310.16 for conductor ampacity.

For 8 AWG copper conductors, under normal conditions at a temperature of 30°C, the base ampacity is typically around 50 amps. However, since the ambient temperature is higher at 40°C, adjustments need to be made according to NEC guidelines.

The NEC provides an adjustment factor for temperature increases. At 40°C, the appropriate adjustment factor is generally 0.82 for conductors rated at 90°C. Thus, calculating the adjusted ampacity involves multiplying the base amperage by this adjustment factor:

• Base Ampacity for 8 AWG THWN at 30°C = 50 A

• Adjustment Factor for 40°C = 0.82

Calculating the adjusted ampacity:

50 A x 0.82 = 41 A

This rounded down leads to a more realistic assessment of the maximum amount of current the conductors can safely carry at a higher temperature. The nearest ampacity value