Ambient temperature for the 750 kcmil aluminum conductor problem was 22°C. Which of the following is the correct ampacity for the cited scenario?

• A. 317.00
• B. 323.40
• C. 329.60
• D. 336.80

Answer: (B)

Ampacity is determined from the NEC ampacity tables using a reference ambient temperature (usually 30°C) and the conductor’s insulation rating. If the actual ambient is higher than the reference, you apply a temperature correction factor that lowers the allowable current; if the ambient is lower, no adjustment is needed. Here, the ambient is 22°C, so no correction is required. The tabulated ampacity for a 750 kcmil aluminum conductor (with the standard insulation rating used in this problem) at the reference ambient is 323.40 A, and since the ambient is below 30°C, that value applies directly. Therefore, the correct ampacity is 323.40 A.