NEC 310.16 Ampacity Chart (60 / 75 / 90°C, Cu & Al)

Which column may you use?

This is NEC Table 310.16, the allowable ampacity of insulated conductors, shown for copper at the 60, 75 and 90 °C insulation ratings and for aluminum at 75 °C. The catch that undersizes more circuits than any other is the termination temperature rule: you may only use the column matching the lowest-rated part of the circuit, which is almost always the terminals on the breaker or device rather than the wire's insulation. Most breakers and receptacles are listed for 60 or 75 °C terminations even when the conductor jacket is rated 90 °C, so the 90 °C column is generally used only as the starting point for derating, never as the final installed ampacity.

The table value is also a ceiling, not the finished number. Ampacity is reduced ("derated") for high ambient temperature and for bundling several current-carrying conductors in one raceway: four to six conductors multiply the value by 0.80, seven to nine by 0.70, and ten to twenty by 0.50. On top of that, the small-conductor rule of NEC 240.4(D) caps 14, 12 and 10 AWG at 15, 20 and 30 A overcurrent devices regardless of the higher table figure.

Let the Ampacity calculator apply the temperature and bundling factors, then protect the conductor with the Breaker / OCPD Size calculator. Values reference the stated NEC edition (2020/2023) — confirm the edition adopted by your authority having jurisdiction.