What is the ambient air temperature upon which the ampacities listed in Table 310.16 are based?

The ampacities listed in Table 310.16 are based on an ambient air temperature of 30°C (86°F). This standard temperature is established to provide a reference point for determining the permissible current-carrying capacity of conductors.

It's important to note that these ampacities can vary based on environmental factors where the conductors are installed. Factors such as higher ambient temperatures, the number of conductors grouped together, and insulation types can affect how much current a conductor can handle safely. Therefore, knowing that the baseline for the ampacity calculations in the code reference is set at 30°C allows electricians and engineers to make informed adjustments when environmental conditions exceed this temperature.

When designing electrical systems, understanding the reference point for ampacity helps ensure safety and compliance with the National Electrical Code (NEC) by allowing professionals to factor in additional considerations when temperatures differ from the baseline.