When installed in free air, what is the ambient temperature corresponding to the ampacities listed in Table 310.17?

The ampacities listed in Table 310.17 are specifically calculated based on an ambient temperature of 30°C (86°F) when conductors are installed in free air. This temperature is critical as it establishes a baseline for determining the maximum current-carrying capacity of conductors under normal conditions.

Using this reference temperature allows for standardized calculations across different installation scenarios to ensure safety and efficiency in electrical systems. When the ambient temperature is higher or lower than this standard, adjustments to the ampacity ratings are necessary to account for temperature effects on conductor performance. Other options present different ambient temperatures, which do not align with the base reference used in the code. Therefore, understanding the significance of the 30°C reference helps in accurately applying the ampacity values found in the table in practical scenarios.