What ambient temperature are the ampacities of Tables 310.18 and 310.19 based on?

The ampacities listed in Tables 310.18 and 310.19 are based on an ambient temperature of 30°C. This standard temperature is essential for ensuring consistent standards for electrical wiring installations. When calculating ampacity, the ambient temperature affects how much electrical current a conductor can safely carry without overheating.

If the temperature is higher than 30°C, adjustments must be made to account for the increased thermal stress on the conductors. Therefore, if the ampacities given in these tables are referenced, it is important to understand that they assume an ambient temperature of 30°C. To use these tables correctly in different temperature conditions, one would need to apply correction factors as specified in the National Electrical Code.