When calculating corrected ampacity for a THHN/THWN conductor, which temperature rating is used?

When calculating the corrected ampacity for a THHN/THWN conductor, the temperature rating used is 90°C. This is because THHN (Thermoplastic High Heat-resistant Nylon-coated) and THWN (Thermoplastic Heat and Water-resistant Nylon-coated) conductors are rated for use at a maximum temperature of 90°C when in a wet or dry location.

Using the 90°C rating is important as it allows for a more accurate and higher ampacity value when determining the current-carrying capacity of these conductors, especially in applications where the conductor may be subjected to higher ambient temperatures. This allows for a margin of safety and efficiency in electrical installations.

Understanding the temperature rating is essential for ensuring that the conductors do not overheat, which can lead to insulation failure and potential fire hazards. Thus, utilizing the 90°C rating when calculating corrected ampacity provides an appropriate reference point for safe and effective electrical design.