What is the ampacity of an 8 AWG THHN cable with 23 other conductors at an ambient temperature of 30°C?

To determine the ampacity of an 8 AWG THHN cable with 23 other conductors at an ambient temperature of 30°C, it is important to understand how the ampacity values are derived and modified based on installation conditions.

THHN (Thermoplastic High Heat-resistant Nylon-coated) wire has a base ampacity that varies depending on several factors, including the number of conductors and the environmental temperature. The National Electrical Code (NEC) provides guidelines on how to adjust the ampacity for more than three conductors in a conduit, which affects the current-carrying capacity.

For an 8 AWG THHN wire in open air, the base ampacity is typically around 55 amperes when considering a single conductor. However, when multiple conductors are installed together (in this case, 23 other conductors), the ampacity must be reduced due to thermal issues that arise from the conductors being bunched together. Specifically, the NEC indicates that if more than three conductors are present, the ampacity must be derated.

In this scenario, applying the appropriate correction factors for the number of conductors, the ampacity adjustments lead us to conclude that the actual ampacity for the 8 AWG