What is the ampacity of an 8 AWG THHN conductor when installed with 23 other conductors in a metal wire way at an ambient temperature of 30°C?

To determine the ampacity of an 8 AWG THHN conductor when installed among 23 other conductors, it is important to start by considering the standard ampacity values for a single conductor. Under normal conditions and at an ambient temperature of 30°C, the nominal ampacity for an 8 AWG THHN conductor is typically around 60 amps. However, when multiple conductors are present, the ampacity must be adjusted due to the heat generated by each conductor and how this affects the others in close proximity.

The National Electrical Code (NEC) mandates that when conductors are grouped together, adjustments need to be made to ensure they do not overheat. Specifically, with 24 conductors (the single one plus the 23 others), the ampacity must be derated. The typical derating factor for this scenario is approximately 80%. Applying this factor:

1. Start with the base ampacity: 60 A for the 8 AWG THHN.

2. Apply the 80% derating factor: 60 A x 0.80 = 48 A.

Since this rounded value is significant but below a practical threshold, installers often round it to the next standard value indicated in code or tables about