What ampacity would be appropriate for three 1/0 AWG THW aluminum conductors in rigid metal conduit at 86 degrees F?

When determining the appropriate ampacity for conductors, it is important to consider several factors, including the type of conductor, its size, the material, the insulation type, the ambient temperature, and the installation method. For three 1/0 AWG THW aluminum conductors in rigid metal conduit at an ambient temperature of 86 degrees Fahrenheit, we refer to the National Electrical Code (NEC) for guidelines on ampacity.

In this case, 1/0 AWG aluminum conductors typically have a base ampacity that might be around 150 amps for a single conductor in free air or a less restrictive environment. However, since these conductors are installed in conduit and subject to ambient temperature and derating factors, we must adjust that number.

When you consider the number of conductors, the NEC indicates that when three conductors are bundled together in raceways or conduits, we would apply a derating factor to account for the heat buildup caused by the current flowing through multiple conductors. This derating generally lowers the ampacity.

After applying the necessary derating factors for three conductors, adjustments due to the insulation type (THW in this case), and the influence of ambient temperature, the ampacity that remains for three