What is the ampacity of three 3/0 AWG THHN copper conductors in PVC conduit at 150 degrees F?

To determine the ampacity of three 3/0 AWG THHN copper conductors in PVC conduit at a temperature of 150 degrees Fahrenheit, it's important to refer to the National Electrical Code (NEC) and applicable ampacity tables.

The ampacity of conductors can vary based on several factors, including the number of conductors, the type of insulation, and the installation conditions. For THHN conductors, the base ampacity listed in NEC tables at a standard temperature (usually 90 degrees Celsius) typically provides a starting point.

When dealing with multiple conductors in a conduit, you often need to apply a derating factor. The NEC specifies that when more than three conductors are installed together in a conduit, the ampacity of each conductor should be reduced to avoid overheating due to mutual heating from adjacent conductors. For three conductors, this factor is considered less significant than for larger quantities, but it still results in a need to reassess the ampacity.

At a higher temperature rating of 150 degrees Fahrenheit, there may be a need to reevaluate based on derating for temperature. The THHN copper conductors have an ampacity that can typically reach about 200 A at an ambient temperature of 30 degrees