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 150 degrees F, it’s essential to reference the National Electrical Code (NEC) guidelines, specifically regarding the ampacity of conductors under certain conditions.

For 3/0 AWG copper conductors, the base ampacity would typically be derived from tables provided in the NEC, which account for factors such as insulation type and ambient temperature. THHN is thermoplastic high-heat-resistant nylon-coated wire, which is rated for higher temperatures. When the temperature is elevated, as in this case at 150 degrees F, derating factors come into play.

The ampacity of copper conductors in conduit is reduced due to the heat generated by multiple conductors. When three conductors are present, the ampacity rating is adjusted according to NEC Table 310.16, then further adjusted for the higher temperature rating of 150 degrees F.

After applying the appropriate derating factors, the calculated ampacity aligns with 131 A. This matches the value derived from NEC guidelines for three 3/0 AWG THHN copper conductors operating in a PVC conduit at the specified elevated temperature.

As a result, the correct answer reflects