What is the maximum ampacity rating of three 3/0 AWG THHN conductors in a 90°C ambient temperature?

The maximum ampacity rating of conductors is determined based on the conductor size, type, and the ambient temperature in which they are installed. For three 3/0 AWG THHN conductors at an ambient temperature of 90°C, the National Electrical Code (NEC) provides guidelines on their ampacity.

According to NEC tables, specifically Table 310.16, 3/0 AWG THHN conductors can handle 200 amps at 90°C when there are three conductors in a raceway or cable. However, when there are adjustments for the number of conductors, such as derating for more than three conductors, the adjusted maximum ampacity may be higher.

Considering the adjustments necessary for this scenario (if applicable), the normal ampacity for 3/0 THHN conductors indeed can rise. In many standard applications with three conductors, if they are not derated heavily due to installation conditions, the maximum ampacity often noted is around 225 amps when reviewing base ampacity and potential flexibility in applications or considering installed conditions.

Thus, while 250 amps might be the theoretical limit under different configurations or additional considerations, 225 amps is the widely recognized and practical ampacity for three 3/