What is the ampacity of each conductor in a 3-conductor (3/C) service-entrance cable assembly using 4 AWG aluminum conductors with 90°C insulation?

To determine the ampacity of each conductor in a 3-conductor service-entrance cable assembly using 4 AWG aluminum conductors with 90°C insulation, it's essential to reference the National Electrical Code (NEC) ampacity tables.

For aluminum conductors, the ampacity ratings are based on the conductor size, insulation type, and installation conditions. According to NEC Table 310.16, a 4 AWG aluminum conductor with 90°C insulation has an ampacity rating of 75 amperes when conditions are normal (such as being in a raceway or in free air under typical environmental conditions).

This rating is a standard value that aligns with the conditions under which conductors are commonly installed. As a 3-conductor assembly typically carries a balanced load, each conductor can safely handle the maximum current indicated by the ampacity rating.

Therefore, the correct answer reflects the appropriate ampacity for a single 4 AWG aluminum conductor with the specified insulation rating, which is 75 A.