What size conductor is required for a 600V system using a separately derived system?

In a 600V system utilizing a separately derived system, the appropriate conductor size is determined based on the current-carrying capacity required for the application, as well as any applicable codes or regulations, such as the National Electrical Code (NEC).

A 4/0 AWG copper conductor is correct because it typically meets the ampacity requirements for circuits operating at this voltage level when considering factors like temperature and the specific installation conditions. The sizes of conductors are defined to ensure safe and efficient operation, with 4/0 being suitable for higher current applications common in such systems.

When using larger conductors, such as 6/0 AWG, even though they would also be adequate, they may exceed the necessary capacity for most common applications at 600V systems, potentially leading to unnecessary and more expensive installations. The other sizes such as 1 AWG or 2 AWG copper do not offer sufficient ampacity for a 600V system under typical load conditions, and thus would not provide the necessary safety margin or efficiency.