What size wire do you use for 300 Amps entrance?

For a 300 Amp service entrance, you typically use a minimum of 250 kcmil (thousand circular mils) copper wire or 350 kcmil aluminum wire, according to the National Electrical Code (NEC). However, the exact wire size can vary based on factors such as the length of the run, ambient temperature, and installation conditions. It's essential to consult local electrical codes and possibly a licensed electrician to ensure compliance and safety.