The basic formular is Power = Current X Voltage (PIE) Therfore ; 7700watts / 240 votls = 32.08 amps If this is in a dwelling you can go to table 210.24 and use #8 wire. Article 240.6(A) allows a 35A circuit breaker. I would then price that out vs. a 30A circuit breaker and my time if I have to go back and replace it.
