Hi Mtrot, I have a modded new Krell 700cx stereo amp, currently, I am useing a 20amp circuit breaker, In the next two or three weeks, I am installing a single pole 30 amp breaker when I install my Furutech GTX-D Gold recepticle, I have a 10awg 3/1 romex cable that is 65 feet or longer I installed my self!, I use the ground in my inside house breaker box, this is code!, a dedicated ground WILL sound better, however, do not do a dedicated ground, your breakers will NOT flip when you have a surge, or ect..., your amp does NOT need a 30 amp breaker!, 20 amp beaker is perfect for your 400cx amp, my info comes from krell them selfs, they want me to use a 30 amp single pole breaker so that my amp will run smoother, less heat, draw more current on demand, my sound stage will sound bigger and taller, and everything else, remember, all this is what krell swears too, they run my amp and the 750mcx amps on a 30 amp breaker thier at the factory, also, Do NOT run anything else on the same breaker-circuit as your amp!, Big no,no!, your amp draws way to much current to do so, I know, I have made that mistake, it was quite funny actually when I attempted to do so, any way, reply back to me when you can if you have questions, cheers.