Hi,
Does the problem occur repeatedly after you reset the breaker? Does the fuse in the amp blow? Often, any device which uses a torroidal transformer in the power supply will have a current inrush that momentarily exceeds the rating of the breaker (I'm assuming the KW500 uses one, though I can't confirm this). Usually, most circuit breakers can handle the momentary current inrush, but as circuit breakers age, they become more finnicky (I wish I knew why). I recently had to replace a 20A breaker in my kitchen circuit, since every time the heating element on the espresso machine cycled, it would blow the breaker. I'd say if the fuse isn't blowing on the amp, or if after resetting the circuit breaker the amp works, then the culprit is most likely the circuit breaker itself. If the fuse is blowing, I'd say there's an issue with the amp, and it must be sent for service. Good luck.
-Richard