Whats the duty cycle on your machine? If its 20 percent or less you may have overloaded it. Duty cycles are based on 10 minute increments, so if your machine is rated at 20 percent, you can only weld constantly for 2 minutes before the internal breaker kicks causing your circuit breaker to also fail. Have you tried it since this happened? If it works fine now that is probably the case. If not, then something internal.