I had this exact same problem on my GE microwave. There are two slots where the door latches closed onto the main microwave unit. The lower slot has a little button in there that is supposed to press in/closed when you close the door. If the button is gummed up with residue then the microwave will trip the circuit breaker. Unplug the microwave then clean that button with a Qtip and alcohol and press the button in and out a few times to free it up again. Plug the microwave back in and you should be good to go.