Lately, one circuit on my box blows. It covers the microwave and
regular oven. I could
understand it blowing when another heat-using appliance, like toaster
oven or toaster runs at same time as microwave. But now it's blowing
all on its own.

Last time, today, only the micro was being used, to "reduce" a glass
dish of chicken drippings.

Can one circuit go bad all on its own? If so, why? And what should I
do about it.

Any info appreciated.