Welcome to the forums. It may be an internal breaker, or a poor electrical connection, internal or in the plug/wiring for the trailer.
It could also be that you didn't have enough voltage coming into the coach, and it shut down because of that. Low voltage at the campground is kind of like breathing through a straw, you could probably do it for a while, but try running while still breathing through the straw, you'll probably pass out. Then regain consciousness later. Try hooking your trailer into known 120 volts, turn on the microwave with a cup of water, and let it run a while. check the voltage while it is running, to make sure it is still getting, oh, 108 volts or so. If it is, and doesn't cut off, your trouble was likely the campground.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.