Except... in my last 5er, there was a 50 amp cable & plug in the outside power compartment for shore power. When I plugged into shore power, I had to flip a switch that was on the power distribution panel located inside the trailer to switch the 120 VAC circuits from the built-in generator to the shore power cable. It was clearly marked with "Generator-Shore Power", but I've seen some that weren't well marked. It looked like a common 30 amp circuit breaker otherwise.
On my Winnebago, there was a relay that automagically switched it over for me.
~Sportsman