Learning about recreational vehicle electrical wiring requires understanding how electricity flows throughout the vehicle. RVs are designed on the chassis of large buses while using the same appliances found in homes. This means that most RVs utilize both a car's 12V system and a home's 120VAC electrical system.
The standard functions found on the 12V side of the RV are the same things found on regular vehicles. This power is derived from a battery found inside the engine bay. It powers the radio, engine, dash accessories and other parts of the powertrain. When this battery is fully charged, most of the appliances inside the RV can be used excluding the microwave, roof air conditioner and some other appliances.
The 120VAC system is used for the more powerful electrical appliances; this is the power that is used for the microwave and roof air conditioner. The 120VAC power source is generally pulled from the outlet provided by the campground itself. However, there are also generators onboard of the RV that use fuel from the gas tank to stay on and power the higher voltage. These generators are designed to shut off when the gas tank reaches a specified minimum in order to avoid running the RV out of gas.