We are getting well off topic, but there is no such thing as a 110/240 main that has a phase angle of 120°.
AC Power in the US (and most of the rest of the world) is distributed as a 3 phase Delta, that is 3 legs tied end to end with no neutral and a phase angle of 120°. This is one of the most efficient methods of distribution power on the fewest number of wires. Look at the output of most large power plants & you will see high tension towers with groups of 3 wires (usually with an additional ground wire on top). Since the distribution is at a high voltage, a transformer is necessary to bring the voltage down to standard levels. Generally, there are a number of transformers between the power plant generator & the end user. Voltage is stepped up for distribution, down a bit for local distribution, then down to user levels at the transformers on poles or in transformer rooms in commercial sites. Transformers are quite efficient - typically over 95% and the gain from dropping the current by raising the voltage to lower resistance losses in the wiring more than makes up for the transformer losses.
In a factory or commercial building, 3 phase may well be used throughout the facility because it allows less expensive & more efficient motors. Typically, a 3 phase Delta is converted in a section of the building's the step down transformer to a 3 phase Wye to provide 120v. Since the "Y" has each leg out of phase by 120°s, and the center of the "Y" is grounded & used as a neutral, the difference between each hot is 208V rather than 240v. If the building only needs a small amount of 120V power, the transformer may be wired to produce a 120v/240v single phase service from one of the Delta windings.
Although a campground could be wired as a 3 phase Wye, I've never seen one, and it would be annoying to anyone that had 240v appliances in their RV since they would be operating at a reduced voltage. I had this problem with 240v clothes dryers installed in a commercial building - they took much longer to dry clothes running on 208V.
More typical is to take the main transformer feeding the campground (assuming it is a 3 phase Delta) and pull off three individual 240V windings, one on each phase, each center tapped. This provides three separate 1 phase feeds @ 120v/240v. These single phase feeds are distributed throughout the campground. In a large campground, there may be individual transformers scattered throughout the sites that are feed high voltage, either as a Delta or a single phase,; each transformer providing 120v/240v single phase to local sections of the campground.
A diagram that shows the difference between Deltas & Wyes is at
Delta / Wye Diagrams
Linear Mode
