My trailer come standard with the Progressive Transfer switch that will catch most if not all transients, but does not shut down with over/under voltage. Rather than buying a more featured switch I installed a Hughes Autoformer to deal with under voltage. Most 30Amp campgrounds can have significant voltage of less than 105vac and the autoformer corrects for that. The 50 amp campgrounds don't seam to have that problem. I never seen a campground that has an over-voltage, so felt the autoformer was a better option than upgrading my transfer switch for under/over voltage protection. It is possible, but rare, for 50 amp campgrounds to have the 110Vac jump up to 220vac depending how well the neutral earth bonding is at the pedestal. I have tester to check for that bonding as well as neutral ground reversal before I connect up. Also a few campgrounds cheat on the 50amp by not using 50 amp split phase and tie the 30 amp hot to L1 and L2 of the pedestal box. This generally is not a problem unless your unit actually needs 220vac, and as far as I know only high end motor homes have that requirement. That type of connection could cause 110voltage loss to trailers because that 30 amp campground wiring would not handle load of 50 amp L! and L2 split phase.
