Just hooked up this afternoon in Yuma, AZ and checked the surge guard mentioned above from Camping World. Mine is hardwired but the same thing.
The power on one leg did not show at all and I had a blinking warning light. Checking the post with a meter I had one good leg and one with 32V. The next site down had similar issues as did the group across the street (no one is in Yuma this time of year!). I found one good box a few sites away and we are good but I sure would have been in for a surprise had I not installed the EMS a year or so back.