Interesting only because a couple years back I had purchased one of those Voltage/Polarity plug in testers(the common RV one with the alarm). So here I was at an older campsite, 30 amp power and my Polarity Alarm goes off. Before I panic, I go out to the pedestal and use my rather large homemade pedestal checker...it also shows a polarity problem. Ummm...so I call the Ranger, they send someone over to check the pedestal. Of course they have fewer tools than I do but he relates how the pedestals are piggybacked.
Rather than drawing this out any further, just as soon as a suspect Motorhome left a site two away from me, as soon as he unplugged, the polarity problem went away. The next person who pulled into that site, plugged in and still we had recurring no issue.
Now I'm sure someone here can explain why another person's RV would interfere with the piggybacked pedestals on the entire circuit? I checked other pedestals in our row of sites and only the ones linked to the suspect RV, including me, had the problem, other ones didn't.
I couldn't explain it....
Don't punish me too hard for going off on a tangent, my apologies to the OP!