I was staying at my favorite state park this holiday weekend, and when testing the 30 amp outlet using the plug-n-play circuit tester I made from the directions from the myrv.us site...it indicated that the hot and neutral wires were reversed.
I pulled out the multitester then to verify, and yes it was correct, they were reversed. As the pics show , the normal hot line at the seven o'clock position is reading 0 volts, and the neutral line at the 5 o'clock position is reading 120 volts with both checked with ground.
The 20 amp is also reversed but may just be slaved off the 30 amp outlet.
The 50 amp was good, so I just used an adapter and all was good for the weekend. I told the parks maintenance guy (who is an excellent electrician) and he said they just had some contract electric work done. He was fully aware of the problem this can cause along with ground problems in a rv....and was going to fix it asap. He even told me a story of where one lady had aluminum siding put on her house and they had screwed into a wire (like we hear happening in the rv industry) along with something with her air-conditioner....and she couldn't get back into her house as the door frame was electrified.
He also was fully aware that those rv'ers with EMS , wouldn't be able to connect to a 30 amp outlet with miswired hot/neutral.
Anyhow, this is another good example of testing all outlets, and reading the good information that Mike Sokol has on the "no shock zone.org " site.
No Shock Zone
Here is a link to a great post from Mike that we made a sticky here in the electrical forums. All RV'ers should know this;
I get shocked when touching RV