http://rvtravel.com/noshockzone/shockzone2.shtml
Most of us don't plug into 20 amp circuits at rv parks - but we do at homes, etc - so this is the start of learning how to properly check that the outlets are wired correctly. I have a tester exactly like what is in this article - and never could follow the directions, so it's stowed away somewhere. Now I think I'll pull it out - as these were clear and easy to follow.
I don't copy the article as it is copyrighted - remember, you can't post copyrighted articles or pictures without permission - but you can provide links to them!