I'll bite...20 amps?

I'm not sure I understand your question...what, specifically, is it you need to know?
If you have a 50-amp rig, but you're in a site that has only a 30-amp hookup, you'll need an adapter on your 50-amp cord to reduce it down to 30-amps (and vice versa if you have a 30-amp rig and are in a site with only a 50-amp hookup). In this case, you won't be able to run everything at the same time like you would if your 50-amp rig was hooked into a 50-amp electrical outlet.