Our church is wanting to put in some 50 and 30amp outlets for RVs. We have singing groups that bring their large busses and need a hookup so they don't have to run their gens for 2-3 days.

The panels are 208/120 and I need 120/240. Can I use the 208v to operate these outlets or do I need to change it to 240. I understand that many 240v motors have run on 208 for years. What's the best thing to do?

Don't sweat nothing.

The VAST bulk of the true loads are 120VAC...

Only a fraction of the RV load uses two poles: air conditioning in the larger sizes.

So...

Hook up 208Y120 as if it were 240/120 and all will be well.

( No RV uses electric power for hot water at 240VAC, nor do any use electric ranges, etc. )

Heating elements are not a concern anyway. They just heat less.
The AC units are the heavy hitter in an RV.

Maybe a peek at a few RV manufacturer specs would answer the question.

I can say with certainty that I've been to many RV parks that use 120/208 Wye services and distribute from there. I really don't think you'll have any trouble at all.

My friend has a motor coach RV that has an electric cooktop in it that only uses a 120 volt circuit, as does the washer/dryer combo. I'm with Tesla: You probably won't see many 240 volt loads, if at all in an RV.

I have worked on lots of RVs Most all but the very largest (and most expensive) use 120v for everything just divided across 2 ckts a very few use dryers that are 240v and fewer use 240V AC units. Most all rooftop AC units are 120v. I see no problem using 120/208.

If you have a handbook look at 2011 NEC 551.40(A). It basically says that equipment be rated 208-230 to allow for 208Y/120 distribution.

Shane