An electrical system puzzle

Harvey51 wrote:

The standard adapters should connect both 50A hots to the single 30A or 20A hot and neutral to neutral. Given that a upstream GFI should not trip.

I don't understand this! Isn't there 240 volts from one hot to the other? Surely connecting them together would trip both circuit breakers.

I would expect the adapter would connect to only one side of the double 50 amp supply. There ought to be a 30 amp breaker in the adapter but it isn't really needed because the RV has one already.

It would be interesting to understand how an adapter causes a GFI to trip.

You're thinking of an adapter working in the opposite direction from what's being described. An adapter to plug a 50A plug into a 30A or 20A supply just connects the two hot leads of the 50A plug to the hot lead of the supply. You no longer have 240V between the two hots (they're on the same leg), which is usually of no consequence in an RV since there typically are not any 240V circuits. The total power you can use is, of course, limited by the supply.

What you're thinking of is an adapter to plug a 30A (or 20A) device into the 50A circuit, and indeed these do only connect to one leg of the 50A split phase service. You're also correct that they should have a fuse or circuit breaker in them for safety, but generally don't. (Usually the makers get around this by putting fine print on the product or packaging that it's only to be used on circuits protected to the lower current rating...presumably knowing full well that this is very rarely what happens in actual use.)