As a licensed, educated, and worn out electrician,(thirty years in the trade, and counting), I'm always amazed at every single internet thread were many passionate folks take the time to give their strong opinion on that which they know little about! It's not worth taking the time to address all the misinformation here. My favorite BTW, is just learning that three phase IS 277V, LOL. I guess all the other variations don't count, eh?
Anyway, back to the subject at hand. The electrician made a series of errors that are common, but inexcusable. First, the required receptacle is an industry standard TT-30. This device has "125v-30A" molded into the face. Ignoring this info. is inexcusable. The second issue is that the terminating clamps on the back of the device are color coded, brass, nickel, and green. This is a universal color code for where to land the hot, neutral and ground, respectively. If it was a straight 220V device, it would not have a neutral screw, just two brass colored ones, and a green ground terminal. Any competent electrician has installed individual circuit conductors thousands of times, following this procedure, as every 15/20 amp. duplex receptacle is marked as such. Third, in order to "stupid-proof" the installation, it is now common to see that the manufacturer has even molded the wire color, or abreviation (I.E. "White" or a capital "W") at the entrance to the terminating clamps. Bottom line is that the electrician made an assumption, and then proceeded to ignore a lot of visual clues that should of caused him to question his assumption. The responsibility for the error, and subsequent damage, lies solely with the professional tradesmen in this case, the RV owner is competely fault free, even if he gave the electrician incorrect info.
This would be no different that the theoretical example of me getting a service call to install a new circuit to feed a microwave in a residential kitchen. The customer states that it is a 220V installation, which raises a red flag. I'm going to do some research when I get to the job. Including inspecting the appliance to read the nameplate, see it if is cord connected, and reviewing the cord end configuration. The reason to do this investigation is that I never have encounted a 220V version of this appliance in a home, and I want to confirm the facts, not assume or rely on the customer's information, before I start. It was the OP's electrician's duty to do the same.
