Hi Andy,
I think you may have quite a hard time just getting a license issued on the basis of existing U.K. qualifications. If you have a browse through many of the older threads at ECN you'll see that in the States licensing requirements vary considerably from state to state, and even county to county and city to city.
You'll be fine on basic theory of course, but U.S. wiring is sufficiently different to Britain that you'd probably have to take a while to learn the intricacies of the NEC and American wiring before taking any of the exams.
We have a few ECN members in Ohio, so maybe they'll be able to give you some specifics for that state.
The other problem you'll face is getting a work permit and going through all the hassle of dealing with the INS.
