Powder coating is a great insulator - though not one I'd want to trust my life on entirely. I've done 1000 VAC hipot tests on powder coated aluminum chassis (what's plural for chassis? Chassiseses? Chassi?) where I've clipped the two "aligator clips" directly onto the piece of metal (covered by the powder coat), and had no current flow at 1KV. Thats with the teeth of the clips trying to dig into the paint - amazing stuff. If I were a heavy equipment operator, I'd want every surface I might contact to be coated with the stuff...just in case I'm digging in the wrong spot.
The UL standards I work with (in telecom) do not consider enamel wire to be real insulation when it is being used for a safety function in an AC mains circuit. Enamel can be used, with no other tape insulation, for transformers requiring only functional insulation in applications that have no safety requirement for any insulation at all (such as ethernet transformers), or for basic insulation in telecom circuits, provided each part manufactured is hipot tested (and a few other minor requiremnts are met).
