Hot tubs can easily become the most complicated of code issues. A lot of this comes from the debate of "what is a hot tub?"
UL can be of little help, as they have several basic listing categories, embracing everythig from individual components to complete assemblies. Plus, several of the most respected names in the business decline to have their products listed.
My simple take? If it comes with a plug, it's an appliance ... and NEC rules pretty much stop at the plug.
