js—I agree with your description of the situation. You don’t always want to bite the hand that feeds, but don’t want your firm to be needlessly exposed to unreasonable liabilities.
Sounds like maybe they're invoking some sort of contorted and misinterpreted ‘carnival-ride exemption.’ They may have the idea that, in effect, moving around country keeps themselves at arms length from building or fire inspections. If they are using unmodified lighting assembles interconnected per NEC, then article 410 [ie, showcase/fixture] may likely apply. If they’re using components removed from, or meant to be installed as replacement parts in fixtures, they could possibly work with an NRTL under contracts/agreements/conditions like that of electric sign builders. A ‘hypothetical’ call with the right person in UL or ETL [or ?] may be in order.
they are assuming a liability here...
Well, in a previous lifetime I handled UL listing for a manufacturing company, so I'll take a shot at this.
Manufacturers are not required by the federal govt. to list their products. They do it because the listing will help sell product and will open doors with local juridictions who will not allow un-listed stuff.
The NEC is an installation code and does not apply to manufactured equipment. In other words.....I make whirlpool tubs, my tubs are listed by UL. UL governs the testing and design requirements of the wiring inside my equipment. The only place the NEC will come into play is during installation of the whirlpool.
"If they modify the fixture do they not void the UL warranty/rating and should then be made to aquire an independent testing agency to test and approve and give a '"label" similar to the UL "label"?? "
Yes, the original listing for the fixture is void.
Answer to the second part depends.....is the booth being sold as listed equipment?? If it is then there has to be a file for the configuration and testing that was done. No testing....No listing.
GJ