I recently conducted an inspection on a commercial building with a flat roof with a roof top HVAC system which required an electrical receptacle. The electrician mounted the receptacle on the roof decking in a metal box face up. It was GFCI protected. It did have an X-tra Duty in use cover but it was face up. I can not find anywhere in Section 406 or elsewhere in the code that says you can not do this. Sure there's discussion about counter-tops or work surfaces which
insinuates that this doesn't just mean dwelling units anymore but can they be face up on a rooftop?