Hi, again...I'm not very well-versed on the etiquette of the Mike Holt Forum. I just send a question and look for an answer. We do mostly industrial consulting for electrical/process/HVAC/structural design.
As I said before, the associated wiring with MG sets is covered in the applicable articles of the NEC (if the facility falls under it). The MG's themself would be under NEMA,UL, and the like.