I think we need to know the specifics; I suspect you have a specific issue you are trying to address.
In the most basic terms, placing a bunch of switchgear and transformers in a box on wheels has the effect of making it all into a single 'appliance.' In certain applications, I can see the AHJ wanting a UL sticker, engineers' stamp, or some such assurance that the various clearance and grounding issues have been properly addressed.
For good or bad, there is a growing bias against any 'home-built' efforts where there is a commercial product available. It's been my practice to research the relevant standards, and be able to demonstrate to all that my assembly almost certainly would pass such an examination.
