3mx3m Non fire rated portable structure(similar to school portables) has been built for a small office. A 25kVA 600-120/208V transformer has been installed on a plywood backboard with a 600V primary disconnect and the secondary 225A, 120/208V panel. This is installed in Ontario Canada.
My first question is
1.Can this type of transformer be installed in this building which will be used as an office
2. Can the transformer be installed on plywood backboard (Does it violate UL approval?). Quick and urgent response is appreciated.

1 yes it must be enclosed on all 6 sides. No open bottom.

2 maybe If the transoformer has wall brackets then yes but the backing wall might be required to be non-combustible. Drywall is combustible so that isn't enough. Steel stud wall and wonder board is non combustible. Some wall hung transformers may be hung on a combustible wall but you need the manufacturers instruction. It is interesting that the transformer cannot be closer than 300 mm to the wall you describe but in many cases you could hang it on the same wall?

I may raise other issue is that the 25 KVA outdoor transfomer as far you are aware with weight of the unit and with portable walls I know some are using the " 2X4 or 2X6 " wall stud the latter may support without issue but the other thing is you may need a local disconnect switch on primary side.

That part you will have to check in your Canada regulations for more details and I know most transformer I mounted they generally recommend on noncombustable walls unless you put in a spacer plate to seperated it somehow { with manufacter instruction } and have it passed it.

Merci,
Marc