'806 â€” It's duck soup. Get a 480∆-240∆ dry-type transformer...15kVA and up are fairly common.
If you don't mind a 2MB pdf, see page 21 at http://www.federalpacific.com/literature/drytrans/FPTS-RTB-0701.pdf
Suggest getting a transformer with both FCAN and FCBN tapsâ€”they work in the opposite direction for a reverse-fed arrangement. For sensitive electronics, electrostatically shielded units are suggested. If heat is an issueâ€¦pick an 80Â°C-rise transformer on page 27.
For reverse-fed operation DO NOT connect the 240V-side X4 terminal to anything.
Overcurrent protection of 480V windings on a ∆-∆ transformer can be by the usual 125% rating on [only] the 240V source. No system grounding is required by NEC for the 480V side.
If you like, contact me off-board for figuring the kVA-rating, breaker/fuse and conductor sizes needed.