I am a little corn-fused here, so please bear with me on these following questions.
[*] Is this a Reverse-Connected Transformer - as in it being a 480 V Delta connection on the "H" side Terminals, and 208Y/120 V on the "X" side Terminals?,
[*] Is the "High Voltage Output" side only to be a 3Ø 3W System, or 4 Wire System?,
[*] Are you bringing a Grounded System Conductor "AKA: Neutral", to the Low Voltage Input side of the Transformer?,
[*] Are you connecting the "Output" side of the Transformer to a Grounding Electrode System?,
[*] What is meant by "HO" - is this an "H" terminal, marked with the Number Zero?
In a nutshell, if this install was using a 480V 3Ø Delta Primary x 208Y/120 3Ø 4W Wye Secondary Isolated Transformer - connected "In Reverse", here's my 2¢:
Feed the Transformer with a 208V 3Ø Circuit (adequately sized), and include an EGC.
Connect the Ungrounded Conductors of the 208V Feeder to the "X1", "X2" and "X3" Terminals only. Do not connect anything to the "X0" Common Terminal - and if there is any jumper from X0 to the Enclosure - remove it.
Connect the EGC from the 208V Feeders to the Transformer's Enclosure/Case.
On the "Now Secondary Side", you have a choice to Ground the new SDS or not. If you do Ground the output, then pick only one "H" Terminal, and physically bond it to a GES, which has been established for that system.
Also bond the Transformer's Enclosure to it.
If you plan not to Ground the system, simply bond the Transformer's enclosure to the new GES (along with all the metallic enclosures + raceways used on that SDS).
Please reply ASAP to this message.