Sounds like you have a Step-Down Transformer within the premisis, which will be driving the 208Y/120 VAC Equipment (a Separately Derived System, in other words), you will connect all the Grounding and Grounded Conductors + the Grounding Electrode Conductor and Main Bonding Jumper to the XO
Terminal of the Secondary.
At the first Panelboard (actual name for "Sub Panel"), the Grounded Conductor - AKA "Neutral"
will terminate on a Bus, which is Isolated / Insulated from the Panelboard's Enclosure (the "Can").
The EGC (Equipment Grounding Conductor) lands on either a Lug, or a Grounding Bus which is Electrically connected to the metallic enclosure - thereby Bonding the Enclosure.
For the IGC (Isolated Grounding Conductor), setup an additional Isolated / Insulated Bus kit - similar to the one for the System's Grounded Conductor (no Electrical connection at the Panelboard), and land the IGCs for both the Branch Circuits and the IGC "Feeder" from the Transformer, on this Bus.
Since there will be quite a few terminations to the "XO"
point, get a multi Conductor lug (3 or 4 Conductor) to mount on "XO"
, land the Grounded Conductor(s), the Grounding Electrode Conductor and the Main Bonding Jumper to "XO"
Use an additional multi Conductor lug on the Transformer's Enclosure, then land the Main Bonding Jumper, the EGCs and the IGCs to this lug.
Below is a drawing that may help - just "convert" the system to an SDS, instead of a PoCo supplied system.
This Drawing is IG Details #1
, which is located in the Technical Reference Section
Many more items may be found in the same area.