In northwest Ohio
The XO is not bonded to the transformer.
As per the state inspectors.
The secondary panel is considered a new service and the green ground screw is installed. A ground rod is installed at the panel. all ground and neutrals attach to the same neutral bar.
The transformer is grounded from its primary panel with a secondary ground rod installed.
I have had only one inspector that wanted a ground wire added from the secondary panel back to the transformer to tie all the groundes together.
