i think if you look at appendix B you will understand the connections better. page 373 of the 20th edition. see where it says source (line side)? imagine that a transformer has been installed along the vertical dotted line at the right side of source between source and service/distribution. on the service/secondary side the neutral is still connected to the transformer XO and from the XO there is a groundING conductor connected back to the main service groundING conductor. thus there is an effective connection to ground thru the ground electrode at the main.
Mikesh i think you might be mistaken about the neutral being needed. if the application is to supply 120/208v to building B all you need is the three phases to transform from 600 down to 208. a connection to the XO derives the 120v. the XO is connected to the system ground thus creating the 120v required. if there is a need for 347v in building B yes a neutral will need to extended from building A.
