The switchboard is a single voltage- 208V L-L delta / 120V L-G wye. The Neutral (center of the star, at 0V reference to ground) is grounded in the switchboard for sure. There are no transformers in series with the maint bypass I'm talking about- it's straight through to the maint bypass switch, and from there to the critical panel.

The UPS comes off of another switchboard (also 208/120V) but the voltage has to be stepped up to 400V because nobody makes a 208V 50Hz UPS in this size.

Could the ground bus from the switchboard be a combined ground/neutral? Does European code allow using a combined ground/neutral?

UPS inverters are fed from switchboard A, and static bypass and maint bypass are from SWBD B. The switchboards can be bus tied together, but normally aren't.
Quote
Code
   SWBD A               SWBD B
-------------       ---------------- 
  |     |               |    |
 xfmr  xfmr           xfmr   |
  |     |               |    |
 UPS   UPS--------------+    |  <- Delta
  |     |                    |
  +^-+-^+                    |
     |                       |
    xfmr                     |
     |                       |
     +-----^------+-----^----+  <- maint bypass switch
                  |
                  |
                 PNL            <- wye?

[This message has been edited by SteveFehr (edited 08-10-2006).]