This is a maint bypass circuit for a UPS system- the UPS operate at a different voltage than the switchboards and thus has step up/step down transformers. This bypass circuit is also coming from a different switchboard than the primary UPS circuits.
The existing system had a UPS working at switchboard voltage, and all feeders (UPSs 1 & 2, static switch & maint bypass) are 3-phase delta bus duct. UPSs being UPSs, they all derive the neutral on the output, no problem there, and the (new) static switch will run through the transformers, but the maint bypass... when in bypass, the UPSs might as well not exist- I can't very well have delta input to the switch and wye output! At least not in the US. Unless it's legal in some codes to just sink a cable to ground anywhere along the run and call it a neutral. Sounds like that MAY be the case? As I stated in my OP, we always like to take the stricter of the two codes, which means I potentially have a "problem" here if the panel *is* wye with a deta feeder.
Unfortunately, I'm in Virginia and this site is in Italy, so I can't easily verify... I'm trying to get someone local to double-check for me, but having trouble finding someone qualified/availible to do so. And kicking myself for not looking closer when I popped open that critical panel in february to look at the bus tap to the other critical panel. Such a fundamental question, but so easy to miss...
[This message has been edited by SteveFehr (edited 08-09-2006).]
