My first job out of college was for a fabless semiconductor company in Southern California. We had a small (~20 racks) data center in the ground floor of the b

My first job out of college was for a fabless semiconductor company in Southern California. We had a small (~20 racks) data center in the ground floor of the building, and I was involved in its design & operation. Top-level execs had made the decision to not get a backup generator. The one compensation was that we got a manual transfer switch, so that we could easily truck in a generator & cooling in case of a planned outage. There was the possibility that we'd be moving at some point, so self-containinment was a big thing. Taking that into account, I suggested getting an Eaton 9390 UPS, with two IBC-L battery cabinets and an IDC breaker/distribution cabinet. (http://lit.powerware.com/ll_download.asp?file=Eaton9390UPSBrochure9390FXA.pdf http://lit.powerware.com/ll_download.asp?file=Eaton9390UPSBr...) The distribution cabinet outputs went to in-rack Eaton RPMs (http://powerquality.eaton.com/Products-services/Power-Distribution/rpm.asp http://powerquality.eaton.com/Products-services/Power-Distri...), and from there to PDUs. This setup gave us ~45 minutes runtime at normal load, and more if we shut down non-prod. The one time we had an outage (during my tenure there), shutting down non-prod allowed us to ride the outage. I also liked this setup because our only connections to the outside (power-wise) were from the fused disconnect input, and the EPO. In the end, the "single-line drawing" looked like this: Building fused disconnect-->Manual Transfer-->IDC cabinet breakers-->UPS-->IDC cabinet-->Rack-->PDUs Outside Generator Hookup---> Switch (input/bypass) dist. panel RPMs Everything after the Manual Transfer Switch was either internal to the UPS, inside the racks, or in flexible conduit. I loved it so much! Unfortunately, the electrical engineer hasn't seen such a thing before. In the past, the 480/208 transformer was external to the UPS, and this is what the electrical engineer was used to. So, the engineer wrote up plans to run an electrical duct from the UPS, to the Manual Transfer Switch, and then on to the transformer (in other words, back to the UPS). I totally missed this mistake on the plans. It was actually caught by the construction crew, who was laying out the ductwork and realized that something looked weird. In the end, one of the conduits was used, and the other one was just left in place. Luckily our connections from the IDC distribution panel to the RPMs were flexible, because that second conduit got in the way of pretty much everything.