In USA for a data center, power is to be provided at the (unusual for USA) voltage of 416Y/240 at 60 Hz. Circuits will be single phase, probably 20 or 30 amps though I have heard of even 60 amps being used for high density blade systems, supplying a rack cabinet (optionally with a UPS ordinarily intended for 230 volts at 50 Hz, but specified as supporting 240 volts at 60 Hz, too). Some USA equipment makers are already recognizing that a number of data centers in USA are operating equipment with this type of system. PDUs are already made for this system, as well, and have IEC 60320 plugs, inlets, and receptacles. However, all the UPSes I have seen for this are hardwired.
So here's an idea. Instead of wiring the UPS to a junction box, how about wiring a cord and plug to the UPS and plug it into a wall outlet? The question I have is what type of plug and receptacle would be appropriate in USA?
Would the appropriate NEMA plug be (L)6-xxP or (L)7-xxP (for xx amps)? Since 6-xxR is normally expected to have 120 volts relative to ground on both conductors, would it be safe to wire it with a neutral and 240 volts relative to ground? I don't see anything in the code that specifies this (I looked in 2008 edition). What about 7-xxR which is normally 277 volts L-N, where equipment being plugged in could potentially be damaged with the 15% higher voltage should there happen to be a real 277 volt receptacle somewhere?
Other possible options might include: C13 or C19 (from IEC 60320) or one of the alternate national receptacle types (CEE 7/4, AS/NZS 3112, etc), or IEC 60309 types, where acceptably listed versions are available. I've looked for C14 and C20 receptacles in a wall mount form factor, but have yet to see one.
If you had a job to install 20 amp single phase wall receptacles for a bunch of computer rack cabinets, and the particular receptacle type was not specified, although the electrical system type is known to be single phase branches from 416Y/240, what would you install?