Data Center Voltage

Er, well, the voltage of the supply is nominal, not absolute. A 220V appliance plugged into a 208V supply ought not to know the difference. +/-5% on the voltage of a supply is not at all uncommon.

Probably economics. 220 1Ø, 3 12 ga wires = 2 circuits, 25 amps, 208 3Ø 4 wires = 3 circuits. In the end, it's all 3.5 and 5 volts DC anyhow.

RichH

208/120 VAC implies a three phase power supply. In my limited experience, three phase is intended for devices that need very steady and relatively high current (eg. startup and near-stall conditions for motors) or can't wait for the next cycle (eg. high speed short duration welders). I have zero experience in datacenters, lots with 120V computers and servers. Other than the HVAC system, I wouldn't think a modern datacenter would require three phase (maybe in the old days with reel-reel tape drives and 16" hard or Winchester drives). Single phase wiring and supply transformers are cheaper, so I'm guessing its economics.

The typical distributed power in a data center in the USA is 208/120, 3 phase, 4 wire + ground. Initially data centers 20 years ago required 3 phase power for some of the computing equipment and disk drives. All data center peripherals were set to use 208 3 phase, 208 single phase or 120 single phase. The PDU (Power Distribution Unit) is a glorified transformer with three phase power panels for breakers to mounted to. The power is then routed to the peripheral equipment via seal tight conduit below the raised floor. All circuit were individually sized and receptacles provided to match the supported loads.

Europe on the other hand has 380/220 three phase, 50 Hz. The manufactures of the equipment today have evidently met a happy medium by making computer equipment today fit all possible both USA and abroad.

Todays PDUs are behind the times. With servers in a rack drawing more power per pole of the distribution panel, many panel are improper loaded. Throwing dual corded power supplies into the mix with redundant PDUs within large Data Center sites presents a problem if all circuits are not properly monitored and identified.

I can be further assistance please fee free to contact me.

Pircus has the correct explanation of the original question and if he will allow me to add an addendum to his thoughts:

Typical data centers also have a UPS (Un-interruptable Power Supply) that is designed to supply 208 / 120, 3 phase, 4 wire, to the PDU's. The UPS is "on line" the entire time and in the event of a "brown out" or "black out" from your energy supplier, will let all of your devices attached to the PDU's, stay "on line" until your back up generator comes "up to speed" or until your transfer switch brings up your "back up" circuit.

As part of the UPS system, there is an extensive battery room with a rather large inverter that converts the DC battery power into 3 phase AC power.

Thanks and good luck with your system!

Because the market for 230/400VAC is bigger, it is so simple as that.