On Tue, Feb 28, 2012 at 4:01 PM, Tracy Reed <[email protected]> wrote:
> I'm not sure how the datacenter's power distribution system > works but they currently have to run me 4 20A per rack. Coudldn't they cut > that > approximately in half (power factor correction etc, as mentioned earlier) > if I > ran 208v? > Yeah, that was the biggest win for me going to 208v. With 2-3 120v (20A) per rack I couldn't fill a rack because I would run out of power, especially if you want power circuit redundancy*. With 2 208v circuits there was power to fill the rack (actually enough to reach the max per-rack cooling capacity of the data center). * Remember, if you have redundant power supplies and also want redundant circuits or PDUs you can't max out your circuits. If a machine consumes 2 amps in total, with dual power supplies it will pull 1 amp per PSU. When one PSU fails it will pull the full 2 amps from remaining PSU. If you have 13 machines and 2 20A circuits, and each machine has a PSU connected to each circuit/PDU, if one PDU or circuit fails it will try to pull 26A from the one remaining 20A circuit (which won't work). Having more than 2 circuits, and balancing the power cables in a round-robin fashion is a way to reduce the overhead needed to withstand a single circuit failure. -Anton
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