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I'm a bit new to the power calculations for electricity at a colocation facility. I have 2 HP DL580s that are pretty maxed out and this is what the HP power calculators gave me for each server.

Total System Input Requirement (A) - UPS/PDU Circuit Breaker Selection = 9.2
Total System Peak Inrush Current (A) - UPS/PDU Circuit Breaker Selection = 24

Do I need a >48A circuit or just a single >24A circuit to acomodate both servers? Do Colos normally charge double for an A and B redundant configuration? For example if the quote says a 30 Amp circuit, should I assume that is redundant power or budget for double that?

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I'm assuming you're talking 120v power, since those numbers line up well with the QuickSpecs on those servers. That server does draw 30A on startup, but does so for only 20 milliseconds. Electronics do this normally. Most DC PDUs can handle that kind of highly transient peak. Startup load, spinning all the fans & disks up, will be higher than run load, but that's going to be at or under the 1034 Watt max for that power-supply at 120v.

When budgeting power for servers with redundant power supplies, you have to budget for full load on both power supplies. In case one fails, the other one has to take all the load. So for a dual-powersupply DL580, you'll need two outlets capable of supplying 9.2A of power. Your run load is likely to be lower (possibly much lower) then startup load, but you still need to budget for startup on a single power supply.

You don't say if you've got redundant supplies, or just two servers. You may need four outlets, or just two. Each outlet will need to supply load for the entire server, though. Or, if you have the 4P models, 8 outlets.

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Hello, Thanks for the response. The servers do have redundant PSUs. I have more than just the two servers, but I'm just trying to simplify. I guess the part I'm missing is whether or not I can draw 20 AMPS from each receptacle on the PDU or if the PDU only supports a total of 20 AMPS spread accross all receptacles, so if I have 3 servers at 9.2 AMPS each, I would need either more AMPs or an additional circuit. My quote just says 20 amps 120v. Thanks again for the help. – Ian Nov 30 '10 at 4:57
I'd go with two circuits for redundancy. It's a good idea to have two circuits anyway. One circuit should be able to run both servers, though perhaps not if both start up at the exact same time. Datacenter power is provided over three electrical phases, so get two circuits on different phases. Just in case a phase goes down, your servers should still be able to stay up. – sysadmin1138 Nov 30 '10 at 5:11
If your quote says 20 amps 120v that is one circuit. If you need two for redundancy then you'll need to order a second circuit. Tell them it is a redundant circuit and they should charge you less for the second circuit. The PDU that you have will be 20A for the entire PDU not for each plug on the PDU. – mrdenny Nov 30 '10 at 8:05

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