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One question I have is in planning. One day we received a shipment of about 5 or 6 Intel systems from out Toronto office. We ordered a rack, switch, and a rack KVM. We initially plugged everything in to a wall outlet. ran fine until it tripped a breaker, and the breaker box was not in the computer room, but somewhere else on the floor where we had to call building management. All I knew that the wall outlets were NEMA 5-20. The solution at that time was to take the two 6U monsters and plug them in to separate outlets in the ceiling. This worked for quite a while until my boss brought in a system he had at home (another 4U Intel whitebox). At that time I had a rack power strip, and the power strip popped a breaker, but the wall circuit was fine. I then bought another strip to split the load. before all that I estimated our power usage by adding up the wattage on the power supplies (each was about 700W). Each wall outlet also went to a separate breaker. It was at this point when we were getting the HP ESX box and IT somewhat dictated that we get 2 240V outlets). Right now I am pulling about 15A (7 on one, 8 on the other). But, the critical factor is at takeoff, or when starting all the systems, such as after a power fail. You've got all your systems spinning up drives and fans. This is what we need to plan. So, I would need a rule of thumb that I can take the wattage of each power supply and figure out my maximum amps. Had I performed that calculation initially, I would have had fewer outages. I can't help when a truck, bus, or tree takes out the entire Riverside T station and us :-) On 10/13/2011 12:29 PM, Tom Metro wrote: > Edward Ned Harvey wrote: >> Hold it. P=VI is a DC rule. Power is more complex in AC. >> What's the difference between VA and W? >> >> If you have inefficient power supplies, you might be overpaying 30% >> for power. > You're referring to power factor: > http://en.wikipedia.org/wiki/Power_factor > > The power factor of an AC electric power system is defined as the > ratio of the real power flowing to the load over the apparent power in > the circuit,[1][2] and is a dimensionless number between 0 and 1 > (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf). > [...] > Circuits containing purely resistive [loads] have a power factor of > 1.0. Circuits containing inductive or capacitive elements (electric > motors, solenoid valves, lamp ballasts, and others ) often have a > power factor below 1.0. > > So when PF=1.0, VA==Watts. The better the quality of your power supply, > the closer its PF will be to 1.0. In the last decade it has become > common for name brand computer power supplies to specify a PF as a > selling point. > > See also: > http://en.wikipedia.org/wiki/Switching_regulator#Power_factor > > for discussion of PF with respect to computer power supplies. > > >> When you're talking about 208, you're talking 3-phase. > You can attach single phase loads to a multi-phase supply, as long as > they are balanced: > http://en.wikipedia.org/wiki/Three-phase_electric_power#Single-phase_loads > > >> If you want to use 3-phase 208, you need a special power supply in the >> server. Generally you don't have such a thing... > Old power supplies used to have a 120V/240V mechanical switch. Most > modern switching supplies will work fine with any input voltage from > like 90V up to 250V (check your supply specifications). The ability to > handle a wide input range is a byproduct of the switching regulator design: > > http://en.wikipedia.org/wiki/Switching_regulator > > -Tom > -- Jerry Feldman<gaf at blu.org> Boston Linux and Unix PGP key id:3BC1EB90 PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66 C0AF 7CEA 30FC 3BC1 EB90
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