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We have a three-phase online data center UPS.

Someone said recently that if the input amperage across the phases were 70-10-10 we'd pay for the kWh represented by 70 amps, but if the same load were spread out to 30-30-30, we'd pay for kWh corresponding to only 30 amps.

Really?? I can believe that balancing the load across phases puts less stress on the UPS. But does it also reduce the power bill so dramatically?

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2 Answers 2

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I'm not sure how your power is metered, but this is possible (it would be a question for your power company as to how your usage is metered - peak phase, averaged across all 3 legs, or total consumption (each phase metered & summed)).

Regardless of utility costs though, you should speak with an electrician and balance your load across all three phases for the other reason you mentioned - It's kinder to your UPS equipment.
Datacenter grade UPS systems are EXPENSIVE to service/repair, and the maintenance windows almost always require putting the UPS into bypass mode (which means no power protection). Re-balancing your load will reduce heat and other stresses on the UPS system and improve your overall operating efficiency.

Additionally I've found it's easier to plan new build-outs and added capacity if your power load is evenly distributed (design each build-out to balance the new load), or at least arranged according to a design plan that splits it up more than what you seem to have.

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Great points, thanks Mike! It's a new site so the numbers are hypothetical. We'll check wiring of the racks/PDUs/phases so servers can be situated to balance load wherever practical. I agree: how it's metered is the key. Wonder if our NJ utility has resisted the temptation to choose peak phase, perhaps with help from regulators? –  Paul Feb 14 '12 at 20:33

It's possible, since it's less efficient. I know you're run time goes down when you have a unbalanced setup, so it's just as likely IMO that it could draw a bit more power. With that being said, I'm not a power guru.

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