Originally posted February 22, 2013, Updated July 10, 2018
While the adoption of high density IT equipment and the management of once-unruly double-digit rack loads is more and more commonplace, there is one thing that is not: higher voltages and three phase PDU(s) at the rack. Some data centers are deploying higher voltage power distribution to feed their computational beasts, but despite the mathematical logic, the practice is not as commonplace as one would think.
To that end, we would like to re-present some of that data center math. Why? First, the data shows that far fewer feeds are required to deliver the same amount of power to the rack. Second, IT equipment operates more efficiently using the highest supported voltage available. And as everyone knows, efficient IT equipment is happy IT equipment.
Provisioning for increased power demand using minimal power feeds into the rack requires increased voltage, current, or both. Take an example of a rack with a power requirement for up to 17kW of continuous current redundant power. We can then determine how many power feeds to the rack would be necessary based on the power delivery system parameters (voltage, amperage, and phase).
To understand the balancing act between the number of power feeds and load in our 17kW rack, we can look at the example of 120V single phase power at 30 amps. In this configuration, since 120V x 30A x .8 = 2.88 kW, six (6) separate feeds (17 / 2.88) would be required. Toss in the need for redundant A&B power sources, and you would be looking at 12 feeds per rack. Ouch.
Even if you move up the food chain to a 208 volt three-phase feed at 30A, it would need four separate feeds to accomplish the same goal since 208V x 30A x 1.732 x .8 = 8.64. This would require two per side (17 / 8.64), or four in total. But what if we wanted to get to the same place with half the number of circuits?
The following outlines the two power distribution methods that would provide up to 17kW of continuous current redundant power with full power redundancy at one feed per side:
- 208V, 60A 3-Phase. This is 208V x 60A x 1.732 x .8 = 17.3 kW, per power feed. The math looks like this: Volts x Amps x square root of 3 (due to line-to-line load with 2 of the 3 phases) x 80% maximum safety rating per NEC. This means the load can be fed with two 3-phase power feeds (A & B) to the rack with full redundancy.
- 240V 30A 3-Phase. This is 240V x 30A x 3 x .8 = 17.3 kW per power feed. The math looks like this: Volts x Amps x 3 (due to line-to-neutral load with 2 of the 3 phases) x 80% maximum safety rating per NEC. In this case, increasing the power by increasing voltage but not amperage (240/415V @30A vs. 208V @ 60A) allows the use of smaller, more pliable inlet cords with smaller connectors at the rack PDU.
And what happens once you get all of that power efficiently delivered to the rack? You guessed it. Server Technology is there to help distribute it by supporting your 240/415V power distribution needs through innovative rack PDUs. Take a peek at our BYOPDU tool to see how you can feed the beast at higher voltages.