A Mathematical Proposition for Implementing 415V PDUs

Annie Paquette
January 20, 2020

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Now that high-density IT equipment is pretty much the standard and the management of double-digit rack loads is more the norm, one would assume that data center managers would embrace higher supply voltages at the rack en masse. Our experience, however, is that adoption of higher voltage three phase PDU(s) at the rack is still lagging behind the curve.

Don’t get me wrong: some data centers are deploying higher voltage 3 phase PDU(s) to feed their computational beasts. Despite the logic for doing so, however, the practice is not as commonplace as one would think.  What the heck?  It occurs to us that once they’re presented with the facts, there may be hope of providing options to these forgotten power distribution units so they can catch up. To that end, we would like to re-present some of that data center math. 

Here’s the deal.  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.

Take as an example 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 3-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?

Let us modestly propose a 240V 30A 3-Phase power distribution scheme for this application.  Here is where 415V units shine.   In mathematical terms, this is 240V x 30A x 3 x .8 = 17.3 kW per power feed.  In this case, increasing the power by increasing voltage but not amperage (240/415V @30A vs. 208V @ 60A) also allows the use of smaller, more pliable inlet cords with smaller connectors at the rack PDU.  And that is on top of using half the number of units.

See what happens once you get all of that power delivered efficiently to the rack?  At Server Technology, we are here to help you distribute all that power. We support 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.

Be efficient and save more money through fewer power transformations by using 415V power. Check out our 415V PDU solutions!


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