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On the Benefits of Alternating Phase

Posted by RJ Tee on Oct 10, 2017 1:40:56 PM

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Lately, we’ve been extolling the virtues of single phase 60A power distribution to the rack.  But there are still may situations in which a three phase deployment is required to power the needs of racks that consume 12kW or more.  In other words, situations that begin with ‘high’ and end with ‘density.’

The tricky part of three phase power is the accompanying balancing act.

We don’t mean from a financial or breaker panel standpoint, or even being able to walk a tightrope.  Just the simple chore of making sure the phases are equally loaded.  That’s easy enough to say about monolithic deployments of IT gear, but much tougher in real-world applications with multiple device types all cozied up in 42U of space.

To be sure, the issue of equally loaded phases is not just a matter of additional heat load or power inefficiency.  Poorly balanced circuits can overheat and breakers can trip.  And ‘trip’ is not a word we like to hear in the mission-critical world.

Now, here is where it gets interesting.

Server Technology takes a unique approach to the placement of the outlets on the power strip with a method called ‘Alternating Phase.’  Traditional PDUs have the X, Y, and Z phases grouped together:  X,X,X; Y,Y,Y; Z,Z,Z.  In an Alternating Phase configuration, those phases are grouped X,Y,Z; X,Y,Z; X,Y,Z.  Plugging into a different phase is then a matter of inches, not a long power cord run to the bottom of the rack.  To get a visual, take a look at our Technical Note to see pictures of the resulting differences between the two methodologies.

Certainly Alternating Phase outlets are more difficult to wire inside the PDU itself, right?  Server Technology has tackled that problem in a unique way.  Instead of using wiring, we keep the form factor of the PDU small by distributing power via a multi-layer circuit board to each of the phases.  Our patented approach also solves two other potential issues:  heat gain within the rack PDU, and the potential for human error during the manufacturing process.

Don’t take it from me.  Look for yourself at our HDOT Alternating Phase Flyer, or venture over to our Online PDU Building Tool to generate your own unique alternating phase rack PDU.  For help getting started, look at all the available PDU features from Server Technology.

Click to

Topics: 3 Phase power, three phase, load balancing, three phase power

What to consider when choosing a Power Distribution Unit

Posted by Bob Parente on Dec 20, 2012 1:13:00 PM

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Considering Power Distribution Units (PDU) for your data center racks and IT equipment should require much more thought than simply selecting a ‘power-strip’ hardware configuration.  If you care about Green energy initiatives and desire to save on electricity cost by making the most efficient use of the energy you use, make the move to intelligent rack PDUs if you haven’t already done so. This is particularly true for a new data center build and collocations.  If you’re considering a collocation space, choosing the right PDU features will provide additional insight into your true energy use and a tool for capacity planning.  We are now seeing large data center growth with collocation providers that charge clients based on actual energy consumed, kilowatt hour (kWh).  A well thought out data center power distribution implementation will lead to reduced downtime, improved power monitoring management & control capabilities, and drive greater energy efficiency.   The best suited Power Distribution solution requires considerable planning. 

In determining the functional feature requirements for a rack PDU, System Solution Level Questions (1) should be evaluated and the Key Issues need to be considered (2) to help determine how any desired feature(s) is to be implementation.  Once an outline of feature “Must Have’s” and “Strong Wants” has been determined, Selecting the Rack PDU Hardware questions (3) need to be answered to make evident the best suitable Rack PDU Hardware.

  1. System Solution Level Questions (What are you attempting to accomplish?):
  • Will you be monitoring the IT equipment load (using PUE, DCIE, or DCeP rating systems) to measure power efficiency?
  • Are you looking to construct a database of power (kW and kWh) information for power monitoring, power reports and power trending?
  • Would it be beneficial to be able to create “clusters” of outlet data to develop power consumption trend data for groups of devices, racks, rows, types of devices, or facilities?
  • Is it helpful to see current load capacity of a given power circuit for capacity planning & load balancing based on actual IT equipment loads (per phase amperage draw to help minimize wasted energy due to unbalanced 3-Phase loads)?
  • Would it be useful to generate SNMP traps and receive an alert delivered to the desktop or portable device when a pre-defined power and/or environmental threshold have been exceeded at the rack or outlet level? 
  • Would automatic load shedding (turn off pre-determined outlets) upon a pre-defined event be beneficial?
  • Would it be advantageous to use a single IP address per rack for power & environmental monitoring, with management and control to the outlet level? 
  1. Key Issues to be considered:
  • Maintaining Uptime
    • Design in Power Redundancy
    • Real-time Status & Alarm Notifications
  • Greater Equipment Densities
    • Maximizing Cabinet/Rack Space
  • Power Monitoring, Management & Control
    • Secure Network Management
    • Current meters & Load Balancing
    • Temperature & Humidity Sensing
    • Capacity Planning
    • Outlet Control
    • Per Outlet Power Sensing
  • Enterprise Level Monitoring
    • kWh Reports
    • Power / Temperature / Humidity Trends
    • Capacity Planning
    • Inventory & Asset location information
  1. Selecting the Rack PDU Hardware questions:
  • What is the expected maximum power needed to the rack? (How was this number determined, from the PS specification, capacity planning tool, etc.?)
  • What voltage can be supplied to the rack?
  • Does the expected max power include planned power redundancy & growth?
  • Will each rack be designed for power redundancy with a standard A & B Input feed configuration?
  • What types of devices are being connecting in the rack?
  • Single or dual power supply devices?
  • Do you know the Power Factor for the devices within the rack?
  • How many outlets are required?
  • What types of outlets are required? (C19, C13, NEMA 5-20R…)
  • What racks are being used?  (Mounting considerations…)

Topics: -48 VDC, Power Distribution Unit, PDU, data centers, 3 Phase power, power strip, power solution, power management, 380V DC, capacity planning, Server Technology, power measurement

Ask the Engineer - How do I calculate power from 3-phase LED readings?

Posted by Robert Faulkner on Oct 9, 2010 9:29:00 AM

Question from Steven G.: How do I calculate the power usage for devices attached to one of your Smart PDU's by looking at the digital readouts on them? I understand the 3-phase power calculation of P=VA*1.73, but is that done on each leg/phase (x,y,z) for the PDU? An example from a CS-24VY-L30MA is X=4.6, Y=4.6, Z=6.3

Answer: the shortcut way to find the power consumption is (X+Y+Z)*120V = 1860W for your example. This is only accurate when loads are fairly well balanced. It turns out that even though one leg is 37% higher than the other two legs, your example is balanced well enough that the power calculation is only 1.6% overestimated.

The more accurate calculation of 1831W must be found by first calulating the outlet branch amperages (XY, YZ, ZX) through an iterative process using the equations:

X = sqrt([XY]*[XY] + [ZX]*[ZX] + [XY]*[ZX])

Y = sqrt([XY]*[XY] + [YZ]*[YZ] + [XY]*[YZ])

Z = sqrt([YZ]*[YZ] + [ZX]*[ZX] + [YZ]*[ZX])

These are derived from the law of cosines with the assumption that the three legs are mutually 120 degrees apart.

Topics: 3 Phase power

3 Phase Power Distribution

Posted by Bruce Auclair on Apr 26, 2007 8:11:00 PM

Lately, we've been getting quite a few questions from customers, channel partners and just about everyone else on 3 phase power. It seems everyone is searching for an effective solution to deliver power to all of the varying devices in their high density cabinets. Rather than trying to re-invent the wheel, we invite you to explore the following resources, all of which we have found to be extremely helpful in discussing 3 phase power with customers.

3 Phase Basics
Ohm's Law Calculator
Three-Phase Circuits (pdf)

Enjoy and if you have any further questions be sure to post them here!

Topics: high density cabinets, Power Distribution Unit, 3 Phase power, power distribution