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Single vs. Three Phase Power Distribution - Know the Difference

Posted by RJ Tee on Nov 17, 2017 10:59:00 AM


Originially Posted Jan 30, 2017 - Updated Nov 17, 2017

Electricity is the single most important resource in a data center, as it’s needed for powering every system — from the servers on the floor to the lights overhead.

At the same time, electricity is incredibly expensive, dangerous and easy to mismanage — especially when considering the sheer volume of power that is typically used. Some facilities, after all, use enough electricity to power hundreds of thousands of homes. Even though energy efficiency is now top of mind for data center administrators, there’s no getting around the fact that data centers consume a great deal of power. As such, it’s vital to have the correct underlying power distribution system in place before moving in and setting up any equipment.

Many customers, however, are still asking whether they should use single or three-phase rack mount PDUs in their data centers. This article will explore the basic differences between the two systems.

single vs three phase power wavelengths

What makes these systems different?

Single-phase power systems distribute up to 120V of alternating current. This current is distributed over two wires: A single, active conductor and a neutral one. The current changes size and direction at regular intervals. Single-phase wires are usually grounded at the switchboard.  

These systems are mostly used in residential settings that have small workloads. They are rarely used in data centers today, as the majority of cabinets are too dense and require more electricity than single-phase systems can provide. And this is where three-phase systems come into play.

What makes three-phase power distribution the better choice for data centers?

Three-phase power systems are comprised of three alternating currents, each varying in phase by 120 degrees.

To illustrate the difference between single and three-phase power distribution, think of waves crashing onto a beach. Normally a wave crashes, recedes back into the ocean and then a few seconds later another wave follows. This is like a single-phase alternating current.

Read more about single-phase rack mount power distrubtion solutions

Now, imagine there is no time between waves as they crash onto shore. As soon as one wave hits, another is there to follow, and then another. This is what three-phase alternating current looks like. The power flow never ebbs; it always flows. It’s the difference between using a single 120V alternating current for power, versus one that combines a 208V circuit with three more 120V circuits.

So, if someone is recommending single-phase power distribution for your data center, make sure you get a second opinion from a certified power expert. If you are operating a large data center that is carrying heavy workloads, you should strongly consider using a three-phase power distribution system.

Server Technology offers a variety of solutions that support three-phase electricity systems, as well as the Sentry Power Manager (SPM), a centralized data center power monitoring and management platform. 

To learn more about Server Technology, click here.

New Application Note Learn about the benefits of the HDOT® single-phase solution

Topics: three phase, single phase, three phase power


Posted by RJ Tee on Sep 26, 2017 3:44:35 PM


How do you balance the electrical needs of a cabinet of equipment with available technology?  Many data center facilities have come to rely on a standard rack PDU configuration fed by 3-phase, 30A circuits running at 208V.  This setup can yield approximately 8 kW to feed your power-hungry IT gear.

Not bad.  But the problem is that you’ll go through pole positions faster than freshmen through tater tots in a high school cafeteria.

Although the 30A 3-phase approach is deployable and commonly used, the reality is that it is not the most efficient approach in the world of breaker panel resources.  To optimize your build, there is an alternate approach using higher ampacity and yielding more power out of fewer breakers.  We’re talking about 1-phase PDUs at 60A.

Wait, what?

Yes, Server Technology offers a 60 amp single-phase PDU that also runs at 208V.  This configuration is available in HDOT, or high-density outlet technology, which allows the user to take advantage of the power gains by specifying up to 54 outlets in a single intelligent PDU.

So, what about power?  The 1ph 60A approach is a 10kW PDU, which provides 20% more power and current flow than the 3-phase 30A that only yielded 8kW. 

And breaker utilization?  Here is where things get even more interesting.  Instead of taking the three breakers required per circuit in the 30A configuration, a 60A feed requires only 2 poles to get the job done.  So in a typical redundant feed with two PDUs per rack, that is 4 poles on the 60A side versus the 6 required at 30A — a panel space savings of 2 poles per rack. 

In other words, for every rack deployed at 60A you save one rack PDU worth of power.  And a whole lot of ketchup.

Server Technology is your power strategy expert.  You can configure your own 60A solution and see the savings for yourself at BYOPDU, or see more about Switched and Smart power distribution options.

New Application Note Learn about the benefits of the HDOT® single-phase solution


Topics: single phase, single phase power

The Secret to Safe, Affordable Three Phase Power Distribution

Posted by Travis Irons on Aug 21, 2014 8:44:00 AM

landing page image   altphase 01

Up until now, you were able to power your servers and applications using a 30A single phase, 208V power distribution unit (PDU) that contained two 20A circuit breakers. This power cord feeding this PDU contained two power wires and a ground wire. In order to properly distribute 30A of power without overloading any branch, you needed two 20A branches with an equal quantity of outlets per branch.

But now, you are investing in denser applications that require more power. To achieve this power density, you are considering upgrading your cabinet power feeds to three-phase distribution and 60A service. Doing so will increase your power availability from 5kW to 17.2 kW, but it will also require tripling the number of branches in your PDU from two to six.  

When utilizing a three-phase six branch PDU, balancing your loads evenly across the six branches is very important so as not to overload a single branch. In addition, as outlined in a recent Server Technology white paper, equally loading all three phases in the data center will result in the highest power usage efficiency, minimizing heat in your cable runs, as well decreasing the likelihood of tripping an upstream circuit breaker.

Traditional PDU’s have branches bunched together in groups along the length of the device, requiring a multitude of different cable lengths from the PDU to the equipment to achieve balanced loads.  This scenario typically results in a large amount of cable in the back of the cabinet which subsequently inhibits air flow increasing heat, and shortening equipment life.

You can overcome these challenges by using an alternating phase PDU from Server Technology.  In alternating phase PDU’s, the six branches are distributed on an outlet by outlet basis instead of grouped together in six discreet zones.  This results in shorter power cords between the rack equipment and PDU, resulting in a cleaner cable structure and maximum air flow.  Assembly also becomes faster and easier, as the installer typically just needs to connect the equipment to the nearest outlet, and the branches inherently balance.  

Are you ready to increase your power flow, safely, efficiently and affordably? Click here to view Server Technology’s complete line of alternating phase PDUs.

Topics: power density, PDU, Server Technology, power usage efficiency, 30A, Alternating phase, single phase

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