Single vs. Three Phase Power Distribution - Know the Difference

RJ Tee
November 17, 2017

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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.  Often the differences between a single phase PDU and a three phase PDU are not as complicated as they may seem, and even more often a 3 phase PDU is the right fit.

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.

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 neutralone. 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.

Take a new look at 3-phase power distribution.  Learn how alternating-phase power on a per-receptacle basis simplifies load balancing and provides greater efficiencies.

To illustrate the difference between single and three-phase power distribution, think of waves crashing onto a beach. Normally a wave crash 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 distribution solutions

Now, imagine there is no time between waves as they crash onto the 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.

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