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What is a PDU vs. a Power Strip?

Posted by Erik Stabile on Mar 6, 2018 11:15:00 AM


Editor's Note: Originally posted Aug 5, 2016 - Updated March 6, 2018

Recently, a customer wondered about the real difference between high-quality power distribution units (PDUs) for the data center, and standard 120V power outlets (like the kind you would find in Home Depot). Why spend the extra money? They both supply power directly to the cabinet, right?

In short, yes—they do. Both the PDU and the power strip, however, are in different classes in terms of what they are capable of providing. Think of it this way: A power outlet is to a power distribution unit like a flip phone is to a smart phone; the former is very basic, while the latter is much more powerful and complex. 

It's okay, we'll break it down for you.

So what is a PDU?

A standard power outlet, in other words, offers 120V of alternating current (AC), seven outlets and, in some cases, surge protection. Conversely, Server Technology’s most basic rack PDU offers up to 230V AC and up to 26 outlets in a slimmer, more compact device that is specifically engineered for use in a high-performance data center. On the other end of the spectrum, Server Technology’s intelligent PDUs can provide up to 42 outlets in a single unit, with up to 415V AC, advanced network cards, power measurement technology, temp and humidity probes, and the list goes on...

Let's see your power strip do that. ;-)

It’s important to note that Server Technology has several different—and highly customizable—products in its PDU family. In addition to the aforementioned basic PDU, there are also metered, smart, switched, smart POPS (Per Outlet Power Sensing) and switched POPS PDUs.

Want to narrow our 12,000+ possible PDU configurations down to a product family?  Learn about our Rack PDU Selection Wizard in this blog.

Here is a look at some of the advanced capabilities of Server Technology’s PDUs:

Remote switching (for switched PDUs and switched POPS): To toggle power on and off with a standard rack mount power strip you need to be standing right next to it. Server Technology’s PDUs enable individual outlet control for remotely switching power on and off. This feature is ideal for large data centers that have hundreds of different cabinets, or those with multiple facilities spread out across the world. Authorized users can use remote switching to control power flows without having to be physically present.  You can read more about Servertech's remote power management solutions here.

Input current monitoring (for metered, smart, switched, smart POPS and switched POPS): The vast majority of power usage in a data center comes from cabinets, where servers run all day and all night, week in and week out. Many servers, for that matter, run even when they are not being used, which wastes electricity and money. (Learn more about zombie servers and what you can do to get rid of them) When using basic power outlets, there is no way to tell how much electricity is being used in each cabinet on a daily basis.  Server Technology’s input current monitoring feature allows managers to see power usage for individual circuits, which is helpful for identifying which devices can be scaled back or eliminated to reduce waste.   

Secure access (for smart, switched, smart POPS and switched POPS): With the ability to monitor input current comes the great responsibility to protect this information from hackers or unauthorized users. Server Technology’s PDUs come with strong access, security and communications controls so that only authorized users can access power usage data and make critical changes to the network.

Greater cable retention (for all PDUs): In a standard power outlet, cables can easily become dislodged, which can lead to unexpected power outages. Server Technology offers server rack power strips that come with lockable, high-retention outlets to ensure that cables stay firmly in place.

Environmental monitoring (for smart, switched, smart POPS and switched POPS): A standard power outlet won’t do much to prevent environmental disasters. Can your data center survive a hurricane with just power strips? That’s because power outlets don’t contain advanced sensors for measuring temperature and humidity levels. Server Technology’s PDUs do contain such sensors, which can transmit critical environmental alerts when cabinets exceed customizable environmental thresholds. This allows managers to prevent equipment from overheating and breaking. What’s more, all of Server Technology PDUs are designed for use in higher temperatures, which means they come with less inherent risk.   

Alternating phase distribution (for 3-phase PDUs): Load balancing is a necessary—also difficult and time-consuming—task that must be performed manually on standard power outlets. Server Technology’s PDUs streamline load balancing with a new, unique method called alternating phase power distribution. The result is a simpler and more efficient process.

Take a new look 3-phase power distribution.  Read the alternating phase executive summary.

Flexible mounting (for all PDUs)
: Standard power outlets rest on the floor, where they get kicked around and abused. Server Technology’s rack mount PDUs are slim and flexible enough to mount directly inside or on top of a cabinet, where they take up less room.

These are just some examples of how Server Technology’s high-quality rack PDUs differ from standard power strips. For more information, click here

Puzzled Picking the Right PDU?  Check Out Our New Rack PDU Buying Guide

Topics: Power Distribution Unit, power strip, Alternating phase, rack PDU, powerstrip, rack mount power strip

What is a PDU?

Posted by RJ Tee on Aug 21, 2017 1:54:50 PM


What is a PDU?

This may seem like a rather existential question, particularly from the blog space of one of the leaders in the marketplace.  So why ask such an obvious question?

Well, because the answer is not entirely clear.  The mission-critical data center world is chock full of acronyms, those pesky, foreshortened forms of communication that allow us to sum up so much in an efficient amount of space.  But when they take on a life of their own, they become like the little monsters in the movie ‘Gremlins.’

I’m dating myself here, but seriously – don’t add water. 


Unlike a UPS, STS, or ATS, all of which are specific electrical components that perform particular functions, the term ‘PDU’ is decidedly unspecific.  Power distribution unit.  Power distribution unit.  Power distribution unit.  Couldn’t those three words apply to any number of devices in an electrical system whose job it is to, uh, distribute power?

And indeed it could – and does.  So the market has abandoned some old phrases and added some new ones to better describe the thing you plug into your rack. 

Remember the term power strip?  Sounds like something you bought at Radio Shack to plug your Tandy computer into, right? Or how about the server rack power strip or the rack mount PDU?  Those were the days. 

Tandy Model 4 Personal Computer

TRS-80 Model 4 - OldComputers.com

Some of the more interesting and newer versions bring the idea of directionality, like the horizontal PDU or the vertical PDU.  Or the approach of adding an acronym to the acronym (0U PDU), or just changing the acronym altogether, like the CDU (cabinet distribution unit).

It would be great if we, as an industry, could settle on a single moniker for that receptacle-laden rectangular bar of power found inside the rack that meters, manages, and brings your IT equipment to life.

But for now we call it a Rack PDU.  We hope you will, too.

Puzzled Picking the Right PDU?  Check Out Our New Rack PDU Buying Guide

Topics: Rack power distribution, Power Distribution Unit, PDU

What to consider when choosing a Power Distribution Unit

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

gameplan resized 600

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 get 120V from a 208V circuit?

Posted by Robert Faulkner on Sep 27, 2010 7:39:00 AM

One of the questions I often get is whether Server Tech has any CDU's that can convert down from 208V to 120V for those handful of legacy devices that "require" 120V.

The quick answer is that no power distribution units include step-down transformation. The questions in return are: First, are you really sure that the devices need 120V? Most devices sold within the last 10 years have full-range (100V-240V) power supplies. Just because the cable has a straight-blade NEMA 5-15P plug, it is not necessarily the case that the device requires 120V. Double check the specs on the device. If the input connector is a C14, there is a strong probability that it is a full-range supply.

Second, consider whether it is really the best choice to continue using legacy equipment. A cost analysis may cause one to find that it is less expensive to buy new devices with full-range supplies than to either run separate 120V circuits or buy a step-down transformer.

Finally, if it turns out that 120V is truly required, various step-down transformers of varying wattage capacity can be found through internet search. Most will be straight 2:1 resulting in 104V, which will still work for most devices. Transformers for 208V:120V are harder to find and typically much more expensive than the 2:1 transformers. Note: Server Tech is vendor agnostic regarding step-down transformers as long as they meet local and national safety standards.


Topics: Power Distribution Unit, data center power, power distribution

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

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