This week we have a post from a guest blogger!

Henry Franc, RCDD OSP, is a Solution Specialist for Belden, responsible for professional support to end-users as well as the professional community. Henry is an active member of various standards development organizations including BICSI, the Telecommunications Industry Association (TIA), and ISO/IEC (through the USTAG). Henry has been involved with standards development and industry best practices for more than 15 years offering professional support on projects in various market segments across the globe. He is sharing his experience with selection criteria of PDUs.

One Size Does Not Fit All

Selecting power distribution units (PDUs) is a lot like buying a new suit. You can simply buy one off the rack at a department store where there might be three or four standard styles in stock, but you will likely not end up with a perfect fit. Or you could hire a tailor to custom make a suit, but you might have to wait a lot longer and ultimately end up spending a lot more for something you might not necessarily need.

As with both PDUs and suits, somewhere in the middle are vendors that offers a wide range of selections in various styles with all the available features you need to consider for a perfect fit. Let’s take a look at what some of those features and considerations for PDUs.

Remember Your Load

Some might think it is ideal to have as many outlets as possible on their PDU, but can you use them all without blowing the circuit? With the adoption of blade servers and virtualization, power within the rack is at an all-time high. Before selecting your PDU, it’s important to calculate the total load of the equipment needing power.

For example, if a simple 42-outlet, three-phase PDU that offers just 4.2 kW of power only allows you to use half of the outlets, what is the point? Take a look at the actual watts of the PDU (Amps X Volts) and compare it to the actual load, allowing a little extra to accommodate changes, growth and redundancy. Vendors with a wide range of PDUs will typically offer several power ratings, ranging from about 2.5 kW to 20 kW.

Advances in Multifiber Connectivity

Cable Management Matters

While cable management is typically a concern when it comes to patch cords and jumpers, it is also a key consideration for PDUs—long power cords can create slack issues and impact airflow. Vertically-mounted PDUs enable the use of shorter power cords while keeping rack units available for equipment.

I’m amazed when data center managers will risk having cable management and airflow issues in a rack filled with hundreds of thousands of dollars worth of equipment by using the longer power cables that come with their equipment instead of buying inexpensive short after-market cables, citing cost as the issue. One of the beauties of using after market cables is that they can also be color coded to improve cable management and ensure redundancy by having separate colors for A-side and B-side PDUs. These after-market cords are inexpensive and color-coding and locking features are available for a small premium.

Monitoring & Management Capabilities

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Monitoring and management capabilities at the receptacle level or phase level are also an option. It is important to know how you plan to monitor or manage the load. For example, if your remote power panels already offer phase-level monitoring, you might not need it in the cabinet. For higher capacity PDU`s (30A+) featuring sub 20A circuits consider PDU`s capable of monitoring circuit level load. On the other hand, if there is a need to calculate power utilization for specific equipment (perhaps for billing), you might need receptacle-level monitoring.

Management capabilities can provide the ability to remotely re-cycle power or shut down specific outlets for security. However, if you’re using a separate third-party management software platform, make sure your PDU management capabilities can be integrated.

Receptacle Types

While C13 and C19 receptacles are typically required for today’s switches and servers, some vendors add standard outlets for convenient plug-in of test equipment or other devices. But having an overabundance of available standard outlets can risk having devices plugged in that shouldn’t be. You certainly don’t want someone plugging in a vacuum cleaner to your PDU.

And don’t forget about locking receptacles that can prevent accidental pull-out of critical equipment plugs, as well as shields to lock out unused receptacles. While Belden’s locking PDUs allow use of standard non-locking cords, some may not.

Click here to check out Belden’s wide range of single- and three-phase rack-mounted and vertical PDUs in various configurations to accommodate a broad range of electrical characteristics, outlet requirements, plug and receptacle styles, and remote monitoring and management.