Seven Steps to Selecting a Rack PDU for Your Data Center

As organizations constantly strive to improve the reliability and the energy efficiency of their data centers, a lot of attention is now being paid to rack power distribution units (PDU). Among the solutions, selecting the correct rack PDU is challenging. Despite being the fundamental building block of any data center that bridges the gap between the power infrastructure and the IT equipment, rack PDUs are one of the aspects of network design that is often overlooked. There are so many different options out there that it becomes difficult and confusing.  

A wide variety of rack PDU configurations are available based on parameters such as - number of phases, voltage, total amps, branch circuits, number of outlets, socket type, plug type, rack units consumed, and physical dimensions. Beyond the functions of the basic rack PDU, additional capabilities are available in rack PDU categories - Metered, Switched, and Intelligent PDUs.

Furthermore, if you cannot find an off-the-shelf rack PDU that matches your specific requirement, some vendors will assemble or even design a custom rack PDU (also called BTO/ETO: built-to-order/engineered-to-order). Here, we'll discuss seven basic steps you should follow to help you to select and deploy the appropriate rack PDUs for your data center.

New data centers and existing data centers where power needs to be deployed to the rack should follow steps 1-7 in order.

Existing data centers, where power is already deployed to the rack, should follow the same steps in the following order : 4, 2, 1, 3, 5, 6, 7.

1. Check the input voltage

• For India, the input voltage is likely to be 230V single phase, 240/415V three phase

2. Estimate the rack kilowatt budget

• Estimate the total power (kW, kVA) required
• Determine the nameplate power rating of each device and calculate a budgeted power requirement, e.g. the sum of the nameplate values x 70%.
• Should additional power headroom be considered to accommodate future growth or accommodate different devices?

3. Determine the circuits, phase, and amperage for the rack

• Determine the PDU input voltage including the number of phases and amperage. This will determine the rack PDU plug type.
• For a data center where the power is already deployed to the rack, one of the best and easiest ways to determine the required PDU input is to know the receptacle into which the PDU will be plugged.

4. Which devices will be in the rack?

• This will determine the PDU outlet type(s) and the number of outlets required.
• What types of plugs are used on the devices in the rack, e.g. C-14 and C-20

5. Decide if Switching is desired and What Level of Metering is required

• Is remote power control required in order to reboot hung servers or keep outlets off to prevent unauthorized access, ensure proper provisioning, and avoid tripped breakers?
• Is PDU inlet-level metering sufficient, or is the additional detail of outlet-level metering desired?

6. Check the Rack PDU Installation Options

• Determine the form factor that best fits the racks: typical horizontal PDU form factors are 1U (1.75 in., 44 mm) and 2U (3.5 in., 88 mm) high, there are also Zero U vertical PDUs of varying lengths
• Find the power inlet location, i.e. where the power feed should enter the PDU. Consider how the input feed cable routes through the rack and cable bend radius.  Typical cable feed options for rack PDUs are bottom/front, bottom/end, and top/end
• Decide on the proper length of the PDU input power cord
• Consider how the device plugs will be prevented from accidentally unplugging. There are retention clips, specially designed locking outlets or secure lock cables.

7. Advanced features

• Will environmental monitoring be used?
• Will the PDU be connected to the LAN via hardwire Ethernet connections, Wi- Fi, or Gigabit Ethernet? Do PDUs need to be cascaded/daisy chained together to minimize Ethernet drops?
• Are colors desired to indicate different power feeds, e.g. A and B feeds, or different power chains?

Another major factor that one needs to consider is the presence of USB ports on rack PDUs. The USB ports would eliminate the need for copper-based network infrastructure, which is very expensive, by providing both Wi-Fi and cascading capabilities. This creates a smart network of PDUs that one can easily manage remotely and use to monitor power loads and ensure uptime.

Choosing the right in-rack power solutions can save companies thousands of rupees from potential crisis situations like a downtime and lead to improved IT efficiency in data center infrastructure management. Rack PDUs have evolved from just supplying electricity to devices to helping the data centers manage their power chain more effectively. Selecting what type of rack PDU is appropriate for your data center is fairly straightforward--An exercise in matching your data center needs to the capability delivered by the PDU one wishes to use.

The author is regional Director, Asia Pacific, Raritan, APAC

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