PDU Buying Guide: How to Choose the Best Server Rack and Data Center PDU

Posted by Robert Faulkner on January 4, 2022

| Categories: Power Distribution Unit

Different lengths and mounting orientations. Varying configurations and features. With so many possible combinations, it can be difficult to choose the best power distribution unit (PDU) for your server rack. That’s why it’s important to evaluate your needs carefully before making a selection. We’ve put together this PDU buying guide to help you choose the optimal PDU for your rack.

Mounting Orientation

PDUs can be mounted horizontally or vertically within the rack or enclosure.

  • Horizontal PDUs are built to fit the standard 19” rack width. They are typically 1U or 2U in height and can be mounted above, below, or between the IT devices in the rack.
  • Vertical PDUs can be much longer, depending on the height of the rack. They are mounted to the upright rails or to dedicated mounting brackets in the 0U space in the back of the enclosure.

Vertical PDUs are often preferred because they have more outlets and don’t take up equipment mounting space. However, horizontal PDUs can be valuable when in-row UPSs are used, the overall power load of the rack is low, or there is insufficient space to mount the PDU in the rear of the cabinet without blocking airflow.

Input and Output Power Requirements

While most office buildings in North America use single-phase power, large commercial buildings and data centers often have three-phase power (single vs. 3-phase power). The type of PDU you buy depends upon the type of power supplied to the racks and cabinets.

You also need to know how much power the equipment in the rack will consume. The maximum power consumption of each device should be printed on a placard on the back of the equipment or in the documentation. The power rating may be listed in volt-amps (VAs) or watts (W). Convert all to a common unit, add them up, and select a PDU with a higher power rating than the total.

In summary, the best PDU for your server rack will sufficiently accommodate your power supply (single or three-phase) as well as the power consumption of each device within the rack.

Type of Plug and Outlets

The PDU plug should match the input power source and the cord should be long enough to reach the power source. Power cords are limited to 15 feet according to UL requirements. Universal PDUs have seven-pin connectors that support multiple types of input power cables, enabling you to use one PDU model across the IT environment and adapt it to the available input power in each facility.

It’s also important to determine the number and type of outlets required for the equipment in the rack. IEC C13 outlets are the most common, but servers and other types of IT equipment may have different types of plugs. It’s a good idea to have a few extra outlets to accommodate future growth — as long as you don’t overload the PDU. Locking outlets prevent accidental disconnects. Check out our blog for more information about PDU power cord types.

Other Features

Basic PDUs simply deliver power to the IT equipment in the rack or cabinet. However, there are also PDUs that provide valuable features that can simplify administration and power management. When choosing the best PDU for your server rack, consider the below configuration options:

  • Metered PDUs display power consumption and other metrics to help you optimize power usage and reduce the risk of overloading.
  • Monitored PDUs connect to the network, allowing you to monitor various metrics remotely and receive alerts.
  • Switched PDUs allow you to turn individual or multiple outlets on and off to power cycle equipment remotely.

7 Questions To Ask When Choosing a PDU

With so many variables to consider, it can be tough to make a decision. Take a look at these 7 questions to ask before selecting a PDU to help guide you into the right configuration for your server rack and data center.

  1. How Many Outlets Does It Have?
    The number of outlets in a vertical PDU depends on its length, which is limited only by the height of the server cabinet. A basic vertical PDU will typically have 40 or more outlets in a staggered configuration. Some PDUs divide the circuit into multiple branches, each with its own fuse or circuit breaker. Alternating phase PDUs distribute power on a per-outlet basis.

  2. Are the Outlets Color-Coded?
    Color-coded outlets and circuit breakers allow easy identification of circuit configuration to reduce the risk of overloading. Traditional PDUs have outlets grouped according to branches. High-density PDUs group alternating phase outlets to reduce cord clutter, simplify load balancing, and allow for more outlets in the same amount of space.

  3. What Is the Footprint of the PDU?
    Although 0U (vertical) PDUs do not take up equipment space, it’s important to consider the footprint of the PDU and its impact on heat dissipation and cable management. Ultra-low-profile designs take up less space, increasing operational efficiency and airflow. This is especially important when multiple PDUs are used to support redundant power supplies.

  4. What Is the Operating Temperature of the PDU?
    Because vertical PDUs are installed in the back of server cabinets, they are subjected to the hot exhaust air from the IT equipment. PDUs with a high-temperature rating reduce the risk of failure.

  5. Does the PDU Provide Metering Capabilities?
    PDUs with metering capabilities reduce the risk of overloading and help data center operators plan for capacity and optimize energy use. Input-metered PDUs monitor circuit breakers and phases in real time. Outlet-metered PDUs also monitor power loads at the outlet level. Network-connected PDUs allow technicians to view this data remotely.

  6. Does the PDU Have Switched Outlets?
    Switched outlets allow technicians to power on, power off, and reboot equipment remotely and sequence the power-up of equipment. Outlet access control helps to prevent the unauthorized use of outlets.

  7. Is It a Universal PDU?
    Universal PDUs feature a seven-pin connector that supports interchangeable input power cables. This allows global organizations to use the same PDUs across their environment, even if data center facilities have different power sources. It also enables data center operators to adapt to changing power requirements.

Enconnex PDUs: Pretty. Darn. Unbeatable.

Enconnex offers a wide range of PDU configurations, features, and options, many of which are readily available for immediate shipping. Enconnex PDUs are manufactured to the highest standards and carry all major certifications, including UL, CE, IEC 62368-1, FCC, NEMKO, and UKCA.

Our team is here to help you select the right PDU not only for your server rack but for your unique use case and environment. Learn why Enconnex PDUs are trusted by some of the largest companies in the world for excellent quality, consistent performance, superb value, and quick delivery. Contact a PDU expert today.


Posted by Robert Faulkner on January 4, 2022

Robert Faulkner is the Vice President of Engineering and Operations at Enconnex. He comes from a strong background in product management with over 20 years in the IT industry. He currently holds an MSME and CDCD certification. He earned his MS degree in Mechanical Engineering at University of Nevada, Reno.

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