What is a power distribution unit in a data center, and what are the different types of PDUs you might encounter?

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A power distribution unit, or PDU, is a device that distributes electrical power to the equipment within a server rack. Think of it as a specialized, enterprise-grade power strip designed for data center use. PDUs receive power from the facility's electrical infrastructure and break it down into individual outlets that connect to servers, switches, storage arrays, and other rack-mounted equipment.

In a typical data center rack, you will find at least two PDUs, one connected to the A power feed and the other to the B power feed. This dual-PDU configuration provides redundancy so that if one power path fails, the equipment continues to receive power from the other. Servers with redundant power supplies are cabled so that one power supply connects to PDU A and the other to PDU B.

There are four main types of PDUs, each offering different levels of functionality. A basic PDU is the simplest type. It receives power and distributes it to its outlets with no monitoring or management capabilities. It functions purely as a distribution point. Basic PDUs are inexpensive but provide no visibility into power usage.

A metered PDU adds a display or network interface that shows the total power draw across the unit. This allows technicians and capacity planners to see how much power the rack is consuming in real time. Some metered PDUs can report at the outlet level, showing exactly how much each device is drawing.

A monitored PDU goes a step further by providing remote monitoring capabilities over the network, typically through SNMP or a web interface. It can send alerts when power consumption exceeds predefined thresholds, helping the operations team detect overloaded circuits before a breaker trips.

A switched PDU includes all the monitoring features plus the ability to remotely power-cycle individual outlets. This is extremely useful for remote management because a technician can reboot a hung server without physically visiting the rack. Switched PDUs can also be configured to control the power-on sequence of equipment, which prevents inrush current from tripping breakers when an entire rack is powered on simultaneously.

The outlets on a PDU come in standard types. C13 outlets are the most common and connect to standard server power cables. C19 outlets provide higher amperage connections for equipment with larger power requirements, such as high-density servers or storage arrays. Understanding which outlet type each piece of equipment requires is a basic but important part of a technician's daily work.