What Is a PDU (Power Distribution Unit)? Rack Power Explained

A rack PDU accepts an input feed — typically a single-phase or three-phase circuit rated for a specific voltage and amperage — through an attached power cord or a fixed connection. Internally it splits that feed across multiple outlets, distributing the available current to whatever is plugged in. The equipment inside the rack draws power on demand; the PDU's job is to deliver it safely within the rating of its input circuit and its outlets.

Beyond distribution, most rack PDUs handle circuit protection and, in higher tiers, measurement. Many models group outlets onto internal breakers or fused branches so a fault on one group does not take down the whole strip. Metered and monitored units add current sensors that report load in amps or watts, letting operators see how close a circuit is to its limit. Switched units add relays behind each outlet so power can be turned on or off remotely, one receptacle at a time.

PDUs are commonly grouped into four capability tiers. A basic PDU simply distributes power with no metering or network connection — reliable and inexpensive, but you cannot see load remotely. A metered PDU adds a local display (and sometimes a network port) showing aggregate or per-branch current, which helps prevent overloading a circuit. A monitored PDU is network-connected and reports power data remotely over protocols such as SNMP, feeding dashboards and DCIM tools without requiring someone at the rack.

A switched PDU adds remote, per-outlet on/off control, so staff can reboot an unresponsive device or sequence startup loads from anywhere. Some vendors further distinguish 'switched with per-outlet metering' units that combine remote control with outlet-level power measurement — useful for billing, capacity planning, and identifying which specific device is drawing power. As a rule, capability and cost rise together across these tiers, so match the tier to what you actually need to measure and control.

Form factor is a separate decision from capability tier. A vertical or '0U' PDU mounts in the rear channel of the rack, running the full height of the cabinet without consuming any of the numbered rack units (hence 0U). Because it sits close to the equipment and offers many outlets along its length, the 0U style is common in dense server racks. A horizontal PDU mounts in the rack like any other device, occupying one or two rack units (1U/2U); it is often used where space is available or where a smaller outlet count is enough, such as in network racks.

Outlet type also matters. Data-center PDUs frequently use IEC 60320 receptacles — C13 outlets for standard servers and larger, higher-current C19 outlets for power-hungry gear — while some regions and lighter deployments use locally standard outlets such as NEMA 5-15/5-20. The input connector must match the facility circuit as well, so a PDU is specified by both its outlet mix and its input plug, voltage, and phase.

Any rack that holds more than a couple of devices needs organized power distribution, so a PDU is standard in server rooms, network closets, and data centers. The question is usually which tier and configuration, not whether to use one. If you only need to spread outlets, a basic unit suffices; if you need to avoid tripping circuits, verify capacity for growth, reboot remotely, or bill by consumption, step up to metered, monitored, or switched models accordingly.

Before buying, confirm the input circuit (voltage, amperage, single- or three-phase) and the matching plug type, then total the load of your equipment and leave headroom below the circuit rating — a common guideline is to keep a continuous load below roughly 80 percent of the circuit's rating. Count and match the outlet types your gear uses, check the physical fit (0U height or horizontal U-space, cord entry, depth), and decide whether you need redundant feeds. Racks with dual-corded equipment typically use two PDUs on separate circuits (A/B feeds) so either can fail without downtime. Finally, weigh monitoring needs: network management, environmental sensor ports, and DCIM compatibility are worth specifying up front because retrofitting them later means swapping the PDU.