Power distribution unit [/ˈpaʊər ˌdɪstrəˈbjuʃən ˈjunɪt/] n - A power distribution unit (PDU) [/ˈpower ˈdistribuʃən ˈunit ˈ(pdu)/] n, in its facility-scale sense, receives the conditioned output of the Uninterruptible power supply and divides it among the many branch circuits that feed the data hall. A floor PDU of the usual kind holds a step-down transformer, a main breaker, and panels of branch breakers, often with revenue-grade metering on each circuit.

It stands between the UPS and the racks:

• Upstream: Uninterruptible power supply → PDU.
• Downstream: the PDU feeds either a Remote power panel set nearer the load, or Busway distribution running overhead along each row, and at last the Rack power distribution unit within the cabinet.

One floor PDU may serve dozens of racks, and so it is a meaningful single point of failure, deployed according to the site’s Redundancy topologies; in a 2N design each rack draws from two PDUs on wholly independent paths.

Mark the trap in the terminology: the device inside a rack is also called a “PDU.” That one is the Rack power distribution unit. The same acronym, a very different box.

The PDU’s transformer re-establishes a Grounding and bonding reference for all that lies downstream of it, and its output is the standard low-voltage The Current That Comes in Threes the racks expect.

Part of The Engines of the Hall.