Rack power distribution unit [/ˈræk ˈpaʊər ˌdɪstrəˈbjuʃən ˈjunɪt/] n - A rack PDU is the power strip, oft mounted vertical, that stands within a cabinet and deals out current to the several servers. Though it shares the acronym, it is a different animal from the floor-level Power distribution unit: no transformer, only outlets, metering, and at times switching.

Of Its Several Degrees of Cunning

• Basic [/ˈbæsɪk/] n - outlets only.
• Metered [/ˈmɛtɛrɛd/] n - measures current, so a rack may be loaded near its limit in safety and its draw reckoned toward Power usage effectiveness.
• Switched [/ˈswɪtkhɛd/] n - each outlet may be powered on or off from afar, for reboots and the governance of capacity.

A rack is commonly fed by two rack PDUs, an A unit and a B unit, each drawn from a wholly independent path (separate Busway distribution or Remote power panel, separate Uninterruptible power supply), so realizing the site’s Redundancy topologies down to the very cabinet. Dual-corded servers put one supply into each; single-corded gear wants a Static transfer switch instead.

Both feeds deliver The Current That Comes in Threes (in the larger racks) or single-phase taps of it, and both bond to the rack’s Grounding and bonding point.

Part of The Engines of the Hall.