infrastructure//data center//power chain//PDU

A PDU (power distribution unit) is the device that takes power from the building's distribution and splits it into many protected outlets for the equipment of a data center, and it is the last stage of the power chain before the servers' own supplies. The word covers two different things that are worth telling apart. A **floor PDU** is a cabinet in the hall that steps down or distributes power from the UPS to many racks, with its own breakers and often a transformer. A **rack PDU** is the vertical strip inside the rack, with dozens of sockets, that each server and switch plugs into.

A PDU (power distribution unit) is the device that takes power from the building's distribution and splits it into many protected outlets for the equipment of a data center, and it is the last stage of the power chain before the servers' own supplies. The word covers two different things that are worth telling apart. A floor PDU is a cabinet in the hall that steps down or distributes power from the UPS to many racks, with its own breakers and often a transformer. A rack PDU is the vertical strip inside the rack, with dozens of sockets, that each server and switch plugs into.

A rack PDU looks like a power strip and is much more. It carries breakers per group of outlets so one fault does not trip the whole rack, it meters current per phase or per outlet so operators see how close each circuit is to its limit, and switched models can cycle a single outlet remotely to reboot a hung machine without anyone walking to it. The current reading matters because breakers trip on overload, and the usual practice is to keep each circuit well below its rating so a load that rises (or a load that moves over when the other side fails) still fits.

Two PDUs are not redundancy until each can carry the whole rack.

Servers in a data center have two power supplies, one plugged into an A-side PDU and one into a B-side PDU fed from a different path. If both sides normally run at 60 % of their rating, losing one puts 120 % on the other and trips it: each side must stay below half its capacity for the pair to protect anything (redundancy level).

The PDU is where power density becomes concrete. A rack of current AI servers needs PDUs rated for tens of kilowatts on three-phase circuits, where an older rack ran on a single-phase strip of a few kilowatts (power density).

Upstream, rack PDUs plug into a busway above the row or into cables from a floor PDU; the choice decides how easily the room can be reconfigured.