Rack Power Distribution Unit

A rack PDU takes one building power feed and distributes it to servers, switches, storage and other rack equipment. It provides the right outlet types, overcurrent protection, surge protection and, in metered or switched models, remote monitoring and outlet-level control.

PDUs are mounted horizontally in 1U of rack space or vertically at the rear of the cabinet in 0U. A cabinet usually has two PDUs on separate feeds so equipment can survive a single feed failure or a maintenance bypass.

The common input ratings are 10 A, 16 A and 32 A at 220–250 V AC, 50/60 Hz. A 16 A single-phase feed provides about 3.5 kW; a 32 A feed provides about 7 kW. For higher loads, use a three-phase PDU or multiple single-phase PDUs on separate circuits.

Outlet count depends on the cabinet layout. A 1U horizontal PDU usually has 6 to 8 C13 outlets; a 0U vertical PDU can have 20 to 30 C13 outlets plus 4 to 6 C19 outlets. Confirm the plug type, outlet type and breaker rating for the destination country.

A basic PDU has a breaker and outlets. A metered PDU adds a local display for current, voltage and power; a monitored PDU adds remote SNMP or Modbus access; a switched PDU adds outlet-level on/off and restart. For colocation and remote sites, switched PDUs reduce truck rolls.

Protection options include MCB or RCBO breakers, surge protective devices (SPD), over-temperature alarms and sequential start. Sequential start powers outlets in a timed sequence after a restart, which avoids the inrush current that can trip the upstream breaker.

A 1U horizontal PDU mounts in the 19-inch frame and is usually placed at the bottom or top of the cabinet. A 0U vertical PDU mounts on the rear side rail or the cabinet frame and keeps the rear cable area clear. Allow space for the input cable bend radius and the breaker access.

Use separate PDUs on A and B feeds for redundant equipment. Label every outlet and cable, and keep power cables away from data cables. For high-density cabinets, use a PDU with outlet-level metering to identify hot spots and balance the load.

Select the PDU by input current, outlet type and count, metering level, mounting format and redundancy. Add 20% to 30% headroom above the calculated load. For a 42U server cabinet with 6 kW of IT load, two 32 A PDUs on separate feeds are a common configuration.

PDUs ship in a carton with mounting brackets and a manual. Typical lead time is 15 to 20 working days after drawing approval, with 10 units as a common minimum order for custom configurations. Confirm the plug type and the local electrical code before ordering.