Power distribution unit
||It has been suggested that Mains Distribution Unit be merged into this article. (Discuss) Proposed since May 2011.|
||The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. (December 2010)|
|This article needs additional citations for verification. (March 2009)|
A power distribution unit (PDU) is a device fitted with multiple outputs designed to distribute electric power, especially to racks of computers and networking equipment located within the data center. PDUs vary from simple and inexpensive rack-mounted "power strips" to larger floor-mounted PDUs with multiple functions including power filtering to improve power quality, intelligent load balancing, and remote monitoring and control by LAN or SNMP.
Two types of PDUs
The term (PDU) may refer to two major classes of hardware power devices; the first and typically the general unqualified term refers to the category of relatively higher-cost floor-mounted power distribution devices which transform one or more larger capacity raw power feeds into any number of lower capacity distributed power feeds. These floor-mounted PDU devices are typically composed of transformers and circuit breakers and may optionally include monitoring controllers using protocols such as Modbus or SNMP. In a typical data center for example, there would be relatively few of these floor-mounted PDU devices, located along the walls or in central locations for larger spaces. Each floor-mounted PDU would feed a much larger number of racks and rows of racks.
The second class of device is a much smaller and lower cost device which is fitted with multiple appliance outlets designed to distribute electric power within a rack, especially to computers and networking equipment located within a data center. The second type of PDU is sometimes called a Smart-PDU, Rack-based PDU, Intelligent PDU or simply "Power Strip" by various IT professionals.
Rack-based PDU refers to what amounts to a well-constructed power strip suitable for data center use. Two basic varieties distinguished by the type of input power are common: single-phase and three-phase. The output power (i.e. the power to the load device) is almost always single-phase, however. In the case of a three-phase PDU, each of the three phases appears individually on one-third of the included receptacles. Rack-PDUs can be dumb—meaning that they have no instrumentation and are not manageable, or they can be metered—meaning that they are equipped with a display that shows current load on each phase, or they can be switched and metered meaning that some or all of their receptacles can be individually switched on or off remotely and the meter usage as well.
In the North American 110 V / 60 Hz systems, rack-based PDUs are used for taking the supplied voltage and current and distributing it electrically to more common outlets, for example from 240 V / 30 A single phase to multiple 120 V / 15 A or 120 V / 20 A electricl plugs. They are used in computer data centers, in stage shows, by DJs, and in other electrically intensive applications. Some premium units have features like remote power monitoring and power state control down to the unit or individual plug level. Certain manufacturers also include environmental monitoring via RS485, USB, Dallas 1-Wire or serial ports. The power outlets themselves are typically IEC-C19, IEC-C13 or NEMA 5-20 style outlets.
In the international 230 V / 50 Hz system, rack-based PDUs simply distribute incoming power, typically from a 230 V / 16 A, 230 V / 10 A or 400 V / 16 A 3-phase == 3 x 230V / 16 A input to multiple individual 230 V outlets, which may either rely on the input fusing or be individually protected by smaller 10 A or 6 A fuses. The outlets are typically either IEC-C13 or one of the country-specific types of power socket. Additional features such as monitoring of power consumption, noise and overvoltage filtering, environment monitoring and remote management are generally the same as in North American rack-based PDUs.
In data centers larger PDUs are needed to power multiple server cabinets. Each server cabinet may require multiple high current circuits possibly from different phases of incoming power or different UPSs. Standalone Cabinet PDUs are self-contained units that include main breakers, individual circuit breakers, and power monitoring/control panels. The cabinets provides internal buss bars for neutral and grounding. Prepunched top and bottom panels allow for safe cable entry.
A typical application area could be a mobile measurement station, where several devices can be supplied with power from a single distribution unit.
In North America the standard 240 V circuit (120 V x2 plus neutral and ground) has two legs at 120 volts. Common current limits are 20 A, 30 A and 50 A. Another option is splitting 3-phase AC into 3 single-phase 208 V circuits. Outside North America, the standard data center circuits are 230 V AC and in higher end telecoms facilities 48 V DC from large UPS installations, neither of which are subdivided into other voltages by PDUs.
Remote control and monitoring
Some PDUs provide remote access. Common methods include a RS-232 serial connection or a LAN network-controller accessible through Telnet, SSH, SNMP, or a web page. This allows an administrator to access the PDU from a remote terminal and interface with it to turn outlets on or off, to schedule power shutdowns, to control load, etc. This can be helpful if a remote machine has gone into an unresponsive state and will not restart through normal means. An administrator can connect to the PDU the machine is plugged into to power-cycle the machine.
One of the challenges in selecting PDUs for a data-center application is to balance the cost of the rack-PDU in the context of an organization's energy-management goals. Inexpensive rack-PDUs may distribute power effectively, but they offer little if any understanding or control of that energy flow. With energy costs rising over the past several years (circa 2010[update]), IT professionals have begun to take a more comprehensive view of power management with rack-PDUs with more intelligence. The trend is more intelligence and higher-quality rack-PDU devices.
- Mains Distribution Unit
- Uninterruptible power supply
- Watchdog timer
- Industrial and multiphase power plugs and sockets
- "Cabinet Power Distribution". APC. Retrieved 2013-11-04.
-  Ardupower an opensource remote powerstrip