Power distribution unit
Encyclopedia
Data center
A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems...
.
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
Modbus
Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers . Simple and robust, it has since become one of the de facto standard communications protocols in the industry, and it is now amongst the most commonly available means of...
or SNMP. In a typical data center for example, there would be relatively few of these floor-mounted PDU devices, located along the walls of 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
Data center
A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems...
. 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 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 plugs. They are used in computer data center
Data center
A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems...
s, 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 manufactures also include environmental monitoring via RS485, USB, Dallas 1-Wire
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal. 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive...
or serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
s. The power outlets themselves are typically IEC-C19, IEC-C13 or NEMA 5-20 style outlets.
Rack-based PDU refers to what amounts to a well-constructed power strip
Power strip
A power strip is a block of electrical sockets that attaches to the end of a flexible cable and allows multiple electrical devices to be plugged in. As such it can be considered a type of trailing socket though that term is more often used for single and double cable mounted sockets...
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.
A typical application area could be a mobile measurement station, where several devices can be supplied with power from a single distribution unit.
Remote control
Some PDUs provide a means of remote access. Common methods are a RS-232RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
serial connection or a LAN network controller that can be accessed though Telnet
TELNET
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...
, SSH
Secure Shell
Secure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...
, SNMP
Simple Network Management Protocol
Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
or a web page
Web page
A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...
. This allows an administrator to access the PDU from a remote terminal and interface with it to turn on or off outlets, schedule power shutdowns, control load, etc. This can be helpful if a remote machine has gone into an unresponsive state and cannot be restarted though normal means. An administrator can connect to the PDU the machine is plugged into to power cycle
Power cycling
Power cycling is the act of turning a piece of equipment, usually a computer, off and then on again. Reasons for power cycling include having an electronic device reinitialize its configuration or recover from an unresponsive state of its mission critical functionality, such as in a crash or hang...
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 the 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), IT professionals are beginning 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.
Note: Important to remember, in North America the standard 240 volt circuit (120 volts x2 plus neutral and ground) has two legs at 120 volts. Most recently, Data Centers are being outfitted with Single-phase 208volt connections.
See also
- Mains Distribution UnitMains Distribution UnitMains Distribution Unit are rackable power distribution electrical devices, mostly used in high availability environments like central apparatus rooms, data centers, server rooms to distribute clean power within racks, each MDU power inlet is fused for surge protection and power fluctuations.MDUs...
- TransformerTransformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
- Uninterruptible power supplyUninterruptible power supplyAn uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
- Watchdog timerWatchdog timerA watchdog timer is a computer hardware or software timer that triggers a system reset or other corrective action if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog A watchdog timer (or computer operating properly (COP) timer) is a computer...