Power Distribution Units (PDU)

Power distribution units (PDUs) have an electrical input and several outputs, often as electrical outlets, for powering multiple devices.  They typically contain features such as circuit breakers and transient voltage suppression.  Unit types can be modular or desktop, monitor shelf, plug strip, cabinet or cabinet mount, rack mount, vertical mount, wall mount, or hardwire mount.  The number of outlets in the power strip or power distribution unit (PDU) also refers to the number of outputs if not in the form of AC outlets.  Outlet configurations can be NEMA, IEC, CEE, or JIS.

Important electrical specifications to consider when searching for power distribution units (PDUs) include nominal voltages, frequency, phase, current rating, and power rating.  Nominal voltages can be 24 VDC, 48 VDC, 115 VAC, 208 VAC, or 230 VAC.  Frequency can be at 50 Hz, 60 Hz or 400 Hz.  50 Hz is common for European power.  60 Hz is common in North American power.  400 Hz is most widely used in aerospace applications.  Phases can be single or three phase.  Single phase is the standard AC Power for instrument, computers, etc.  Three-phase power is used for industrial power applications such as drive motors, pumps, etc., where power efficiency and higher loads are critical considerations.  Current rating is the rated current for the power distribution unit, typically given for maximum continuous current.  The power rating is the total power rating for the PDU; includes all outlets and circuits.  An important environmental operating parameter to consider is the operating temperature.

Features for power distribution units generally fall into two categories, protection features and configuration features.  Protection features include circuit breaker, fuse, thermal sensors, EMI / RFI protection, and transient voltage surge suppression.  Circuit breakers are protective devices for overvoltage; circuit breakers trip at overload and may be reset.  Fuses are safety devices that are activated in the event of extended overvoltage; they take the device power off line.  Fuses include replacement types and resettable fuses, often thermal sensing.  Thermal sensors detect high thermal conditions, indicating current overload or other non-design condition.  This may open a fuse or circuit breaker, send an alarm signal, etc.  A device with EMI or RFI protection has filtering and protection to guard against adverse impacts of radio frequency interference (RFI) and electromagnetic interference (EMI).  A PDU with transient voltage surge suppression features clamping or other suppression of transient voltage spikes or other irregularities.  Configuration features include AC adapter spacing, battery backup, twist lock plug, on/off switch, and remote control.  A unit with AC adapter spacing has outlets that are spaced to allow the insertion of multiple AC adapters.  A unit with battery backup has a backup to prevent interruption of power during power supply failure; typically fairly short-term protection is provided.  A twist lock plug is a safety feature to prevent unintended disconnecting or reconnecting.  An on/off switch allows the unit to be plugged in, but not powered.  Remote control units may be controlled via a remote device such as a computer or other switch, either for on/off control, performance monitoring, or control and reading of other parameters.

• Choosing Power Distribution Units (PDUs) for Networking, Server and Telecom Applications (.pdf)
  Faced with increasingly complex networks, managers are responsible for identifying reliable power sources for all of their equipment. This white paper establishes Power Distribution Units (PDUs) as a...
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