p  - pico used to express 0.000000000001 (10 to the -12th power) times the standard unit, i.e. pF

Parallel Online UPS - Online UPS technology that provides redundant sources of conditioned backup power so that the critical load is protected even in the event of UPS component failure.

Peak Voltage - Also called peak-to-peak voltage, it is a measure of an AC waveform of the highest peak-to-peak voltage present on the waveform.  A proper 120V AC waveform will have a peak voltage of about 170 volts. See RMS.

PDU - Power Distribution Unit. This electrical device is used to control the distribution of power to the individual loads. Control may be as simple as a series of switch or circuit breakers to interlocked logic operating solidstate relays. Available as a stand-alone unit or integrated into the UPS.

Power Factor (PF) - Power Factor, the cosine of the phase angle between the Watts (real power) used relative to the VA (apparent power), (Watts = VA x PF). Can be expressed as a percent or decimal number, i.e. a PF of 0.65 is the same as a PF of 65%.

Power Factor Correction (PFC) - An active or passive input circuit to change the power factor of the input current to a device so that it is closer to a PF of 1.0. Numerous benefits include reduced input line current and lower input harmonics.

Power Conditioner (Line Conditioner) - A unit that provides clean, well regulated power. Input and output voltages may also be converted as well.

Power Management Software - Provides monitoring and shutdown for UPS and connected load.

Push-Pull - Converter topology usually configured as a forward converter, but uses two transistor switches and a center tapped transformer. The transistor switches turn on and off alternately. Also see Boost Regulator, Buck Regulator, Bridge Converter, Flyback Converter and Resonant Converter.

PWA (PCA) - Printed Wiring Assembly (Printed Circuit Assembly), refers to the individual assembled electronic cards used in an electronic product.

PWB (PCB) - Printed Wiring Board (Printed Circuit Board), refers to the bare circuit cards used in PWAs.

Q (Q Factor) - A measure of the relative losses in an inductor. It is also known as the quality factor, defined as the ratio of inductive reactance to effective resistance. Q is zero at the SRF of an inductor.

Rack - A mechanical structure for mounting electrical equipment. Size and mounting patterns are defined by EIA 310.

Rack unit (U) - A common increment of equipment space height as defined by EIA 310. Typically 1 U equals 1.75 inches in height. Racks are sized in whole number of unit, i.e. 45 U rack has 78.75 inches of panel space.

Rackmount - A piece of electronic equipment such as a UPS that can be mounted in a rack along with servers, hubs, and other devices.

Receptacle - A contact device installed at an outlet designed to accept a single plug. Receptacles on the rear of a UPS accept plugs from supported system equipment such as computers or monitors.

Rectifier - An electronic device that converts AC power to DC power (AC/DC)

Redundancy - Duplication of elements in a system or installation to enhance the reliability or continuity of operation.

Regulation - A method of limiting voltage to a narrow range.

Redundant Operation - Parallel configuration of converters used in distributed power system to increase system reliability. Converters may be used in a N+1 architecture.

Remote Sensing - Using sense leads connected at the output load provides feedback to voltage regulation circuits of a converter. This arrangement is used to compensate for voltage losses from long leads to a load.

REPO - Remote Emergency Power Off. See Emergency Shutdown.

Resonant Converter - Switching converter technology in which a resonant tank circuit operating at very high frequencies is used to transfer energy to the output.

Reverse Voltage Protection - Converter feature that prevents damage to internal components if a reverse voltage is inadvertently applied to the input or output terminals.

RMS - Root Mean Square. The square root of the average value of the squares of all instantaneous values of voltage or current during one half cycle in an AC circuit. For a sine wave, the RMS value is approximately equal to 0.707 times the peak value of the waveform. RMS is also called the effective value.

Rolling Blackout - A condition where power utilities purposely impose blackouts over a portion of their service area to free up capacity so that the remaining service area can continue to be served.  After a time, another portion of the service area has a blackout imposed on it, so that power can be restored in the original area.

Rolling Brownout - A condition where power utilities purposely impose brownouts over a portion of their service area to free up capacity so that the remaining service area can continue to be served.  After a time, another portion of the service area has a brownout imposed on it, so that power can be restored in the original area.

RS-232 - Also called serial ports; a method of communicating digital information in which the data bits are transmitted sequentially over one line.