AC- AlternatingCurrent. Current flows first in one direction, then reverses and flows the opposite direction, typically in a sinusoidal fashion. The number of times this change takes place per second is called frequency. 

AFCEA-Armed Forces Communications Electronics Association

Agent- See SNMP Agent.  

Alarm Enable/Disable- The switch used to disable the Audible Alarm feature. It does not affect the Visual Alarm indicators.

ALICE-All-purpose Lightweight Individual Carrying Equipment, as in ALICE ruck pack.

Ambient temperature -The range of air temperature on a normal basis surrounding the equipment.

Ampacity -The current carrying capacity, expressed in amperes, of a conductor under stated thermal conditions.

Ampere (Amp or A) -The mks unit of measure for current flow in electrical conductors or devices. May be AC or DC Amps. One ampere equals one coulomb passing a point in a conductor in one second. Or the unit of measurement of electrical current produced in a circuit by 1 volt acting through a resistance of 1 ohm.

ANSI-American National Standards Institute. An industry group that establishes and publishes standards.

Apparent Power -Volt-Amperes, VA. The product of voltage times current in a circuit including inductive and/or capacitive elements.

Audible Alarm -The horn that sounds when an alarm condition occurs.

AUSA-Association of the United States Army

Audible Noise -The measure of the noise emanating from equipment in audible frequencies. Usually represented in dBA.

AutorangingInput- Refers to ETI products being able to automatically select input voltage. For example, the autoranging can select either 115 or 230 VAC input, providing an input range of 85 to 270 VAC having either a 50 or 60 Hz frequency. This covers 99+% of the world.

Autotransformer- A transformer used to step voltage up or down. The primary and secondary windings share common turns, and it provides no isolation.

AWG- American Wire Gauge. A gauging system used to size wire. Every increase of 3 wire gauges is a 50% reduction in cross sectional area of the wire.


Bandwidth- A term now used to describe the capacity or amount of traffic (data, voice or video) a certain communications medium is capable of accommodating.

Battery- An electro-chemical device used to store and generate electrical power. Basic technologies used with UPS products include lead-acid and nickel-cadmium (NICAD).

Battery Backup- A battery or a set of batteries in a UPS system. Its purpose is to provide an alternate source of power if the main source is interrupted.

Battery Charger -An electronic device that provides a controlled voltage and current to a battery to maintain the battery in a fully charged state. 

Battery Charger Modes -A Constant Current Rate of Charge Mode is used until the battery is just below float level. Once the batteries have reached this point, the charging mode changes to a Constant Voltage Mode (Trickle Charge Mode) that is used to maintain the float level of the batteries.

Battery Self Discharge -The internal current flowing in a battery when it is not connected to a circuit. The rate of self discharge is proportional to the storage temperature, thus batteries have a longer self life at lower temperatures.

BEM- Battery Extension Module. A specific group of batteries in a self contained enclosure with circuit protection and interface connector.

Bi-Directional Converter- A device which changes (or converts) alternating-current power to direct-current power and vice versa.

Blackout- A total loss of the AC utility (commercial power). A zero-voltage condition that lasts for more than two cycles. It may be caused by the tripping of a circuit breaker, power distribution failure or utility power failure. This condition can lead to data damage, data loss, file corruption and hardware damage.

Boost- See buck and boost.

Break-Before-Make- Operational sequence of a switch or relay where the existing connection is opened prior to making the new connection.

Breaker- See Circuit Breaker.

Bridge Converter- Switching converter topology that employs four switching elements (full bridge) or two switching elements (half-bridge). This topology is more often used in off-line supplies rather than DC-DC converters. Bridge converters provide high output power and low ripple, but are significantly more complex than other types of converter topologies and thus are more expensive and prone to failure. Also see Boost Regulator, Buck Regulator, Flyback Converter, Forward Converter, Push-Pull Converter and Resonant Converter.

Brownout- The term used to describe when the power grid voltage is something less than the normally accepted tolerance, but voltage is still present. Power companies sometime lower voltage during power shortages to reduce load on several customers rather than completely dump customers. It occurs more often as an uncontrolled condition during high peak demand. Each piece of electronic equipment has a low voltage limit it can tolerate. When this happens, computer systems can experience data corruption, data loss and premature hardware failure.

BTU- British Thermal Unit. The quantity of heat required to raise the temperature of 1 pound of water by 1 °F starting from 60 °F. This is equal to 1054.6 joules or 252 calories. 3.7 BTUs per hour is equivalent to 1 Watt.

Buck and Boost- A proprietary voltage regulation process used when an overvoltage or undervoltage situation occurs in the UPS. Undervoltage is boosted to make the voltage greater, and overvoltage is bucked to reduce it. The result is less reliance on the UPS battery, extending overall battery life.

Buck Regulator- A basic DC-DC switching converter topology that takes an unregulated input voltage and produces a lower regulated output voltage. The lower output voltage is achieved by chopping the input voltage with a series connected switch (transistor) which applies pulses to an averaging inductor and capacitor.

Burn In- The process of operating newly manufactured equipment for some period of time prior to shipment. The intent is to stabilize the electronics and eliminate infant mortality by aging the device. The time period and conditions (input power cycling, load switching, temperature, etc.) varies from vendor to vendor.

Bypass- A circuit used to change the path of the electrical power so that it goes around (or bypasses) its normal path. In the UPS, the bypass circuit is used to route the power around the major electronics in the UPS so they can be serviced without power interruption.


C4ISR-Command, Control, Communications, Computers, Intelligence, Surveillance, Reconnaissance

Calorie- A unit of heat. One calorie is the amount of energy required to raise the temperature of one gram of water by one degree of Celsius.

Capacitor- A device that stores electrostatic energy in a manner similar to the way an inductor stores electromagnetic energy. Often used for filtering or DC blocking. The unit of capacitance is the Farad (F).

CBEMA- Computer and Business Equipment Manufacturers Association. Organization originally responsible for the AC voltage disturbance tolerance specification used by related equipment designers. Specifies overvoltage and undervoltage events that computing equipment must withstand. Effective December 1994, CBEMA changed its name to the Information Technology Industries Council (ITI).

CE- European Union regulatory community symbol. Symbolizes compliance with all applicable safety, public health and consumer protection requirements. See UL, CSA, ETL, VDE and TÜV.

Celsius (°C)- A metric measure of temperature level, degrees Celsius.

CFM -Cubic feet per minute, which is a measure of the volume of air flowing in a system.

Choke -An inductor used as part of an electrical filter that resists the flow of current at specified frequencies, usually used to block high-frequency transients from incoming a/c power. See Inductor.

Circuit Breaker (CB)- A resettable overcurrent protective device that operates (trips) after a certain current level is exceeded for a certain length of time. Common designs include thermal, magnetic and combinations of both.

Clean Power- Electrical power which has been conditioned and/or regulated to remove electrical noise from the output power.

Cold Start- The ability to start the UPS from its batteries without having the Input AC present.

Common Mode (CM)- The term refers to electrical interference which is measurable as a ground referenced signal. In true common mode, a signal is common to both the current carrying conductors.

Common Mode Noise Rejection (CMNR)- The ability of an electronic device, like a UPS, to block common mode noise between input and output.

Conduit- A flexible or rigid tubular raceway for data or power cables. Metallic conduit is common, although non-metallic forms may also be used.

CONUS -Continental United States. Typically refers to an electronic device designed to operate from standard US power, 120 VAC, 60 Hz.

Converter -An electronic device that takes on level of DC power and converts it to another level, up or down (DC/DC).A device which changes electrical energy from one form to another, such as from alternating current to direct current.

Coulomb-The combined negative electrical charge of 6.24 X 1018 electrons.

CPC -Circular Plastic Connector. A type of modular connector by AMP that is less expensive than the metal shell connectors.

Crest Factor -The ratio of the non-linear peak current to the true RMS current. A sine wave has a crest value of 1.4142. For switchmode power supplies this ratio ranges from 2 to 4.

Critical Load -Equipment that requires an uninterrupted power input to prevent damage or injury to personnel, facilities, or itself.

Crowbar -A circuit that crowbars or rapidly shuts down a converter's output if a preset voltage level is exceeded. The circuit places a low resistance shunt across the output when an overvoltage condition exists.

CSA- Canadian Standards Association, a Canadian safety agency that sets standards for product safety. See UL, ETL, CE, VDE and TÜV.

Current -The measure of electrical charge passing a particular point. Commonly measured in Amperes. See Ampere.

Current limiting- Feature that protects the electrical equipment from damage under overload conditions such as a short circuit. The maximum output current is automatically limited to a predetermined safe value. If the equipment is specified for auto restart, normal operation is automatically restored when overload condition is removed. 

Current rating- The maximum current which a piece of electrical equipment was designed to carry or produce.

Current Transformer (CT)- Usually used as a sensing device, current transformers customarily have a one turn primary. The number of secondary turns is determined by the sensitivity required and is terminated with a resistor. Toroidal in shape, cores of silicon steel, nickel alloy, or ferrite are used. Choice of core material influences cost and accuracy.