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Glossary of Electrical Terms 

Enercon can help you understand the ins and outs of the critical power industry. This glossary of electrical terms is intended to provide you with accurate and up-to-date definitions to better equip you when navigating through this complicated sector. Enercon's expertise in critical power and controls will give you a comprehensive understanding of the wide range of terminology used in this specialized field. With Enercon's commitment to the highest quality standards, rest assured that you are getting the most detailed and accurate knowledge about the latest trends in vital power regulations.

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ABL — Airborne Laser. Armored Box Launcher

AEGIS — The Navy's advanced, fast reaction, high firepower, shipboard anti-air warfare area defense system (Note: Aegis is the Greek word for "shield").

Alternating Current (AC) — An electric current that reverses its direction many times a second at regular intervals.

Ammeter — An instrument for measuring the flow of electrical current in amperes. Ammeters are always connected in series with the circuit to be tested.


Ampacity — The maximum amount of electric current a conductor or device can carry before sustaining immediate or progressive deterioration.


Ampere-Hour (Ah) — A unit of measure for battery capacity. It is obtained by multiplying the current (in amperes) by the time (in hours) during which current flows. For example, a battery that provides 5 amperes for 20 hours is said to deliver 100 ampere-hours.


Ampere (A) — A unit of measure for the intensity of an electric current flowing in a circuit. One ampere is equal to a current flow of one coulomb per second.

Anti-Ballistic Missile (ABM) Treaty — The ABM Treaty, which was signed by the United States and the former Soviet Union on May 26, 1972, and entered into force on October 3, 1972, constrained strategic missile defenses to a total of 200 launchers and interceptors per country- 100 at each of two widely separated deployment areas. These restrictions were intended to prevent the establishment of a nationwide defense or the creation of a base for deploying such a defense. The treaty was modified in 1974, reducing the number of ABM deployment areas permitted each side from two to one and the number of ABM launchers and interceptors from 200 to 100. However, on June 13, 2002, the United States officially withdrew from the ABM Treaty in order to pursue the development of missile defenses that would have been banned by this agreement.


Apparent Power — Measured in volt-ampers (VA). Apparent power is the product of the RMS voltage and the RMS current.


Armature — The movable part of a generator or motor. It is made up of conductors which rotate through a magnetic field to provide voltage or force by electromagnetic induction. The pivoted points in generator regulators are also called armatures.



Ballistic Missile — A missile that travels, or releases a payload that travels, to its target after being launched and at a velocity such that it will follow a flight trajectory to a desired point. Part of the flight of longer-range ballistic missiles may occur outside the atmosphere and involve the “reentry” of the missile. Missiles that are not ballistic are aerodynamic, operating in the atmosphere. Aerodynamic missiles include cruise and air-to-air missiles.

Boost-phase — That part of the ballistic missile flight path that begins at launch and lasts up to five minutes for a primitive liquid-fueled inter-continental ballistic missile (ICBM) or as little as 80 seconds for an advanced solid-fueled ICBM. During boost phase, the booster and sustainer engines operate, and warheads have not yet been deployed.

Breaker — Short for Circuit Breaker. Is a device for interrupting an electric circuit to prevent excessive current, such as that caused by a short circuit, from damaging the apparatus in the circuit or from causing a fire.

Buss — Separate, metallic strips that extend through the center of the service panel that the breakers snap onto.



Capacitance — The ability of a body to store an electrical charge. Measured in farads is the ratio of the electric charge of the object (Q, measured in coulombs) to the voltage across the object (V, measured in volts).

Capacitor — A device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator. Commonly used for filtering out voltage spikes.

Circuit — A closed path in which electrons from a voltage or current source flow. Circuits can be in series, parallel, or in any combination of the two.

Circuit Breaker — An automatic device for stopping the flow of current in an electric circuit. To restore service, the circuit breaker must be reset (closed) after correcting the cause of the overload or failure. Circuit breakers are used in conjunction with protective relays to protect circuits from faults.

Conductor — Any material where electric current can flow freely. Conductive materials, such as metals, have relatively low resistance. Copper and aluminum wire are the most common conductors.

Corona — A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the electric field strength.

Current (I) — The flow of an electric charge through a conductor. An electric current can be compared to the flow of water in a pipe. Measured in amperes.

Cycle — The change in an alternating electrical sine wave from zero to a positive peak to zero to a negative peak and back to zero. See Frequency.



Demand — The average value of power or related quantity over a specified period of time.

Dielectric constant — A quantity measuring the ability of a substance to store electrical energy in an electric field.


Dielectric strength — The maximum electric field that a pure material can withstand under ideal conditions without breaking down (i.e., without experiencing failure of its insulating properties).


Diode — A semiconductor device with two terminals, typically allowing the flow of current in one direction only. Diodes allow current to flow when the anode is positive in relation to the cathode.

DSP — A system of non-imaging infrared satellites in geo-stationary orbits, fixed and mobile ground processing stations, one multi-purpose facility, and a ground communications network (GCN). DSP’s primary mission is to provide warning and limited attack assessment of a ballistic missile attack.



Electrolyte — Any substance which, in solution, is dissociated into ions and is thus made capable of conducting an electrical current. The sulfuric acid-water solution in a storage battery is an electrolyte.


Electromotive Force (EMF) —  A difference in potential that tends to give rise to an electric current. Measured in volts.


Electron — A tiny particle that rotates around the nucleus of an atom. It has a negative charge of electricity.


Electron theory — The theory which explains the nature of electricity and the exchange of "free" electrons between atoms of a conductor. It is also used as one theory to explain the direction of current flow in a circuit.

EWR — Early Warning Radar located in Alaska and other U.S. locations.



Farad — A unit of measure for capacitance. One farad is equal to one coulomb per volt.

Ferroresonance — (nonlinear resonance) is a type of resonance in electric circuits which occurs when a circuit containing a nonlinear inductance is fed from a source that has series capacitance, and the circuit is subjected to a disturbance such as the opening of a switch. It can cause overvoltages and overcurrents in an electrical power system and can pose a risk to transmission and distribution equipment and to operational personnel.

Frequency — The number of cycles per second. Measured in Hertz. If a current completes one cycle per second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz.

Fuse — A circuit interrupting device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level. To restore service, the fuse must be replaced using a similar fuse with the same size and rating after correcting the cause of failure.



Generator — A device that converts mechanical energy into electrical energy.


Ground — The reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.

Ground Based Interceptor (GBI) — The missile intercept of the proposed U.S. Ballistic Missile Defense (BMDS) System, the GBI will intercept incoming ballistic missile warheads outside the earth’s atmosphere (exo-atmospheric) and collide with the incoming ballistic missile, thereby destroying the missile. The NMD Battle Management, Command, Control, and Communications (BMC3) will transmit information on the location of the incoming missile to the GBI during its flight. The GBI would consist of a multi-stage solid propellant booster and an exo-atmospheric kill vehicle.


Ground Fault Circuit Interrupters (GFCI) — A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit.



Henry — A unit of measure for inductance. If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry.

Hertz — A unit of measure for frequency. Replacing the earlier term of cycle per second (cps).



Impedance — The measure of the opposition that a circuit presents to a current when a voltage is applied. Impedance extends the concept of resistance to AC circuits and possesses both magnitude and phase, unlike resistance, which has only magnitude.


Inductance — The property of a conductor by which a change in current flowing through it induces (creates) a voltage (electromotive force) in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance). Measured in henry (H).


Inductor — A coil of wire wrapped around an iron core. The inductance is directly proportional to the number of turns in the coil.


Insulator — Any material where the electric current does not flow freely. Insulative materials, such as glass, rubber, air, and many plastics have relatively high resistance. Insulators protect equipment and life from electric shock.

Intercontinental Ballistic Missile (ICBM) — Ballistic missiles with ranges greater than 5,500 kilometers (3,400 miles)


Inverter — An apparatus that converts direct current into alternating current.



Kinetic Energy Interceptor (KEI) —  A planned U.S. missile defense program whose goal was to design, develop, and deploy kinetic energy-based, mobile, ground and sea-launched missiles that could intercept and destroy enemy ballistic missiles during their boost, ascent and midcourse phases of flight.

Kilowatt-hour (kWh) — The product of power in kW and time in hours. Equal to 1000 Watt-hours. For example, if a 100W light bulb is used for 4 hours, 0.4kWhs of energy will be used (100W x 1kW / 1000 Watts x 4 hours). Electrical energy is sold in units of kWh.

Kilowatt-hour Meter — A device used to measure electrical energy use.


Kilowatt (kW) — Equal to 1000 watts.



Land-based missile systems — Missile systems located on land usually in hardened bunkers and underground silos or on mobile launchers, which are more vulnerable to first-strike attacks. The mobile land-based missile systems are less vulnerable to first-strike because the positions of the missiles can be changed.

Load — Anything which consumes electrical energy, such as lights, transformers, heaters, and electric motors.


Load Rejection — The condition in which there is a sudden load loss in the system which causes the generating equipment to be over-frequency. A load rejection test confirms that the system can withstand a sudden loss of load and return to normal operating conditions using its governor. Load banks are normally used for these tests as part of the commissioning process for electrical power systems.

Large Phased Array Radar (LPAR) —  An electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving the antennas.

Layered BMDS —  The current and planned integrated U.S. Ballistic Missile Defense System consists of several sets of defensive interceptors that operate against incoming ballistic missiles at different phases in the missile’s trajectory. Thus, there could be a first layer (e.g., boost phase) of defense with remaining targets passed on to succeeding layers (e.g., midcourse and terminal). The Bush Administration uses the terms “BMDS” in lieu of the “TMD” and “NMD” phrases that were preferred by the Clinton Administration.



Medium Extended Air Defense System (MEADS) — A lightweight, highly transportable, low-to-medium altitude air defense and theater missile defense system designed to protect critical fixed and theater missile defense system designed to protect critical fixed and mobile targets.

Midcourse Phase (Mid-Phase) — That part of the ballistic missile’s trajectory, after the boost phase, when the re-entry vehicle and warhead travel freely through space outside the atmosphere. For an ICBM, this stage lasts about 20 minutes.

Multiple Kill Vehicle (MKV) —  An experimental concept that would put multiple guided kill vehicles on a single interceptor booster, allowing each to destroy multiple objects.

Mutual Induction — Occurs when changing current in one coil induces voltage in a second coil.



National Missile Defense (NMD) — A ground-based anti-ballistic missile system designed to protect a country against ballistic missile threats. The proposed U.S. system consists of four elements: ground-based interceptors (GBI); a ground-based radar (GBR); a battle management command, control, and communications (BM/C 3) system; and a constellation of Space and Missile Tracking System (SMTS) satellites. The term was used by the Clinton Administration to differentiate systems able to intercept long-range missiles from systems able to intercept only short-range, or “theater”-range missiles. The Bush Administration integrated the concept into the larger BMDS’.



Ohm — (Ω) A unit of measure of resistance. One ohm is equivalent to the resistance in a circuit transmitting a current of one ampere when subjected to a potential difference of one volt.


Ohm's Law — The mathematical equation that explains the relationship between current, voltage, and resistance (V=IR).


Ohmmeter — An instrument for measuring the resistance in ohms of an electrical circuit.


Open Circuit — An open or open circuit occurs when a circuit is broken, such as by a broken wire or open switch, interrupting the flow of current through the circuit. It is analogous to a closed valve in a water system.



Parallel Circuit — A circuit in which there are multiple paths for electricity to flow. Each load connected in a separate path receives the full circuit voltage, and the total circuit current is equal to the sum of the individual branch currents.

PAC-2/-3 — ATRIOT Advanced Capability, Level 2/Level 3. Formerly called ERINT.

PATRIOT Advanced Capability (PAC) — The Army’s premier guided air and missile defense (AMD) system providing highly reactive hit-to-kill capability in both range and altitude while operating in all environments.

Piezoelectricity — Electric polarization in a substance (especially certain crystals) resulting from the application of mechanical stress (pressure).


Polarity — A collective term applied to the positive (+) and negative ( - ) ends of a magnet or electrical mechanisms such as a coil or battery.


Power — The rate at which electrical energy is transferred by an electric circuit. Measured in Watts.


Power Factor — The ratio of the actual electrical power dissipated by an AC circuit to the product of the r.m.s. values of current and voltage. The difference between the two is caused by reactance in the circuit and represents a power that does no useful work.


Protective Relay — A relay device designed to trip a circuit breaker when a fault is detected.



Reactive Power — The portion of electricity that establishes and sustains the electric and magnetic fields of AC equipment. Exists in an AC circuit when the current and voltage are not in phase. Measured in VARS.


Rectifier — An electrical device that converts an alternating current into a direct one by allowing a current to flow through it in one direction only.


Relay — An electrical coil switch that uses a small current to control a much larger current.


Reluctance — The resistance that a magnetic circuit offers to lines of force in a magnetic field.


Resistance — The opposition to the passage of an electric current. Electrical resistance can be compared to the friction experienced by water when flowing through a pipe. Measured in ohms.


Resistor — A device usually made of wire or carbon which presents a resistance to current flow.


Rotor — The rotating part of an electrical machine such as a generator, motor, or alternator.



SBX — Sea-based X-band Radar – A moveable platform for the BMDS test bed.

Self Induction — Voltage occurs in a coil when there is a change of current.


Semiconductor — A solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. Devices made of semiconductors, notably silicon, are essential components of most electronic circuits.


Series-Parallel Circuit — A circuit in which some of the circuit components are connected in series and others are connected in parallel.


Series Circuit — A circuit in which there is only one path for electricity to flow. All of the current in the circuit must flow through all of the loads.


Service — The conductors and equipment used to deliver energy from the electrical supply system to the system being served.


Short Circuit — When one part of an electric circuit comes in contact with another part of the same circuit, diverting the flow of current from its desired path.


Solid-State Circuit — Electronic (integrated) circuits which utilize semiconductor devices such as transistors, diodes, and silicon-controlled rectifiers.

Space Based Infrared System (SBIRS) — A United States Space Force system intended to meet the United States' Department of Defense infrared space surveillance needs through the first two to three decades of the 21st century. The SBIRS program is designed to provide key capabilities in the areas of missile warning, missile defense, battlespace characterization and technical intelligence via satellites in geosynchronous Earth orbit (GEO), sensors hosted on satellites in highly elliptical orbit (HEO), and ground-based data processing and control.

Space Tracking and Surveillance System (STSS) — A constellation of low-earth orbiting satellites that will detect and provide critical tracking information about ballistic missiles globally. The program is employing a capabilities-based, block upgrade acquisition approach. The first block, termed Block 06 by the Missile Defense Agency (MDA), will be deployed in 2007 to support the missile defense testbed. STSS is designed to support the BMDS which will negate missiles/warheads in boost, mid-course, and terminal phases of flight. STSS will provide tracking through all three phases; discriminate between warheads and decoys; transmit data to other systems that will be used to cue radars and provide intercept handovers; and provide data for intercept hit/kill assessments. STSS provides unique characteristics including global coverage with no foreign basing issues, continual watch on emerging and known threats, and dual phenomenology for discrimination to ensure efficient use of interceptors.



Terminal-phase — The final phase of a warhead’s trajectory when it re-enters the earth’s atmosphere and strikes the target.

Theater High Altitude Air Defense (THAAD) — The U.S. Army’s air defense program designed to provide extended defense and to engage an incoming missile at ranges of up to several hundred kilometers. THAAD will deploy a hit-to-kill interceptor equipped with an infrared seeker. Unlike fragmentation warheads that explode near an object in order to destroy it, the THAAD interceptor is designed to collide with the target ballistic missile. The interception is intended to occur outside the earth’s atmosphere, or high in the atmosphere.

Theater Missile Defense (TMD) — Missile interceptors designed to destroy shorter-range ballistic missiles aimed at deployed troops or overseas facilities. Because the ABM Treaty prohibited NMD, but permitted defenses against shorter-range missiles, the Clinton Administration sought to separate TMD and NMD. The Bush Administration eliminated the distinction between NMD and TMD and incorporated both programs into the BMDS.

Theater Missile — Short-range delivery system (missile) with a range of 1,000 kilometers or less.

Transistor — A semiconductor device with three connections, capable of amplification in addition to rectification.


True Power — Measured in Watts. The power manifested in tangible forms such as electromagnetic radiation, acoustic waves, or mechanical phenomena. In a direct current (DC) circuit, or in an alternating current (AC) circuit whose impedance is a pure resistance, the voltage and current are in phase.



VARS — A unit of measure of reactive power. Vars may be considered as either the imaginary part of apparent power or the power flowing into a reactive load, where voltage and current are specified in volts and amperes.


Variable Resistor — A resistor that can be adjusted to different ranges of value.


Volt-Ampere (VA) — A unit of measure of apparent power. It is the product of the RMS voltage and the RMS current.


Volt (V) — A unit measure of voltage. One volt is equal to the difference of potential that would drive one ampere of current against one-ohm resistance.


Voltage — An electromotive force or "pressure" that causes electrons to flow and can be compared to water pressure which causes water to flow in a pipe. Measured in volts.


Voltmeter — An instrument for measuring the force in volts of an electrical current. This is the difference of potential (voltage) between different points in an electrical circuit. Voltmeters that have a high internal resistance are connected across (parallel to) the points where voltage is to be measured.



Watt-hour (Wh) — A unit of electrical energy equivalent to the power consumption of one watt for one hour.


Watt (W) — A unit of electrical power. One watt is equivalent to one joule per second, corresponding to the power in an electric circuit in which the potential difference is one volt and the current one ampere.


Wattmeter — The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit.


Waveform — A graphical representation of electrical cycles which shows the amount of variation in amplitude over some period of time.

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