A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | R | S | T | U | V | W | Z

Abbreviation for alternating current.

AC waveform
See sine wave.

Alternating current (AC)
An electrical current that reverses direction at regular intervals (once every half-cycle) as a result of a change in voltage that occurs at the same frequency.

An electric generator that produces an alternating current.

Ambient temperature
The surrounding temperature.

American National Standards Institute (ANSI)
A private organization whose purpose is to coordinate and/or approve certain US standards, including those relating to the electrical industry.

American Wire Gauge (AWG)
A standard measure of wire size. The larger the number, the smaller the wire.

Short form of ampere. A measure of the amount of current flowing in a wire. Similar to the flow rate (gallons per hour) of water in a hydraulic system.

The maximum continuous current that a conductor can carry without overheating and rising above its temperature rating.

The amperage of a circuit is equal to the current flow expressed in amps.

Named after French physicist Andre M. Ampere (1775-1836). A measure of the rate of energy transfer in a conductor, equal to one Coulomb per second. One ampere is equal to the current that passes through a one-ohm resister, when a one-volt potential is applied.

The flow of electricity equal to one ampere for one hour. Commonly used to rate the capacity of batteries.

Amp meter
An instrument that indicates the rate of flow of electricity through a circuit.

American National Standards Institute.

ANSI C84.1
The standard for voltage delivery to customers to which electrical utilities in the US must conform. This standard limits the range of acceptable voltage to between 114 and 126. During emergency situations, the low end may be temporarily lowered to 110 volts, which is called a brownout.

Apparent power (S)
Also called volt ampere or VA. The mathematical product of voltage and current on AC systems, which includes the effects of reactive power. Since voltage and current may not be in phase on AC systems, the apparent power thus calculated may not equal the real power, but may actually exceed it. Reactive loads (inductance and/or capacitance) on AC systems will cause the apparent power (VA) to be larger than the real power (watts). Apparent power can be graphically represented in vector form as the hypotenuse of a right triangle, where watts and reactive power represent the other two sides of the triangle. See Power factor.

Household devices, such as air conditioners (window or central), clothes washers and dryers, computers, copiers, dishwashers, floor and table lamps, fluorescent lights, freezers, garbage disposals, gas forced-air furnaces, hot tubs, light bulbs, microwave ovens, printers, refrigerators, phantom loads, stereos and televisions.

The flow of electric current across a gap in a circuit that causes a spark, light, or glow. Generally not considered to be a good thing.

The rotating part of a motor or generator.

Abbreviation for American Wire Gauge. The smaller the AWG, number the larger the wire diameter–e.g., 1 AWG is larger than 10 AWG.

Actually, “transformer bank” or “capacitor bank”; a group of transformers or capacitors connected together.

A group of two or more cells connected together to provide electrical current. Sometimes also used to describe a single cell which converts chemical energy to electrical current.

Battery cycle life
The number of discharge and recharge cycles that a battery can undergo before degrading below its capacity rating.

Battery self-discharge
The gradual loss of chemical energy in a battery that is not connected to any electrical load.

Lack of illumination caused by an electrical power failure. If the demand for electricity exceeds the supply, the utilities will implement plans for temporary, rotating outages, which are conducted under utility control (rather than due to system collapse). Under this system, utilities manage the outages by rotating them in a controlled fashion between groups of customers to ensure that no one customer is disproportionately inconvenienced.

Black start
Refers to certain utility-generating units that can start upon demand without any outside source of electric power. These are often combustion turbines that have stationary battery banks to provide backup power to energize all the controls and auxiliaries necessary to get the unit up and running. In the event of a widespread blackout, these units are critical to restoring the utility grid. Most utility-generating units do not have black-start capability.

An electrical conducting path formed by the permanent joining of metallic parts. Intended to ensure electrical continuity and the capability to safely conduct any likely current. Similar to bonding jumper or bonding conductor.

Also called circuit-breaker. A safety device that senses current overloading and interrupts energy flow by “opening” the circuit.

British Thermal Unit (BTU)
The quantity of heat required to raise one pound of water one degree Fahrenheit at or near 39.2°F. A unit of measurement for heat. One BTU is equal to .293 watt-hours.

A reduction of voltage on the distribution system — usually to 110V. Systems in the eastern parts of the US, where networks are integrated, use brownouts as a means of reducing demand during emergencies.

BURD transformer
“Buried Underground Residential Distribution.” A transformer that is normally located in an enclosure, below ground level, and is energized with underground cable.

A conductor or group of conductors that serves as a common connection within a substation or switchyard.

A conductor composed of a number of wires twisted together–i.e. a large wire.

Candle power
A measure of light intensity, based on Candelas as the unit of measurement.

The ability to hold or store an electric charge. Measured in Farads. See capacitor.

Having or exhibiting capacitance.

Also called condenser. Two conductors separated by an insulating material that is capable of holding an electrical charge. A capacitor can alternately absorb or supply small amounts of electricity. Capacitors are used to absorb surges or alleviate voltage sag on a distribution system feeder line. The effectiveness, called “capacitance,” is measured in Farads. Capacitors are analogous to a balloon; both can absorb energy if empty or supply energy if full.

Capacitor bank
A group of capacitors connected together in order to supply greater capacitance or Farads.

A single device that stores chemical energy and then can convert that chemical energy into electrical current. Typically, several cells are combined to form a battery.

The path taken by electrical current flowing through a conductor from one terminal of the source of supply to the other.

Circuit breaker
Also called “breaker.” A safety device that senses current overloading and interrupts energy flow by “opening,” or interrupting, the circuit.

Also called “jaws.” Point of contact between the revenue meter and customer load. Jaws are located in the meter base, and the meter plugs into them.

Closed circuit
A complete electric circuit through which current will flow when voltage is applied.

Cogeneration involves a variety of methods that capture waste heat from the industrial process and use it to produce electricity with generators on the customer’s side.

A material through which a current of electricity flows, such as a wire or a trace on a printed circuit board. Aluminum, copper, silver and gold are common conductors.

Constant power load
A load that tends to draw constant power, meaning that as the voltage to the load decreases, its current draw increases, or visa versa. Examples include compact fluorescent lamps, computer power supplies, and solid-state televisions. Constant power loads are slightly more efficient under CVR conditions, but they do not yield a significant savings like other types of loads. Motors are often considered to be a constant power load. This is true only if they are running at their rated horsepower. Most motors run at an average of 60% of their rated load, and therefore are not constant power loads.

A large switch used for controlling large loads (usually motors). Contactors are controlled remotely, using a low-voltage control circuit.

Unbroken connection–a complete or closed circuit through which current can flow.

The practical unit of electric charge transmitted by a current of one ampere for one second. It is the charge carried by 6.2418 x 1018 electrons. Named for the French physicist Charles A. de Coulomb (1736-1806).

An arm fastened at the top of a power pole to separate and support conductors and apparatus in a distribution system.

The flow of electrical energy though a circuit measured in amperes.

Current transformer (CT)
A transformer that steps down the current in a circuit by a fixed percentage from a high value to a low value in order to provide a useable current for metering purposes.

Reduction of voltage to the lower end of the ANSI C84.1 standard to conserve energy. Short for Conservation Voltage Regulation, or Conservation Voltage Reduction.

One complete period of the reversal of an alternating current from positive to negative and back again. In the US, this period is 1/60th of a second, or 60 Hertz.

Measure of the frequency in an AC electric system. Abbreviated cps or cycles. Now replaced with the unit Hertz.

An abbreviation for direct current.

A logarithmic measure of the ratio of two quantities. Abbreviated dB. For electrical power, 1 dB = 10 x log10 P1/P2. For electric voltage or current, 1 dB = 20 x log10 E1/E2. Usually used to compare relative strengths of electronic signals or sounds.

Delta system
A method of connecting transformers for three-phase application. Usually used for three-phase, three-wire systems, but can be found in three-phase, four-wire, High Leg Delta systems.

The amount of electric current needed to power a utility distribution system (or individual load) at any one moment. See Peak demand.

Demand charge
An additional cost applied to a consumer’s bill when demand exceeds a predetermined level.

Demand side management (DSM)
A utility program intended to reduce consumption during peak demand periods. It is often differentiated from conservation programs, which attempt to reduce the base demand at all times. DSM is accomplished by using one or more methods such as disabling electric heat, electric hot water heaters, or other large loads during peak demand periods.

An electronic semiconductor device that allows current to flow in only one direction.

Direct access
The ability of customers to buy electricity generation directly from power producers or through power marketers.

Direct current (DC)
An electric current flowing through a conductor in one direction only; as apposed to an AC circuit, where the direction of current flow reverses once every cycle. DC systems are most commonly found in automobiles, home electronics, and the majority of devices that run on batteries.

To remove an electrical device from a circuit. To make it inoperative either by opening a switch or a contactor, or by unplugging the device.

Displacement power factor (DPF)
Displacement power factor is a measure of how closely the current flow is synchronized in time with the voltage. It is predominantly caused by motors. Motors are said to have a lagging power factor, since current flow in a motor does not occur until after the voltage has risen and built up the magnetic field. Capacitors have a leading power factor; therefore, they are used to compensate for motors. DPF is expressed as a decimal number between 0 and 1. A DPF of 1 is ideal, .8 is about average for small motors, and .4 is very poor.

Distributed generation (DG)
Also called distributed resources. The concept of using a multitude of small-generation sources located at the distribution level of the system to satisfy growing demand. Locating small generation close to the demand has some advantages when used as a complement to the classic large power plant, to transmission line, to substation, to distribution model currently in use. Distributed generation devices include microturbines, diesel gensets, fuel cells and other devices that are capable of producing electricity on demand, and for that reason are often differentiated from “green” sources such as wind and solar.

Distribution system
Also called distribution. The whole circuit or system of distribution lines, and all of its branches, which distribute electricity from the substation to the consumers.

An electrical symbol for volts.

The ratio of the amount of power or work obtained from a machine and the amount of power used to operate it. Mathematically represented by the Greek symbol ç.

Electrical codes
Rules and regulations for the installation and operation of electrical devices and currents that state the minimum safety conditions. In the US, this is the National Electrical Code (NEC).

Electrical noise
A high frequency signal superimposed on top of the normal AC sine wave. Noise can be created on the power line by a variety of devices such as welders, arc furnaces and switch-mode power supplies; or it can be picked up on the power line from external sources such as radio and television transmitters, or radar.

Invisible energy capable of moving 186,000 miles per second. It is a natural phenomenon that is most commonly perceived as lightning or static. It is magnetic, colorless, weightless and odorless. More specifically, it is a form of energy transmitted via charged particles such as electrons, protons or ion flow.

A nonmetallic conductor of electricity usually consisting of a liquid or paste through which electricity flows via ions or charged particles .

The instantaneous capacity for mechanical work or available power. Energy is often used interchangeably with the word power, but there are subtle differences. Energy is defined as the force required to move a given mass a given distance within a given time. Power, on the other hand, is the conversion of this energy into work over time. The unit of measurement for energy is the joule, which is also the unit of measurement for power, which adds to the confusion. Energy is joules times distance, whereas power is joules divided by time. Electric utilities sell energy, not power. The energy they sell is converted to power over time by electrical devices such as heaters or motors. The energy of 746 watts is convertible to one horsepower of work.

Electric Service Provider. A third party from whom you can purchase direct access services, like electricity generation.

Enterprise Voltage Regulator™. MicroPlanet’s patented product for lowering and stabilizing the voltage consumed by split-phase businesses. A method of implementing conservation voltage regulation at the point of consumption.

A unit of capacitance. One coulomb of charge will produce a potential difference of one volt across a capacitance of one Farad. Named for the English physicist Michael Faraday (1791-1867).

A short-circuit, which causes higher-than-normal current flow, or current flowing through an unintended path, such as to ground.

Federal Energy Regulatory Commission (FERC)
FERC is an independent regulatory agency within the US Department of Energy that approves rates for wholesale electricity transactions and transmission of electricity in interstate commerce for utilities, power marketers, power pools, power exchanges and independent system operators.

FERC also regulates the transmission and sale for resale of natural gas in interstate commerce; regulates the transmission of oil by pipeline in interstate commerce; licenses and inspects private, municipal and state hydroelectric projects; and oversees related environmental matters. The FERC board of governors is composed of five commissioners. The chairman, designated by the President, serves as the commission’s administrative head. FERC is based in Washington, D.C.

Also called feeder lines. Electrical lines supplying all the branch circuits with the main supply of current. Loosely used to describe all or parts of the medium voltage distribution system used to transmit power to your home or business.

A device made up of circuit elements designed to pass desirable frequencies and block all others. It typically consists of capacitors and inductors.

Also called nameplate current. Full-load amperes, also sometimes abbreviated “RLA,” for “running load amperes.” This is the current in amperes that a motor requires to produce rated nameplate horsepower output when rated nameplate voltage and frequency is provided to its terminals.

Flexible conduit
Nonrigid conduit made of plastic or metal strip wound spirally. Conduit is used for added protection of wire from physical damage.

Fluctuating voltage
Unstable voltage, which is most commonly noticed when lights go from bright to dim and back to bright intermittently. Can also shut down computers and other sensitive electric equipment. There are many possible causes. Some involve problems with the consumer’s internal wiring; others involve the utility.

The number of complete alternations or cycles per second of an alternating current. It is measured in Hertz. The standard frequency in the US is 60 Hz. However, in Europe and other countries, the standard is 50 Hz.

Fuel cell
A device that converts hydrogen or another hydrocarbon directly into electricity using a complex form of oxidation. Ideally the only byproducts would be heat and water.

A general term for a rotating machine that converts mechanical energy into electrical energy. In the automotive industry, traditional terminology uses the word “generator” to refer to only those machines designed to produce DC current, as opposed to an alternator, which produces alternating current.

Producing electricity at power plants using one or more generators.

Green power
Another name for renewable energy sources such as wind, solar, and tidal.

Greenhouse gas
Primarily carbon dioxide (CO2), and to a lesser extent sulfur dioxide (SO2) and other gases produced as a byproduct of burning fossil fuels. While these gases are normally present in the earth’s atmosphere and are naturally recycled by plants, industrial nations are creating these gases at an unprecedented rate that exceeds the biosphere’s ability to recycle them. Elevated levels of greenhouse gases caused by increased volcanic activity have been linked to geologic periods of global warming in the earth’s past.

Also called power grid or distribution grid. Refers to the electrical utility distribution network, which is often laid out in a gridlike pattern. The term is often used loosely to refer to the entire system: Beginning with generation, the electricity is transmitted via the high-voltage transmission system to the substations. At the substation the high voltage is reduced to medium voltage and redistributed through feeder lines to the distribution transformers. From there it travels through the secondary drop to your service entrance, where it is again redistributed via interior wiring to the outlets, lights, and appliances in your home or business.

A path of electrical current to the earth.

A term used for any device that has a dedicated conductor that connects it to earth or ground. Transformers are typically grounded to stabilize their voltage. Appliances have their chassis grounded for safety. In case of a ground fault, the ground conductor provides a low-resistance path for the energy to travel to ground, which reduces risk of electrocution to the user.

Ground fault
A short-circuit or mechanical failure that results in electrical energy leaving the intended circuit and flowing to ground. The circuit becomes grounded.

Ground fault interrupter (GFI)
A device that senses when an appliance on an electrical circuit becomes grounded. In the event of a ground fault, the GFI initiates the opening of a circuit-breaker to de-energize the circuit. It is primarily intended to reduce the risk of fire from ground faults, and to reduce the risk of electrocution by the user of the appliance.

A sine wave that is an integral multiple of a base frequency. E.g., the third harmonic on a 60Hz system has a frequency of 180Hz and the fifth harmonic is 300Hz

Harmonic distortion
Also called total harmonic distortion (THD). A measure of the degree to which the normal sinusoidal waveform is distorted by harmonics on the system. The fundamental sinusoidal waveform is distorted when the higher-frequency harmonic components are added to it. Harmonic distortion can be seen in the voltage, current, or power wave forms. Total harmonic distortion (THD) is expressed as a percentage of distortion; the lower the percentage, the better.

Also called harmonic currents. Certain types of electrical equipment called “nonlinear loads” generate harmonics that interfere with the proper function of other devices connected to the same system, and lower the system efficiency. Harmonic currents are power flowing at frequencies higher than the system was designed for. They actually flow backwards through the system to the source transformer, and then back through the neutral to the originating device. The electrical system must be oversized to accommodate this unintended energy flow. One crude analogy would be an automobile that has three round wheels and one octagonal wheel (eight harmonic). The car would still be drivable, but definitely less efficient.

The practical unit of inductance. One Henry is equal to the inductance in which the change of one ampere per second results in an induced voltage of one volt. Abbreviated H. Named for the American physicist Joseph Henry (1797-1878).

A unit of frequency. One hertz equals one complete cycle per second of an AC source. Abbreviated “Hz.” Named after German physicist Heinrich R. Hertz (1857-1894).

A unit of power equal to 746 watts. Most commonly used to describe the power of an electric motor. Equivalent to cycles-per-second.

Hot conductor
A term that has come to refer to a conductor or wire that is energized. The term probably has its origins in the fact that a wire has some resistance, and therefore as current flows through it, its temperature increases proportional to the current. So a wire that is physically “hot” is probably also energized.

Hydroelectric plant
A generating facility that uses falling water as the source of energy to produce electricity. (See Renewable energy.)

The electrical symbol for current.

The total effects of a circuit that oppose the flow of an AC current consisting of inductance, capacitance, and resistance. It can be quantified in the units of ohms. Represented by the symbol Z.

The characteristic of an electric circuit by which a voltage is electromagnetically induced in it by a variation of current. This can be a variation of the current in the circuit itself (self-inductance) or in a nearby circuit (mutual inductance). The magnitude of the characteristic is measured in the units of Henries. Represented by the symbol L.

Also called chokes and coils. A device that stores energy magnetically, and resists any change in the current flowing through it–demonstrating the property of inductance. Inductors are used to smooth out short pulses in current and provide a smooth average current flow on their output. They are similar in function to the mechanical flywheel, which uses its inertial energy to smooth out the pulses of power coming from an automobile engine.

In rush current
Also called in rush. The initial surge of current that occurs when a device or circuit is energized. The current normalizes after the circuit components balance out.

Institute of Electrical and Electronics Engineers (IEEE)
An independent organization that develops electrical standards and furthers the profession of electrical and electronics engineers.

A material such as glass or some plastics that are difficult for electricity to flow through. Wires are insulated so that the electrical energy stays in the wire. A short-circuit is often caused by damage to this insulation.

An electrical device designed to convert direct current into alternating current. This was originally done with rotating machines that produced true sine wave AC output. More recently this conversion has been performed more economically and efficiently using solid-state electronics. However, except for the most expensive models, these devices usually do not produce perfect sine wave output. This can result in electromagnetic interference with other sensitive electronic devices, as well as increased harmonic distortion.

A positively or negatively charged molecule, atom or subatomic particle, capable of transferring electrical energy.

The unit of energy required to accomplish one newton-meter of work. The joule is the unit of measurement shared by energy and power; therefore, one joule is also equal to one watt-second. One kilowatt hour equals 3,600,000 joules. Named after James P. Joule, an English physicist (1818-1889).

Joule’s law
Defines the relationship between current in a wire and the thermal energy produced. In 1841 an English physicist James P. Joule experimentally showed that W = I2 x R x t, where I is the current in the wire in amperes, R is the resistance of the wire in ohms, t is the length of time that the current flows in seconds, and W is the energy produced in joules.

See clips.

Kilovar (kVAR)
Unit of AC reactive power equal to 1000 vars. Abbreviated kVAR or KVAR.

Kilovolt (kV)
Unit of electrical potential equal to 1000 volts. Abbreviated kV or KV.

Kilovolt amperes (kVA)
Unit of apparent power equal to 1000 volt amperes. Here, apparent power is in contrast to real power. On AC systems the voltage and current will not be in phase if reactive power is being transmitted. Usually abbreviated kVA or KVA.

Kilowatt (kW, kW)
Unit of power equal to 1000 watts. Abbreviated kW or KW.

kilowatt-hour (kwh, kWH)
Unit of energy or work equal to one kilowatt for one hour. Abbreviated kwh or KWH. This is the normal quantity used for metering and billing electricity customers. The price for a kwh varies from approximately 4 cents to approximately 15 cents. At a 100% conversion efficiency, one kwh is equivalent to about 4 fluid ounces of gasoline, 3/16 pound liquid petroleum, 3 cubic feet natural gas, or 1/4 pound coal.

Symbol for inductance.

Line sags
See Voltage sags.

Line surges
See Transient voltage.

Line swell
See Voltage swell.

A listed electrical device or material is one that has been tested by a recognized organization and shown to meet appropriate standards. Many local governmental authorities require that installed electrical products be listed. North American listing organizations include UL, CSA, and ETL.(UL).

A device that consumes power and is connected to a source of electricity. In utility terms, the words “load” and “demand” are synonymous, and refer to the amount of energy that all the combined loads on that feeder line are consuming at any moment.

Line drop compensation (LDC)
A method used to implement CVR on a feeder line. A voltage sensor is placed near the end of the feeder line, which reports the end-of-line voltage back to the substation. The voltage is regulated at the substation so that the end of line voltage stays at a minimum level defined by the utility, usually about 118V. The net result is that the average voltage of the customers on that feeder line is lower than it would normally be without LDC.

Normally the voltage is set at the substation based on some assumptions about how much the voltage on a feeder line drops as its load varies. Since these are only educated assumptions and there is no real time feedback of the actual end of line voltage, the substation settings are usually on the high side in order to ensure the end of the line never goes too low.

Load tap changers (LTC)
Large tap-changing transformers used in substations to control the voltage on the feeder lines, usually in 5/8% steps.

Locked rotor amperes. This is the current that a motor would require if the rotor were locked in place and prevented from rotating, and rated nameplate voltage and frequency were applied to its terminals. This is also the current that could appear briefly during motor starting. As the motor starts and comes up to speed, this current drops off and rapidly falls to the full load amperage (FLA) value. Often the starting current is less than the LRA value, because the voltage at the motor terminals dips during starting. This LRA value is important when sizing a generator, because the generator’s surge rating must be large enough to handle it.

Minimum circuit amperes. This is the minimum current rating allowed for the wiring and circuit-breaker or fuse protection for the equipment. It is used by the installer and electrician to size the branch circuit to feed the equipment.

National Electrical Code (NEC)
A code for the safeguarding people and property from hazards related to the use of electricity. Compliance with this code, along with proper maintenance, will result in an installation essentially free from hazard. The NEC was first developed in 1897 as a result of the efforts of various insurance, electrical, architectural, and allied interests. It is sponsored and regularly updated by the National Fire Protection Association.

Opposite of positive; attractive to a positive charge. In a DC circuit, the current is generally considered to flow from the positive pole of the power supply to the negative pole. Having a value less than zero, as in negative voltage.

Net metering
If a consumer has small-scale generation capacity (such as wind, solar or micro-turbine) that is primarily intended to offset the amount of power they need to buy “off the grid,” net metering is a legal agreement that allows them to sell their excess power back onto the grid under certain circumstances.

Also called grounded conductor. A conductor of an electrical system that usually operates with minimal voltage to ground. Depending on the type of system, it may carry little current or only unbalance current. Systems that have one conductor grounded use the neutral for this purpose.

The newton is the basic metric unit of force, named in honor of Isaac Newton (1642-1727). One Newton is a mass of one kilogram times an acceleration of one meter per second (sec) per second (1 N = 1 kg.m/sec2). A newton-meter is a unit of torque that is a force of one newton, applied at a radius of one meter and in a direction perpendicular to the radius arm.

Nonlinear loads
A group of electrical devices characterized by the fact that they draw energy from the system in short pulses rather that in a sinusoidal manner, which is the way the system was designed to function. Nonlinear loads are problematic in that they create harmonics. Devices such as florescent lights, light dimmers, motor speed controllers, rectifiers and computers are typical examples of nonlinear loads.

Nonrenewable energy
An electricity-generating energy source that can be used only once, such as oil, coal, natural gas and nuclear energy.

A unit of electrical resistance. A circuit resistance of one ohm will pass a current of one ampere with a potential difference of one volt. Abbreviated using the Greek letter omega (Ù). Named for the German physicist George Simon Ohm (1787-1854).

Ohm’s Law
Defines the relationship between voltage, resistance and current. In 1828 the German physicist George Simon Ohm showed by experiment that the current in a conductor is equal to the difference of potential between any two points divided by the resistance between them. This is mathematically expressed as I = E / R, where E is the potential difference in volts, R is the resistance in ohms, and I is the current in amperes.

Open circuit
A circuit in which the path of conduction has been broken, disrupted or opened. When you turn a light off, you are “opening” the circuit. When you turn it on, you are “closing” the circuit. This is typically accomplished with a switch, fuse, circuit-breaker or contactor.

Open circuit voltage
The maximum voltage produced by a power source with no load connected.

Operating reserves
Operating reserves are the amount of electrical generation that is available in excess of current demand. If the demand for electricity exceeds the operating reserves of a utility, additional energy must be imported from outside of the system, or demand must be reduced by using brownouts or rotating blackouts.

Also called drop out. Complete loss of voltage that may last from ½ cycle up to two minutes. Typically caused by major faults (short-circuits) anywhere on the power grid. See sustained outage, UPS.

Operation beyond the continuous rated current capacity of the conductor or equipment. This value may be slightly above the rating, as in the case of an overload, or may be far above the rating, as in the case of a short-circuit. Fuses and circuit-breakers are designed to interrupt this condition if it continues too long.

Operation of electrical equipment above its normal full-load rating or of a conductor above its rated ampacity. An overload condition will eventually cause dangerous overheating and damage. When a large motor starts, it is momentarily operating in an overload condition. As soon as it gets up to speed, the current reduces to the nominal value. Fuses and circuit-breakers are designed to interrupt this condition if it continues too long.

Over voltage
Line voltage in excess of 126 volts lasting more than 2 seconds. Causes are generally short-circuiting of higher voltage lines to distribution feeders, loss of neutral connection or mechanical failure of voltage regulation devices.

The Symbol for True Power.

Peak demand
Also called Peak load, peak period. The highest load on an electrical system or generator, occurring during a particular period of time. Peak demand normally occurs once or twice every day, and typically is even higher on unusually hot or cold days. When demand exceeds operating reserves, utilities either import extra power from outside their normal system or limit the demand by implementing rotating blackouts. Because of the marginal pricing structure of the electric utilities, the energy needed to meet the demand at peak load is several times more costly than normal.

Phantom loads
Loads that typically are not switched–i.e., they are “on” all the time. They are usually small, but numerous, and they can represent 2 – 5% of the total load of a residence. Examples include your doorbell, plug-in power supplies for phones, dust busters, televisions and remote-controlled home electronics (even when they are off they consume power).

A voltage-carrying conductor. In a three-phase, four-wire system, there would be three phases and a neutral wire, which is not considered to be one of the phases.

Point of common coupling (PCC)
The place where the utility responsibility ends and the building owner’s responsibility begins. This is usually the revenue meter for residential and commercial customers.

Opposite of negative; in a DC circuit, the current is generally considered to flow from the positive pole of the power supply to the negative pole. Having a value greater than zero, as in positive voltage.

The pressure or voltage forcing electrical current through a circuit. (See volts.)

The rate at which energy is converted into work, or that work is performed. Power is defined as the number of joules of energy converted per second. One joule per second equals one watt. Although power and energy are commonly used as interchangeable words, they are subtlety different concepts. Energy is an instantaneous valve – power is energy converted to work over time. Strictly speaking, electric utilities sell energy, although it is commonly measured in watt/hours or kilowatt/hours.

Power circuit-breaker
This breaker will open the circuit under fault or overload conditions.

Power distribution utility
See Utility distribution company (UDC).

Power factor (PF)
Also called true power factor. The ratio of true power (watts) to apparent power (volt amperes). A relative measure of how well the current waveform matches the voltage waveform. Ideally this ratio should be 1:1, or a power factor of 1. If the apparent power is twice the real power, the ratio would be 1:2 and the power factor would be .5. Poor power factor is another form of system inefficiency that requires all the system components to be larger in size.

Two conditions can cause the apparent power to be greater than the real power. First, nonlinear loads will draw current in a nonsinusoidal manner and distort the current waveform. This is the cause of true power factor. Second, the current may be nearly sinusoidal in shape but displaced in time relative to the voltage waveform. This is called displacement power factor, since it is displaced in time.

Power generation utility
A utility that generates power using one or more generators.

Power source adjustment
A source of revenue based on the efficiency/inefficiency of customer equipment.

Input or source side of transformer. Primary service is power taken at between 2,000 and 50,000 V, and at only one stage of transformation lower than the local transmission system voltage.

Primary lines
Also called feeder lines. Distribution lines (4 kV, 6.9 kV, 12 kV, 16 kV, etc.) used to carry power from the substation to the immediate area to be transformed to lower voltages for individual customers. The line running from the pole top distribution transformer to your house or business is called the low voltage or secondary drop. (See secondary circuit.)

Prime mover
An engine, turbine or water wheel that drives or operates an electric generator.

The symbol for Reactive Power

The electrical symbol for

Rated nameplate
Also called nameplate. A label affixed to a motor that lists the installation requirements, size and performance characteristics of that motor. A motor will have nameplate voltage and frequency requirements which if met, will result in the stated name plate horsepower, full load amps (FLA), locked rotor amps (LRA), speed, temperature, etc.

Reactive loads
Examples of reactive loads include motors, capacitors and inductors. These types of loads will draw current, but since their current is out of phase with the applied voltage, they actually consume no real power in the ideal sense. Reactive loads alternately generate and then consume reactive power, which resonates through the system, lowering the system’s efficiency. An ideal system has equal amounts of induct and capacitance, which have opposite characteristics and cancel each other out.

Reactive power (kVAR) (Q)
The mathematical product of voltage and current associated with reactive loads. This energy resonates through the system between reactive loads, but for the most part it is never converted into work, and therefore it is differentiated from real power (watts). The system needs to accommodate this energy flow, nonetheless. For this reason, reactive power decreases the efficiency of the system. Reactive power’s effect is accounted for in the calculation of apparent power, and is also measured by power factor.

Real power
The rate at which work is performed or that energy is converted to work. Electric power is commonly measured in watts or kilowatts. The term “real power” is often used in place of “power” to differentiate it from reactive power. Also called active power.

A utility would reconductor a feeder line when the current demand on a feeder line exceeds its rating. The feeder line is retrofitted with a larger conductor that has a larger current rating. This is called reconductoring, and is an expensive task, especially for buried feeder lines.

Device that is initiated when a power circuit-breaker is opened and will close the breaker for a test after a pre-set length of time. Reclosure operation is usually the cause of your lights blinking off and on, two to three times in rapid succession. In the event that a tree branch short-circuits, the line and causes an over-current situation, the circuit-breaker will open. The recloser will close the circuit-breaker a couple times in rapid succession in the hope that the branch will have “burned off” and is no longer short-circuiting the circuit.

A device that converts AC power into DC power. A nonlinear load.

A device for controlling the voltage of an electrical circuit.

Steady, predictable electric service. Continued reliability is a key component of industry restructuring.

Renewable energy
Naturally occurring energy sources used to generate electricity, such as wind, solar, tidal and hydro.

The characteristic of materials to oppose the flow of electricity in an electric circuit. Resistance is expressed in ohms. The lower the ohms, the lower the resistance. Wires have low resistance, which allow electricity to flow efficiently. Glass and some plastics have high resistance to the flow of electricity and therefore they are used as insulators.

Resistive load
Loads such as incandescent lighting and electric heaters, which consume electrical energy in a sinusoidal manner, meaning the current flow is in time with and directly proportional to the voltage.

Revenue meter
Typically a kilowatt-hour meter that records electrical energy consumption of the customer and is the basis of your monthly bill, although the newer digital meters can record all three types of power–kilovolts, kilovolt amperes and kilovars.

Running load amperes, also sometimes abbreviated FLA, for full load amperes. This is the current in amperes that a motor requires to produce rated nameplate horsepower output when rated nameplate voltage and frequency is provided to it’s terminals.

Short for “Root-mean-square”, a method of computing the effective value of a time-varying electrical wave. RMS is equivalent to the energy, which is represented by the area under the voltage waveform curve. For example, a 120 V AC waveform has a peak voltage of 170 V, but the RMS average over time is 120 V.

Revolutions per minute, a measure of a motor’s speed.

The symbol for Apparent Power

See voltage sag.

Short for silicon controlled rectifier, which is an electronic switch that is used to functionally reduce the RMS value of AC voltage. SCRs switches reduce voltage by staying off for some percentage of time every half-cycle of the AC waveform, and then turning on for the remainder of the half-cycle. They conduct until the current drops to zero (at the zero crossing point), at which time they turn off and stay off until triggered on again. This is an inexpensive method to control the average voltage and power. Residential light dimmers are just one of many devices that use SCRs. The main draw back is that they disrupt the normal flow of energy. They are nonlinear loads, and therefore create harmonics.

Output side of transformer. Low-voltage lines, 120/240 volt for residential, 120/240, 120/208, 244/480, and 277/408 volt for commercial, that carry power from the pole top or buried transformer to the service entrance nearby. See service wires.

Secondary circuit
The wiring that connects the secondary terminals of a transformer to the customer service entrance.

Service entrance
Also called service. The point where the service wires enter a building, usually considered to include the weather head, meter box, and service panel or main disconnect.

Service limiter
Limits electricity use to 120 volts and 5 or 10 amps–approximately 600-1,200 watts, usually the result of an unpaid bill.

Service panel
Also called breaker box, breaker panel, service equipment. The circuit-breaker or fused switch located near where the service conductors enter the building, which is intended as the primary means of disconnecting the supply.

Service switch
Also called service disconnect, service breaker, mains, mains breaker, main disconnect. The main switch that connects all loads in a building to the service wires.

Service wires
Also called secondary drops, service lines, drops. Lines that carry power from secondary side of the distribution transformer to each customer.

The sensory impression caused by an electrical current flow through the body.

Also called short-circuit, fault. A low-resistance connection unintentionally made between points of an electrical circuit, which may result in current flow far above normal levels. Circuit breakers and fuses are intended to interrupt this condition.

Shunt filter
Also called harmonic shunt filter. A harmonic shunt filter is an electrical device that helps mitigate the harmful effects of harmonic currents. It allows certain high-frequency currents to pass through it while resisting the passage of the fundamental line frequency.

Sine wave
Also called sinusoidal waveform, AC waveform. In ideal electric systems, the characteristic shape of the alternating voltage or current wave. This shape matches the trigonometric sine function of the acute angle in a right triangle and equals the ratio of the side opposite the angle to the hypotenuse.

A generator or circuit in which only one alternating current voltage is produced. A true single-phase circuit will have two wires. A single-phase circuit may be changed at the transformer into a split-phase circuit, which is a variation of a single-phase circuit but with three wires. A large percentage of the world uses true single-phase services (two wires), as apposed to the US, which uses a split single-phase service (three wires).

Single-phase motor
An alternating current motor designed to operate from a single-phase circuit. Single-phase motors are less expensive but have lower efficiency than three-phase motors. The reason they are less efficient is that between the main pulses of positive power there are short pulses of negative power, which act as a braking force. For these reasons, they are typically used in applications requiring low power that don’t run very long, such as consumer appliances.

Sinusoidal waveform
See sine wave.

Small business
Business that operates on a split single-phase 200 amp circuit, rather than on a three-phase circuit–in other words, a business that does not require delivery of large amounts of power.

Solar energy
The term “solar energy” refers to the conversion of sunlight into heat or electricity. See renewable energy.

The joining of the ends of two wires or cables together.

Also called split single-phase. A type of single-phase circuit in which a second phase is created in a transformer, which is exactly the opposite (180° out of phase) of the original phase. The phase to neutral voltage is 120V. The phase to phase voltage is 240V. This is a simple way to get both 120 and 240 volts for residential service from a single-phase circuit. This type of system is simpler than three-phase but has substantial disadvantages when large amounts of power have to be delivered. Split phase circuits are often mistakenly called single phase.

Starting current
The current consumed by a motor when starting. This current can be four to ten times the normal current of a running motor, but generally lasts less than one second. See overload, in rush current.

The stationary part of a motor or generator.

Step down
To reduce the voltage of a circuit, from a higher to a lower value, by means of a transformer.

Step up
To increase the voltage of a circuit, from a lower to a higher value, by means of a transformer.

A fenced or walled area controlled by the utility for the purpose of stepping down voltage and redistributing electricity at a lower voltage within the surrounding local area. Substations typically contain transformers, circuit-breakers, transfer switches, regulators and VAR compensation equipment.

Surge capacity
The ability of an electrical supply to tolerate a momentary current surge or inrush imposed by the starting of motors or the energizing of transformers.

Surge suppressor
Also called transient voltage surge suppressor (TVSS). A device that senses transient voltage resulting from lightning or other causes, and either absorbs that energy or more commonly creates a very brief ground fault that diverts the high-energy transient to ground before it causes damage to electronic devices. TVSS devices should comply to UL 1449-2 (Second Edition) standards.

Sustained outage
An electrical outage that lasts longer than two minutes. Typically caused by mechanical failure, such as downed lines or failed transformers.

See voltage swell.

A device for opening or closing a circuit, or otherwise changing the connections to a circuit.

A panel or supports on which are placed the switches, controls and meters for the control of electrical machines and systems.

Switching center
A staffed substation, where all switching operations are communicated and logged, and the status of all electrical circuits are monitored.

Tap changer
Also called load tap changer (LTC). A mechanical means to change between taps on a transformer, thereby changing the turns ratio of the transformer that changes the voltage output of the transformer.

Short for total harmonic distortion.

An AC electric system consisting of three conductors energized by alternating voltages that are out of phase by one third of a cycle. This type of system has advantages over single-phase, including the ability to deliver greater power using the same size conductors and the fact that it provides a constant power throughout each cycle rather than a pulsating power, as in single-phase. Large power installations are three-phase.

Three-phase bank
Two or three single transformers connected together to serve a three-phase circuit.

Three-phase motor
An alternating current motor that is operated from a three-phase circuit. Typically used in commercial and industrial applications where their higher cost is offset by their higher efficiency compared with single-phase motors.

Tidal Energy
Refers to the production of electricity using the regular ebb and flow of the ocean tides. The tides are directed through reversible turbines in a dam, which turn generators to produce electricity.

Time-of-Use (TOU)
A TOU rate gives customers the option of operating during off- peak periods to reduce energy costs. (see peak loads)

Total harmonic distortion (THD)
See Harmonic distortion.

A device that changes AC voltage. Transformers couple electric energy from one circuit to another via a magnetic field, for the purpose of changing the voltage between the circuits.

Transformer ratio
Also called turns ratio. The ratio of primary to secondary voltages–e.g., a transformer with a 1:2.5 ratio would divide a 600 V primary by 2.5, yielding a reduced output voltage of 240 volts on its secondary.

Transient voltage
Also called spikes, impulses, surges, voltage surges. Very short high-energy pulses, usually caused by lightning or inductive loads switching off. Transients are usually less than 50 microseconds in duration; however, they can contain lots of energy, sometimes more than 10,000 amps at 20,000 V.

Transmission system
Also called High Voltage lines, transmission lines. Large towers that support large conductors that traverse up to 300 miles cross-country and carry electricity at up to 765,000 volts. Transmission lines connect generation to substations. See Power grid.

True power (P)
Also called active power. True power is electrical energy that is converted to power or work. The watt is the unit of measure of true power.

Turns ratio
See Transformer ratio.

Those lines and apparatus below ground, in vaults or manholes, or buried in the ground itself.

Underground cable
An insulated cable placed in an underground conduit or buried in the ground itself.

Under voltage
Also called brownout. Line voltage below 114 volts. This occasionally occurs in rural areas during peak demand periods, because where the customer density is low, it is frequently not possible (or cost effective) to keep the customers at the end of the feeder in compliance during peak demand periods. One symptom of under voltage is your television picture shrinking in size.

Underwriters Laboratories (UL)
A nonprofit organization that was established by the insurance industry to write safety standards and test electrical devices to those standards.

Uninterruptible power supply (UPS)
A device that provides a constant regulated voltage output in spite of interruptions of the normal power supply. It stores energy in batteries or fly wheels and usually powers computers or related equipment that would otherwise shut down during brief interruptions of voltage. See voltage sag, voltage swell, outage.

Utility distribution company (UDC)
Also called power distribution utility. A distribution wires business and a regulated retailer that serves end-use customers. Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric are UDCs. The deregulated utility market could be split into three basic segments–generators, transmission systems and UDCs.

Abbreviation for volt ampere, a unit of apparent power.

Abbreviation for volt ampere reactive. Unit of AC reactive power. VARs are energy used by motors to build up their magnetic field. VARs are a form of electrical energy that is not converted into work. Displacement power factor is a measure of the ratio of VARs to watts used by an electric motor. See energy, reactive power, reactive loads.

Variable auto transfer
Also called variac. An auto transformer that has a continuously variable turns ratio, i.e., a transformer with a variable output voltage.

A unit of electrical pressure expressed in volts. The amount of power or work that an electrical system can supply is directly related to the system voltage. A circuit that can deliver 10 amps at 240 volts is twice as powerful as a circuit delivering 10 amps at 120 volts. This is why power is moved from generators to the substation at very high voltages, often greater than one-half million volts. In contrast, most household appliances run on 120 volts and a few large appliances, such as electric ranges and clothes dyers, run on 240 volts. Voltage is analogous to water pressure in a hydraulic system.

Voltage drop
The difference in electrical pressure between two points in a circuit caused by the resistance, or impedance opposing the flow of current.

Voltage sag
Also called line sags, voltage sags, dips. A voltage sag is a momentary decrease in the line voltage lasting 4-10 cycles. Sags are frequently caused by large increases in the load on a feeder line, ground faults, lightning, or large motors starting.

Voltage swell
Also called line swell, swell. A momentary increase in the line voltage that can last up to 30 cycles. Longer swells are considered over voltage. Most swells are the result of a sudden decrease in loads, and exceed the normal line voltage by 20%.

Volt amperes (VA) (S)
Also called apparent power. A unit of apparent power that is the product of electrical pressure (voltage) times the current (amps). It is a measure of electrical power that includes the combined effects both real power (watts) and reactive power (VAR) on the system. Many utilities are beginning to charge based on VA rather than on watts, because it is a truer measure of the total burden on the system. VA is graphically represented in vector form as the hypotenuse of a right triangle, where watts and reactive power represent the other two sides of the triangle. Given a fixed amount of real power the apparent power increases as the reactive power increases.

One volt is the electrical potential difference or pressure across a 1-ohm resistance carrying a current of one ampere. Named after Italian physicist Count Alessandro Volta (1745-1827).

A unit of measurement of electrical power (true power) that is equal to one joule of energy converted per second or one ampere flowing through a potential difference of one volt. Named after James Watt, the Scottish inverter of the steam engine (1736 – 1819).

A unit of measurement equal to one watt of power used for one hour. The typical unit of consumption used for energy-billing purposes.

Watt-hour meter
Also called revenue meter. An instrument that records the power used in watt-hours.

Also called mast head. The point of entrance to service conduit from the service drop. A device to keep water from entering the service conduit.

Wind energy
Refers to the kinetic (in motion) energy of the wind that can turn a wind turbine to generate electricity.

Wye system
Also called star system. A method of connecting three single transformers for three-phase application used in three- or four-wire systems.

The symbol for impedance.