A refresher course in the terminology of electricity.

GLOSSARY

A refresher course in
the terminology of
electricity.

PACIFIC VOLT GLOSSARY

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.

Alternator

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.

Amp

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.

Ampacity

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

Amperage

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

Ampere

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.

Ampere-hour

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.

ANSI

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.

Appliances

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.

Arc

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.

Armature

The rotating part of a motor or generator.

AWG

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

Bank

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

Battery

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.

Blackout

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.

Bonding

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.

Breaker

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.

Brownout

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.

Bus

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

Cable

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.

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

Capacitive

Having or exhibiting capacitance.

Capacitor

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.

Cell

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.

Circuit

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.

Clips

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.

Conductor

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.

Contactor

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

Continuity

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

Coulomb

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).

Crossarm

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

Current

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.

CVR

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.

Cycle

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.

Cycles-per-second

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

An abbreviation for direct current.

Decibel

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.

Demand

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.

Diode

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 opposed 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.

Disconnect

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.

Efficiency

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.

Electricity

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.

Electrolyte

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

Energy

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.

ESP

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

Farad

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).

Fault

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.

Feeder

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.

Filter

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

FLA

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 electronic equipment. There are many possible causes. Some involve problems with the consumer’s internal wiring; others involve the utility.

Frequency

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.

Generator

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.

Generation

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.

Grid

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.

Ground

A path of electrical current to the earth.

Grounded

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.

Harmonic

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 waveforms. Total harmonic distortion (THD) is expressed as a percentage of distortion; the lower the percentage, the better.

Harmonics

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.

Henry

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).

Hertz

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).

Horsepower

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.

Impedance

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.

Inductance

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.

Inductor

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.

Insulators

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.

Inverter

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.

Ion

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

Joule

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.

Jaws

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.

Listed

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).

Load

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)

A load tap changer (LTC), also known as an on-load tap changer, is a device in a transformer that allows for the adjustment of the transformer's turns ratio while the transformer is energized and under load. This adjustment regulates the output voltage of the transformer, maintaining a stable voltage level despite variations in load or input voltage.

LRA

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.

MCA

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.

Negative

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.

Neutral

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.

Newton-meter

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

Nonlinear loads are electrical loads where the current waveform is not a scaled version of the voltage waveform, meaning the current drawn is not directly proportional to the voltage. This contrasts with linear loads, where current and voltage waveforms are proportional and sinusoidal. Nonlinear loads, often containing power electronic devices, introduce harmonics into the power system, causing issues like voltage distortion, equipment overheating, and interference with sensitive electronics. 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.

Ohm

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.

Outage

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.

Overcurrent

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.

Overload

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

In electrical and electronic systems, refers to a voltage level that exceeds the specified or normal operating voltage of a circuit or device. This excess voltage can be temporary, like a spike, or sustained, and it can damage or disrupt the operation of connected equipment. 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).

Phase

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.

Positive

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.

Potential

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

Power

The rate at which electrical energy is transferred or converted in an electrical circuit. It's essentially a measure of how quickly energy is used or supplied by an electrical component or system. The standard unit for electrical power is the watt (W), which is equivalent to one joule per second. 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

An automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. It acts as a safety device, interrupting the current flow when it detects a fault, thus preventing overheating, fires, and other hazards. Unlike fuses, circuit breakers can be reset and reused after tripping

Power distribution utility

See Utility distribution company (UDC).

Power factor (PF)

A measure of how effectively electrical power is being used in an AC circuit. It's the ratio of real power (the power that does useful work) to apparent power (the total power supplied). A power factor of 1 (or 100%) is ideal, meaning all the supplied power is used efficiently. 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.

Power generation utility

A company or entity that owns and operates facilities to produce electricity, often for sale to other companies or directly to consumers. They are a key part of the electric power industry, responsible for the initial step of generating electricity before it's transmitted and distributed.

Power source adjustment

Primary

In a transformer, the primary side is where the electrical energy is fed in, typically connected to the power source. It's the input side of the transformer, and the winding on this side is called the primary winding. The primary winding is responsible for establishing the magnetic flux that induces a voltage in the secondary winding.

Primary distribution lines

The part of an electric power distribution system that carries medium voltage electricity from substations to distribution transformers, which then lower the voltage for delivery to end-users. These lines operate at higher voltages than secondary distribution lines, typically ranging from 2,300 to 39,000 volts. Also called feeder lines. 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 resistance.

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

In an electrical system is one where the current and voltage are out of phase, meaning the energy oscillates back and forth between the source and the load without being fully consumed. This non-working power is known as reactive power and is measured in volt-amperes reactive (VAR). Reactive loads are typically associated with inductors and capacitors, and they are essential for maintaining magnetic fields in devices like motors and transformers.

Reactive power

(kVAR) 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

Also known as active power, it is the portion of electrical power that is converted into useful work, such as heat, light, or motion, within an electrical system. It's measured in watts (W) and represents the actual energy being utilized by a load. Real power is the power that performs the "actual work" in a circuit.

Reconductor

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.

Recloser

An automatic, high-voltage electric switch used in power distribution systems to interrupt and reclose a circuit after a fault. It acts like a circuit breaker, but unlike a typical circuit breaker, it automatically tests the circuit and attempts to reclose, restoring power if the fault has cleared. This helps minimize power interruptions by automatically clearing temporary faults.

Rectifier

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

Regulator

A device for controlling the voltage of an electrical circuit.

Reliability

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.

Resistance

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

An electrical load where the current and voltage are in phase, meaning they reach their maximum and minimum values simultaneously. Examples are incandescent lighting and electric heaters.

Revenue meter

An electric revenue meter, also known as a revenue-grade meter (RGM), is a highly accurate device used to measure electrical energy consumption for billing and other financial transactions. These meters are essential for ensuring precise measurements and are often required for tenant billing, utility rewards programs, and other applications where accurate energy consumption data is critical.

RLA

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 its terminals.

RMS

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.

RPM

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

The symbol for Apparent Power.

Sags

See Voltage sag.

SCR

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 drawback is that they disrupt the normal flow of energy. They are nonlinear loads, and therefore create harmonics.

Secondary

In a transformer, the secondary winding is the coil of wire that receives energy from the primary winding through electromagnetic induction and delivers it to the load. It's essentially the output side of the transformer, where the transformed voltage is available. The secondary winding is typically designed with a larger wire gauge than the primary to handle the potentially higher current resulting from the voltage transformation.

Secondary circuit

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

Service entrance

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

An electric service limiter, also known as a power meter limiter or load limiter, is a device installed by an electricity provider to restrict the amount of electricity a customer can use without completely shutting off their power. This is often used by utility companies as a way to manage delinquent accounts and encourage customers to pay their bills, while still allowing them to maintain minimal service.

Service panel

A service panel, also known as an electrical panel, breaker box, or load center, is the main distribution point for electricity in a building. It receives power from the utility company and distributes it to individual circuits, each protected by a circuit breaker or fuse. Essentially, it's the central command center for your home's electrical system.

Service switch

A service switch is a building's main electrical switch, typically located in the service box (or breaker box), which acts as a disconnecting means to cut off power to the entire building. It is the primary switch used to isolate the building's electrical system from the power grid. In modern electrical systems, it's often the main breaker within the breaker box.

Service wires

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

Shock

An electric shock occurs when an electrical current passes through the body, causing involuntary muscle contractions and other physiological effects. It happens when a person comes into contact with an energized electrical source, such as a power line, appliance, or outlet. The severity of an electric shock depends on factors like the voltage, current, duration of contact, and path of the current through the body.

Short

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 or AC waveform. A smooth, oscillating waveform that can be visualized as an S-shaped curve, repeating over time. It is defined by the mathematical function y = sin(x), where 'x' represents the angle or time. In ideal electric systems, the characteristic shape of the alternating voltage or current wave.

Single-phase

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 opposed 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.

Solar energy

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

Splice

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

Split-phase

Also known as dual-phase or two-phase, is a type of single-phase electrical power distribution system commonly used in North America for residential and light commercial applications. It essentially splits a single-phase AC power supply into two 120V lines that are 180 degrees out of phase with each other. This configuration allows for both 120V and 240V power to be supplied to different appliances and devices within a building.

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.

Stator

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.

Substation

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.

Sustained outage

A sustained voltage outage, also known as a sustained interruption, is a prolonged loss of electrical power where the voltage is zero for more than one minute. It differs from momentary outages, which are brief interruptions of less than a minute. Sustained outages often require human intervention to repair the system and restore power. Typically caused by mechanical failure, such as downed lines or failed transformers.

Swell

See Voltage swell.

Switch

A device that controls the flow of electricity in a circuit by opening or closing the circuit. It acts as a simple on/off mechanism, allowing or preventing current flow. When the switch is closed, it completes the circuit, allowing current to flow and the device connected to it to operate. When open, the circuit is broken, stopping the flow of current and turning off the device.

Switchboard

Switching center

An electrical switching center is a facility where multiple electrical circuits are connected and switched, allowing for the redirection or interconnection of power flow. It's a crucial part of power distribution networks, facilitating the control and routing of electrical current. In essence, it acts as a hub where electricity can be directed to different paths or circuits as needed.

Tap changer

A mechanism in a transformer that adjusts the voltage by changing the number of turns in one of the transformer's windings. This adjustment alters the voltage ratio and allows for fine-tuning the output voltage of the transformer. Tap changers are categorized into two main types: on-load tap changers (OLTC) and de-energized tap changers (DETC)(also known as off-load tap changers).

THD

Short for total harmonic distortion.

Three-phase

A type of electrical power distribution system that uses three alternating current (AC) voltage waveforms, each offset by 120 degrees, to deliver electrical power. It's a common method for generating, transmitting, and distributing electricity, particularly in industrial and commercial settings, due to its efficiency and ability to handle high power loads. This type of system has advantages over single-phase, including the ability to deliver greater power using the same size conductors.

Three-phase bank

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

Three-phase motor

An electric motor that operates using a three-phase circuit, converting electrical energy into mechanical energy. It utilizes three alternating currents that are 120 degrees apart, resulting in a rotating magnetic field that drives the motor. These motors are known for their efficiency, high starting torque, and compact size compared to single-phase motors. 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.)

Torque

The standard unit of torque is the newton-meter (N⋅m). Torque is a measure of the rotational force that tends to cause an object to rotate. It's calculated by multiplying the force applied (measured in newtons) by the perpendicular distance (measured in meters) from the point of force application to the axis of rotation.

Total harmonic distortion (THD)

See Harmonic distortion.

Transformer

An electrical transformer is a device that transfers electrical energy between two or more circuits through electromagnetic induction. It primarily changes voltage levels (either increasing or decreasing) without altering the frequency of the alternating current.

Transformer ratio

The transformer ratio, also known as the turns ratio or transformation ratio, is the ratio of the number of turns in the primary winding of a transformer to the number of turns in the secondary winding. It essentially describes how voltage is stepped up or down in a transformer. 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

A transient voltage is a short-duration, sharp increase or decrease in voltage within an electrical circuit. These voltage spikes, also known as surges or impulses, are temporary and can be caused by various events like lightning strikes, switching operations, or faults in electrical equipment. They are typically measured in microseconds or milliseconds and can be dangerous to electronic equipment.

Transmission system

The infrastructure that moves large amounts of electricity, generated at power plants, over long distances to local utilities for distribution to end-users. It acts like the "motorways" of the electricity grid, carrying high-voltage power, while the distribution system handles the "local roads" for delivery to homes and businesses. 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.

Underground

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

Refers to a situation where the voltage supplied to a device or system is lower than the intended or rated voltage. This can lead to various issues, including reduced performance, overheating, and potential damage to equipment.

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)

A utility distribution company (UDC) is a company that owns and operates the infrastructure (like power lines, gas pipelines, or water mains) that delivers energy or other essential services to end-users. In simpler terms, it's the company that ensures electricity, gas, or water reaches your home or business. 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.

VAR

Abbreviation for Volt Ampere Reactive. It is a unit of measurement for reactive power in AC electrical systems. See reactive power.

Variable auto transfer

Often called a Variac, it is a type of transformer with a single, continuous winding that serves as both the primary and secondary circuit. It allows for adjustable output voltage by varying the number of turns used in the secondary circuit, making it useful for applications needing precise voltage control.

Voltage

Voltage is the measure of electrical potential difference between two points in an electrical circuit. It represents the amount of energy required to move a unit of electric charge from one point to another. Essentially, it's the "push" or "pressure" that drives electric current through a circuit. Voltage is measured in volts (V). Voltage is analogous to water pressure in a hydraulic system.

Voltage drop

The reduction in electrical potential along the path of current flow in an electrical circuit. It occurs when current encounters resistance within conductors, connectors, or other components, causing a decrease in voltage between two points in the circuit. Essentially, it's the loss of voltage as electricity travels from the power source to the load.

Voltage sag

A voltage sag, also known as a voltage dip, is a short-duration decrease in voltage magnitude in an electrical power system. It occurs when the voltage drops below 90% of its nominal or normal value for a brief period, typically ranging from a few milliseconds to a minute. Voltage sags are a common power quality issue that can cause problems for sensitive electronic equipment. They 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 10% or more.

Volt amperes (VA)

Also called apparent power defined as the total power flowing in an AC circuit, representing the combined effect of real (or active) power and reactive power. It is the product of the voltage and current in the circuit, measured in volt-amperes (VA). While apparent power indicates the total power demand, not all of it is used for doing work;some is due to reactive components.

Volts

Unit of electromotive force, the difference of potential that would drive one ampere of current against one ohm resistance. Named after Italian physicist Count Alessandro Volta (1745-1827).

Watt

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).

Watt-hour

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.

Weatherhead

Also known as a service head or service entrance cap, is a waterproof fitting at the top of a service mast (or riser) where overhead electrical or telephone wires enter a building. It's designed to protect the connection point from weather, preventing water from entering the conduit and potentially causing damage or electrical hazards.

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.

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