Terminology and Definitions

Terminology and Definitions

Alternating Current The term alternating current refers to a current that reverses at regular recurring intervals of time and that has alternately positive and negative values of equal amplitude.

Ammeter Device that measures the current flow in amperes in a circuit. An ammeter is connected in series with the load.

Ampere (A) The unit of measurement of electric current flow. If a 1-Ω resistance is connected to a 1-V source, 1 A will flow. Ohm’s law states that I = E/R, where I is amperage, E is voltage, and R is resistance.

Anode The positive pole of a DC device, or preferably the path by which the current passes out and enters the device on its way to the other pole, opposite of the cathode.

Branch Circuit The circuit conductors between the final overcurrent device protecting the circuit and the device(s).

Calorie The calorie is a pre–International System of Units metric unit of energy. The unit was first defined by Professor Nicolas Clement in 1824 as a unit of heat.

Capacitance Measure, in farads, of the opposition to voltage changes in an AC circuit, causing voltage to lag behind current. Capacitance is the ability of a body to hold an electrical charge. Capacitance is also a measure of the amount of electrical charge stored (or separated) for a given electrical potential.

Capacitive Reactance The opposition to the flow of current in a alternat- ing or pulsating current.

Capacitor A capacitor or condenser is a passive electronic or electrical component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference occurs between the conductors, an electric field occurs in the dielectric. This field can be used to store energy, to resonate with a signal, or to link electrical and mechanical forces.

Running capacitors are used in starting winding to increase the run- ning torque of the motor. Starting capacitors are used in starting wind- ing to increase the starting torque of the motor.

Circuit A complete path through which an electric current can flow.

Circuit Breaker A device designed to open and close a circuit by nonau- tomatic or automatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself, when properly applied within its rating. Circuit breakers can be reset. They can be tripped remotely with a shunt trip.

Circuit (Series) A circuit supplying energy to a number of devices con- nected in series. The same current passes through each device, and the voltage is divided between the devices in completing its path to the source of supply.

Closed Circuit A closed path formed by the interconnection of electrical or electronic components through which an electric current can flow.

Coil An assemblage of successive windings of a conductor. A winding consisting of one or more insulated conductors surrounded with insula- tion and arranged to interact with or produce a magnetic field.

Conductance The measurement of the ease by which electricity flows through a substance. Conductance is measured in mhos because it is the opposite of resistance which is measured in ohms.

Conductor An electrical path that offers comparatively low resistance. A wire or combination of wires not insulated from one another, suitable for carrying a single electric current. Conductors may be classed with respect to their conducting power as (a) good (gold, silver, copper, alu- minum, zinc, brass, platinum, iron, nickel, tin, lead); (b) fair (charcoal and coke, carbon, acid solutions, seawater, saline solutions, metallic ores, living vegetable substances, moist earth); (c) partial (water, the body, flame, linen, cotton, mahogany, pine, rosewood, lignum vitae, teak, marble).

Coulomb A unit of electrical charge; the quantity of electricity passing in 1 s with a steady current of 1 A.

Counter EMF The total opposition to the flow of current in an alternat- ing current (AC) circuit.

Cross-Circuit Any accidental contact between electric conductors or wires.

Current (I ) The movement of electrons through a conductor; measured in units of amperes.

Cycle A complete reversal of current in an alternating circuit, passing through a complete set of changes or motions in opposite directions, from zero to a rise to maximum amplitude, to a return to zero, to a rise to maximum amplitude in the other direction, and to another return to zero. One complete positive and one complete negative alternation of current or voltage.

Deci A Latin prefix often used with a physical unit to designate a quan- tity one-tenth (1/10) of that unit. 1 deciampere = 0.1 ampere.

Decibel (dB) The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. Usually it is used for sound or signal strength. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit. A decibel is one-tenth (1/10) of a bel (B).

Deflection The angle distance by which one line or unit departs from another.

Deka A Greek prefix often used with a physical unit denoting a factor of 101 or 10. 1 dekaampere = 10 amperes.

Diagram A geometric representation or drawing that illustrates the principles of application of a mechanism or circuit.

Diode A two-electrode electronic device containing an anode and a cathode. Diodes are used as rectifiers, detectors, and light emitters (LEDs).

Direct Current In direct current, the electric charges flow in a constant direction, positive with respect to ground, distinguishing it from alter- nating current (AC).

Dissipation The loss of electric energy as in the form of heat.

Drop The voltage drop developed across a resistance due to current flowing through it.

E The standard symbol for voltage; short for electromotive force.

Earth The ground reference considered as a grounding medium for an electrical circuit.

Electrical Horsepower By definition, exactly 746 W at 100 percent efficiency.

Electrical Units In an electrical system, electrical units consist of the volt, ampere, ohm, watt, watthour, coulomb, henry, mho, joule, and farad.

Electric Circuit The path (whether metallic or nonmetallic) of an electric current typically consisting of wire(s) and device(s).

Electrician A tradesman specializing in electrical wiring of buildings and related equipment. A tradesman typically begins as an apprentice, working for and learning from a journeyman or master, and after a number of years is released from his or her master’s service as a jour- neyman.

Electricity Electricity [from the Greek word ηλεκτρον (electron), mean- ing amber, and finally from the New Latin electricus, “amber-like”] is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily rec- ognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction.

Electrocution The annihilation of life by means of electric current.

Electromagnet A type of magnet in which the magnetic field is produced by the flow of electric current in a conductor. The magnetic field disap- pears when the flow current ceases.

Electromotive Force (EMF) The flow of current in an alternating current (AC) circuit. An energy-charge relation that results in electric pressure (voltage), which produces or tends to produce charge flow.

Electron A subatomic particle that carries a negative electrical charge.

Energy Efficiency The efficiency of an entity (a device, component, or system) in electronics and electrical circuits. Defined as useful power output divided by the total electrical power consumed. Efficiency = useful power output/total power input.

Farad (F) The unit of electrostatic capacity in the electromagnetic system. A condenser or capacitor is said to have a capacity of 1 farad (1 F) if it will absorb 1 coulomb (1 C) (1 A/s) of electricity when subjected to a pressure of 1 V. The unit of capacitance.

Faraday Effect A discovery made by Michael Faraday. In physics, a magneto-optical phenomenon, or an interaction between light and magnetic field in a medium.

Fathom A measure of length equal to 2 yards (6 ft), used chiefly in taking soundings, measuring cordage, etc. Based on the distance between the fingertips of a man’s outstretched arms.

Fiber Optics A glass or plastic fiber that carries light along its length.

Fluorescence A luminescence that is mostly found as an optical phe- nomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of a photon with a longer (less energetic) wave- length. That property by which certain solids and fluids become lumi- nous under the influence of radiant energy.

Force An elementary physical cause capable of modifying the motion of a mass; it is measured in newtons.

Formula In mathematics and in the sciences, a formula (plural: for- mulae, formulæ, formulas) is a concise way of expressing information symbolically. A rule or principle expressed in algebraic language.

Frequency The number of periods occurring in the unit of time periodic process, such as in the cycles of electric charge. The number of complete cycles per second existing in any form of wave motion, such as the number of cycles per second of an alternating current.

Fuse A strip of wire or metal inserted in series with a circuit which, when it carries an excess of current over its rated capacity, will burn out, thus protecting the circuit’s other components from damage due to excessive current.

Galvanometer A type of ammeter—an instrument for detecting and measuring electric current. It is an analog electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through its coil. The term has been expanded to include uses of the same mechanism in recording, positioning, and servomechanism equipment.

Generator A device that converts mechanical energy to electrical energy, generally using electromagnetic induction.

Ground The term ground or earth has several meanings depending on the specific application areas. Ground may be the reference point in an electrical circuit from which other voltages are measured, a common return path for electric current (earth return or ground return), or a direct physical connection to the earth.

Grounded The term grounded refers to the act of connecting the elec- trical circuit to a ground or earth reference. This may be done for safety purposes during installation or maintenance.

Heat (Electric) The power loss produced in a conductor having electric current flow through it. Electric heaters and stoves use electromagnetic dissipation to produce heat.

Horsepower (hp) Unit used to express rate of work, or power. 1 horse- power (hp) = 746 watts (W) at 100 percent efficiency. Work is done at the rate of 33,000 foot-pounds per minute or 550 foot-pounds per second. The term horsepower is being slowly replaced by kilowatt (kW) and megawatt (MW).

I Standard symbol for electric current.

Impedance (Z ) The total opposition to the flow of current in an alternat- ing current (AC) circuit at a given frequency; combination of resistance and reactance, measured in ohms.

Inductance (L) The property of an alternating current electrical circuit where the change in the current through that circuit induces a counter electromotive force that opposes the change in current.

Induction The production of current flow in a conductor in a magnetic field.

Input The entrance point in an electrical circuit or device, as in the input to a sensor or motor.

Insulator Also called a dielectric; a material that resists the flow of electric current. A device for fastening and supporting a conductor.

Ion An atom or a molecule that has lost or gained one or more electrons, giving it a positive or negative electrical charge.

Joint The connection of electrical conductors so that the union will be good, both mechanically and electrically.

Joule’s Law Also known as the Joule effect. A physical law expressing the relationship between the heat generated by the current flowing through a conductor. It is named for James Prescott Joule, who studied the phenomenon in the 1840s.

Kilovolt (kV) A unit of measurement equal to 1000 volts. 1000 V = 1 kV.

Kilowatt (kW) Equal to 1000 watts. Typically used to state the power output of engines and the power consumption of tools and machines. A kilowatt is approximately equivalent to 1.34 horsepower (hp). An elec- tric heater with one heating element might use 1 kW. 1000 W = 1 kW.

A distinction should be made between kilowatts, which is the mea- surement of resistance, and kilovolt amperes reactive, which is the mea- surement of impedance in an AC circuit.

Leakage The loss of electric current through defects in insulation or other causes.

Loss Power used or expended without accomplishing useful work.

Megavolt A unit of measurement equal to 1 million volts. 1 MV = 1,000,000 V.

Meter An electric measuring instrument such as a voltmeter, ammeter, kilowatthour meter, etc.

Negative The opposite of positive. A potential less than that of another potential. In electrical apparatus, the pole or direction toward which the current flows. A negative value can have a positive sign. It is negative with respect to another potential.

Network In the context of an electrical circuit, a collection of inter- connected components. The components are connected in some special manner.

Neutron A subatomic particle with no net electric charge and a mass slightly larger than that of a proton.

Ohm (W) Defined as the resistance between two points of a conductor when a constant potential difference of 1 V, applied to these points, produces in the conductor a current of 1 A, the conductor not being the seat of any electromotive force.

where R = resistance, Ω

E = volts

I = amperes

R = E/I

Open Circuit A circuit in which the electrical continuity has been interrupted.

Output The result of an action or sensor that produces current or volt- age in a circuit or device.

P Standard abbreviation for power.

Peak The maximum measurable value of a varying voltage or current. Peak Current The maximum measurable value of an alternating current. Period A measurement of time. The time required for a complete cycle of alternating current or voltage; for 60 cycles per second, a period is ¹/₆₀ s.

Photoelectric A phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation such as visible light.

Photoelectric Sensor Electronic device recognizing changes in light intensity and converting these changes to a change in output state.

Photon An elementary particle, the quantum of the electromagnetic field, and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force.

Positive This is a relative term. It is positive relative to another poten- tial. A positive value can have a negative sign in respect to a less posi- tive value.

Power (P ) Defined as the rate at which electrical energy is transferred by an electric circuit, measured in watts or horsepower. P = I ⋅ E, where P = power in watts, I = current measured in amperes, and E = volts.

Proton A subatomic particle with an electric charge of +1 elementary charge. The smallest quantity of electricity that can exist in the free state. A positive charged particle in the nucleus of an atom.

Quick-Break A switch, circuit breaker, or contact that has a high contact opening speed.

R Standard symbol for resistance.

Reactance (X ) Opposition to the flow of current in an AC circuit by the inductance or capacity of a part; measured in ohms.

Relay An electromagnetic or solid-state device with contact(s) either Normally Open or Normally Closed, which permits control of current in a circuit.

Resistance (R ) The opposition to the flow of current in a circuit that produces heat. Pure resistance can only be found in a DC circuit.

Resistor A device that introduces resistance to a circuit, producing a voltage drop in its terminals in proportion to the current.

Semiconductor A solid material that has an electrical conductivity between those of a conductor and an insulator; it can vary over that wide range either permanently or dynamically.

Series Circuit A circuit supplying energy to a number of loads connected in series. The same current passes through each load, and the voltage drops in proportion to the resistance of the device in completing its path to the source of supply.

Series Parallel Circuit An electric circuit containing parallel connected devices and serial connected devices.

Short Circuit A fault in an electric circuit or apparatus due to human error or an imperfection in the insulation. The current flows through a path not intended.

Shunt A device that short-circuits an electrical circuit.

Shunt Trip A coil that allows the remote disconnection of electrical power by mechanically tripping the circuit breaker.

Solenoid A coil or transducer that, when an electric current passes through it, causes a linear motion in a mechanical operator.

Steady Current An electric current of constant value measured in amperes.

Transformer A device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field. This changing magnetic field induces a changing voltage in the second circuit (the secondary). This effect is called mutual induction.

Transformer (Current) A transformer that is used to measure the cur- rent in a circuit. Care should be taken with the secondary of the current transformer. The secondary should not be disconnected from the load while current is flowing. The transformer will attempt to continue driv- ing current across the effectively infinite impedance. This will produce a high voltage across the secondary, which can be in the range of several kilovolts and can cause arcing. This voltage will compromise your safety and permanently affect the accuracy of the transformer.

Transistor A semiconductor device commonly used to amplify or switch electronic signals.

Unit of Current The standard unit of measurement for current is the ampere, which is the current produced by 1 volt in a circuit having a resistance of 1 ohm.

Unit of Pressure Pressure or volts in an electrical circuit that will pro- duce a current of 1 ampere against a resistance of 1 ohm.

Unit of Resistance The unit of measurement is the ohm, which is the resistance that permits a flow of 1 ampere when the pressure is 1 volt.

Volt (V) The unit of measurement of electric pressure; the pressure that will produce a current of 1 ampere against a resistance of 1 ohm.

Voltage Drop The drop of voltage in an electric circuit due to the resis- tance of the conductor.

Watt (W) The unit of measurement of electrical power, being the amount of energy expended per second by an unvarying current of 1 ampere and 1 volt.

X Standard symbol for reactance.

Y Connection This method of transformer connection consists of con- necting primaries and/or secondaries in a star grouping.

Z Standard symbol for impedance.