Active Filter
Any of a number of sophisticated power electronic devices for eliminating harmonic distortion.

Air-Gap Switch
A mechanical switch or relay that disconnects power to a load by physically separating two contacts, resulting in an air gap between the contacts.

Alternating Current (AC)
Electrical current that continually reverses direction, with this change in direction being expressed in Hertz, or cycles per second.

Alternating Voltage
A voltage which periodically changes its polarity.

Ambient Temperature
The average temperature of the surroundings.

Amp (Ampere)
A unit that measures the strength/rate of flow of electrical current.

Ampere-Hour Capacity
The quantity of electricity measured in ampere-hours (Ah) which may be delivered by a cell or battery under specified conditions.

Ampere-Hour Efficiency
The ratio of the output of a secondary cell or battery, measured in ampere-hours, to the input required to restore the initial state of charge, under specified conditions (also coulombic efficiency).

Anode
The electrode in an electrochemical cell where oxidation takes place. During discharge, the negative electrode of the cell is the anode. During charge, the situation reverses and the positive electrode of the cell is the anode.

ANSI C62.41-1991
A technical Standard that characterizes the electrical power line surge environment. Originally published by the Institute of Electrical and Electronic Engineers as Standard IEEE 587-1980, it was updated in 1991 and now recognized as an American National Standard.

Armature
That part of an electric generator in which the voltage is induced.

Armored Cable
Electrical wires protected by metal sheathing.

Autotransformer
A transformer with a single winding.

Average Value
The average of the instantaneous values through which an alternating voltage or current passes during one alternation. The average value of a sine curve is equal to .637 times its peak value.



Back-Cover
Enclosure on back of control which houses the electrical and mechanical components.

Ballast
An electrical device used in fluorescent and HID fixtures. It furnishes the necessary starting and operating characteristics to the lamp for proper performance.

Battery
Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term "battery" is often applied to a single cell.

Branch Circuits
The circuits in a house that branch from the service panel to boxes and devices.

Breaker
A switch-like device that connects/disconnects power to a circuit.

Brownout
A temporary drop in electric power without the power going completely off. A brownout may make the computer screen flicker, and can cause loss of data that has been entered but not saved yet.

Buss Bar (also Bus Bar)
Separate, metallic strips that extend through the service panel. Breakers slide onto the "hot" busses and neutral and ground wires screw down in their respective busses.

BX Cable
An old type of armored cable now illegal.



Cable Clamps
Metal clips inside an electrical box that hold wires in place.

Canadian Standards Association (CSA)
An organization that provides testing and certification services for manufacturers that wish to use the CSA mark on products that conform to the appropriate CSA standard.

Capacitance
The property of a capacitor that determines the quantity of electric energy that it can store.
Capacitor
A device consisting of two conducting surfaces separated by an insulator and having the ability of storing electric energy. Also called a condenser.

Capacity
The total number of ampere-hours (or watt-hours) that can be withdrawn from a cell/battery under specified conditions of discharge.

Cathode
The electrode in an electrochemical cell where reduction takes place. During discharge, the positive electrode of the cell is the cathode. During charge, the situation reverses, and the negative electrode of the cell is the cathode.

CBEMA Curve
A set of curves representing the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance. Developed by the Computer Business Equipment Manufacturers Association (CBEMA), it has become a de facto standard for measuring the performance of all types of equipment and power systems, and is commonly referred to by this name.

Cell
The basic electrochemical unit used to generate or store electrical energy.

Charge
The number of electrons held on the capacitor plates. The act of forcing electrons onto the capacitor plates.

Charge
The conversion of electrical energy, provided in the form of a current from an external source, into chemical energy within a cell or battery.

Charged
The condition of a capacitor which has the full charge it can receive from a given applied voltage.

Circuit
A continuous loop of current (i.e. incoming "hot" wire, through a device, and returned by "neutral" wire).

Circuit Breaker
The most common type of "overcurrent protection." A breaker trips when a circuit becomes overloaded or shorts out.

Class 2 circuit
An isolated secondary circuit involving not more than 42.2V (peak) with specific current level limitations.

Closed Circuit Voltage (CCV)
The difference in potential between the terminals of a cell/battery when it is discharging (on- load condition).

Coefficient of coupling (k)
A numerical rating between 0 and 1 that specifies the degree of magnetic coupling between two circuits. Maximum coupling is 1 and no coupling is 0.

Common Mode Voltage
The noise voltage that appears equally from current-carrying conductor to ground.

Conduit
A protective metal tube that wires run through.

Conditioner


Continuous Discharge
A test in which a cell/battery is discharged to prescribed cut-off voltage.

Counter Electromotive Force (CEMF)
The voltage induced in a wire by self-induction which opposes the applied voltage. Also called back emf.

Coupling
Circuit element or elements, or network, that may be considered common to the input mesh and the output mesh and through which energy may be transferred from one to another.

Crest Factor
A value reported by many power quality monitoring instruments representing the ratio of the crest value of the measured waveform to the rms of the fundamental. For example, the crest factor of a sinusoidal wave is 1.414.

Critical Load
Devices and equipment whose failure to operate satisfactorily jeopardizes the health or safety of personnel, and/or results in loss of function, financial loss, or damage to property deemed critical by the user.

Cumulative Capacity
The total number of ampere-hours (or watt hours) that can be withdrawn from a cell/battery under specified conditions of discharge over a predetermined number of cycles or the cycle life.

Cut-Off Voltage
The cell/battery voltage at which the discharge is terminated.

Current Distortion
Distortion in the ac line current. See Distortion.

Cycle
The complete set of values through which an alternating voltage or current passes successively.

Cycle Life
The number of cycles under specified conditions which were available from a rechargeable cell/battery before it fails to meet specified criteria as to performance.



Derating
Reducing the capacity of a control when side sections are removed.

Deep Discharge
Withdrawal of at least 80% of the rated capacity of a cell/battery.

Depth of Discharge
The ratio of the quantity of electricity (usually in ampere-hours) removed from a cell/battery on discharge to its rated capacity (usually expressed in %).

Dielectric
The insulating material between the plates of a capacitor.

Dielectric Constant (K)
The property of the dielectric material that determines how much electric energy can be stored in a capacitor of a particular size by a value of applied voltage.

Dielectric Strength
The ability of a dielectric material of specified thickness to withstand high voltages without breaking down.

Differential Mode Voltage
The voltage between any two of a specified set of active conductors.

Diode
Any two-electrode device that conducts in only one direction.

Dip. See Sag.
Distortion. Any deviation from the normal sine wave for an ac quantity.

Direct Current (DC)
DC is the unidirectional flow or movement of electric charge carriers, usually electron. The intensity of the current can vary with time, but the general direction of movement stays the same at all times. As an adjective, the term DC is used in reference to voltage whose polarity never reverses.

Discharge
The conversion of chemical energy of a cell/battery into electrical energy and withdrawal of the electrical energy into a load.

Discharge Rate
The rate, usually expressed in amperes, at which electrical current is taken from the cell/battery.

Discharged
The removal of the charge in a capacitor by completing a circuit between the plates.

Displacement Current
The current flows in a circuit containing a capacitor whenever the capacitor charges or discharges.

Dropout
A loss of equipment operation (discrete data signals) due to noise, sag, or interruption.

Dropout Voltage
The voltage at which a device will release to its de-energized position (for this document, the voltage at which a device fails to operate).

Duplex Receptacle
The commonly used receptacle (outlet). Called "duplex" because it has two plug-in sockets.



Eddy Current
Circulating current produced in connecting materials by a varying magnetic field. Eddy currents are undesirable in the core of a transformer.

Effective Value
The value of an alternating current that produces the same heating effect in a pure resistance as a corresponding value of dc. The effective value of a sine curve is equal to .707 times its peak value. Also called ROOT MEANS SQUARED (RMS) VALUE.

Electric Field
A field of force that exists between positively and negatively charged surfaces. In a capacitor, the field is assumed to consist of lines of force which extend through the dielectric from the positive to the negative plate.

Electrode
The site, area, or location at which electrochemical processes take place. An element of an electron tube or semiconductor device that takes part in conduction, such as the plate, anode, cathode and filament.

Electrolyte
The medium which provides the ion transport mechanism between the positive and negative electrodes of a cell.

Electromagnetic Induction
The process of developing a voltage in a wire that is being either cut by or is cutting a magnetic field.

Electromagnetic Compatibility
The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.

Electron Emmission
The escape of electrons from certain materials.

Electronic low-voltage
Electronic low-voltage lighting uses an electronic (solid-state technology) transformer to convert normal line voltage (120 VAC) to low voltage (typically 12 VAC).This lower voltage is then used power an incandescent low-voltage lamp. Only use a dimmer specifically designed for an electronic low-voltage transformer.

Energy Density
The ratio of the energy available from a cell or battery to its volume (Wh./L). Also used on a weight basis (Wh/kg).

Equipment Grounding Conductor
The conductor used to connect the non-current carrying parts of conduits, raceways, and equipment enclosures to the grounded conductor (neutral) and the grounding electrode at the service equipment (main panel) or secondary of a separately derived system (e.g., isolation transformer). See NFPA 70-1990, Section 100.



Failure Mode
The effect by which failure is observed.

Farad
The unit of measure for capacitance. It is the capacitance of a capacitor in which an applied voltage of one volt will store a charge of one coulomb. The more practical units of capacitance are the microfarad and picofarad.

Fast Tripping
Refers to the common utility protective relaying practice in which the circuit breaker or line recloser operates faster than a fuse can blow. Also called fuse saving. Effective for clearing transient faults without a sustained interruption, but is somewhat controversial because industrial loads are subjected to a momentary or temporary interruption.

Fault
Generally refers to a short circuit on the power system.

Fault, Transient
A short circuit on the power system usually induced by lightning, tree branches, or animals which can be cleared by momentarily interrupting the current.

Field
The windings of an electric generator which are supplied with dc to produce the steady electromagnetic field. Generators used for demonstration purposes may use permanent magnets to produce the magnetic field.

Filter
An electrical circuit which is part of every Lutron dimmer that is intended to reduce radio frequency interference and lamp buzz.

Fixture
Any permanently connected light or other electrical device that consumes power.

Flicker
Impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time.

Flux Linkage
The linking of the magnetic lines of force with the conductors of a coil. The value obtained by multiplying the number of turns in the coil by the number of magnetic lines of force passing through the coil.

Forward Bias
A dc voltage applied to a PN junction semiconductor so that the positive terminal of the voltage source connects to the P-type material and the negative terminal to the N-type material. It produces forward current in the circuit.

Forward Current
Current in a circuit of a semiconductor device due to conduction by majority carriers across the PN junction.

Frequency
The number of cycles of alternating voltage or current which occur during a particular amount of time, usually one second.

Frequency Deviation
An increase or decrease in the power frequency. The duration of a frequency deviation can be from several cycles to several hours.

Frequency Response
In power quality usage, generally refers to the variation of impedance of the system, or a metering transducer, as a function of frequency.

Front Accessible Service Switch (FASS)
An air-gap switch that can be conveniently activated without removing the wallplate of a control. When switch is turned off, power is completely removed from the device's load circuit by an air-gap switch.

Full-range Dimming
Continuous dimming, full intensity to minimum, with no visibly discernable increments in light level.

Fundamental (Component)
The component of order 1 (50 to 60 Hz) of the Fourier series of a periodic quantity.

Fuses
Removable devices that link a circuit at the fuse box. Fuse connections blow apart and break the circuit if an overload or short occurs.



Gassing
The evolution of gas from one or more of the electrodes in a cell. Gassing commonly results from local action (self-discharge) or from the electrolysis of water in the electrolyte during charging.

GFCI or GFI (Ground Fault Circuit Interrupter)
A specific type of circuit protection (commonly required in kitchens & bathrooms) that helps safeguard against shocks. GFCI protection can come from an outlet or a breaker.

Generators
Machines used to convert mechanical energy into electric energy. They accomplish this by causing one or a series of interconnected coils to either cut or be cut by a strong magnetic field.

Ground
A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth, or to some conducting body of relatively large extent that serves in place of the earth. Note: It is used for establishing and maintaining the potential of the earth (or of the conducting body) or approximately that potential, on conductors connected to it, and for conducting ground currents to and from earth (or the conducting body).

Ground Electrode
A conductor or group of conductors in intimate contact with the earth for the purpose of providing a connection with the ground.

Ground Fault
Current misdirected from the hot (or neutral) lead to a ground wire, box, or conductor.

Gang Single-gang
one control mounted in a single wallbox.
Multigang = two or more controls mounted side-by-side in a series of connected wallboxes.

Ground Grid
A system of interconnected bare conductors arranged in a pattern over a specified area and on or buried below the surface of the earth. The primary purpose of the ground grid is to provide safety for workmen by limiting potential differences within its perimeter to safe levels in case of high currents which could flow if the circuit being worked became energized for any reason or if an adjacent energized circuit faulted. Metallic surface mats and gratings are sometimes utilized for the same purpose . This is not necessarily the same as a Signal Reference Grid.

Ground Loop
A potentially detrimental loop formed when two or more points in an electrical system that are nominally at ground potential are connected by a conducting path such that either or both points are not at the same ground potential.

Ground Window
The area, through which, all grounding conductors, including metallic raceways enter a specific area. It is often used in communications systems through which the building grounding system is connected to an area that would otherwise have no grounding connection.



Harmonic (component)
A component of order greater than one of the Fourier series of a periodic quantity.

Harmonic Content
The quantity obtained by subtracting the fundamental component from an alternating quantity.

Harmonic Distortion
Periodic distortion of the sine wave. See Distortion and Total Harmonic Distortion (THD).

Harmonic Filter
On power systems, a device for filtering one or more harmonics from the power system. Most are passive combinations of inductance, capacitance, and resistance. Newer technologies include active filters that can also address reactive power needs.

Harmonic Number
The integral number given by the ratio of the frequency of a harmonic to the fundamental frequency.

Harmonic Resonance
A condition in which the power system is resonating near one of the major harmonics being produced by nonlinear elements in the system, thus exacerbating the harmonic distortion.

Henry (H)
The basic unit of inductance. One henry is the inductance which induces a cemf of 1 volt when the current is changing at the rate of 1 ampere per second.

Hertz (Hz)
The unit of frequency. One hertz is equal to 1 cycle per second (cps).

Hot, Neutral, Ground
The three most common circuit wires. The hot brings the current flow in, the neutral returns it to the source, and the ground is a safety route for returning current. The ground and neutral are joined only at the main service panel.

Hysteresis
The lagging of induced magnetism behind the magnetizing force.



Impulse
A pulse that, for a given application, approximates a unit pulse or a Dirac function. When used in relation to the monitoring of power quality, it is preferred to use the term impulsive transient in place of impulse.

Impulsive transient
A sudden non-power frequency change in the steady state condition of voltage or current that is unidirectional in polarity (primarily either positive or negative).

Ion
A particle in solution that can carry a negative or positive charge. impurities.

Inductance
The property of a circuit or coil that causes an electro-motive force to be set up due to a change of current in the circuit or coil.

Inductive Coupling
The coupling or linkage of two circuits by the changing magnetic lines of force. See also Mutual Induction.

Inductor (L)
A coil of wire which has the property of inductance.

Instantaneous
When used to quantify the duration of a short duration variation as a modifier, refers to a time range from one-half cycle to 30 cycles of the power frequency.

Instantaneous Reclosing
A term commonly applied to reclosing of a utility breaker as quickly as possible after interrupting fault current. Typical times are 18-30 cycles.

Instantaneous Value
The value of an alternating current or voltage at any specified instant in a cycle.

Interharmonic (component)
A frequency component of a periodic quantity that is not an integer multiple of the frequency at which the supply system is designed to operate (e.g. 50 Hz or 60 Hz).

Intermittent Test
A test during which a cell or battery is subjected to alternate periods of discharge and rest according to a specified discharge regime.

Interruption, Momentary (electric power systems)
An interruption of duration limited to the period required to restore service by automatic or supervisory-controlled switching operations or by manual switching at locations where an operator is immediately available. Note: Such switching operations must be completed in a specified time not to exceed 5 minutes.

Interruption, Momentary (power quality monitoring)
A type of short duration variation. The complete loss of voltage (<0.1 pu) on one or more phase conductors for a time period between 30 cycles and 3 seconds.

Interruption, Sustained (electric power systems)
Any interruption not classified as a momentary interruption.

Interruption, Sustained (power quality)
A type of long duration variation. The complete loss of voltage (<0.1 pu) on one of more phase conductors for a time greater than 1 minute.

Interruption, Temporary
A type of short duration variation. The complete loss of voltage (<0.1 pu) on one or more phase conductors for a time period between 3 seconds and 1 minute.

Inverter
An electric or electronic device for producing alternating current from direct current.

ISO 9001
A series of quality standards established by the International Organization of Standardization, that outline the requirements for quality management systems.

Isolated Ground
An insulated equipment grounding conductor run in the same conduit or raceway as the supply conductors. This conductor is insulated from the metallic raceway and all ground points throughout its length. It originates at an isolated ground-type receptacle or equipment input terminal block and terminates at the point where neutral and ground are bonded at the power source. See NFPA 70-1990, Section 250-74, Exception #4 and Section 250-75, Exception.

Isolation
Separation of one section of a system from undesired influences of other sections.



Joule
A joule is a measure of the energy contained in an impulse or conversely it is a measure of the absorption capability of a surge protection device. 1 joule = 1 watt x 1 second.

Junction (Electrical) Box
A square, octagonal, or rectangular plastic or metal box that fastens to framing and houses wires, and/or receptacles and/or switches.

Junction Diode
A diode consisting of a PN junction and suitable connecting leads.



Knockout
A removable piece of an electrical box or panel that's "knocked out" to allow cable to enter the box.



Laminations
Thin layers or sheets. The term refers to the thin pieces of iron used to build up the core of a transformer.

Lead
The short length of a conductor that hangs free in a box or service panel. (i.e. a wire end)

Leakage
Leakage appears as a clear caustic or white solid at the negative terminal of a RAM cell.

Leakage Inductance
A small inductance associated with those flux lines of a transformer winding which are not magnetically coupled to the other windings of the transformer.

Left Hand Generator Rule
A method of determining the direction of current flow (polarity) in a conductor, as follows: Extend the thumb first finger, and second finger of the left hand at right angles to each other. When the thumb is pointed in the direction (upward or downward) of conductor motion as it passes through the magnetic field, and the first finger is pointed to the south pole of the magnetic field (matching the direction of magnetic flux), the second finger will point in the direction of current flow (toward the negative pole or terminal).

Life
For rechargeable batteries, the duration of satisfactory performance, measured in years (float life) or in the number of charge/discharge cycles (cycle life).

Linear Load
An electrical load device which, in steady state operation, presents an essentially constant load impedance to the power source throughout the cycle of applied voltage.

Load
A load is an energy consuming device. The device can be an actual device such as a bulb of a flash light, radio, cassette player, motor, etc., a resistor or a constant current load.

Long Duration Variation
A variation of the rms value of the voltage from nominal voltage for a time greater than one minute. Usually further described using a modifier indicating the magnitude of a voltage variation (e.g., Undervoltage, Overvoltage, or Voltage Interruption).

Low-Side Surges
A term coined by distribution transformer designers to describe the current surge that appears to be injected into the transformer secondary terminals upon a lightning strike to grounded conductors in the vicinity.



Magnetic Induction
The process of setting up magnetism in an object that is placed in a magnetic field.

Magnetic linens
The imaginary lines of force that make up a magnetic field.

Magnetic Low-Voltage
Magnetic low-voltage lighting uses a magnetic (core and coil technology) transformer to convert normal line voltage (120 VAC) to low voltage (typically 12 VAC). This lower voltage is then used to power an incandescent low-voltage lamp. Only use a dimmer specifically designed for a magnetic low-voltage transformer.

Magnetic pole
The point at which the magnetic lines are concentrated. In every magnet, there is one north pole and one south pole.

Magnetic Shield
A piece of magnetic material used to carry the magnetic lines around and object to prevent the object from being affected by the magnetic field.

Magnetism
The property of certain materials to attract iron and other magnetic materials.

Magnetomotive Force(mmf)
The force that sets up a magnetic field within and around an object.

Mutual Inductance (M)
The ability of one conductor to induce an emf in a nearby conductor when the current in the first conductor changes.

Memory Effect
A phenomenon in which a cell, operated in successive cycles to the same, but less than a full, depth of discharge experiences a depression of its discharge voltage and temporarily loses the rest of its capacity at normal voltage levels.

Momentary
When used to quantify the duration of a short duration variation as a modifier, refers to a time range at the power frequency from 30 cycles to 3 seconds.

Mutual Induction
The electromagnetic induction produced by one conductor in another nearby conductor, due to the moving flux of the first circuit cutting the conductors of the second circuit.



Natural Magnet
A material which, in its natural state, possesses the qualities of a magnet. Magnetite is a natural magnet.

Noise
Unwanted electrical signals which produce undesirable effects in the circuits of the control systems in which they occur. (For this document, "control systems" is intended to include sensitive electronic equipment in total or in part.)

Negative Electrode
The electrode acting as an anode when a cell or battery is discharging.

NM
Nonmetallic-sheathed (plastic).

NMC
Solid plastic nonmetallic-sheathing used in wet or corrosive areas, but not underground (see UF).

Nominal Voltage (Vn)
A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (as 208/120, 480/277, 600).

Nonlinear Load
Electrical load which draws current discontinuously or whose impedance varies throughout the cycle of the input ac voltage waveform.

Normal Mode Voltage
A voltage that appears between or among active circuit conductors.

Notch
A switching (or other) disturbance of the normal power voltage waveform, lasting less than a half-cycle; which is initially of opposite polarity than the waveform, and is thus subtracted from the normal waveform in terms of the peak value of the disturbance voltage. This includes complete loss of voltage for up to a half cycle.

N-type Semiconductor
A doped semiconductor in which the majority current carriers are electrons.



Ohm
A unit that measures the resistance a conductor has to electricity.

Open Circuit Voltage (OCV)
The difference in potential between the terminals of a cell/battery when the circuit is open (no-load condition).

Oscillator
An electronic device for converting dc energy into ac energy.

Oscillatory Transient
A sudden, non-power frequency change in the steady state condition of voltage or current that includes both positive or negative polarity value.

Overvoltage
When used to describe a specific type of long duration variation, refers to a voltage having a value of at least 10% above the nominal voltage for a period of time greater than 1 minute.

Overcharge
Discharge past the point where the full capacity of the cell has been obtained.



P-type semiconductor
A doped semiconductor in which the majority current carriers are holes.

Passive Filter
A combination of inductors, capacitors, and resistors designed to eliminate one or more harmonics. The most common variety is simply an inductor in series with a shunt capacitor, which short-circuits the major distorting harmonic component from the system.

Peak Inverse Voltage
In an electron tube, the maximum negative voltage that can be applied to the plate without danger of arc-over. In a semiconductor diode, the maximum reverse bias voltage that can be applied without reaching the zener (or breakdown) voltage.

Peak-to-Peak Value
The maximum voltage change occuring during one cycle of alternating voltage or current. The total amount of voltage between the positive peak and the negative peak of one cycle or twice the peak value.

Peak Value
The highest or maximum value of an alternation of alternating current or voltage. This peak value occurs twice during each cycle.

Permeability
A measure of how easily magnetic lines of force can pass through a material.

Permanent Magnet
An artificial magnet that retains its magnetism after the magnetizing force has been removed. Steel, when properly processed, can be made into a permanent magnet.

Phase Shift
The displacement in time of one voltage-waveform relative to other voltage-waveform(s).
Power Factor, Displacement. The power factor of the fundamental frequency components of the voltage and current wave forms.

Pigtail
A short, added piece of wire connected by a wire nut. Commonly used to extend or connect wires in a box.

Plates
In a capacitor, the plates are the conducting surfaces.

Plate Voltage
In an electron tube, the difference of potential between plate and cathode.

PN Junction
A junction between an N-type semiconductor and a P-type semiconductor made by some method of diffusing, fusing or melting.

Power Conditioner
A device used to isolate sensitive equipment from the hazards of ?dirty power. Varying degree?s of protection can be provided for electrical noise and voltage fluctuations like transient (spikes), surges, sags (brownouts) and outages (blackouts).

Power Factor (True)
The ratio of active power (watts) to apparent power (voltamperes).

Power failure memory
Circuitry that ensures that if lights are off when power fails, they will remain off when power is restored. If lights are on when power fails they will return to the previously set level when power is restored.

Positive Electrode
The electrode acting as a cathode when a cell or battery is discharging.

Power Density
The ratio of the power available from a battery to its weight (W/kg) or volume (W/L). Also used on a weight basis (W/Kg).

Primary
That winding of a transformer which is connected to and receives energy from an external source of electrons. Also frequently referred to as the input winding.

Primary Cell (or Battery)
A cell or battery which is not intended to be recharged and is discarded when the cell or battery has delivered all its electrical energy.

Pulse
An abrupt variation of short duration of a physical quantity followed by a rapid return to the initial value.






Radio frequency interference (RFI)
An audible buzz or noise in some sensitive audio and radio equipment caused by the dimmer's rapid current switching in conjunction with sharp current rise.

Raise/lower Controls
An actuator (slider, rocker, toggle, paddle, etc.) which when engaged increases or decreases the intensity of light controlled, then returns to its normal place of rest after disengaging.

Rated Capacity
The number of ampere-hours a cell/battery can deliver under specific conditions (rate of discharge, cut-off voltage, temperature).

Recharge/Charge
The conversion of electrical energy, provided in the form of a current from an external source (charger), into chemical energy within a cell/battery.

Reclosing
The common utility practice on overhead lines of closing the breaker within a short time after clearing a fault taking advantage of the fact that most faults are transient, or temporary.

Recombination
The action by which current carriers (electrons and holes) combine and cancel each other.

Recovery Time
Time interval needed for the output voltage or current to return to a value within the regulation specification after a step load or line change. Also may indicate the time interval required to bring a system back to its operating condition after an interruption or dropout.

Recovery Voltage
The voltage that occurs across the terminals of a pole of a circuit interrupting device upon interruption of the current.

Rectification
The conversion of ac to pulsating dc.

Rectifier
A device which converts ac to pulsating dc.

Reluctance
The opposition of a material to magnetic lines of force. Reluctance in the magnetic circuit corresponds to resistance in the electric circuit.

Reverse Bias
A dc voltage applied to a PN junction so that the positive terminal of the voltage source connects to the N-type material and the negative terminal to the P-type material. It produces reverse current in the circuit.

Reverse Current
Current in a circuit of a semiconductor device due to conduction by minority carriers across PN junction.

Romex
A brand name of nonmetallic-sheathed cable made by General Cable Corporation. Often mistakenly used as a collective term for NM sheathed cable.

Root Mean Square (rms) Value
See effective value.

Rotor
The rotating member of a generator.

Rough-In
Installing the boxes, cables, and making "in-wall" connections while the walls are still open. Later, final connections are made and the devices and appliances are installed during the trim-out.

Rough service lamp
A lamp with extra filament support which can help reduce lamp buzz.



Sag
A decrease to between 0.1 and 0.9 pu in rms voltage or current at the power frequency for durations of 0.5 cycles to one minute.

Scene
The lighting effect created by adjusting several zones/channels of lighting to the desired intensity.

Secondary
That winding of a transformer which receives its energy by electromagnetic induction from the primary. Also, frequently referred to as the output winding. A transformer may have one or more secondaries.

Secondary Battery
A galvanic battery which, after discharge, may be restored to the fully charged state by the passage of an electric current though the cell in the opposite direction to that of discharge.

Self Discharge
The loss of useful capacity of a cell or battery due to internal chemical action.

Self-Inductance
The ability of a circuit or coil to induce a voltage within itself.

Self-Induction
The process by which a changing current induces a voltage into the conductor or coil carrying the current.

Separator
An ion permeable, electronically nonconductive, spacer or material which prevents electronic contact between electrodes of opposite polarity in the same cell.

Sequencing
The mode during which preset lighting scenes change in a designated order using fade times that have been programmed.

Series
The interconnection of cells or batteries in such a manner that the positive terminal of the first is connected to the negative terminal of the second, and so on. Series connections increase the voltage of the resultant battery.

Service Entrancebr
The location where the incoming electrical line enters the home.

Service Life
The period of useful like (usually in hours or minutes) of a primary cell/battery before a predetermined cut-off voltage is reached.

Service Panel
The main circuit breaker panel (or fuse box) where all the circuits tie into the incoming electrical supply line.

Service/Supply Leads
The incoming electrical lines that supply power to the service panel.

Shallow Discharge
Withdrawal of less than 50% of the rated capacity of a cell/battery.

Shelf Life
The duration of storage under specified conditions at the end of which a cell or battery still retains the ability to give a specified performance.

Shield
As normally applied to instrumentation cables, refers to a conductive sheath (usually metallic) applied, over the insulation of a conductor or conductors, for the purpose of providing means to reduce coupling between the conductors so shielded and other conductors which may be susceptible to, or which may be generating unwanted electrostatic or electromagnetic fields (noise).

Shielding
Shielding is the use of a conducting and/or ferromagnetic barrier between a potentially disturbing noise source and sensitive circuitry. Shields are used to protect cables (data and power) and electronic circuits. They may be in the form of metal barriers, enclosures, or wrappings around source circuits and receiving circuits.

Shielding (of utility lines)
The construction of a grounded conductor or tower over the lines to intercept lightning strokes in an attempt to keep the lightning currents out of the power system.

Short Circuit
When current flows "short" of reaching a device. Caused by a hot conductor accidentally contacting a neutral or ground. A short circuit is an immediate fault to ground and should always cause the breaker to trip or the fuse to blow. (also see ground fault)

Short Duration Variation
A variation of the rms value of the voltage from nominal voltage for a time greater than one-half cycle of the power frequency but less than or equal to one minute. Usually further described using a modifier indicating the magnitude of a voltage variation (e.g. Sag, Swell, or Interruption) and possibly a modifier indicating the duration of the variation (e.g., Instantaneous, Momentary or Temporary).

Shunt Mode
Shunt type surge protector which divert large surge current directly to ground, are not constrained by the continuous power line currents and thus are employed effectively on power systems with capabilities exceeding 5000 Amps (rms).

Side section (fin)
A scored section along each side of the mounting plate designed to be removed to facilitate ganging.

Signal Reference Grid (or Plane)
A system of conductive paths among interconnected equipment, which reduces noise-induced voltages to levels which minimize improper operation. Common configurations include grids and planes.

Single Phase
The portion of a power source that represents only a single phase of the three phases that are often available.

Single Pole
A single pole dimmer provides full-range dimming from one location only.

Sinusoidal
The graphical plot of the output of an alternator.

Slide-to-off dimmer
Slide-to-off models have an on/off switch activated at the bottom of the linear slide travel.

Slip Rings
The rotating contacts which are connected to the loops of a generator.

Space Charge
In an electron tube, a cloud of free electrons surrounding the emitter.

Spike
See Surge

Stator
The stationary group of plates of a variable capacitor. See Equipment Grounding Conductor.

Step-down
This refers to a transformer that has fewer turns of wire in the secondary than in the primary, which causes a decrease or step-down of the voltage.

Step-up
This refers to a transformer that has more turns of wire in the secondary than in the primary, which causes an increase or step-up of the voltage.

Surge
A brief transient wave of voltage, current or power in an electrical circuit, lasting for less than 1% of the power wave cycle duration.

Sustained
When used to quantify the duration of a voltage interruption, refers to the time frame associated with a long duration variation (i.e., greater than one minute).

Swell
A temporary increase in the rms value of the voltage of more than 10% the nominal voltage, at the power frequency, for durations from 0.5 cycle to one minute.

Synchronous Closing
Generally used in reference to closing all three poles of a capacitor switch in synchronism with the power system to minimize transients.



Taper Charge
A charge regime delivering moderately high rate charging current when the battery is at a low state of charge and tapering the charging current to lower rates as the battery is charged.

Thermionic Emission
The liberation of electrons from a solid metal as a result of heat (thermal energy).

Temperature Coefficient (T.C.)
In a capacitor, the rating which determines the change in capacitance corresponding to a given change in operating temperature. It is usually expressed as the change in capacitance per unit of capacitance per degree Celsius.

Temporary Magnet
An artificial magnet that loses its magnetism after the magnetizing force is removed. Soft iron is an example of a temporary magnet.

Temporary
When used to quantify the duration of a short duration variation as a modifier, refers to a time range from 3 seconds to 1 minute.

Tesla
Standard unit of magnetic flux density equal to one weber per square meter. The previously used unit of flux density was the gauss, which was equal to one magnetic line per square centimeter.

Toroid
This refers to a circular, donut shaped core used in transformers Toroid cores are generally molded from powdered iron or wound with silicon steel strips.

Total Demand Distortion (TDD)
The ratio of the root-mean- square of the harmonic current to the root-mean-square value of the rated or maximum demand fundamental current, expressed as a percent.

Total Disturbance Level
The level of a given electromagnetic disturbance caused by the superposition of the emission of all pieces of equipment in a given system.

Total Harmonic Distortion (THD)
The ratio of the root-mean- square of the harmonic content to the root-mean-square value of the fundamental quantity, expressed as a percent of the fundamental.

Transformer
An electric device, without moving parts, for transferring electric energy from one or more circuits to one or more other circuits by electromagnetic induction.

Transient
Pertaining to or designating a phenomenon or a quantity which varies between two consecutive steady states during a time interval that is short compared to the time scale of interest. A transient can be a unidirectional impulse of either polarity or a damped oscillatory wave with the first peak occurring in either polarity.

Trickle Charge
A charge at a low rate, balancing losses through a local action and/or periodic discharge, to maintain a cell or battery in a fully charged condition.

Triplen Harmonics
A term frequently used to refer to the odd multiples of the third harmonic, which deserve special attention because of their natural tendency to be zero sequence.

TVSS
Transient Voltage Surge Suppressor.



UF (Underground Feeder) cable
Cable designed and rated for underground, outdoor use. Cable wires are molded into solid plastic.

UL Listed
A product adhering to standards of Underwriters Laboratories, an independent, non-profit testing laboratory organized for the purpose of investigating products and materials with respect to hazards affecting life and property.

Undervoltage
When used to describe a specific type of long duration variation, refers to a measured voltage having a value at least 10% below the nominal voltage for a period of time greater than one minute.

UPS
Uninterruptible Power System is a system that utilizes batteries or other form of energy supply to provide continuous power (ranging from a fraction of a Watt to Mega Watts) during brownouts and blackouts for a predetermined timeframe ranging from seconds to hours.



Variable Capacitor
A capacitor in which the capacitance can be varied by some mechanical means.

Vent
A normally sealed mechanism which allows for the controlled escape of gases from within a cell.

Volt
A unit that measures the amount of electrical pressure.

Voltage Change
A variation of the rms or peak value of a voltage between two consecutive levels sustained for definite but unspecified durations.

Voltage compensation
Voltage compensation reduces changes in lighting level that occur when air conditioners, refrigerators, and other electrical appliances switch on/off.

Voltage Dip
See Sag.

Voltage Distortion
Distortion of the ac line voltage. See Distortion.

Voltage Fluctuation
A series of voltage changes or a cyclical variation of the voltage envelope.

Voltage Imbalance (Unbalance)
A condition in which the three phase voltages differ in amplitude or are displaced from their normal 120 degree phase relationship or both. Frequently expressed as the ratio of the negative sequence or zero sequence voltage to the positive sequence voltage, in percent.

Voltage Interruption
Disappearance of the supply voltage on one or more phases. Usually qualified by an additional term indicating the duration of the interruption (e.g., Momentary, Temporary, or Sustained.)

Voltage Magnification
The magnification of capacitor switching oscillatory transient voltage on the primary side by capacitors on the secondary side of a transformer.

Voltage Regulation
The degree of control or stability of the rms voltage at the load. Often specified in relation to other parameters, such as input-voltage changes, load changes, or temperature changes.



Watt
A unit that measures the amount of electrical power.

Waveform Distortion
A steady state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation.

Weber (Wb)
Standard unit of magnetic flux measurement equal to 100,000,000, or 10 to the 8th power lines of force. The previously used unit of magnetic flux was the MAXWELL, which was equal to one magnetic line of force.

Working Voltage (WV)
The maximum voltage that may be applied continuously to a capacitor without risking breakdown.









Zener Diode
A junction diode designed to operate in the reverse bias region.

Zone
A fixture or group of fixtures controlled simultaneously as a single entity.

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