BASIC ELECTRICAL DEFINITIONS

BASIC ELECTRICAL DEFINITIONS
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Accent Lighting - Directional lighting to emphasize a particular object or draw attention to a part of the field of view.
Accessible - (As applied to wiring methods) Capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in by the structure or finish of the building.
Accessible - (as applied to equipment) Admitting close approach: not guarded by locked doors, elevation, or other effective means. (see Accessible, Readily)
Accessible, Readily - (Readily Accessible) Capable of being reached quickly for operation, renewal, or inspections, without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, chairs, etc.
Ambient Temperature - The temperature of the air, water, or surrounding earth. Conductor ampacity is corrected for changes in ambient temperature including temperatures below 86°F. The cooling effect can increase the current carrying capacity of the conductor. (Review Section 310-10 of the Electrical Code for more understanding)
Ammeter - An electric meter used to measure current, calibrated in amperes.
Ampacity - The current-carrying capacity of conductors or equipment, expressed in amperes.
Ampere - The basic unit measuring the quantity of electricity.
Anodizing - Any electrolytic or chemical process by which a protective or decorative film is released on a metal surface.
Apparent Power -The product of voltage and current in a circuit.
Arc -Sparking that results when undesirable current flows between two points of differing potential. This may be due to leakage through the intermediate insulation or a leakage path due to contamination.
Armature Coil -A winding that develops current output from a generator when its turns cut a magnetic flux.
Arrester -A nonlinear device to limit the amplitude of voltage on a power line. The term implies that the device stops overvoltage problems (i.e. lightning). In actuality, voltage clamp levels, response times and installation determine how much voltage can be removed by the operation of an arrester.
Asymmetric - Unequal distribution about one or more axes.
Attenuation -The reduction of a signal from one point to another. For an electrical surge, attenuation refers to the reduction of an incoming surge by a limiter (attenuator). Wire resistance, arresters, power conditioners attenuate surges to varying degrees.
AWG -American Wire Gage. This term refers to the U.S. standard for wire size.
Autotransformer -A transformer used to step voltage up or down. The primary and secondary windings share common turns, and it provides no isolation.
Auxiliary Source -A power source dedicated to providing emergency power to a critical load when commercial power is interrupted.

Ballast
- An auxiliary electrical device for fluorescent and other discharge light sources.
Bonding Jumper - A bare or insulated conductor used to ensure the required electrical conductivity between metal parts required to be electrically connected. Frequently used from a bonding bushing to the service equipment enclosure to provide a path around concentric knockouts in an enclosure wall: also used to bond one raceway to another.
BTU -British Thermal Unit. Energy required to raise one pound of water one degree Fahrenheit. One pound of water at 32 degrees F requires the transfer of 144 BTUs to freeze into solid ice.
Buck-Boost Transformer -A small, low voltage transformer placed in series with the power line to increase or reduce steady state voltage.
Busbar -A heavy, rigid conductor used for high voltage feeders.
Candlepower (or Candela) - Basic unit for measuring luminous intensity from a light source in a given direction.
Coefficient of Utilization - The amount of light (lumens) delivered in a workplace as a percent of the rated lumens of the lamp.
Cold Cathode Lamp - An electric-discharge lamp whose mode of operation is that of a glow discharge (Neon Lights).
Common Mode (CM) -The term refers to electrical interference which is measurable as a ground referenced signal. In true common mode a signal is common to both the current carrying conductors.
Common Node Noise -An undesirable voltage which appears between the power conductors and ground.
Conduit -A tubular raceway for data or power cables. Metallic conduit is common, although non-metallic forms may also be used. A conduit may also be a path or duct and need to be tubular.
Continuity - The state of being whole, unbroken.
Continuous Load - A load where the maximum current is expected to continue for three hours or more. Rating of the branch circuit protection device shall not be less tan 125% of the continuous load.
Current -The movement of electrons through a conductor. Measured in amperes and its symbol is "I".
Current Transformer-(or CT) - A transformer used in instrumentation to assist in measuring current. It utilizes the strength of the magnetic field around the conductor to form an induced current that can then be applied across a resistance to form a proportional voltage.

Demand Factor - For an electrical system or feeder circuit, this is a ratio of the amount of connected load (in kV or amperes) that will be operating at the same time to the total amount of connected load on the circuit. An 80% demand factor, for instance, indicates that only 80% of the connected load on a circuit will ever be operating at the same time. Conductor capacity can be based on that amount of load.
Dropout -A discrete voltage loss. A voltage sag (complete or partial) for a very short period of time (milliseconds) constitutes a dropout
Dustproof - Constructed or protected so that dust will not interfere with its successful operation.
Dust-tight - Constructed so that dust will not enter the enclosing case under specified test conditions.
Duty, continuous - A service requirement that demands operation at a substantially constant load for an indefinitely long time.
Duty, intermittent - A service requirement that demands operation for alternate intervals of load and no load, load and rest, or load, no load, and rest.
Duty, periodic - A type of intermittent duty in which the load conditions regularly reoccur.
Duty, short time - A requirement of service that demands operations at a substantially constant load for a short and definitely specified time.
Duty, varying - A requirement of service that demands operation at loads, and for intervals of time, both of which may be subject to wide variation.

Earth Ground -A low impedance path to earth for the purpose of discharging lightning, static, and radiated energy, and to maintain the main service entrance at earth potential.
Efficiency -The percentage of input power available for used by the load. The mathematical formula is: Efficiency = Po/ Pi Where "Po" equals power output, "Pi" equals power input, and power is represented by watts.
Electrical Degrees- One cycle of AC. power is divided into 360 degrees. This allows mathematical relationships between the various aspects of electricity. Also, what the mothers of many liberal arts majors wish their daughters had married (or vice-versa)
Electromagnetic -A magnetic field cause by an electric current. Power lines cause electromagnetic fields which can interfere with nearby data cables.
Electromechanical -A mechanical device which is controlled by an electric device. Solenoids and shunt trip circuit breakers are examples of electromechanical devices.
Electrostatic -A Potential difference (electric charge) measurable between two points which is caused by the distribution if dissimilar static charge along the points. The voltage level is usually in kilovolts (volts times 1000).
EMF -Electromotive force or voltage
EMI, RFI -Acronyms for various types of electrical interference: electromagnetic interference, radio frequency interference.
ESD -Electrostatic Discharge (static electricity). The effects of static discharge can range from simple skin irritation for an individual to degraded or destroyed semiconductor junctions for an electronic device.
Explosion-proof - Designed and constructed to withstand and internal explosion without creating an external explosion or fire.

Feeder - A circuit, such as conductors in conduit or a busway run, which carries a large block of power from the service equipment to a sub-feeder panel or a branch circuit panel or to some point at which the block power is broken into smaller circuits.
Ferroresonance -Resonance resulting when the iron core of an inductive component of an LC circuit is saturated, increasing the inductive reactance with respect to the capacitance reactance.
Ferroresonant Transformer -A voltage regulating transformer which depends on core saturation and output capacitance.
Filter Frequency Range –The frequency range within which the filter operates.
Flashover -Flashing due to high current flowing between two points of different potential. Usually due to insulation breakdown resulting from arcing.
Fluctuation -A surge or sag in voltage amplitude, often caused by load switching or fault clearing.
Flux -The lines of force of a magnetic field.
Forward Transfer Impedance -The amount of impedance placed between the source and load with installation of a power conditioner. With no power conditioner, the full utility power is delivered to the load; even a transformer adds some opposition to the transfer of power. On transformer based power conditioners, a high forward transfer impedance limits the amount of inrush current available to the load.
Frequency (Noise) Attenuation –The range of attenuation (limiting) for a given frequency range. In this case, the greater the negative number, the more noise reduction.

Ground - A large conducting body (as the earth) used as a common return for an electric circuit and as an arbitrary zero of potential.
Grounded, effectively - Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connect equipment or to persons.
Grounded Conductor - A system or circuit conductor that is intentionally grounded, usually gray or white in color.
Grounding Conductor - A conductor used to connect metal equipment enclosures and/or the system grounded conductor to a grounding electrode, such as the ground wire run to the water pipe at a service; also may be a bare or insulated conductor used to ground motor frames, panel boxes, and other metal equipment enclosures used throughout electrical systems. In most conduit systems, the conduit is used as the ground conductor.
Grounding Equipment Conductor - The conductor used to connect the non-current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, of the circuit at the service equipment or at the source of a separately derived system.
Grounding Electrode - The conductor used to connect the grounding electrode to the equipment-grounding conductor, to the grounded conductor, or to both, of the circuit at the service equipment or at the source of a separately derived system.
Ground Fault Circuit Interrupter - A device intended for the protection of personal that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than required to operate the overcurrent protection device of the supply circuit.
Ground Fault Protection of Equipment - A system intended to provide protection of equipment from damaging line to ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operations of a supply circuit overcurrent device.

High Intensity Discharge Lamps (HID.) - A general group of lamps consisting of mercury, metal halide, high-pressure sodium, and low pressure sodium lamps.
High-pressure Sodium Lamps - A sodium vapor in which the partial pressure of the vapor during operation is the order of 0.1 atmospheres.
Hot Cathode Lamp - An electrical discharge lamp whose mode of operation is that of an arc discharge.
mpedance -Forces which resist current flow in AC circuits, i.e. resistance, inductive reactance, capacitive reactance.
Inductance -The ability of a coil to store energy and oppose changes in current flowing through it. A function of the cross sectional area, number of turns of coil, length of coil and core material.
Input Power Frequency –This is the frequency range that can be input into the suppressor without damaging it.
In Sight From - (within sight from, within sight) Where this Code specifies that one equipment shall be "in sight from", "within sight from" or "within sight", etc. of another equipment, the specified equipment is to be visible and not more that 50´ distant from the other
Interrupter Rating - The highest current at rated voltage that a device is intended to interrupt under standard test conditions.

Joule - A measure of the amount of energy delivered by one watt of power in one second, or 1 million watts of power in one microsecond. The joule rating of a surge protection device is the amount of energy that it can absorb before it becomes damaged. In comparing surge protection performance, the Joule rating of a surge suppressor is less important than the let-through voltage rating. This reflects the fact that surge suppressors may protect equipment by deflecting surges as well as absorbing them. There is no standard for measuring the joule rating of surge suppressors which has resulted in wildly exaggerated claims by unscrupulous vendors.
Kilo--(K) -A metric prefix meaning 1000 or 103.
KVA -(Kilovolt amperes) (volts times amperes) divided by 1000. 1 KVA=1000 VA. KVA is actual measured power (apparent power) and is used for circuit sizing.
KW -(Kilowatts) watts divided by 1000. KW is real power and is important in sizing Uninterruptible Power Supplies, motor generators or other power conditioners. See also "power factor".
KWH -(Kilowatt hours) KW times hours. A measurement of power and time used by utilities for billing purposes.

Labeled - Items to which a label, trademark, or other identifying mark of nationally recognized testing labs has been attached to identify the items as having been tested and meeting appropriate standards.
Lagging Load -An inductive load with current lagging voltage. Since inductors tend to resist changes in current, the current flow through an inductive circuit will lag behind the voltage. The number of electrical degrees between voltage and current is known as the "phase angle". The cosine of this angle is equal to the power factor (linear loads only).
LC Circuit -An electrical network containing both inductive and capacitive elements.
Leading Load -A capacitive load with current leading voltage. Since capacitors resist changes in voltage, the current flow in a capacitive circuit will lead the voltage.
Linear Load -A load in which the current relationship to voltage is constant based on a relatively constant load impedance.
Line Conditioner - This term isn't used consistently, therefore its meaning has been blurred. The term is sometimes used to describe equipment that provides some type of filtering or Regulation to an AC power source and may be any of the following devices: Surge Suppressor, Ferroresonant Transformer, AC Filter or Tap Changing Regulator.
Line Imbalance -Unequal loads on the phase lines of a multiphase feeder.
Listed - Equipment or materials included in a list published by an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of listed equipment or materials, and whose listing states either that the equipment or material meets appropriate designated standards or has been tested and found suitable for use in specified manner.
Load- The driven device that uses the power supplied from the source.
Load Balancing -Switching the various loads on a multi-phase feeder to equalize the current in each line.
Load Fault -A malfunction that causes the load to demand abnormally high amounts of current from the source.
Load Regulation -A term used to describe the effects of low forward transfer impedance. A power conditioner with "load regulation" may not have voltage regulation. Removing the power conditioner altogether will improve load regulation.
Load Switching- Transferring the load from one source to another.
Load Unbalance -Unequal loads on the phase lines of a multi- phase system.
Location, damp - A location subject to moderate amount of moisture such as some basements, barns, cold storage, warehouse and the like.
Location, dry - A location not normally subject to dampness or wetness: a location classified as dry may be temporarily subject to dampness or wetness, as in case of a building under construction.
Location, wet - A location subject to saturation with water or other liquids.

Maximum Operating Voltage –This is the maximum 50 to 60 Hz AC voltage the unit can sustain without damage or failure of the suppressor.
Measured Limiting (used to be known as "let-through") Voltage –This is the maximum voltage measured across the terminals of the suppressor during the time the testing voltages were applied to the unit..
Mega--(M) -A metric prefix meaning 1,000,000 or 106.
Megger - A test instrument for measuring the insulation resistance of conductors and other electrical equipment; specifically, a mega-ohm (million ohms) meter; this is a registered trademark of the James Biddle Co.
Mega-ohm - A unit of electrical resistance equal to one million ohms.
Mega-ohmmeter - An instrument for measuring extremely high resistance.
Megger - A test instrument for measuring the insulation resistance of conductors and other electrical equipment; specifically, a mega-ohm (million ohms) meter; this is a registered trademark of the James Biddle Co.
Mercury Lamps - An electric discharge lamp in which the major portion of the radiation is produced by the excitation of mercury atoms.
Metal Halide Lamps - A discharge lamp in which the light is produced by the radiation from the mixture of metallic vapor and the products of disassociation.
Metal Oxide Varistor-(MOV) -A MOV is a voltage sensitive breakdown device which is commonly used to limit overvoltage conditions (electrical surges) on power and data lines. When the applied voltage exceeds the breakdown point, the resistance of the MOV decreases from a very high level (thousands of ohms) to a very low level (a few ohms). The actual resistance of the device is a function of the rate of applied voltage and current.
Micro--(U)-A metric prefix meaning one millionth of a unit or 10-6.
Micron -A metric term meaning one millionth of a meter.
Milli--(m) -A metric prefix meaning one thousandth of a unit or 10-3
Motor, Shunt- Wound - This type of motor runs practically constant speed, regardless of the load. It is the type generally used in commercial practice and is usually recommended where starting conditions are not usually severe. Speed of the shunt-wound motors may be regulated in two ways: first, by inserting resistance in series with the armature, thus decreasing speed: and second, by inserting resistance in the field circuit, the speed will vary with each change in load: in the latter, the speeds is practically constant for any setting of the controller. This latter is the most generally used for adjustable-speed service, as in the case of machine tools.
Motor, DC, Series- Wound - This type of motor speed varies automatically with the load, increasing as the load decreases. Use of series motor is generally limited to case where a heavy power demand is necessary to bring the machine up to speed, as in the case of certain elevator and hoist installations, for steelcars, etc. Series-wound motors should never be used where the motor can be started without load, since they will race to a dangerous degree.
Motor, DC, Compound- Wound - A combination of the shunt wound and series wound type, which combines the characteristics of both. Varying the combination of the two windings may vary characteristics. These motors are generally used where severe starting conditions are met and constant speed is required at the same time.
Motor, Squirrel-Cage-Induction - The most simple and reliable of all electric motors. Essentially a constant speed machine, which is adaptable for users under all but the most severe starting conditions. Requires little attention as there is no commutator or slip rings, yet operates with good efficiency.
Motor, Wound-Rotor (Slip Ring) Induction - Used for constant speed-service requiring a heavier starting torque than is obtainable with squirrel cage type. Because of its lower starting current, this type is frequently used instead of the squirrel-cage type in larger sizes. These motors are also used for varying-speed-service. Speed varies with this load, so that they should not be used where constant speed at each adjustment is required, as for machine tools.
Motor, Single-Phase Induction - This motor is used mostly in small sizes, where polyphase current is not available. Characteristics are not as good as the polyphase motor and for size larger that 10 HP, the line disturbance is likely to be objectionable. These motors are commonly used for light starting and for running loads up to 1/3 HP Capacitor and repulsion types provide greater torque and are built in sizes up to 10 HP.
Motor, Synchronous - Run at constant speed fixed by frequency of the system. Require direct current for excitation and have low starting torque. For large motor-generators sets, frequency changes, air compressors and similar apparatus which permits starting under a light load, for which they are generally used. These motors are used with considerable advantage, particularly on large power systems, because of their inherent ability to improve the power factor of the system.
MTBF -(Mean Time Between Failure) the probable length of time that a component taken from a particular batch will survive if operated under the same conditions as a sample from the same batch.

Nano--(n) -A metric prefix meaning one billionth of a unit or 10-9.
NEMA -National Electrical Manufacturers Association.
NEC -National Electrical Code.
Neutral -The grounded junction point of the legs of a wye circuit. Or, the grounded center point of one coil of a delta transformer secondary. Measuring the phase to neutral voltage of each of the normal three phases will show whether the system is wye or delta. On a wye system, the phase to neutral voltages will be approximately equal and will measure phase to phase voltage divided by 1.73. On a center tapped delta system, one phase to neutral voltage will be significantly higher than the other two. This higher phase is often called the "high leg".
Neutralizing Winding -An extra winding used to cancel harmonics developed in a saturated secondary winding, resulting in a sinusoidal output waveform from a ferroresonant transformer.
Nominal Voltage -The normal or designed voltage level. For three phase wye systems, nominal voltages are 480/277 (600/346 Canada) and 208/120 where the first number expresses phase to phase ( or line to line) voltages and the second number is the phase to neutral voltage. The nominal voltage for most single phase systems is 240/120.
Non-inductive Circuit - A circuit in which the magnetic effect of the current flowing has been reduced by one several methods to a minimum or to zero.
Non-linear Load - A load where the wave shape of the steady state current does not follow the wave shape of the applied voltage.

Ohm - The derived unit for electrical resistance or impedance; one ohm equals one volt per ampere.
Ohmmeter - an instrument for measuring resistance in ohms. Take a look at this diagram to see how an ohmmeter is used to check a small control transformer. The ohmmeter's pointer deflection is controlled by the amount of battery current passing through the moving coil. Before measuring the resistance of an unknown resistor or electrical circuit, the ohmmeter must first be calibrated. If the value of resistance to be measured can be estimated within reasonable limits, a range selected that will give approximately half-scale deflection when the resistance is inserted between the probes. If the resistance is unknown, the selector switch is set on the highest scale. Whatever range is selected, the meter must be calibrated to read zero before the unknown resistance is measured.
Overcurrent - Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit or ground fault.
Overload - Load greater than the load for which the system or mechanism was intended. A fault, such as a short circuit or ground fault, is not an overload.

Panelboard - A single panel or group of panel units designed for assembly in the form of a single panel: includes buses and may come with or without switches and/or automatic overcurrent protective devices for the control of light, heat, or power circuits of individual as well as aggregate capacity. It is designed to be placed in a cabinet or cutout box that is in or against a wall or partition and is accessible only from the front.
Peak Surge Current –The maximum current allowed for a single impulse with continuous voltage applied.
Plenum - Chamber or space forming a part of an air conditioning system
Power -Electrical energy measured according to voltage and current (normally watts). Power in watts equals volts times amperes for DC circuits. For single phase AC circuits, watts equal volts times amperes times power factor.
Power Factor -Watts divided by voltamps (VA), KW divided by KVA. Power factor: leading and lagging of voltage versus current caused by inductive or capacitive loads, and 2) harmonic power factor: from nonlinear current.
Propagation-The travel of an electrical waveform along a medium. In other words, a surge passing along a power cord to a system.
Protector -A protector is another name for an arrester or diverter.

Rainproof - So constructed, projected, or treated as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions.
Rain-tight - So constructed or protected that exposure to a beating rain will not result in the entrance of water.
Real Power -Watts.
Reactance -Opposition to the flow of alternating current. Capacitive reactance is the opposition offered by capacitor, and inductive reactance is the opposition offered by a coil or other inductance.
Recloser -The automatic closing of a circuit-interrupting device following automatic tripping.
Rectifier -An electrical device used to change AC power into DC power. A battery charger is a rectifier.
Redundancy -The inclusion of additional assemblies and circuits (as within a UPS) with provision for automatic switchover from a failing assembly or circuit to its backup counterpart.
Reflection -The return wave generated when a traveling wave reaches a load, a source, or a junction where there is a change in line impedance.
Reliability -The statistical probability of trouble-free operation of a given component or assembly. Used principally as a function of MTBF (Mean Time Before Failure) and MTTR (Mean Time to Repair).
RFI -Radio Frequency Interference.
Ride through-The ability of a power conditioner to supply output power when input power is lost.
RMS -(Root mean square)- used for AC voltage and current values. It is the square root of the average of the squares of all the instantaneous amplitudes occurring during one cycle. RMS is called the effective value of AC because it is the value of AC voltage or current that will cause the same amount of head to be produced in a circuit containing only resistance that would be caused by a DC voltage or current of the same value. In a pure sine wave the RMS value is equivalent to .707 times the peak value and the peak value is 1.414 times the RMS value. The normal home wall outlet which supplies 120 volts RMS has a peak voltage of 169.7 volts.

Separately Derived System - A premises wiring system whose power is derived from a battery, a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including solidly connected grounded circuit conductor, to supply conductors originating in another system.
Service Drop - Run of cables from the power company's aerial power lines to the point of connection to a customer's premises.
Service Conductors - The supply conductors that extend from the street main or transformers to the service equipment of the premises being supplied
Service Entrance Conductors - (Overhead) The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop.
Service Entrance Conductors - (Underground) The service conductors between the terminals of the service equipment and the point of connection to the service lateral.
Service Equipment - The necessary equipment, usually consisting of a circuit breaker or switch and fuses and their accessories, located near the point entrance of supply conductors to a building and intended to constitute the main control and cutoff means for the supply to the building.
Service Lateral - The underground service conductors between the street main, including any risers at a pole or other structure or from transformers, and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure with adequate space, inside or outside the building wall. Where there is no terminal box, meter, or other enclosure with adequate space, the point of connection is the entrance point of the service conductors into the building.
Service Point - The point of connection between the facilities of the serving utility and the premises wiring.
Surge -A short duration high voltage condition. A surge lasts for several cycles where a transient lasts less than one half cycle. Often confused with "transient".
Switchboard - A large single panel, frame, or assembly of panels having switches, overcurrent, and other protective devices, buses, and usually instruments mounted on the face or back or both. Switchboards are generally accessible from the rear and from the front and are not intended to be installed in cabinets.
Switch, general use - A switch intended for use in general distribution and branch circuits. It is rated in amperes and is capable of interrupting its rated voltage.
Switch, general-use snap - A type of general-use switch so constructed that it can be installed in flush device boxes or on outlet covers, or otherwise used in conjunction with wiring systems recognized by the National Electric Code.
Switch, isolating - A switch intended for isolating an electrical circuit from the source of power. It has no interrupting rating and is intended to be operated only after the circuit has been opened by some other means.
Switch, knife - A switch in which the circuit is closed by a moving blade engaging contact clips.
Switch, motor-circuit - A switch, rated in horsepower, capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage.
Switch, transfer - A transfer switch is an automatic or non-automatic device for transferring one or more load conductor connections from one power source to another.
Switch-Leg - That part of a circuit run from a lighting outlet box where a luminaire or lamp-holder is installed down to an outlet box that contains the wall switch that turns the light or other load on or off: it is a control leg of the branch circuit.

Tap Changing Regulator - a device that improves the regulation of an AC power source. The regulator is placed between an AC power source and the load to be protected. A tap-changing regulator has a special transformer with multiple outputs or taps. Typically, one of the output taps provides a voltage equal to the input voltage, while other taps provide various voltages which are a few percent higher or lower than the input voltage. An automatic selector switch chooses the tap which provides the voltage closest to the desired output voltage. In operation, if the AC power source were to suddenly decrease in voltage by 5% from nominal and remain at that voltage, then the Tap-Changing Regulator would respond by choosing a transformer tap 5% higher than the input voltage and would supply this corrected voltage to the load. Tap-Changing Regulators are especially useful in situations where a site is experiencing chronically high or low line voltage.
Three-Phase Power -Three separate outputs from a single source with a phase differential of 120 electrical degrees between any two adjacent voltages or currents. Mathematical calculations with three phase power must allow for the additional power delivered by the third phase. Remember, both single phase and three phase have the same phase to phase voltages, therefore you must utilize the square root of 3 in your calculations. For example, KVA equals volts times amps for DC and for single phase. For three phase the formula is volts times the square root of three times amps.
Total Harmonic Distortion (THD) -The square root of the sum of the squares of the RMS harmonic voltages or currents divided by the RMS fundamental voltage or current. Can also be calculated in the same way for only even harmonics or odd harmonics.
Transformer -A static electrical device which , by electromagnetic induction, regenerates AC power from one circuit into another. Transformers are also used to change voltage from one level to another. This is accomplished by the ratio of turns on the primary to turns on the secondary (turns ratio). If the primary windings have twice the number of windings as the secondary, the secondary voltage will be half of the primary voltage.
Transient -A high amplitude, short duration pulse superimposed on the normal voltage wave form or ground line.
Transient Response -The ability of a power conditioner to respond to a change. Transient step load response is the ability of a power conditioner to maintain a constant output voltage when sudden load (current) changes are made.
Transmission Line -The conductors used to carry electrical energy from one location to another.
Transverse Mode Noise -(Normal mode)- An undesirable voltage which appears from line to line of a power line.

UL 1449 - a UL (UNDERWRITER'S LABORATORIES) safety specification that surge suppression products are tested against. This specification includes a requirement that surge suppression devices be marked with the surge let-through voltage for a specific UL test
UL Approved - This is a widely used term which is technically not correct. The correct terms are UL Listed or UL Recognized.
UL Listed - UL grants this form of approval to equipment that will be user installed or operated and that is found to meet the safety requirements of the applicable UL standards. If a product is UL Listed, then it must be marked with the UL insignia.

UL Recognized - This is a form of formal approval granted by UL to devices that are not used as free standing equipment on their own, but are to be installed into some other system by a manufacturer, electrician, or possibly by an end user. Examples of UL Recognized equipment are wall switches, wire connectors, wires, fuses, and circuit breakers. (See also UL Listed above).

VAC -Volts of alternating current.
VDC -Volts of direct current.
Volt (V) -The unit of voltage or potential difference.
Voltage Drop - The loss of voltage between the input to a device and the output from a device due to the internal impedance or resistance of the device. In all electrical systems, the conductors should be sized so that the voltage drop never exceeds 3% for power, heating, and lighting loads or combinations of these. Furthermore, the maximum total voltage drop for conductors for feeders and branch circuits combined should never exceed 5%.
VOM -Volt ohm-meter.
Voltage -Electrical pressure, the force which causes current to flow through a conductor. Voltage must be expressed as a difference of potential between two points since it is a relational term. Connecting both voltmeter leads to the same point will show no voltage present although the voltage between that point and ground may be hundred or thousands of volts. This is why most nominal voltages are expressed as "phase to phase" or "phase to neutral". The unit of measurement is "volts". The electrical symbol is "e".
WATT (W)-The unit of power. Equal to one joule per second
Watertight - So constructed that water/moisture will not enter the enclosure under specified test conditions.
Weatherproof - So constructed or protected that exposure to the weather will not interfere with successful operation.
Zero Signal Reference -A connection point, bus, or conductor used as one side of a signal circuit. It may or may not be designated as ground. Is sometimes referred to as circuit common.

Last Updated: Sunday, September 8, 2002
©1999-2002 Stedi-Power, Inc.
All trademarks are the property of their respective owners
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Electrical Generator Terminology and Concepts
Electrical generator terminology, generator concepts & terms guide with complete info to helpt you to know more about electrical generator terminology & concept.
The best way to understand electricity and its terminology is to develop some analogies between electricity and topics that are easy to understand. Even though electricity and water don't mix, the concepts are actually fairly similar. By comparing electrical terminology to water flowing in a pipe, we should be able to with a simpler understanding of electricity.
Pressure and VoltageThe pressure in a pipe can be compared to electrical voltage across a wire. If the pressure on both ends of a pipe is the same, then no water will flow. If you took two water tanks of the same size, where one was full and the other was empty, and connected them together with a hose at their bottoms, water would flow from the full tank into the empty tank. The water would stop flowing when the depth of the water in each tank was the same.
The full tank has a higher pressure at the bottom (where the hose is connected) than the empty tank. When the depth of the water is equal in each tank, then the pressure at the bottom of both tanks is equal.If both ends of a wire are connected to the same voltage (for example, the positive terminal of a battery) then no current will flow either. In either case, it is the difference in pressure or voltage that causes the water or electricity to flow.
CurrentRegardless whether we are referring to water flow or electrical current, current is the movement of water or electricity.When discussing the flow of water, we are referring to how many gallons per minute are passing though a hose.
For electricity, we are looking at how many electrons per second are passing a point. Literally, 1 Ampere is equal to 6.24x1018 electrons per second. (The way this number is written is called scientific notation, and is used for very large numbers. This number, if written out would be 6,240,000,000,000,000,000.)
Since it is too difficult to work with numbers this large on a daily basis; we use the much simpler term of Amperes, or Amps for short. The flow of water through a pipe, or electrical current through a wire, is directly related to the pressure or voltage difference across the pipe or wire.
Going back to the example of our two tanks. If you were to fill one tank with a couple of inches of water, the flow of water wouldn't be very fast filling the empty tank. If you then filled the first tank with several feet of water, the speed at which the water flowed out of the hose into the second tank would be much higher.
The same is true with electricity--the greater the difference in voltage from one end of the wire to the other, the higher the current. Pipe Diameter and Resistance The more resistance in a circuit, the lower the current will be. Similarly, the smaller the diameter of a water pipe, the less water can flow through the pipe. Looking at the tank example, it should be obvious that if we connect the two tanks with a small hose, the time it takes to fill the second tank will be longer.
If we make the hose much longer, the additional resistance to flow from the inside of the hose will also slow down the flow (increase its' resistance). Therefore, resistance is related to not only the size of a wire, but also the length of a wire. Consider the windings of a motor…they are made up of a very long and very thin piece of copper wire. The reason this wire doesn't just melt is because it is long enough and thin enough to act as a resistor, which slows down the flow of electricity.
Ohms' Law
In electrical systems, there is a relationship between current, voltage, and resistance. This is known as ohms law, and can be written in many different forms, but always boils down to V=IR, where V is voltage, I is current, and R is resistance.
This equation holds true whether we are dealing with AC, DC, Capacitive, Inductive, Three Phase, or any other type of circuit. However, it should be noted that sometimes the values for current and/or voltage are no longer simple values. The V and I of Ohms' Law can be replaced by complex mathematical expressions, but they still represent the current and voltage.
In fact, it isn't that the equations change, it is the values of current and voltage, which become complex. For example, we may replace the simple term "I" with the complex term "I*cos(p)", where p represents a shift in the phase angle, or timing, of the current.
Ohm's law can be written in different forms, but are still the same equation. The three common forms of Ohms law are:
V=I *R
I=V/R
R=V/I
AC versus DC
A battery is direct current (DC). The polarity of a battery is always the same--positive on one side and negative on the other. In an AC system, the polarity is constantly changing every 1/60th of a second (60 times per second, or 60 Hz).
f you had a very small (and very fast) person sitting on that 9-volt battery inside your TV's remote control, and he was switching the positive and negative wires back and forth 60 times every second, you would have a 9-volt AC power source.
In the AC system in our homes, this switching between positive and negative is a little smoother, and if you could look at it, it would look like a sine wave.
The electrons traveling through a wire aren't actually moving up and down like the picture, this is just a mathematical representation of their movement. The electrons are actually moving forward, then backward in the wire, where their speed is represented by the height of the sine wave.
Ground, Neutral, and Hot
These are terms we use to describe the parts of an electrical wiring system. These are just relative terms, and are the names we have given to the wires used in a standard electrical system. They are kind of like nicknames.
Ground
If you had a really big voltmeter, and placed one probe way out in space and one probe on the Earth, you would show a voltage between the Earth and Space. I don't know what this voltage would be, it could be one volt or it could be a million volts. In simple terms, we use the Earth as a reference point (we say the Earth is at zero volts, even though we know it is not).
The Ground wire in your home or shop is literally connected to an eight foot copper rod driven into the Earth. Therefore, we say the Ground wire is at zero volts. (Believe it or not, the Earth is a conductor of electricity. Not as good as copper, but it does conduct.)
If our equipment were not grounded (electrically free-floating), it would have a voltage difference with respect to Earth, just as the free-floating Earth has a voltage difference with respect to outer space. The equipment chassis is connected to the Ground wire, which of acts like an anchor to keep the chassis' voltage at zero. In short, the Ground wire is a safety device that anchors our equipment to zero volts, but is not supposed to carry any current unless something with the appliance is malfunctioning. (An appliance is a generic term for any device, such as a lamp, saw, oven, motor, and so on. It is not limited to the typical home appliance.)
If something does go wrong with the appliance, then the ground wire will, and should, carry current. But the main purpose of the ground wire is to always ensure that the chassis of the appliance remains at zero volts.
Neutral and Hot
The only difference between the Neutral wire and Hot wire(s) of a modern electrical system is that the Neutral wire is forced to be at zero volts (anchored) by connecting it to Ground back at the circuit breaker panel.
If we did not anchor Neutral to Ground, then both the Neutral wire and the Hot wire would be at some intermediate voltage (both would be free-floating). This is done as a safety issue. It is much easier to work on a system when we only have one wire with a non-zero voltage. Unlike the Ground wire however, the Neutral wire is designed to carry current during normal operation.
Since the Neutral wire is at zero volts though, there is no voltage difference between it and Ground, and that means there is little chance for a user to get electrocuted by touching the Neutral. This is why it is normal electrical procedure to have the Neutral wire pass directly to an appliance without going through a switch or circuit breaker. Switches and circuit breakers are placed on the Hot leg of a system.
Circuit Protection (Circuit Breaker)
The purpose of the circuit breaker is to protect the wires between the breaker and the load, although it can also serve as a service disconnect (a means of disconnecting power from the circuit).
A circuit breaker is not intended to protect the appliance, only the wire between the breaker and the outlet. In your home, you will have 15 or 20 amp breakers, but the motor that you plug into the outlet may self-destruct if the current exceeds 10 amps. The motor is responsible to protect itself if the current goes over 10 amps, not the circuit breaker.
National Electric Code mandates that ALL Hot wires going to a load must, not only have a circuit breaker, but ALL circuit breakers feeding that device must trip together. Therefore, a 240-volt tool must use a two-pole breaker, and a three-phase tool must use a three-pole breaker.
Circuit Path and Safety
You should of course already know to always turn the power off before you do any electrical work, but you should take this concept a little further.
You should remove all possibility for someone else to turn the power back on. If a tool has a plug, then unplug it and place the cord within your line of sight, so that you can see if someone goes to plug it back in. If the tool only has a circuit breaker, and it is out of your line of sight, find a way to lockout the breaker in the off position.
Most breakers have a small hole through the trip handle, and this can be used with a small lock, or similar object to prevent the breaker from being turned on. At the same time, you should label the lockout with a tag to indicate the circuit is being serviced.
There may be times when there is no way of turning the power off. In these instances, only qualified persons with experience working with this condition should have anything to do with the circuit.
Whether a circuit is energized or not should make no difference in the way you work. If you always work on the equipment under the assumption that is energized, you will not be injured in the event someone reapplies power to the circuit.
Current passing through their body electrocutes people, not voltage. Voltage can kill, but it is the difference in voltage which causes the problem, and the difference in voltage is what causes current to flow through a person's body.
A bird does not get electrocuted when it lands on a power line, because its entire body is elevated to that voltage (free-floating). If the wingtip of the bird touched a different voltage source, like Ground or another wire, it completes a path to a different voltage potential and the result would be electrocution.
In order for current to flow, there must be a path from a higher voltage to a lower voltage. If there is no path, current cannot flow. This path can include a wire, a metal water pipe, the chassis of an electrical panel, or waterlogged shoes on earth-ground.
Apply this principle whenever performing wiring. Assure that you allow no part of your body to come into contact with a ground or other source of voltage.
Whenever possible, perform tasks with only one hand to ensure that the other hand does not inadvertently touch somewhere it shouldn't. In the event you do inadvertently complete a circuit with your body, current will pass through your single hand instead of traveling across your body to get to ground.
Back Fed Voltage/Current
What makes the above-entioned approach all the more important is the unlikely occurrence of a back fed voltage. This situation has killed and maimed many professional electrical workers. This doesn't apply to a situation where you can unplug the entire system, like a tool with a plug. It applies to working on a system, or part of a system that is not completely isolated from all other parts, like a wall outlet.
You may have disconnected the Hot wire from the source, and maybe even the Neutral too, but there could be a circuit path somewhere downstream from your location that you don't consider, or are unaware of.
Capacitors and Inductors (Motors)
Capacitors and inductors are two types of devices that store energy, like a battery does. Each of these stores different types of energy in different ways. It is this ability to store energy that makes capacitors and inductors somewhat complicated when evaluating electrical systems.
Capacitors
In very simple terms, a capacitor is made from two parallel plates of metal, which are separated by an insulating material. Since this insulating material separates the plates of a capacitor, no current actually flows through the capacitor, although it does sometimes appear to. Each plate of the capacitor will hold an electrical charge kind of like a battery, where one plate will have a negative charge and the other plate will have a positive charge [you can picture this as static electricity, like when you rub a balloon over your hair. Your head will have a positive charge, and the balloon will have a negative charge (or vise versa)].
Since no current can flow across the insulating material, energy is stored in the capacitor in the form of electric charge between the two plates. When you put voltage to a capacitor and then remove the wires, the capacitor will hold that voltage until it is discharged. (This is why capacitors can pose a grave safety hazard: They can seriously shock a person long after a tool is unplugged.)
Inductors
An inductive device is any coil of wire, which includes motors, transformers, and generators. Every time electricity flows through a wire, it creates a small magnetic field around the wire. (This is the same type of magnetism that holds a refrigerator magnet to the refrigerator, except that it is only present when current is flowing.) This magnetic field forms circular lines of flux around the wire. When we coil up a wire, we not only concentrate the wire itself into a small area, but we also concentrate the wire's magnetism into a small area too.
An inductor stores energy in the magnetic field around the coils. It takes energy to develop the magnetic field around the coils, and the magnetic field gives off energy as it collapses (it collapses when the current is stopped or reversed.)
In an AC circuit, remember that the voltage is changing from positive, through zero, to negative 60 times every second. When we connect an inductor, like a motor or transformer, to an AC circuit, the magnetic field around the wires are also constantly changing as a result. They are continually expanding and contracting as the current is reversing.
Effects of Capacitive and Inductive Devices
To summarize the above information, capacitors will store voltage, while inductors will store current. When we put a voltage to a motor, the effect of storing this current will delay the flow of current by a fairly small amount of time. This is referred to as a phase shift in the current. I will return to this topic after we discuss some graphical tools, as this then becomes easier to visualize, and has a significant bearing on a motor or generator's ability to provide power.
Types of Electricity in Commercial Applications
There are three common terms used to describe the electricity used in commercial applications. Single-phase 120 volt, Single-phase 240 volt, and three-phase voltage (which can be supplied in varying amounts, usually expressed as 120/208, 120/240, or 277/480).
Don't be confused if you hear the terms 110 volts instead of 120 volts, or 220 volts instead of 240 volts. These are out of date terms which people still refer to, but all public utilities in the US deliver 120 volts and 240 volts for consistency and load sharing. Most tools and motors use these other terms (110/220) just to indicate that they will still perform if the voltage drops to that level.
Single Phase 120/240
Single phase 120 volt and 240 volt lines, are just different parts of the same system. This is actually a 240-volt system, but we split it in half to get two, 120-volt systems. This is the reason why it is called a single-phase system.
It is just one phase of power at 240 volts. To get the 120 volts, we use what is called a center-tap. Standard outlets use the Neutral wire (the center tap) and one Hot wire, where the voltage between the Neutral and Hot is 120 volts. The 240 outlets use both Hot wires, where one wire is 120 volts above the Neutral and the other is 120 volts below the Neutral (as before, we anchor the Neutral to Ground, and let the two Hot lines "float" above and below). It is said that each of the Hot legs (called poles) of a single phase system are 180° out of phase.
It can be confusing that this system is called single phase, but it might be helpful to refer to this as a two pole system. (Using the term two pole is correct, but calling it a two-phase system is incorrect.)
Three Phase Systems
Where the single phase system has two poles 180° out of phase, the three phase system has three poles which are 120° out of phase (note 3*120° = 360° = full circle). Just as before, the voltage between the Hot and Neutral is 120 volts, but because of the phase angle, the voltage between any two Hot wires is 208 volts, which is 40*(0.866) = 208 volts. (Where 0.866 is the cosine of 120°.)
The majority of three phase motors don't use the Neutral wire. This is called a Delta Connected system. When the Neutral is used, it is called a wye-connected system. The majority of power sources are "wye- connected". A delta-connected load (motor) can always be connected to a wye source by just ignoring the Neutral wire, but the reverse is virtually never true. (It can be done, but it requires a center tap, three-phase, transformer to artificially create the Neutral.)
Current in the Neutral Wire
This is a question I get asked by even very experienced people. "If the current through the Neutral wire is the sum of the currents through each of the Hot wires, then shouldn't the maximum current in the Neutral be three times that of any one leg (at maximum power)?" That is, if 20 amps of current are flowing through each of the three Hot wires, then shouldn't the Neutral have 60 amps flowing through it? The answer is NO. (The following explanation is based on the three-phase system, but it also holds true for the single phase, two-pole system.) The current flowing through the Neutral wire is the sum of the currents flowing though each of the phases; yes, but what complicates this, is that each of the phase currents has both a magnitude and direction. Any time we have an expression which has both magnitude and direction, it can be expressed as a vector (the arrows I have drawn in the above diagram are vectors). We can't just add the magnitude of vectors without considering the direction as well.
Vector Mathematics
In order to explain the current in the Neutral wire, we need to understand some principles of vector mathematics. Vectors can be used to describe anything that has a magnitude and direction. One example deals with travel, where the length of travel is the magnitude, and the direction is just that, direction.
If we walk 10 feet East then turn around and walk 10 feet West, it is said that our net travel is zero (we are at the same point we started at.) If we walk 10 feet East and 10 feet North, then we could have accomplished the same travel by walking 14 feet Northeast (@45°).
In determining the 14 feet Northeast, we could either draw a picture, or use trigonometry. The drawing method is called tip-to-tail because we redraw the vectors such that the second one starts where the first one stops.
To prepare for the examples discussed in the section below: if we walk 20 feet at 120°( 120° from north), and then turn and walk 20 feet at 240° from north, we could accomplish the same travel by walking 20 feet due south. (By the way, the reason for the 20 feet due South, and not 24 feet or some other number, is because 120° and 240° make up what is called a perfect triangle. If it weren't for these nice angles, it would have resulted in some other length, not 20 feet.
One Phase at Max Current, Two at Zero
To understand how the current through the Neutral is determined, we will examine three worst-case situations. First, when one phase is at twenty amps, and the other two phases are at zero, the current in the Neutral will of course be 20 amps.
Two Phases at Max Current, One at Zero
When the current in two phases is 20 amps and the third is zero (the one pointing straight up is zero), the current in the Neutral will be 20 amps at 180°. The sum of 20 amps at 120° plus 20 amps at 240° is 20 amps at 180°.
All Three Phases at Max Current
When all three phases carry the maximum current, they all cancel out, and the net current through the Neutral is zero amps.
In short, the current through the Neutral can never exceed the maximum current in any one of the Hot legs.
Apparent Power, Real Power, and Power Factor
Power is the ability of a system to perform work. Water performs work when it turns the turbine blades of a hydroelectric plant. Electricity performs work when it heats up a heating element or turns a motor. It takes power to store energy, like in capacitive or inductive devices, while these devices then release some energy, or power, at a later time. (These devices can both expend power and deliver power.)
Power (in General)
For DC systems, power is the product of Current times Voltage, and will take on the form P=I*V. For AC systems with only resistive loads, the same holds true. But in capacitive or inductive circuits on an AC system, the device will momentarily store some power (or delay it), and so the issue becomes slightly more complicated. We need to compensate for this delay in power transmission, and this is where the term Power factor comes in.
Power factor
When we us any capacitive or inductive device on an AC circuit, the current or voltage flowing through the circuit will be slightly delayed, or out of phase. A motor is an inductive element, and the current lags behind the voltage (remember, the inductor had the ability to store current). In a capacitor the voltage lags behind the current (the capacitor stores voltage).
You may sometimes hear the phrase: the current leads voltage in a capacitor, but this is just a matter of convention where the voltage is assumed to always be the same and the current either leads or lags. This will now be rephrased to the standard convention: Current LAGS voltage in an Inductor and Current LEADS voltage in a Capacitor.
For a purely capacitive or inductive circuit with zero resistance, the angle of lead/lag is 90°. Adding resistance to the circuit will decrease the leading/lagging angle.
The term "Power factor", is the cosine of the phase angle. For a purely inductive circuit, the lag angle is 90°, and the power factor is zero [cosine(90)=0]. A common power factor for electric motors is 0.8, which gives us a lagging angle of 36° (This is because there is some resistance inside the motor windings).
Apparent Power (KVA)
Apparent power is defined as the power that is "apparently" absorbed by a system. That is, the product of current times voltage tells us a device appears to be using a certain amount of power. However, this does not take into account the fact that the device can store (or delay) current or voltage, and this results in the calculations being slightly skewed.
Apparent power is useful when we have a device like a diesel-electric generator, where the wires inside have a limited capacity to pass current, and we may not know in advance what will be connected to the generator. In other words, it doesn't matter what the delay (or phase angle) is, the generator can only allow a limited amount of current to pass through its wires.
Because of this, many generators (and most transformers) are rated in volt-amperes (VA), or thousand-volt-amperes (KVA). A 25 KVA generator (or transformer) can deliver no more than 70 amps per phase @ 208 volts before it burns out the windings. This can therefore power 25 kilowatts of heaters, but only 20 kilowatts for motors (assuming 80% power factor), because both of these loads will use 70 amps. Since the manufacturer does not know what the generator will ultimately be used for, they rate it in KVA because this indicates the maximum current regardless of the load's power factor.
Real Power (Watts)
The real amount of power a device is using, or results in actual work performed, is called the "real power". Real power takes into account the fact that current or voltage is stored, or delayed. The real power tells us how much actual work can be performed, or how many horsepower our motor is delivering.
For a resistive and/or DC circuit, the apparent power and the real power are the same, but for a capacitive or inductive circuit, the real power is heavily dependent on the amount that the current or voltage is delayed.Real power is presented in Watts.
There is mathematically no difference between watts and volt-amperes, except that we use one term for apparent power, and one for real power, but they are both units of power. We use the power factor to go from apparent power to real power.
The real power of a system is equal to the apparent power times the power factor. In every day use, this boils down to P=I*V*pf.
Efficiency
Regardless of the type of system, Efficiency is the difference between power in and power out. If you are peddling a bike, your legs are Power in, and the tire against the road is Power out. The difference between these two is the efficiency of power transmission.
For a bike, this loss of power, or efficiency, would be primarily the friction of the chain (even the friction of your trousers against your legs), wind resistance in the spokes, and even small frictional losses between the tire and the road, but it is not due to the steepness of the hill or wind resistance against you and the bike's frame, as this is a portion of the work the bike is performing (the load).
In a motor, the loss of power is due to the resistance of the windings, friction in the bearings, air resistance inside the motor, and what is known as "hysteresis losses" in the iron core of the motor.
Magnetic Poles
All magnets, regardless of type or origin, will have a north and south pole. This is very similar to a battery always having a positive and negative terminal. If you have two magnets, the poles with opposite polarity will attract one another, while poles with the same polarity repel one another. These attraction and repulsion forces can be quite strong, and this is what will make a motor turn.
Induction
If you have a magnet, and you are physically moving a wire near this magnet, it will create a current in the moving wire. The faster you move the wire, the larger the current. Furthermore, the bigger the magnet, the larger the current. If you change the direction the wire moves, the current will also change direction. This is the basic premise for a simple generator, where we use a diesel engine to move wires past a magnetic field.
Electromagnets
Any flowing electric current creates a magnetic field. When this current is flowing through a wire, the magnetic field forms circular rings around the wire. We can concentrate the magnetic field by coiling the wire into tight loops, thereby making an electromagnet.
We can concentrate the magnetic field even more, by wrapping the wire around an iron bar. This electromagnet also has both north and south poles like any other magnet, but the polarity of the poles changes as the electricity changes. If we send 60hz line power through an electromagnet, the polarity of the magnetic poles will alternate sixty times per second.
Parts of the Motor
A motor is made up of electric and/or permanent magnets that are constantly attracting and/or repelling one another. This creates movement of the spinning rotor. The only thing that differs from one type of motor to another is how these magnets are created and controlled.
Stator
This is the stationary magnetic component in motors, and constitutes the chassis in some cases. On most motors, the stator's magnetic field is created from electromagnets. One notable exception is small DC motors found in such items as toy trains etc., where these use small permanent (bar-type) magnets.
Permanent magnets are not normally used in larger motors because they can loose their magnetism if the magnetic field in the windings is too strong. This would saturate the permanent magnet, and re-magnetize the stator in reverse polarity.
Rotor
The rotor is the component that makes up the spinning shaft of the motor. It is almost always electromagnetic in nature (coils).
Windings
These are the coils of wire that make up the electromagnet. They are usually wrapped around a laminated stack of iron sheets. The reason for the laminations is too complex to get into, but for those already familiar with the basic concepts, it is to reduce hysteresis losses in the iron core.
Commutator
This is found in universal and DC motors. These devices, along with the brushes serve to switch the polarity of the windings as the motor makes a revolution. (A forward and reversing switch, in short)
Brushes
These are typically carbon/graphite bars which carry the current from the incoming wires to the commutator, and then to the rotor windings. The brushes are soft such that they will form to the commutator contacts as it spins.
Calculations
Due to the principles of Conservation of Energy (energy can neither be created nor destroyed, only converted from one form to another.), we can say that the power into the motor, as electricity, is equal to the power out of the motor, as horsepower, minus any losses or inefficiencies in this conversion process.
A motor is nothing more than a converter of energy. It converts electrical energy into mechanical energy plus a little heat as a byproduct. (Note that losses or inefficiencies do not violate the physical law of "conservation", these losses result in heat or other forms of energy.)
The overall equation for converting electrical power to mechanical horsepower is: HP=W/745. Where HP is horsepower, W is watts, and 745 is a conversion factor. We know from our previous discussion that power, in volt-amperes, is given by the following equation: P=I*V. For an inductive device like a motor, we also need to take into account the phase angle between current and voltage by adding the power factor term (pf). Our equation for power becomes P=I*V*pf. Our final equation then becomes: HP=I*V*pf/745.
Shared Ground System
A shared ground system is one where there is a ground wire or path that is common to all panels. In a shared ground system, only the main load center can be bonded (neutral tied to ground). At no other point in the system can there be a connection between ground and neutral.
Any, and all, sub-panels must be wired with separate wires for neutral and ground which originate back at the main load center. By default, all electrical systems within the same building are of the shared ground type. Because of this, if you add a sub-panel in your basement or attached garage, then you must carry a ground wire from the main panel to the sub-panel, and you must remove the bonding screw from the sub-panel.
Split Ground System
In a split-ground system, you have two totally separate grounding systems. The electrical systems cannot be contained in the same building, and there must be no path to ground which they have in common (this must also include water pipes). When there is a completely separate grounding system between two electrical systems, then each system must be bonded.
One simple example of a split system is where incoming power from the utility enters a distribution panel (a splitter panel), and passes to two separate buildings. In each of these buildings, there is a separate load center, and a separate ground rod. There is no ground wire that connects the two buildings. In this case, there is no sub-panel, as each panel is considered a main load center.



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Basic Electrical Concepts

COM 2400
Basic Video Editing
Fall, 1999

Perhaps we should begin our discussion of the technical side of video production with a brief introduction to electricity. This makes a lot of sense because the picture and sound in video travel from source to destination as electrical signals. Part of the editing process involves looking at these signals on different types of monitoring equipment and possibly adjusting these signals if they do not appear as we think they should. Knowing something about electricity may help you to understand these monitoring devices and the adjustments you make.

Let’s begin by looking at a basic electrical circuit. In this case, our circuit is one contained in a common flashlight. In electrical terms, this particular flashlight has 4 components or building blocks. The batteries are an example of a voltage source. The flashlight case (a metal case or metal imbedded in a plastic case) constitutes a path for electricity to travel from the voltage source to the lamp and back. We say the metal components are conductors because they conduct electric current (allow electric current to flow). The lamp is an example of an operating device, something that does useful work when current is caused to flow through it. Operating devices are often referred to as loads. The switch is a control device, allowing us to start or stop the flow of current in the flashlight. If these components are assembled in the proper manner, we have what is known as a circuit.

A proper electrical circuit that will work normally must have three things, a voltage source, a load, and conductors connecting the source and load. A switch is not a required part of a circuit; it’s just handy to control the operation of the load. Voltage sources and loads must each have at least two terminals or contact points (most have just two) and we normally need two separate conductors to make our circuit; each conductor connects one terminal of the voltage source to one terminal of the load.

Below are two illustrations representing circuits. One is our flashlight without a switch; one has the switch included. The lamp in the circuit without the switch will burn as long as the conductors are connected as shown and the batteries can generate voltage. The function of the switch can be duplicated by connecting and disconnecting one of the conductor ends from its respective terminal. Any of the four terminals could be used.




Voltage is defined as electrical pressure. Voltage pushes electricity through a circuit. Electricity or electrical current is defined as the orderly flow of electrons (you all know what electrons are, right?) through a conductor. The operating device provides an opposition to the flow of current and thus limits how much current can flow in the circuit. Many beginning classes in electricity often refer to an analogy to help students understand what’s going on. It is not a perfect analogy, but it may help. A water faucet is an example of a source of pressure (in this case, water pressure). A hose attached to the faucet is like a conductor. The water that flows in the hose when the faucet is turned on is like electricity or current. In this analogy, turning on the faucet is much like closing the switch. There are some interesting differences between the water system and an electrical circuit. To begin with, our voltage source has two terminals, the faucet represents only one. Second, for electricity to flow, you must have a complete path from voltage source through a load and back to the source. The hose, on the other hand, will let water run out of it onto the ground at its end. The water doesn’t have to return to the faucet in order to flow. Third, an electrical circuit without a load is usually trouble. The hose, on the other hand, doesn’t have to have anything attached to it. And finally, the hose likely had no water in it when first attached to the faucet. The water had to fill the hose before it reached the end. As explained below, electrical conductors are different from hoses in this respect.

The two terminals of a voltage source are sometimes labeled plus and minus to distinguish between them. This is certainly true for batteries. We normally think of electrons being pushed out from the negative terminal and pulled into the positive terminal. Electrons are everywhere in the material of the voltage source, the conductors, and the load. An analogy might be a string of cars around a circular track, bumper to bumper. The track represents our circuit and each car is like an electron. The voltage source applies a pressure to make one of the cars move. But if one car moves, all cars must move simultaneously. Electrons in a circuit can be thought of similarly. When electrons move out of the voltage source, other electrons are moving through the conductors, the load, and back into and through the voltage source. An electron doesn’t have to travel all the way from the source to the load before work can be done. For work to occur, electrons must move in an orderly fashion in the load. This implies they are moving in an orderly fashion throughout the entire circuit. We say that current flows in all parts of the circuit simultaneously or it doesn’t flow at all.

We mentioned that electrons were present in the voltage source, conductors, and load. The load represented an opposition to current flow. This means the electrons in it (in the materials that make up the load) could not be made to flow in an orderly fashion as easily as the electrons in the conductors or source. When we open a switch or disconnect a wire from a terminal, we create a short distance of “air” in our circuit. Air contains some electrons too but they are really difficult to make flow in an orderly fashion. The flow of current in the circuit stops. If the pressure from the battery were great enough, we could make a current flow through air. Lightning strikes are an example of when extreme voltages cause electricity to flow through air.

Electrical pressure or voltage is measured in volts. Batteries typically have 1.5 volts, 9 volts or 12 volts. Opposition to current flow is measured in ohms. The amount of current is measured in amperes or amps. One volt can push one amp through one ohm of opposition.

Voltage sources can be divided into two types. In one, (a battery is an example) the negative terminal is always the same. Electrons always leave one terminal and enter the other. Current would always flow in one direction (when it’s flowing) when a battery is the voltage source. We call this direct current or DC. Another type of voltage source has the positive and negative terminals constantly switching (a common wall outlet in the home is an example). The current flows out of one terminal (slot in the receptacle) for a brief period and then flows out of the other terminal. The direction of current flow alternates and we say the voltage source is for alternating current or AC.

Opposition to DC is called resistance and is measured in ohms. Opposition to AC is called impedance and is measured in ohms. When you study electricity, resistance is pretty straight forward; it’s like friction. Impedance is much more complex. I won’t try to explain impedance here. It’s like friction, inclines, and declines all combined to make the flow of electricity more difficult. It’s like DC isn’t bothered or affected by inclines and declines, only friction, while AC is influenced by all three and the relative steepness of the inclines and declines must be factored in. The math for AC involves trigonometry while DC is much simpler algebra.

If you haven’t studied electricity before, I’m sure your head is spinning and you’re asking what does this have to do with video production and editing. Well, let me try to explain. In production and editing, you often hook different pieces of equipment together to accomplish some task. Maybe it’s a camera and recorder; perhaps with a mic attached for sound. Maybe you connect two video decks together to allow you to play a recorded tape and make a copy of it. Perhaps your decks will allow you to edit the video in the process of transferring it from one deck to the other. Video cameras and microphones are examples of voltage sources. They generate voltages that represent pictures and sounds. Input terminals on recorders (where signals go into a device) represent loads. You hook them together with appropriate cables that contain the proper conductors. Output terminals on a deck (where signals come out of a device) are examples of voltage sources. Video monitors, headphones, and speakers are examples of loads (devices that do useful work when current flows through them.

Part of the editing process that we will look at in this class involves observing, analyzing, and manipulating the electrical signals that represent picture and sound. We will also spend some time (not much) discussing how we connect different pieces of equipment together to accomplish our editing tasks. I hope that this brief introduction to electricity will prove helpful to your understanding of these topics as we disucss them during the semester.