Glossary of Terms


alternating current (AC)

An electrical current that changes strength and direction of flow with a certain regular cycle. For example, 60 Hertz AC is an electrical current that changes its polarity (from positive to negative and back to positive; a complete cycle) sixty times per second.

ampere (amp, A)

A unit of measure for electric current.


Magnetic flux density, measured in gauss (G) or milligauss (mG).


Refers to the degree that each circuit phase carries equal amounts of current.


Connecting together the normally non-current-carrying components of an electrical system such as metal conduits, appliance frames, building reinforcing steel, etc. The purpose of bonding is to allow all non-current-carrying components of an electrical system to be connected to ground to reduce hazard of electrical shock.


"Buried Underground Residential Distribution," system of equipment (transformers/ switches) located entirely below ground.

bus, busbar

Large conductors in panelboards or switchboards made of copper or aluminum, usually rectangular in cross section. Busbars allow connection of the large feeder wires supplying the switchboard to make the transition to smaller wires through switches or circuit breakers, which are in turn connected to the electrical circuits supplied by the board.


The electrical property of matter that is responsible for creating electric fields. Charge is either positive or negative.


In electrical context usually refers to the National Electrical Code (NEC), published by the National Fire Prevention Association, which is revised every three years.


A material which passes electric current. Good conductors are generally made of metal, although other substances such as the earth or the human body can be relatively good conductors.


Pathways intended for enclosing electrical wiring. Conduits may be made of steel, aluminum, PVC or other materials. Conduits are permitted to act as grounding conductors for electrical circuits as provided by codes.


The flow of electric charge through a power line or an electric wire. The electric current in a wire is like water flowing through a pipe. Currents produce magnetic fields.

direct current (DC)

An electrical current that flows in one direction only. The current in batteries is DC.

distribution line

Power lines carrying power to neighborhoods (primary distribution) and to one or several buildings (secondary distribution). These carry less than 35 kV.

electric field (EF)

The force electric charges exert on other objects. It is measured in volts per meter (V/m). An electric field is a function of voltage and not of current.

electric and magnetic fields (EMF)

The force fields around an electric conductor that has voltage and current. "EMF" is often used (as in this document) to describe power-frequency-induced magnetic fields.

electromagnetic spectrum

A breakdown of electromagnetic fields according to their frequency and wavelength. The spectrum is divided into extra low-frequency (ELF), very low frequency (VLF), radio-frequency (RF), microwave, visible light, and ionizing radiation (X-rays and gamma rays).

ELF radiation

Extremely low frequency field at the end of the electromagnetic spectrum, from zero to 3,000 Hz. The 60-Hz power frequency is in this ELF range.


The capacity for doing work or producing heat.


An area of influence surrounding an electromagnetic source. Time-varying magnetic fields are capable of inducing electric currents in conductors, including humans.


A computer program developed by Southern California Edison Company that models transmission and distribution lines. This program calculates the magnetic and electric fields for long parallel conductors, both overhead and underground. This program allows the designer to calculate expected magnetic and electric fields for various design configurations, loading and voltages.

frequency (f)

The rate at which a wave completes one full cycle. The rate per second is expressed in Hertz (Hz). On the spectrum, energy is organized by frequency, with direct current (DC) having the lowest frequency (0) and gamma rays having the highest. Power frequency is 60 Hz in the United States but 50 Hz in most other industrialized nations.

gauss (G)

A unit used for measuring magnetic flux density fields. Since gauss is a large measure, milligauss (mG) is more commonly used for environmental measurements. One gauss equals 1,000 milligauss, 10,000 gauss equal 1 tesla.


A device used to measure magnetic fields.


Can be used as a verb or noun. As a verb it means to connect in some way to either earth or to a conductor which serves in place of the earth. Sometimes used when the more accurate term would be "bond." Paradoxically, it is not the earth connection which protects a circuit from a "ground fault," but a solid connection back to the transformer neutral.


Integer multiples of a fundamental frequency. In the U.S. the fundamental power frequency is 60 Hz so the "third harmonic" would be 3 x 6O, or 180 Hz. These harmonic frequencies appear as "noise" or "distortion" superimposed on the fundamental wave, thereby producing a distorted waveform.

Hertz (Hz)

A unit used to measure the rate at which charge changes polarity of an AC electric current. One Hertz is one cycle per second. A 60 Hz system has sixty cycles per second.


[see neutral ]

impedance (Z)

The property of an electrical circuit which tends to impede the flow of electrical current. In alternating current circuits, impedance is the vector sum of reactance and resistance. Reactance may be either capacitive or inductive. In practical electrical circuits, impedance is usually the result of conductor resistance and circuit inductance.


A material which conducts electric current poorly.

kilovolt amps (kVa)

The product of circuit current and voltage and a constant.

kilowatt (kW)

A unit equal to 1,000 watts. A unit of power or the rate of doing work. KW differs from kVA in that KW represents actual power and kVA represents "apparent" power. The two terms differ because of power factor.

knob-and-tube wiring

A system of routing conductors separately inside a building used until the 1940s and in some cases longer. The hot and neutral conductors are spatially separated by inches or feet, and there is no equipment grounding conductor. The separation produces high magnetic field levels. Found in many older buildings which have not been fully upgraded.

magnetic field (MF)

The force field produced by an electric current.

magnetic flux density (B)

The measurement of the strength and direction of a magnetic field in a given area.

maximum B

The upper range limit of magnetic flux density "B" as it varies through a minimum and maximum over a period of 1 cycle.

microwaves (MW)

Electromagnetic radiation with a frequency at the high end of radio-frequency radiation. A form of nonionizing radiation. Radar is a form of microwave radiation. Microwave ovens operate at 2,400,000,000 Hz.

milligauss (mG)

One-thousandth of a gauss.


A combination of conductors consisting of two (duplex), three (triplex), or four (quadraplex) individual conductors twisted around each other. These are generally used as services or secondary wiring.

Mu metal

The symbol Mu stands for magnetic permeability. It is a name for a general group of alloys which allow magnetic lines of force to concentrate within them, thus freeing the space outside the material of high permeability of those force lines which would otherwise constitute a magnetic field. This metal is useful for shielding purposes and is produced in thicknesses down to foil gauge.


National Electrical Code (see code).

net current

The current unbalance left over when two or more conductors running together do not balance out each other in amps and/or phase angle. Detected by either a gaussmeter or a clamp-on ammeter clamped around the entire circuit. The magnetic field produced by net current acts the same way as a field from the same current traveling in a single conductor.

net-through unbalance

A balanced 3-phase network is one where the currents are equal in magnitude and separated in phase by 120 degrees. If the currents are not equal in magnitude or not separated by 120 degrees they are said to be unbalanced. In the case of parallel circuits, unbalanced currents can circulate in a loop between the parallel circuits or they can flow through the network (through unbalance).


Current or conductor completes the electrical circuit and directs current back to the source. Neutrals are at ground potential and not considered a "phase" of the circuit. Earth may act as a neutral path back to the source.

nonionizing electromagnetic radiation

The range of the electromagnetic spectra, comprising direct current, extremely low frequencies, very low frequencies, radio frequencies, microwaves, infrared, visible light, and part of ultraviolet. Sometimes referred to by its acronym "NIER," it is unlike ionizing radiation in its inability to break chemical and electrical bonds of an atom or group of atoms to lose or gain one or more electrons. X-rays are one example of ionizing radiation; radio broadcasts are an example of NIER.

overhead (OH)

Overhead refers to electrical overhead conductors and equipment mounted on poles.


Equipment (transformers, switches, etc.) which sits on the ground on concrete or plastic "pads" fed by underground conductors.

permeability (Mu)

A physical constant that reflects a material or medium’s relative "ease" or "difficulty" conducting or "shunting" magnetic fields.


The timing of an AC electric current. Some 60 Hz current is a three-phase system, with each of the three phases reaching its peak at a different point in the cycle. The three work together in transmission lines and circuit wiring.

phased, phasing

The physical positioning of each phase of the circuit(s) on a utility line with respect to the other phases so as to minimize EMF through cancellation.


Signifies voltage or conductors carrying voltage greater than 600 volts on the distribution system. Also refers to the "high side" voltage on a transformer.


Energy that is propagated through space in waves or particles. Some common forms of radiation are x-rays, microwaves, light, and radio waves.

radio frequency (RF)

Electromagnetic energy in the approximate frequency range of 3,000 Hz (3 kHz) to 1 billion Hz (l gHz).


The property of an alternating current circuit to resist the flow of current due either to capacitance or inductance. Reactance, unlike resistance, does not dissipate energy. Reactance is responsible for the phenomenon known as phase shift, which is the tendency for current in an alternating current circuit to be out of step in time with the voltage of the circuit. Reactance is a function of frequency and relates to harmonics.


The properly of a material to resist the flow of electrical current. Resistance is a property of all practical circuits to some degree. Current flowing through resistance always results in dissipation of energy, usually in the form of heat.


Voltage or conductors carrying voltage less than 600 volts on the distribution system. Also refers to the "load" voltage on a transformer.


The point of connection between the electrical utility and the customer’s electrical system.

service drop

The overhead or underground cable which brings power to a residence or business from the distribution line. It usually attaches to the eave of the building if overhead.


A substance or device that attenuates electric or magnetic fields.

short circuit

An abnormal connection (including an arc) of relatively low impedance between two points of different potentials.

single-phase service

Service where a single phase from a three-phase primary distribution line goes to a transformer's primary coil. The transformer's secondary coil provides two hot legs from the opposite ends of the coil and a grounded neutral from the center of the coil. These three conductors are twisted together and go to the panel providing 120/240V service.

split phasing

A single-circuit line constructed as two parallel circuits that can be phased to achieve maximum field cancellation.

stray voltage

Excess electric charge returning to the transmission or distribution system, usually through the ground. Electric power distribution systems allow some unused current that goes into a home or business to return to the system via ground current, that is, electricity sent to ground (literally into the ground) which seeks to find its way back to an electric power source such as a transformer. In some instances, most often on farms where transmission lines cross the property, this current creates electric current on metal equipment such as feeding bins for livestock. When this happens, the animals can receive shocks sufficiently strong to change their behavior.

sub transmission

Power delivery system at voltages between 50,000 and 161,000 volts (50 kV - 161 kV).

tesla (T)

A very large unit of measure of magnetic fields. One tesla equals 10,000 gauss. A microtesla (mT), one millionth of a tesla, is a smaller measure that is sometimes used. One microtesla equals 10 milligauss.

three-phase service

Service that brings in all three phases from the power line plus the neutral. Common in commercial buildings.

transmission line

A power line carrying high-voltage electricity between regions. Most transmission lines are built on steel towers and operate at voltages between 60 and 765 kV.

transmission system

An interconnected group of electric transmission lines and associated equipment which transfers electric energy in bulk between points of supply and points of delivery.

two-phase service

Service that brings in two of the three phases from the power line plus a neutral. Each phase is 120V to ground and 208V phase to phase. This type of service always produces significant neutral current since the two phases never balance. Common in commercial buildings supplied with three-phase to the main panel. Two-phase goes out to subpanels.


Situations where there is unequal flow in the various circuit conductors.

underground (UG)

Underground refers to electrical conductors and equipment located below ground surface.

very low frequency (VLF)

Electromagnetic energy in the approximate frequency range of 3,000 hertz (3 kHz) to 30,000 hertz (30 kHz).

volt (V)

The unit used to measure electrical potential. The electrical force which propels current in a conductor. This is analogous to the water pressure in a water hose.

volts per meter (V/M)

Electric fields are measured in volts per meter or in thousands of volts per meter (kV/m).


A regular, periodic disturbance in space. In electricity and for EMFs and electromagnetic radiation, the disturbances (the electric and magnetic fields) are at right angles to the direction the wave is traveling. The main characteristics of a wave are the speed it is traveling, its frequency, its wavelength, and its amplitude. The wavelength is equal to the speed of propagation divided by the frequency.


The distance between comparable points of two successive waves. As a wave's frequency increases, its wavelength decreases, and vice versa. At 60 Hz the wavelength is about 3,100 miles. At radio frequency ranges the wavelength is closer to thirty or forty feet, and at microwave ranges it is approximately one inch.

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