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Glossary of Terms

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Absorber: A material that readily absorbs photons to generate charge carriers (free electrons or holes).

Absorbers: Dark-colored objects that soak up heat in solar collectors.

Absorption coefficient: The factor by which photons are absorbed as they travel a unit distance through a material.

Acceptor: A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole, which can accept a free electron.

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.

Actinide: an element with atomic number of 89 (actinium) or above.

Activation product: A radioactive isotope of an element (e.g., in the steel of a reactor core) which has been created by neutron bombardment.

Active solar heater: A solar water or space-heating system that moves heated air or water using pumps or fans.

Affected employee: An employee whose job requires him or her to operate or use a machine or equipment on which servicing or maintenance is being performed under lockout or tagout, or whose job requires him or her to work in an area in which such servicing or maintenance is being performed.

Air mass: The ratio of the mass of atmosphere in the actual observer-sun path to the mass that would exist if the observer was at sea level, at standard barometric pressure, and the sun was directly overhead. Note: (sometimes called air mass ratio). 

Air mass 1.5 (AM1.5) standard reference spectrum: The solar spectral irradiance distribution (diffuse and direct) incident at sea level on a sun-facing 37-degree tilted surface. The atmospheric conditions for AM1.5 are: precipitable water vapor, 14.2 mm; total ozone, 3.4 mm; turbidity (base e, lambda=0.5 mm), 0.27. [ASTM E 892, Table 2]

Alternating current: Electric current in which the direction of flow is reversed at frequent intervals: usually 100 or 120 times per second (50 or 60 cycles per second or 50//60 Hz).

ALARA: As Low As Reasonably Achievable, economic and social factors being taken into account. This is the optimization principle of radiation protection.

Alpha particle: A positively-charged particle from the nucleus of an atom, emitted during radioactive decay. Alpha particles are helium nuclei, with 2 protons and 2 neutrons.

Alternative fuels: Solid fuels such as municipal solid waste (MSW), refuse derived fuel (RDF), biomass, rubber tires, and other combustibles that are used instead of fossil fuels (gas, oil, or coal) in a boiler to produce steam for the generation of electrical energy.

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 (A) or amp: The basic SI unit measuring the quantity of electricity. The unit for the electric current; the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm.

Ampere-hour (Ah): Quantity of electricity or measure of charge. (1 Ah = 3600 C [Coulomb])

Amorphous semiconductor: A non-crystalline semiconductor material that has no long-range order.

Annual solar savings: The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

Anthropogenic: Referring to alterations in the environment due to the presence or activities of humans.

Antireflection coating: A thin coating of a material, which reduces the light reflection and increases light transmission, applied to a photovoltaic cell surface.

Armored Cable: A cable provided with a wrapping of metal, usually steel wires or tapes, primarily for the purpose of mechanical protection.

Arc-over Voltage: The minimum voltage required to cause an arc between electrodes separated by a gas or liquid insulation.

Array: Any number of photovoltaic modules connected together to provide a single electrical output. Arrays are often designed to produce significant amounts of electricity.

Atom: A particle of matter which cannot be broken up by chemical means. Atoms have a nucleus consisting of positively-charged protons and uncharged neutrons of the same mass. The positive charges on the protons are balanced by a number of negatively-charged electrons in motion around the nucleus.

Attendant: An employee assigned to remain immediately outside the entrance to an enclosed or other space to render assistance as needed to employees inside the space.

Attenuation: (l) The ratio of the input to output power levels in a network (transmission line) when it is excited by a matched source and terminated in a matched load. (2) Power loss in an electrical system.

Authorized employee: An employee who locks out or tags out machines or equipment in order to perform servicing or maintenance on that machine or equipment. An affected employee becomes an authorized employee when that employee's duties include performing servicing or maintenance covered under this section.

Automatic circuit re-closer: A self-controlled device for interrupting and re-closing an alternating current circuit with a predetermined sequence of opening and re-closing followed by resetting, hold-closed, or lockout operation.

Autonomous system: A stand-alone Photovoltaic system that has no back-up generating source. May or may not include storage batteries.

Availability: Describes the reliability of power plants. It refers to the number of hours the turbines are available to produce power divided by the total hours in a year.

Avoided cost: The minimum amount an electric utility is required to pay an independent power producer, under the PURPA regulations of 1978, equal to the costs the utility calculates it avoids in not having to produce that power (usually substantially less than the retail price charged by the utility for power it sells to customers).



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Background radiation: The naturally-occurring ionizing radiation which every person is exposed to, arising from the earth's crust (including radon) and from cosmic radiation.

Balance of system: Represents all components and costs other than the Photovoltaic modules. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs.

Band gap: In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.

Band gap energy (EG): The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state and, thus, to promote it from the valence level to the conduction level.

Band-to-band Auger recombination: Recombination of an electron and a hole occurring between bands of the same energy in which no magnetic radiation is emitted.

Bare Conductor: A conductor not covered with insulating material.

Barricade: A physical obstruction such as tapes, cones, or A-frame type wood or metal structures intended to provide a warning about and to limit access to a hazardous area.

Barrier: A physical obstruction which is intended to prevent contact with energized lines or equipment or to prevent unauthorized access to a work area.

Barrier energy: The energy given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the barrier.

Barrier, fire: A continuous membrane, either vertical or horizontal, such as a wall or floor assembly, that is designed and constructed with specified fire resistance rating to limit the spread of fire and that will also restrict the movement of smoke. Such barriers can have protected openings.

Base load: That part of electricity demand which is continuous, and does not vary over a 24-hour period. Approximately equivalent to the minimum daily load.

Base power: Power generated by a utility unit that operates at a very high capacity factor.

Baseline performance value: Initial values of short-circuit current, open-circuit voltage, and current at maximum power measured by the accredited laboratory and corrected to Standard Test Conditions, used to validate the manufacturer's performance measurements provided with the qualification modules per IEEE 1262.

Battery energy storage: The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter. Battery storage has also been suggested for holding down air emissions at the power plant by shifting the time of day of the emission or shifting the location of emissions.

Bayonet Coupling: A quick coupling device for plug and receptacle connectors, accomplished by rotation of a cam operating device designed to bring the connector halves together.

Becquerel: The SI unit of intrinsic radioactivity in a material. One Bq measures one disintegration per second and is thus the activity of a quantity of radioactive material which averages one decay per second. (In practice, GBq or TBq are the common units.)

Beryllium Copper (BeCu): A relatively expensive contact material with properties superior to brass and phosphor bronze. It is recommended for contact applications requiring repeated extraction and reinsertion because of its resistance to fatigue at high operating temperatures.

Beta particle: A particle emitted from an atom during radioactive decay. Beta particles may be either electrons (with negative charge) or positrons.

BIPV (Building-Integrated Photovoltaic): A term for the design and integration of Photovoltaic into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading "eyebrows" over windows; or other building envelope systems.

Biological shield: A mass of absorbing material (e.g., thick concrete walls) placed around a reactor or radioactive material to reduce the radiation (especially neutrons and gamma rays respectively) to a level safe for humans.

Blocking diode: A diode used to restrict or block reverse current from flowing backward through a module. [UL 1703] Alternatively, diode connected in series to a Photovoltaic string; it protects its modules from a reverse power flow and, thus, against the risk of thermal destruction of solar cells.

Boiling water reactor (BWR): A common type of light water reactor (LWR), where water is allowed to boil in the core thus generating steam directly in the reactor vessel. (cf PWR)

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.

Boron (B): A chemical element, atomic number 5, semi-metallic in nature, used as a dopant to make p-semiconductor layers.

Boule: A sausage-shaped synthetic single-crystal mass grown in a special furnace, pulled and turned at a rate necessary to maintain the single-crystal structure during growth.

Breakdown Voltage: The voltage at which an insulator or dielectric ruptures, or at which ionization and conduction take place in a gas or vapor.

Breed: To form fissile nuclei, usually as a result of neutron capture, possibly followed by radioactive decay.

Breeder reactor: see Fast Breeder Reactor and Fast Neutron Reactor.

British thermal unit (Btu): The amount of heat energy required to raise the temperature of one pound of water from 60 degrees F to 61 degrees F at one atmosphere pressure.

Burnable poison: A neutron absorber included in the fuel which progressively disappears and compensates for the loss of reactivity as the fuel is consumed. Gadolinium is commonly used.

Burnup: Measure of thermal energy released by nuclear fuel relative to its mass, typically Gigawatt days per tonne (GWd/tU).

Bushing: An insulating structure, including a through conductor or providing a passageway for such a conductor, with provision for mounting on a barrier, conducting or otherwise, for the purposes of insulating the conductor from the barrier and conducting current from one side of the barrier to the other.

Bypass diode: A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. [UL 1703] Alternatively, diode connected anti-parallel across a part of the solar cells of a Photovoltaic module. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.



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Cable: A conductor with insulation, or a stranded conductor with or without insulation and other coverings (single-conductor cable), or a combination of conductors insulated from one another (multiple-conductor cable).

Cable Assembly: A cable with plugs or connectors on each end.

Cable sheath: A conductive protective covering applied to cables. Note: A cable sheath may consist of multiple layers of which one or more is conductive.

Cadmium (Cd): A chemical element, atomic number 48, used in making certain types of solar cells and batteries.

Cadmium telluride (CdTe): A polycrystalline thin-film photovoltaic material.

Calandria: (in a CANDU reactor) a cylindrical reactor vessel which contains the heavy water moderator. It is penetrated from end to end by hundreds of calandria tubes which accommodate the pressure tubes containing the fuel and coolant.

CANDU: Canadian deuterium uranium reactor, moderated and (usually) cooled by heavy water.

Capacitance: That property of a system of conductors and dielectrics that permits the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of quantity of electricity to a potential difference. A capacitance value is always positive.

Capacity factor: The amount of energy that the system produces at a particular site as a percentage of the total amount that it would produce if it operated at rated capacity during the entire year. For example, the capacity factor for a wind farm ranges from 20% to 35%. Thirty-five percent is close to the technology potential.

Cathodic protection: A method of preventing oxidation (rusting) of exposed metal structures, such as bridges and pipelines, by imposing between the structure and the ground a small electrical voltage that opposes the flow of electrons and that is greater than the voltage present during oxidation.

Cell: The basic unit of a photovoltaic system.

Cell barrier: A very thin region of static electric charge along the interface of the positive and negative layers in a photovoltaic cell. The barrier inhibits the movement of electrons from one layer to the other, so that higher-energy electrons from one side diffuse preferentially through it in one direction, creating a current and thus a voltage across the cell. Also called depletion zone, cell junction, or space charge.

Cell junction: The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.

Central power: The generation of electricity in large power plants with distribution through a network of transmission lines (grid) for sale to a number of users. Opposite of distributed power.

Chain reaction: A reaction that stimulates its own repetition, in particular where the neutrons originating from nuclear fission cause an ongoing series of fission reactions.

Charge carrier: A free and mobile conduction electron or hole in a semiconductor.

Chemical vapor deposition (CVD): A method of depositing thin semiconductor films. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

Chlorofluorocarbon: A family of chemicals composed primarily of carbon, hydrogen, chlorine, and fluorine whose principal applications are that of refrigerants and industrial cleansers and whose principal drawback is the tendency to destroy the Earth's protective ozone layer.

Circuit: A conductor or system of conductors through which an electric current is intended to flow.

Cladding: The metal tubes containing oxide fuel pellets in a reactor core.

Clearance (between objects): The clear distance between two objects measured surface to surface.

Clearance (for work): Authorization to perform specified work or permission to enter a restricted area.

Cleavage of lateral epitaxial films for transfer (CLEFT): A process for making inexpensive GaAs photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.

Closed Entry Contact: A female contact designed to prevent the entry of a pin or probing device having a cross-sectional dimension (diameter) greater than the mating pin.

Coal: A black, solid fossil fuel found in the Earth. Coal is often burned to make electricity.

Coaxial Cable: A high-band width cable consisting of two concentric cylindrical conductors with a common axis that is used for high-speed data communication and video signals.

Cogeneration: The process in which fuel is used to produce heat for a boiler-steam turbine or gas for a turbine. The turbine drives a generator that produces electricity, with the excess heat used for process steam.

Combined collector: A photovoltaic device or module that provides useful heat energy in addition to electricity.

Compact fluorescent lights: Lights that use a lot less energy than regular light bulbs. We can use compact fluorescent lights for reading lights and ceiling lights.

Component Lead: The solid or stranded wire or formed conductor that extends from a component and serves as a readily formable mechanical or electrical connection or both.

Compressed-air energy storage (CAES): CAES plants use off-peak electrical energy to compress air into underground storage reservoirs for storage until times of peak or intermediate electricity demand. Wind power offers a good opportunity for charging CAES storage. The storage is typically underground in natural aquifers, depleted oil or gas fields, mined salt caverns, or excavated or natural rock caverns. To generate power, the compressed air is first heated by gas burners, then passed through a turbine.

Concentrator: A Photovoltaic module that uses optical elements to increase the amount of sunlight incident on a Photovoltaic cell.

Concentrating: arrays must track the sun and use only the direct sunlight because the diffuse portion cannot be focused onto the Photovoltaic cells.

Concentrate: See Uranium oxide concentrate (U₃O₈).

Concentrator (module, array, or collector): An arrangement of photovoltaic cells that includes a lens to concentrate sunlight onto small-area cells. Concentrators can increase the power flux of sunlight hundreds of times.

Concentricity: In a wire or cable, the measurement of the location of the center of the conductor with respect to the geometric center of the surrounding insulation.

Conductance: The reciprocal of resistance. It is the ratio of current passing through a material to the potential difference at its ends.

Conduction band; Conduction level: Energy level at which electrons are not bound to (orbiting) a specific atomic nucleus but are free to wander among the atoms. An energy band in which electrons can move freely in a solid, producing a net transport of charge.

Conductivity: The ability of a material to conduct electric current. It is expressed in terms of the current per unit of applied voltage. It is the reciprocal of resistivity.

Conductor: A wire or combination of wires not insulated from one another, suitable for carrying electric current.

Connection: That part of a circuit that has negligible impedance and that joins components, devices, etc., together.

Connector: A device providing electrical connection/disconnections. It consists of a mating plug and receptacle. Various types of connectors include DIP, card edge, two-piece, hermaphroditic and wire-wrapping configurations. Multiple contact connectors join two or more conductors with others in one mechanical assembly.

Connector Discontinuity: An ohmic change in contact resistance.

Connector Insert: For connectors with metal shells, the insert holds contacts in proper arrangement while electrically insulating them from each other and from the shell.

Connector Shell: The case that encloses the connector insert and contact assembly. Shells of mating connectors can protect projecting contacts and provide proper alignment.

Constant-speed wind turbines: Turbines that operate at a constant rotor revolutions per minute (RPM) and are optimized for energy capture at a given rotor diameter at a particular speed in the wind power curve.

Contact, Female: A contact located in an insert or body in such a manner that the mating contact is inserted into the unit. It is similar in function to a socket contact.

Contact, Male: A contact located in an insert or body in such a manner that the mating portion extends into the female contact. It is similar in function to a pin contact.

Contact Plating: Plated-on metal applied to the base contact metal to provide the required contact resistance and/or wear resistance.

Contact Resistance: Maximum permitted electrical resistance of pin and socket contacts when assembled in a connector under typical service use.

Contact Retainer: A device either on the contact or in the insert to retain the contact.

Contact Size: Defines the largest size wire that can be used with the specific contact. By specification dimensioning, it also defines the diameter of the engagement end of the pin.

Contact resistance: The resistance between metallic contacts and the semiconductor.

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.

Control rods: Devices to absorb neutrons so that the chain reaction in a reactor core may be slowed or stopped by inserting them further, or accelerated by withdrawing them.

Conversion: Chemical process turning U₃O₈ into UF₆ preparatory to enrichment.

Conversion efficiency (cell or module): The ratio of the electric energy produced by a photovoltaic device (under one-sun conditions) to the energy from sunlight incident upon the cell.

Coolant: The liquid or gas used to transfer heat from the reactor core to the steam generators or directly to the turbines.

Copper indium diselenide (CuInSe₂, or CIS): A polycrystalline thin-film photovoltaic material (sometimes incorporating gallium (CIGS) and/or sulfur).

Core: The central part of a nuclear reactor containing the fuel elements and control devices.

Critical mass: The smallest mass of fissile material that will support a self-sustaining chain reaction under specified conditions.

Criticality: Condition of being able to sustain a nuclear chain reaction.

Current at maximum power (Imp): The current at which maximum power is available from a module. [UL 1703]

Cycle life: Number of discharge-charge cycles that a battery can tolerate under specified conditions before it fails to meet specified criteria as to performance (e.g., capacity decreases to 80-percent of the nominal capacity).

Czochralski process: A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.



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Dangling bonds: A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.

dc to DC converter: Electronic circuit to convert DC voltages (e.g., Photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker (MPPT).

Decay: Disintegration of atomic nuclei resulting in the emission of alpha or beta particles (usually with gamma radiation). Also the exponential decrease in radioactivity of a material as nuclear disintegrations take place and more stable nuclei are formed.

Decommissioning: Removal of a facility (e.g., reactor) from service, also the subsequent actions of safe storage, dismantling and making the site available for unrestricted use.

De-energized: Free from any electrical connection to a source of potential difference and from electric charge; not having a potential different from that of the earth. Note: The term is used only with reference to current-carrying parts, which are sometimes energized (alive).

Deep discharge: Discharging a battery to 20-percent or less of its full charge.

Deflagration: Propagation of a combustion zone through a fuel-oxidizer mixture at a rate that is less than the speed of sound in the un-reacted medium and capable of producing a significant increase in pressure.

Demand Factor: For an electrical system or feeder circuit, this is a ratio of the amount of connected load (in kva 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.

Dendrite: A slender threadlike spike of pure crystalline material, such as silicon.

Dendritic web technique: A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.

Depletion zone: Same as cell barrier. The term derives from the fact that this microscopically thin region is depleted of charge carriers (free electrons and holes).

Depleted uranium: Uranium having less than the natural 0.7% U-235. As a by-product of enrichment in the fuel cycle it generally has 0.25-0.30% U-235, the rest being U-238. Can be blended with highly-enriched uranium (e.g., from weapons) to make reactor fuel.

Designated employee (designated person): An employee (or person) who is designated by the employer to perform specific duties under the terms of this section and who is knowledgeable in the construction and operation of the equipment and the hazards involved.

Detachment: The locating of a combustible particulate solid process in the open air or in a separate building.

Deuterium: "Heavy hydrogen", a stable isotope having one proton and one neutron in the nucleus. It occurs in nature as 1 atom to 6500 atoms of normal hydrogen, (Hydrogen atoms contain one proton and no neutrons).

Diallyl Phthalate (DAP): A thermosetting plastic that offers outstanding dimensional stability and resistance to most chemicals and chemical compounds. It is used in the production of connector housings.

Dielectric: (l) Any insulating medium that intervenes between two conductors. (2) A material that, having the property required to establish an electric field, is recoverable in whole or in part as electric energy.

Dielectric Constant: That property of a dielectric that determines the electrostatic energy stored per unit volume for a unit potential gradient. Permittivity is the preferred term.

Dielectric Strength: The maximum voltage that a dielectric material can withstand, under specified conditions, without rupturing. It is usually expressed as volts/unit thickness. Also called Disruptive Gradient or Electric Strength.

Dielectric Withstanding Voltage: Maximum potential gradient that a dielectric material can withstand without failure.

Diffuse insulation: Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insulation.

Diffusion furnace: Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

Diffusion length: The mean distance a free electron or hole moves before recombining with another hole or electron.

Direct current (dc): Electric current in which electrons flow in one direction only. Opposite of alternating current.

Direct gain: In direct-gain buildings, sunlight directly enters the home through the windows and is absorbed and stored in massive floors or walls. These buildings are elongated in the east-west direction, and most of their windows are on the south side. The area devoted to south windows varies throughout the country. It could be as much as 20% of the floor area in sunny cold climates, where advanced glazings or moveable insulation are recommended to prevent heat loss at night. These buildings have high insulation levels and added thermal mass for heat storage.

Direct insulation: Sunlight falling directly upon a collector. Opposite of diffuse insulation.

Discharge rate: The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

Distributed power: Generic term for any power supply located near the point where the power is used. Opposite of central power. See 'stand-alone'; 'remote site.'

Distributed systems: Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.

DOD: 'Depth of Discharge,' from 100-percent state of charge (SOC), in a battery or battery system.

Donor: An n-type dopant that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.

Donor level: The level that donates conduction electrons to the system.

Dopant: A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).

Doping: The addition of dopants to a semiconductor.

Dustproof: Constructed or protected so that dust will not interfere with its successful operation.

Dusttight: 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 of service that demands operation at loads, and for intervals of time, both of which may be subject to wide variation.



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Edge-defined film-fed growth (EFG): A method for making sheets of polycrystalline silicon in which molten silicon is drawn upward by capillary action through a mold.

Elastomer: A material that at room temperature stretches under low stress to at least twice its length and snaps back to original length upon release of stress.

Electric circuit: Path followed by electrons from a power source (generator or battery) through an external line (including devices that use the electricity) and returning through another line to the source.

Electric current: A flow of electrons; electricity.

Electrical grid: An integrated system of electricity distribution, usually covering a large area.

Electric line truck: A truck used to transport personnel, tools, and material for electric supply line work.

Electric Strength: The maximum potential gradient that a material can withstand without rupture. Also called Dielectric Strength and Disruptive Gradient.

Electric supply: Conductors used to transmit electric energy and their necessary supporting or containing structures. Signal lines of more than 400 volts are always supply lines within this section, and those of less than 400 volts are considered as supply lines, if so run and operated throughout.

Electric supply equipment: Equipment that produces, modifies, regulates, controls, or safeguards a supply of electric energy.

Electric utility: An organization responsible for the installation, operation, or maintenance of an electric supply system.

Electrodeposition: Electrolytic process in which a metal is deposited at the cathode from a solution of its ions.

Electrolyte: A liquid conductor of electricity.

Electron volt: An energy unit equal to the energy an electron acquires when it passes through a potential difference of one volt; it is equal to 1.602 x 10^-19 volt.

Element: A chemical substance that cannot be divided into simple substances by chemical means; atomic species with same number of protons.

Emc: Electromagnetic compatibility.

Emi: Electromagnetic interference.

Enclosed space: A working space, such as a manhole, vault, tunnel, or shaft, that has a limited means of egress or entry, that is designed for periodic employee entry under normal operating conditions, and that under normal conditions does not contain a hazardous atmosphere, but that may contain a hazardous atmosphere under abnormal conditions.

Note: Spaces that are enclosed but not designed for employee entry under normal operating conditions are not considered to be enclosed spaces for the purposes of this definition. Similarly, spaces that are enclosed and that are expected to contain a hazardous atmosphere are not considered to be enclosed spaces for the purposes of this definition. Such spaces meet the definition of permit spaces in 1910.146, and entry into them must be performed in accordance with that standard.

Energized (alive, live): Electrically connected to a source of potential difference, or electrically charged so as to have a potential significantly different from that of earth in the vicinity.

Energy audit: A survey that shows how much energy you use in your house or apartment. It will help you find ways to use less energy.

Energy contribution potential: Recombination occurring in the emitter region of a photovoltaic cell.

Energy density: The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg).

Energy isolating device: A physical device that prevents the transmission or release of energy, including, but not limited to, the following: a manually operated electric circuit breaker, a disconnect switch, a manually operated switch, a slide gate, a slip blind, a line valve, blocks, and any similar device with a visible indication of the position of the device. (Push buttons, selector switches, and other control-circuit-type devices are not energy isolating devices.)

Energy levels: The energy represented by an electron in the band model of a substance.

Energy source: Any electrical, mechanical, hydraulic, pneumatic, chemical, nuclear, thermal, or other energy source that could cause injury to personnel.

Enriched uranium: Uranium in which the proportion of U-235 (to U-238) has been increased above the natural 0.7%. Reactor-grade uranium is usually enriched to about 3.5% U-235, weapons-grade uranium is more than 90% U-235.

Enrichment: Physical process of increasing the proportion of U-235 to U-238.

Environment: All the natural and living things around us. The earth, air, weather, plants, and animals all make up our environment.

Epitaxial growth: The growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.

Equipotential zone: A zone of equal potential used to protect workers from hazardous step and touch potentials.

Extrinsic semiconductor: The product of doping a pure semiconductor.

Explosionproof: Designed and constructed to withstand and internal explosion without creating an external explosion or fire.

Exposed: Not isolated or guarded.



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Fast breeder reactor (FBR): A fast neutron reactor configured to produce more fissile material than it consumes, using fertile material such as depleted uranium in a blanket around the core.

Fast neutron reactor: A reactor with little or no moderator and hence utilizing fast neutrons. It normally burns plutonium while producing fissile isotopes in fertile material such as depleted uranium (or thorium).

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.

Fermi level: Energy level at which the probability of finding an electron is one-half. In a metal, the Fermi level is very near the top of the filled levels in the partially filled valance band. In a semiconductor, the Fermi level is in the band gap.

Fertile (of an isotope): Capable of becoming fissile, by capturing neutrons, possibly followed by radioactive decay; e.g., U-238, Pu-240.

Fill factor: The ratio of a photovoltaic cell's actual power to its power if both current and voltage were at their maxima. A key characteristic in evaluating cell performance.

Fire Barrier Wall: A wall separating buildings or subdividing a building to prevent the spread of fire and having a fire resistance rating and structural stability.

Fire loading: The amount of combustibles present in a given area, expressed in Btu/ft² (kJ/m²).

Fire point: The lowest temperature at which a liquid in an open container will give off sufficient vapors to burn once ignited. It generally is slightly above the flash point.

Fire protection rating: The time, in minutes or hours, that materials and assemblies used as opening protection have withstood a fire exposure as established in accordance with test procedures of NFPA 252, Standard Methods of Fire Tests of Door Assemblies, and NFPA 257, Standard on Fire Test for Window and Glass Block assemblies, as applicable.

Fissile (of an isotope): Capable of capturing a slow (thermal) neutron and undergoing nuclear fission, e.g., U-235, U-233, Pu-239.

Fissionable (of an isotope): Capable of undergoing fission: If fissile, by slow neutrons; if fertile, by fast neutrons.

Fission: The splitting of a heavy nucleus into two, accompanied by the release of a relatively large amount of energy and usually one or more neutrons. It may be spontaneous but usually is due to a nucleus absorbing a neutron and thus becoming unstable.

Fission products: Daughter nuclei resulting either from the fission of heavy elements such as uranium, or the radioactive decay of those primary daughters. Usually highly radioactive.

Flammable liquid: Any liquid having a flash point below 100°F (37.8°C) and having a vapor pressure not exceeding an absolute pressure of 40 psi (276 kPa) at 100°F (37.8°C).

Flat-plate photovoltaic module: An arrangement of photovoltaic cells mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.

Flat-plate Photovoltaic: Refers to a Photovoltaic array or module that consists of non-concentrating elements. Flat-plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation to the array.

Float charge: Float charge is the voltage required to counteract the self-discharge of the battery at a certain temperature.

Float life: Number of years that a battery can keep its stated capacity when it is kept at float charge (see float charge).

Float-zone process: A method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes single crystal.

Fossil fuel: A fuel based on carbon presumed to be originally from living matter, e.g., coal, oil, gas. Burned with oxygen to yield energy, used in a boiler to produce steam for the generation of electrical energy.

Fresnel lens: An optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point. Fresnel lenses are flat rather than thick in the center and can be stamped out in a mold.

Fuel: Any material that can be burned to make energy.

Fuel assembly: Structured collection of fuel rods or elements, the unit of fuel in a reactor.

Fuel cell: A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions; because there are no moving parts, fuel cells are quiet.

Fuel fabrication: Making reactor fuel assemblies, usually from sintered UO₂ pellets which are inserted into zircalloy tubes, comprising the fuel rods or elements.



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Gallium (Ga): A chemical element, atomic number 31, metallic in nature, used in making certain kinds of solar cells and semiconductor devices.

Gallium arsenide (GaAs): A crystalline high-efficiency semiconductor/photovoltaic material.

Gamma rays: High energy electro-magnetic radiation from the atomic nucleus, virtually identical to X-rays.

Gassing current: Portion of charge current that goes into electrolytic production of hydrogen and oxygen from the electrolytic liquid. This current increases with increasing voltage and temperature.

Gel-type battery: Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Genetic mutation: Sudden change in the chromosomal DNA of an individual gene. It may produce inherited changes in descendants. Mutation in some organisms can be made more frequent by irradiation (though this has never been demonstrated in humans).

Gigawatt (GW): One billion watts. One million kilowatts. One thousand megawatts.

Glazings: Clear materials (such as glass or plastic) that allow sunlight to pass into solar collectors and solar buildings, trapping heat inside.

Grain boundaries: The boundaries where crystallites in a polycrystalline material meet.

Graphite: Crystalline carbon used in very pure form as a moderator, principally in gas-cooled reactors, but also in Soviet-designed RBMK reactors.

Gray: The SI unit of absorbed radiation dose, one joule per kilogram of tissue.

Greenhouse effect: The effect of the Earth's atmosphere, due to certain gases, in trapping heat from the sun; the atmosphere acts like a greenhouse.

Greenhouse gases: Gases that trap the heat of the sun in the Earth's atmosphere, producing the greenhouse effect; the two major greenhouse gases are water vapor and carbon dioxide; lesser greenhouse gases include methane, ozone, chlorofluorocarbons, and nitrogen oxides.

Grid-connected (Photovoltaic system): A Photovoltaic system in which the Photovoltaic array acts like a central generating plant, supplying power to the grid.

Grid-interactive (Photovoltaic system): See 'Grid-connected (Photovoltaic system).'

Ground: A large conducting body (such 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 noncurrent-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.

Guarded: Covered, fenced, enclosed, or otherwise protected, by means of suitable covers or casings, barrier rails or screens, mats, or platforms, designed to minimize the possibility, under normal conditions, of approach or accidental contact by persons or objects. Note: Wires which are insulated, but not otherwise protected, are not considered as guarded.



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Half-life: The period required for half of the atoms of a particular radioactive isotope to decay and become an isotope of another element.

Hazardous atmosphere: An atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from an enclosed space), injury, or acute illness from one or more of the following causes:

Heat pump: Like an air conditioner or refrigerator, a heat pump moves heat from one location to another. In the cooling mode, heat pumps reduce indoor temperatures in the summer by transferring heat to the ground. Unlike an air conditioning unit, however, a heat pump's cycle is reversible. In winter, a heat pump can extract heat from the ground and transfer it inside. The energy value of the heat thus moved can be more than three times the cost of the electricity required to perform the transfer process.

Heavy water: Water containing an elevated concentration of molecules with deuterium ("heavy hydrogen") atoms.

Heavy water reactor (HWR): A reactor which uses heavy water as its moderator, e.g., Canadian CANDU (pressurized HWR or PHWR).

Heterojunction: A region of electrical contact between two different semiconductor materials.

High-level wastes: Extremely radioactive fission products and transuranic elements (usually other than plutonium) in spent nuclear fuel. They may be separated by reprocessing the spent fuel, or the spent fuel containing them may be regarded as high-level waste.

Highly (or High)-enriched uranium (HEU): Uranium enriched to at least 20% U-235. (In weapons it is about 90% U-235.)

High-power tests: Tests in which fault currents, load currents, magnetizing currents, and line-dropping currents are used to test equipment, either at the equipment's rated voltage or at lower voltages.

High voltage direct current (HVDC) converter station: A facility that functions as an electrical rectifier (ac-dc) to control and transmit power in a high voltage network. There are two types of HVDC valves: the mercury arc valve and the present-day technology solid state thyristor valve. Both types of valves present a fire risk due to high voltage equipment that consists of oil-filled converter transformers, wall bushings, and capacitors in addition to various polymeric components.