Confused by electrical terminology? Just learning about photovoltaic options? Brush up your expertise with our handy Red Top glossary of electrical terms. Our glossary is conveniently divided into sections to provide easy, immediate access.
| Adapter | An accessory used for interconnecting non-mating devices or converting an existing device for modified use. |
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| Ballast | An electromagnetic or electronic transformer that steps down AC line voltage to voltage that can be used by fluorescent or other types of lighting. |
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| BTU | A British thermal unit, the standard unit for measuring heat energy, is the amount of heat required to raise the temperature of water one degree Fahrenheit. One KWH = 3,414 BTU's. |
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| Flanged Inlet | A plug intended for flush mounting on appliances or equipment to provide a means for power connection via a cord connector. |
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| Flanged Outlet | A receptacle intended for flush mounting on appliances or equipment to provide a means for power connection via an inserted plug. |
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| Horsepower | The basic unit of power measurement generally used to describe motor capability. A one-horsepower motor operating for one hour will use approximately one kwh. |
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| Kilowatt-hour | A kilowatt-hour (kWh) is 1,000 watts of electricity used for one hour. |
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| R-value | Thermal resistance to the transfer or flow of heat. |
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| Receptacle | A device with female contacts designed for fixed installation in a structure or piece of equipment and which is intended to establish electrical connection with an inserted plug. |
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| Switch | A device for making, breaking, or changing the connections in an electric circuit. |
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| Ton (refrigeration) | A unit of measurement of cooling capacity. One ton of refrigeration equals approximately 12,000 BTU's per hour of cooling. |
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| Voltage | A measure of the force or "push" given the electrons in an electrical circuit; a measure of electrical potential. One volt produces one amp of current when acting against a resistance of one ohm. |
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| Watt | The basic unit of measurement of electricity. |
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| Bayonet | Designed for incandescent lamps having an unthreaded metal shell with two diametrically opposite keyways that mate with the keyways on the lampholder. Pushing down on the bulb and turning it clockwise in the lampholder locks the bulb in place. |
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| Candelabra | A small screw-base threaded lampholder designed for candelabra-base incandescent lamps commonly used in chandeliers, night lights, and ornamental lighting. |
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| Circline | A four-contact, double-ended lampholder designed for use with tubular, circular fluorescent lamps. |
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| Compact Fluorescent | A lampholder designed for the Compact Fluorescent Lamps (CFL's) that are increasingly being used to replace incandescent lamps for energy efficiency. |
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| Dimmer | An electronic device with a round knob, slide lever or fingertip controlled buttons used to dim/brighten incandescent lighting. |
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| Double-Contact Recessed | Designed for high-output fluorescent lamps. |
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| Edison Base | Widely used internally threaded lampholder, with the inner shell approx. 1" in diameter. |
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| Electrolier | Similar to the Edison Medium Base lampholder, but with a smaller outer diameter. |
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| Incandescent | Designed for use with most threaded bases, incandescent lamps. |
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| Intermediate | Mostly used in decorative lighting-a lampholder with a threaded screw shell designed for intermediate base lamps that have a 13/32" threaded base. |
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| Key | A lampholder with a flat or round "key" knob that operates an internal switching mechanism ("Keyless" lampholders do not provide an internal switching mechanism). |
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| Lumiline | A specially designed lampholder for tubular Lumiline-type incandescent lamps typically used in bathrooms and retail display cases. |
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| Medium Base | Same as the Edison base lampholder. An internally threaded lampholder, with the inner shell approx. 1" in diameter. Designed for widely used standard medium base lamps. |
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| Miniature | Designed for the smallest available incandescent lamps with a screw-in base, approx. 3/8" diameter. Widely used in flashlights and toys, etc. |
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| Mogul | The largest screw-in type lampholder, designed for mogul incandescent lamps with a screw base of approx. 11/2" diameter. Used in streetlights and numerous commercial/industrial applications. |
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| Medium Bi-Pin | A fluorescent lampholder with two contacts, used in pairs. For type T-8 tubular fluorescent lamps, approx. 1" in diameter. |
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| Miniature Bi-Pin | Similar to medium bi-pin lampholders, but designed for type T-5 tubular fluorescent lamps, approx. 5/8" in diameter. |
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| Push-Through | An incandescent lampholder with an insulated lever that is pushed from either side to activate an internal ON/OFF switching mechanism. |
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| Slimline Single-Pin | A fluorescent lampholder with a single contact designed for Slimline fluorescent lamps such as the T-12 (11/2" diameter), T-8 (1" diameter), and the smaller T-6 (3/4" diameter). |
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| Snap-In | An incandescent or compact fluorescent lampholder with factory-assembled spring clips that securely snap into a panel cutout without requiring additional fasteners. |
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| Surface-Mounted | A lampholder of any type that mounts on a flat or plane surface. |
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| Ampere (amp) | A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere. One ampere is equal to 6.235 x 10 18 electrons per second passing a given point in a circuit. |
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| Ampere Hour (AH) | A measure of current over time, used to measure battery capacity. |
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| Angle Of Incidence | The angle between the direct solar beam and the normal (90 degrees) to the active surface. |
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| Array | Any number of photovoltaic modules connected together electrically to provide a single electrical output. An array is a mechanically integrated assembly of modules that form a freestanding field installed unit that produces DC power. |
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| Battery Energy Capacity | The total energy available, expressed in kilowatt-hours, that can be withdrawn from a fully charged cell or battery. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere-hours. |
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| Battery Cycle Life | The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria. |
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| Battery Life | The time period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. |
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| Blocking Diode | A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. |
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| Cathodic Protection | Systems that protect underground metal from corrosion by running small electrical currents along the metal. Most often used to protect well heads, oil, gas, and water pipelines. |
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| Cell (Battery) | A single unit of an electrochemical device (usually consisting of several cells electrically connected together to produce higher voltages) capable of producing direct voltage by converting chemical energy into electrical energy. |
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| Cell (Solar) | The smallest, basic photovoltaic device that generates electricity when exposed to light. |
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| Charge Controller | A component of photovoltaic system that controls the flow of current to and from the battery to protect the batteries from over-charge and over-discharge. It may also indicate operational status. |
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| Concentrator | A photovoltaic module, including optical components such as lenses, that directly face and/or track and concentrate sunlight onto a solar cell of smaller area. |
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| Depth Of Discharge (DOD) | The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. |
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| Diffuse Insolation | The radiant energy from the sky incident upon unit surface area during a specified time period (Same units as for direct insolation). |
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| Direct Insolation | The radiant energy from the sun (and a small area of sky surrounding it, defined by the acceptance angle of the pyrheliometer) incident upon unit surface area during a specified time period. (MJ/m2 per hour, day, week, month or year, as the case may be). |
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| Efficiency | The ratio of power output of a Photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insolation conditions. |
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| Electrolyte | The fluid used in batteries as the transport medium for positively and negatively charged ions. |
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| Equalization | The process of restoring all cells in a battery to an equal state-of-charge. For lead-acid batteries, this is a charging process designed to bring all cells to 100% state-of-charge. Some battery types may require a complete discharge as a part of the equalization process. |
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| Equalizing Charge | A continuation of normal battery charging, at a voltage level slightly higher than the normal end-of-charge voltage, in order to provide cell equalization within a battery. |
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| Float Service | A battery operation in which the battery is normally connected to an external current source; for example, a battery charger which supplies the battery load under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power. |
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| Gassing | The evolution of gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from local action self-discharge) or from the electrolysis of water in the electrolyte during charging. |
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| Hermetic Seal | Being impervious to external influences. Typically associated with the sealing of a package so that oxygen, moisture, and other outside environments cannot enter the package. |
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| Insolation | The amount of sunlight reaching an area. Usually expressed in milliwatts per square centimeter, or langleys. |
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| Open Circuit Voltage (VOC) | Voltage produced by a photovoltaic cell with no load applied when the cell is exposed to standard insolation conditions, measured with a voltmeter. |
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| Panel | A collection of one or more modules fastened together into a single unit, often factory pre- assembled and wired, forming a field-installable unit. |
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| Parallel Connection | A wiring configuration used to increase current (amperage). Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection. |
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| Peak Power Point | Operating point of the I-V (current-voltage) curve for a Photovoltaic cell or module where the product of the current value times the voltage value is a maximum. |
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| Peak Watts | The measurement of electricity produced by a solar generator at noon on a sunny day, under predetermined standard conditions. |
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| Photon | The actual (physical) particle unit of light, as the electron is of electric charge and the atom and molecule are of matter. Photons not captured by the cell are either reflected or converted to heat in the solar array. |
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| Photovoltaic Cell | A device composed of specially prepared semiconductor material or material combinations exhibiting the ability to convert incident solar energy directly into electrical energy. |
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| Photovoltaic Effect | The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. With the addition of circuitry, current will flow and electric power will be available. |
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| Photovoltaic System | An installed aggregate of solar arrays generating power for a given application. |
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| Power Conditioner | The electrical equipment used to convert power from a photovoltaic array into a form suitable for subsequent use. Loosely, a collective term for inverter, transformer, voltage regulator and other power controls. |
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| Power Factor | The ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. Displacement power factor is the ratio of fundamental watts to fundamental RMS volts times |
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| Regulator | Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs. |
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| Single-Crystal Structure | A material having a crystalline structure such that a repeatable or periodic molecular pattern exists in all three dimensions. |
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| Solar Cell | The basic photovoltaic device which generates electricity when exposed to sunlight. |
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| Solar Panel | A collection of solar modules connected in series, in parallel, or in series-parallel combination to provide greater voltage, current, or power than can be furnished by a single solar module. Larger collections of solar panels are usually called solar arrays. |
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| Sulfation | The formation of lead-sulfate crystals on the plates of a lead-acid battery which can be caused by leaving the battery in a discharged state for long periods of time. |
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| Telemetry Device | Devices used to transmit or receive data in a digital form. |
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| Tilt Angle | A fixed angle measured from the horizontal to which a solar array is tilted chosen to maximize output. Depending upon latitude, season and time of day this angle will vary. |
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| Tracking Array | An array that is mounted on a movable structure that attempts to follow the path of the sun. Some tracking arrays are single axis while others are dual. |
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| AL/CU | 30A, 50A or 60A receptacles designated for use with aluminum or copper circuit conductors, identified by "AL/CU" stamped on the device. Receptacles without this designation must never be used with aluminum circuit conductors. |
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| Clock Hanger | A single, recessed receptacle with a specialized cover plate that provides a hook or other means of supporting a wall clock. |
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| CO/ALR | 15A or 20A receptacles designated for use with aluminum or copper circuit conductors, identified by "CO/ALR" stamped on the device. Receptacles without this designation must never be used with aluminum circuit conductors. |
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| Corrosion Resistant | A receptacle constructed of suitably plated metal parts that is designed to pass the ASTM B117-13 five hundred hour Salt Spray (Fog) Test with no visible corrosion. |
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| Display | Receptacle with a special cover plate intended for flush mounting on raised floors or walls. |
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| Duplex | Two receptacles built with a common body and mounting means; accepts two plugs. |
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| Dust Proof | A receptacle designed so that dust will not interfere with its operation. The IP Suitability Rating designates the degree of protection a device offers against the ingress of foreign objects (e.g. IP 20). |
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| Explosion Proof | A receptacle constructed to meet the requirements of hazardous locations as defined by the National Electrical Code, NFPA-70. |
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| Fan Hanger | A single receptacle with a specialized cover plate that provides a hook or other means of supporting a wall fan. |
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| Four-In-One or "Quad" | A receptacle in a common housing that accepts up to four plugs. Four-In-One receptacles can be installed in place of duplex receptacles mounted in a single-gang box, providing a convenient means of adding receptacles without rewiring. |
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| GFCI (Ground Fault Circuit Interrupter) | Required by the NEC NFPA-70 in a variety of indoor and outdoor locations, a receptacle with a built in circuit that detects leakage current to ground on the load side of the device. When detected, it will interrupt power to the load side of the device, preventing a hazardous ground fault condition. GFCI receptacles conform to UL Standard 943 Class. |
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| Hospital Grade | A connector or plug tested to the Hospital Grade requirements of UL Standard 498 to meet the performance requirements typically found in hospital facilities. |
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| Interchangeable | A receptacle or combination of receptacles with a common mounting dimension that may be installed on a single or multiple-opening mounting strap. |
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| Isolated Ground | Receptacles intended for use in an Isolated Grounding system where the ground path is isolated from the facility grounding system. |
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| Lighted (Illuminated) | A receptacle with a face that becomes illuminated when the device is connected to an energized electrical circuit. |
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| Locking | A receptacle designed to lock an inserted plug with a matching blade configuration when the plug is rotated in a clockwise direction. |
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| Pin and Sleeve | A receptacle with cylindrical sleeve-type contacts. |
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| Safety or Tamper-Resistant | Tamper-resistant receptacles limit access to its energized contacts required by the National Electric Code NFPA-70 in specific pediatric care areas in health care facilities. |
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| Single | A receptacle that accepts only one plug. |
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| Snap-In | A receptacle with factory-assembled spring clips that securely snap into a panel cutout without requiring additional fasteners. |
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| Split-Circuit | A duplex receptacle that allows each receptacle to be wired to separate circuits. Most duplex receptacles provide break-off tabs that allow them to be converted into split-circuit receptacles. |
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| Straight Blade | A non-locking receptacle into which mating plugs are inserted at a right angle to the plane of the receptacle face. |
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| Surface-Mounted | Any receptacle that mounts on a flat or plane surface. |
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| Surge-Suppression | A receptacle with built-in circuitry designed to protect sensitive electronic equipment on its load side from high-voltage transients and surges. |
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| Triplex | A receptacle with a common mounting means which accepts three plugs. |
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| Weatherproof | A receptacle specially constructed so that exposure to weather will not interfere with its operation. |
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| AC/DC | A switch designated for use with either Alternating Current (AC) or Direct Current (DC). |
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| Door | A momentary contact switch, usually installed on a doorjamb that is activated when the door is opened or closed. |
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| Double-Pole, Single-Throw (DPST) | A switch that makes or breaks the connection of two circuit conductors in a single branch circuit. This switch has four terminal screws and ON/OFF markings. |
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| Double-Pole, Double-Throw (DPDT) | A switch that makes or breaks the connection of two conductors to two separate circuits. This switch has six terminal screws and is available in both momentary and maintained contact versions, and may also have a center OFF position. |
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| Feed-Through | An in-line switch that can be attached at any point on a length of flexible cord to provide switching control of attached equipment. |
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| Flush-Mounted | A switch designed for flush installation with the surface of a panel or equipment. |
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| Four-Way | A switch used in conjunction with two 3-Way switches to control a single load (such as a light fixture) from three or more locations. This switch has four terminal screws and no ON/OFF marking. |
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| Horsepower Rated | A switch with a marked horsepower rating, intended for use in switching motor loads. |
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| Interchangeable | A switch or combination of switches with a common mounting dimension that may be installed on a single or multiple-opening mounting strap. |
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| Locking | A switch equipped with a locking mechanism that requires a key to operate the switching functions. |
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| Low-Voltage | A switch rated for use on low-voltage circuits of 50 volts or less. |
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| L-Rated | A switch specially designated with the letter "L" in its rating that is rated for controlling tungsten filament lamps on AC circuits only. |
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| Maintained Contact | A switch where the actuator makes and retains circuit contact when moved to the ON position. The contacts will only be opened when the actuator is manually moved to the OFF position. Ordinary light switches are maintained contact switches. |
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| Manual Motor Controller | A switch designed for controlling small DC or AC motor loads, without overload protection. |
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| Mercury | A type of switch that uses mercury as the contact means for making and breaking an electrical circuit. |
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| Momentary Contact | A switch that makes circuit contact only as long as the actuator is held in the ON position, after which it returns automatically to the OFF position. This is a "Normally Open" switch. A "Normally Closed" switch will break circuit contact as long as it is held in the OFF position, and then automatically return to the ON position. |
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| Pendant | A type of switch designed for installation at the end of a length of portable cord or cable. |
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| Pilot Light | A switch with an integral lamp in its actuator that illuminates when the switch is connected to an energized circuit and the actuator is in the ON position. |
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| Pull | A switch where the making or breaking of contacts is controlled by pulling downward or outward on the actuator mechanism. |
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| Push Button | A switch with an actuator mechanism that is operated by depressing a button. |
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| Rotary | A switch where rotating the actuator in a clockwise direction makes the circuit connection, and then rotating the actuator in either the same or opposite direction breaks the connection. |
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| Single-Pole, Double-Throw (SPDT) | A switch that makes or breaks the connection of a single conductor with either of two other single conductors. This switch has 3 terminal screws, and is commonly used in pairs and called a "Three-Way" switch. |
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| Single-Pole, Single-Throw (SPST) | A switch that makes or breaks the connection of a single conductor in a single branch circuit. This switch has two screw terminals and ON/OFF designations. It is commonly referred to as a "Single-Pole" Switch. |
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| Slide | A switch with a slide-action actuator for making or breaking circuit contact. Dimmer switches and fan speed controls are also available with slide-action mechanisms for lighting and fan speed control |
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| Surface-Mounted | Any switch that mounts on a flat or plane surface. |
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| Three-Position, Center OFF | A two-circuit switch, either maintained or momentary contact, where the OFF position is designated as the center position of the actuator. |
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| Three-Way | A switch, always used in pairs, that controls a single load such as a light fixture from two locations. This switch has three terminal screws and has no ON/OFF marking. |
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| Time Delay | A switch with an integral mechanism or electronic circuit that will automatically switch a load OFF at a predetermined time interval. |
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| Timer | A switch with an integral mechanism or electronic circuit that can be set to switch an electrical load ON at a predetermined time. |
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| Toggle | A switch with a lever-type actuator that makes or breaks switch contact as its position is changed. |
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| T-Rated | A switch specially designated with the letter "T" in its rating that is rated for controlling tungsten filament lamps on direct current (DC) or alternating current (AC) circuits. |
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