Electricity: the movement of “electrons” from atom to atom. (Shultz, 737) In our homes, the flow of electrons through wires. (Chiras, 27) A secondary source of energy that is produced from a primary source of “renewable” or “nonrenewable energy.” It is commonly measured in “kilowatt-hours.” (Hall, 9/19/09) All matter has some electrical properties. The electrical behavior of matter varies according to the physical makeup of the matter. Some matter, such as “copper,” allows electricity to easily move through it and can act as a “conductor.” Some matter, such as rubber, plastic, air, glass, and paper, does not allow electricity to move through it easily and can act as an “insulator.” A material that exhibits electrical conductivity between that of a conductor (high conductivity) and that of an insulator (low conductivity) is a “semiconductor.” Includes “carbon,” “germanium,” and “silicon.” (Shultz, 2) ‘Electric’ and ‘electrical’ - adjectives.
Electric Energy: see “energy.”
Electric Field: a “field” of “force” which is electrical in nature. (Oxford)
Electric Motor: a rotating device that converts electrical power into a rotating mechanical force. The force is used to perform work, such as moving products on a conveyor. Motors are used in fans, compressors, cranes, conveyors, mixers, etc. (Shultz, 160)
Electric(al) Power: see “electricity properties.”
Electric Shock: a condition that results any time a body becomes part of an “electrical circuit.” (Shultz, 737)
Electrostatic Field: the electric field that surrounds charged particles. (Shultz, 15)
Generated Electricity: electricity produced either by pressure, light, heat, chemical action, or magnetism. Used in “circuits” that are specifically designed to carry electrical charges through a controlled path in order to operate specific “loads.” (Shultz, 15)
Law of Electric Charges: opposite charges attract, and like charges repel. Therefore, a positively charged particle attracts a negatively charged particle and repels another positively charged particle. A negatively charged particle attracts a positively charged particle and repels another negatively charged particle. (Shultz, 15)
Static Electricity: an electrical charge at rest. Lightning is an example of the transfer of a static charge by spark. (Shultz, 14)
Electrical Arc: see “grounding.”
Electrical Circuit: the route followed by a confined electric current. (Oxford) The continuous path of electron flow from a voltage source through a conductor to a load and back to the source. (SEI, 11) All electrical circuits must have a source of power to produce work. (Shultz, 23) An assemblage of “conductors” and electrical devices through which “electrons” flow. Electrical circuits consist of a complete path for the flow of electrons between two or more points. The most fundamental electrical circuit is a simple circuit in which a single energy source supplies current to a single “load” through electrical “conductors. All simple circuits must offer some opposition to the flow of electrons. (Shultz, 150) Also referred to as a ‘circuit.’ See also “solar PV system circuit.”
Bond (Bonding, Bounded): connect to establish electrical continuity and conductivity. (Soares, 81) The act of bonding metal parts or enclosures of “electrical (circuit)components” and “conductors” connects them together electrically and mechanically, establishing electrical “continuity” and “conductivity.” Essentially the desired outcome when bonding metal parts together is to make them electrically become one. (Soares, 137)
Closed Circuit: an electrical circuit in which electrons flow uninterrupted from the
“negative terminal” of the “voltage” source, through the “load,” and back to the “positive terminal” of the voltage source. (Shultz, 150)
Disconnecting Means: a device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply. (NEC, 100)
Open Circuit: an electrical circuit in which the flow of electrons is interrupted. An open circuit has no electron flow. (Shultz, 150) See also “switch.”
Overcurrent: a condition that exists in an electrical “circuit” when the normal “load” “current” is exceeded. An overcurrent condition exists during a “short circuit” or “overload” situation. (Shultz, 162) Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault. (NEC, 100)
Overcurrent Protection Device: see “solar PV system circuit protection.”
Overload: a condition that occurs when “circuit” current rises above the “current” level at which the “load” and/or circuit is designed to operate. Overloads are caused by defective circuit components, overloaded equipment, or too many loads on one circuit. (Shultz, 164) A situation in which the current flowing through a circuit or a circuit “conductor” exceeds the safe operating “ampacity” of the conductor. (Litchfield, 247) Operation of equipment in excess of normal, ‘full-load’ rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a “short circuit” or “ground fault,” is not an overload. (NEC, 100)
Parallel Circuit: see “solar PV system circuit.”
Series Circuit: see “solar PV system circuit.”
Short Circuit: any “circuit” in which “current” takes a shortcut around the normal path of current flow. (Shultz, 744) Short-circuiting most “current” sources, such as an “AC” wall outlet or a “battery,” is extremely dangerous. Since there is essentially no “resistance,” the current flow is very high and can cause a potentially fatal electric shock and extremely high temperatures that may cause electrical burns or fire. Furthermore, short-circuiting a battery can cause it to explode, scattering acid and other toxic materials onto nearby people or components. (Dunlop, 126) Also referred to as a ‘short.’
Surge: a large, but brief rise in pressure, voltage in an electric circuit. (Oxford) Also referred to as ‘spike,’ ‘surge current,’ ‘transient current’ or ‘transient voltage.’
Electrical Circuit Components: interconnected “devices” such as transistors, resistors, etc., for achieving a particular electric effect. (Oxford)
Cable: a protective casing used for carrying electric signals and electric power. (Oxford) Most modern house wiring is flexible cable. Inside cables are individual wires, or ”conductors,” that vary in thickness according to the “load” they carry. (Litchfield, 30)
Cable Stamps: information in abbreviations stamped into cable sheathing. (Litchfield) See also “conductors: conductor stamps.”
Size/Number/Ground: indicates the wire size and the number of individual conductors inside a cable. ’12/2 w/grd,’ for example, indicates two insulated 12-AWG wires plus a ground wire. ’14/3 W/G’ has three 14-AWG wires plus a ground wire. The maximum voltage, as in ‘600v,’ may also be indicated. (Litchfield, 31)
NM: non-metallic sheathing. (Litchfield, 31)
NM-B:‘newer’ non-metal cable (Romex). Note cable without the final ‘B’ has an old-style insulation that is not as heat resistant as NM-B cable. (Litchfield, 30)
UF: a factory assembly of one or more insulated conductors with an integral or an overall covering of nonmetallic material suitable for direct burial in the earth. (NEC, 340.2)
Metallic: metal sheathed cable. Includes ‘armor clad’ (AC) and ‘metal clad’ (MC). (Litchfield, 31)
Romex: nonmetallic (NM) sheathed cable. Covered with a flexible ‘thermoplastic’ sheathing. Easy to route, cut, and attach. Cable designations printed on the sheathing and the sheathing color indicate the “gauge” and the number of conducting wires inside. (Litchfield, 30)
Service Entrance Cable: a single conductor or multi-conductor assembly provided with or without an overall covering, primarily used for services. (NEC, 338.2) Permitted in interior wiring systems where all of the circuit “conductors” of the cable are of the rubber-covered or ‘thermoplastic’ type. (Soares, 163)
Type SE: service-entrance cable having a flame-retardant, moisture-resistant covering. (NEC, 338.2)
Type USE: service-entrance cable, identified for underground use, having a moisture-resistant covering, but not required to have a flame-retardant covering. (NEC, 338.2)
Cable Bus: an assembly of insulated conductors with fittings and conductor terminations in a completely enclosed, ventilated protective metal housing. Cablebus is ordinarily assembled at the point of installation from the components furnished or specified by the manufacturer in accordance with instructions for the specific job. This assembly is designed to carry fault current and to withstand the magnetic forces of such current. (NEC, 370.2)
Cable Tray: unit or assembly of units or sections and associated fittings forming a structural system used to securely fasten or support cables and raceways. (NEC, 392.2) Also referred to as a ‘cable tray system.’
Capacitor: (a device that) consists of two conductors that are separated by an insulator. A capacitor stores ‘electrical stress.’ (Soares, 11) An electrical device designed to store electrical energy my means of an “electrostatic field.”
Capacitance: the ability of a component or circuit to store energy in the form of an electrical charge. (Shultz, 352)
Circuit Breaker: see “solar PV system circuit protection.”
Conduit: (tubing) used to protect exposed wiring. Most “solar PV” systems are installed in conduit. Conduit provides physical protection for “conductors.” Outdoor conduit must be rated for high temperatures, sunlight resistance, and moisture resistance. (Dunlop, 305)
Metallic Conduit: Metallic conduit provides fire resistance and a “ground-fault” path for ground fault protection devices. (Dunlop, 304) Metal tubing serves as its own “ground.” Apart from service entrances, conduit is seldom used in home wiring. (Litchfield, 30)
Electrical Metal Tubing (EMT): Commonly thin-wall steel. (Litchfield, 30) 3/4” EMT has an inner diameter: 0.824" (20.9mm) and an outer diameter 0.922" (23.4mm) (fastenal.com)
Flexible Metal Conduit (EMC): a raceway of circular cross section made of helically wound, formed, interlocked metal strip. (NEC, 348.2)
Liquidtight Flexible Metal Conduit (LFMC): A raceway of circular cross section having an outer liquidtight, nonmetallic, sunlight-resistant jacket over an inner flexible metal core with associated couplings, connectors, and fittings for the installation of electric conductors. (NEC, 350.2)
Intermediate Metallic Tubing (IMT): A steel threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings. (NEC, 342.2) May be used when extra protection is needed. (Dunlop, 304)
Rigid Metal Conduit (RMC): a threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings. Generally made of steel (ferrous) with protective coatings or aluminum (nonferrous). (NEC, 344.2) May be used when extra protection is needed. (Dunlop, 304)
Non-metallic Conduit: conduit option for PV Systems. (Dunlop, 304)
Rigid Polyvinyl Chloride Conduit (PVC): rigid nonmetallic conduit (RNC) of circular cross section, with integral or associated couplings, connectors, and fittings for the installation of electrical conductors and cables. (NEC, 352.2) Polyvinyl chloride (plastic) Schedule 40 or Schedule 80. (Litchfield, 30) Also referred to as ‘electrical PVC.’
High Density Polyethylene Conduit (HDPE). A nonmetallic raceway of circular cross section, with associated couplings, connectors, and fittings for the installation of electrical conductors. (NEC, 353.2)
Liquidtight Flexible Nonmetallic Conduit (LFNC). A raceway of circular cross section of various types. LFNC is flame resistant and with fittings and is approved for the installation of electrical conductors. (NEC, 356.2)
1) A smooth seamless inner core and cover bonded together and having one or more reinforcement layers between the core and covers, designated as Type LFNC-A.
(2) A smooth inner surface with integral reinforcement within the conduit wall, designated as Type LFNC-B.
(3) A corrugated internal and external surface without integral reinforcement within the conduit wall, designated as LFNC-C.
Main Bonding Jumper: the connection, between the “grounded (circuit) conductor” and the “equipment grounding conductor” at the “service.” (Soares, 81) The primary purpose of the main bonding jumper is to carry the ground fault current from the service enclosure and from the equipment grounding system that is returning to the source during ground fault conditions. (Soares, 80)
Metal Wireways: sheet metal troughs with hinged or removable covers for housing and protecting electrical wires and cable and in which conductors are laid in place after the wireway has been installed as a complete system. (NEC, 376.2)
Nonmetallic Wireways: flame retardant, nonmetallic troughs with removable covers for housing and protecting electrical wires and cables in which conductors are laid in place after the wireway has been installed as a complete system. (NEC, 378.2)
Raceway: an enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. Raceways include, but are not limited to, “rigid metal conduit,” “rigid nonmetallic conduit,” “intermediate metal conduit,” liquid tight flexible conduit, “flexible metallic tubing,” “flexible metal conduit,” “electrical nonmetallic tubing,” “electrical metallic tubing,” underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways. (NEC, 100)
Strut-Type Channel Raceway: metallic raceway that is intended to be mounted to the surface of or suspended from a structure, with associated accessories for the installation of electrical conductors and cables. (NEC, 384.2)
Surface Metal Raceway: metallic raceway that is intended to be mounted to the surface of a structure, with associated couplings, connectors, boxes, and fittings for the installation of electrical conductors. (NEC, 386.2)
Surface Nonmetallic Raceway: nonmetallic raceway that is intended to be mounted to the surface of a structure, with associated couplings, connectors, boxes, and fittings for the installation of electrical conductors. (NEC, 388.2)
Receptacle: a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke. (NEC, 100)
Receptacle Outlet. An outlet where one or more receptacles are installed. (NEC, 100)
Resistor: a resistive component in a circuit. (LeDue, 9/21/09) Substance connecting two regions which allows a slow flow of energy between the regions. (Olwell, 2/1/10)
Resistivity: a property of the material a “circuit” component is made from, typically, a metal. (Chapple, 205)
Service: conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served. (NEC, 100)
Service Cable: service conductors made up in the form of a cable. (NEC, 100)
Service Conductors: conductors from the service point to the service “disconnecting means.” (NEC, 100)
Service Drop: overhead service conductors from the last pole or other aerial support to and including the splices, if any, connecting to the service-entrance conductors at the building or other structure. (NEC, 100)
Service-Entrance Conductors, Overhead System: service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop. (NEC, 100)
Service-Entrance Conductors, Underground System: service conductors between the terminals of the service equipment and the point of connection to the service lateral. (NEC, 100)
Service Equipment: necessary equipment, usually consisting of a “circuit breaker(s)” or “switch(es)” and “fuse(s)” and their accessories, connected to the “load” end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply. (NEC, 100)
Service Lateral: underground service conductors between the street main, including any risers at a pole or other structure or from transformers, and the first point of connection to the service-entrance conductors in a terminal box or meter or other enclosure, inside or outside the building wall. Where there is no terminal box, meter, or other enclosure, the point of connection is considered to be the point of entrance of the service conductors into the building. (NEC, 100)
Service Point: the point of connection between the facilities of the serving utility and the premises wiring. (NEC, 100)
Switch: a “mechanical,” “electronic,” or “solid-state” electrical device that is used to start, stop, or redirect the flow of “electrons” in an electrical “circuit.” (Shultz, 152) Controls the continuity of “current” flow. If the switch is turned off (an “open circuit”), the wire between the source and the load is disconnected. If the switch is turned on (a “closed circuit), the wire between the source and the load is connected. (SEI, 11) A device that opens and closes a circuit, controlling the operation of a light fixture, fan, appliances, or other equipment. (Litchfield, 247) Switches are added to a circuit as a control device. (Shultz, 152)
Relay: any electrical device whereby a “current” or signal in one “circuit” can open or close another circuit. (Oxford) Relay switching devices are often used as controls to open or close a circuit. Relays are rated by voltage, type of current (AC or DC), and whether the circuit is normally open or closed. (SEI, 11)
Transformer: an electrical device that uses “electromagnetism” to change “voltage” from one level to another, or to isolate one voltage from another. Voltage is either increased or decreased based on need and the type of transformer. Because transformers do not create power, whenever voltage is increased, current is decreased, and whenever voltage is decreased, current is increased. (Shultz, 649-650) A device that transfers energy from one circuit to another through magnetic coupling. (Dunlop, 218) Two “coils” wound on a single core thereby enabling electrical power to be transmitted between two “circuits” which are electrically isolated from one another. (Chapple, 256) A device used to step up or step down “power.” When stepping down, i.e. from 240 volts to 120 volts, voltage is reduced but amps are doubled. When stepping up, i.e. from 120 volts to 240 volts, voltages increases but amps are cut by 50%. (LeDue, 9/21/09)
Wiring Systems: “direct current” (DC) wiring systems are substantially different from conventional household “alternating current” (AC) wiring systems. DC systems generally use lower voltage and the current flows only in one direction Because DC systems use lower voltage, they often have larger wire sizes compared to AC systems. (SEI, 92)
Electric Circuit: see “electrical circuit.”
Electricity Distribution: most electricity is distributed through an electrical utility grid to millions of customers from a relatively small number of large power plants. (Dunlop, 3)
Centralized Electricity Distribution: an electric utility produces electricity at a power plan and distributes it to consumers through power lines, substations, and transformers. (Dunlop, 4)
Distributed Generation: a system in which many smaller power-generating systems create electrical power near the point of consumption. Can provide electrical power in remote locations. Can include “solar PV” systems, wind turbines, engine generators, or other relatively small-scale power systems. (Dunlop, 4) A distributed generation system may serve as the only source of power for a consumer, or as back-up or supplemental power for a utility grid connection. Distributed-generation systems can include “solar PV systems,” wind turbine, and engine generators. (Wanek, 10/10/09)
Electricity Properties:
Bonding: connected (in order) to establish electrical continuity and conductivity. (NEC, 100)
Bonding Jumper: a reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected. (NEC, 100)
Bonding Jumper, Equipment: the connection between two or more portions of the equipment grounding conductor. (NEC, 100)
Conductance: the ability of “voltage” to produce electron flow through a “resistance. Measures in Siemans. Conductance of a material is the reciprocal of its “resistance.” (LeDue, 9/21/09)
CONDUCTANCE (G) = AMPS
VOLTS
Continuity: the presence of a complete path for current flow. (Shultz, 736)
Current (I): a flow of electricity: the rate of this, measured as quantity of charge per second. (Oxford) A measure of the number of “electrons” flowing past a point in a wire at any one time. (Chiras, 27) The flow of “electrons” in a “conductor.” Electrons enter a conductor, which provides a path of the current to flow. (Shultz, 14) The movement or flow of electricity. In most cases, the current of a circuit consists of the motion of “electrons.” (Soares, 11) The amount of electrons flowing through an electrical circuit. Current flows through a circuit when a source of power is connected to a “device” that uses electricity. (Shultz, 22) For electrons to flow in a circuit, there must be a complete path for the electrons to move from the “negative terminal” of the power source, through the conductors, switches, protective devices, and loads, and back to the positive terminal of the power source. (Shultz, 195) In reality, current will take all paths or circuits that are available. Where more than one path exists, current will divide among the paths. Before we can have current there needs to be a complete circuit. (Soares, 12) In any complete circuit or path that is available, current, be it normal current or fault current, will always try to return to its source. (Soares, 14) The amount of current that can be sent through any electrical circuit depends on three things: the size or “gauge” of the wire being used, the “voltage” of the system, and the one way wire run distance. (Kyocera.com, solar:electricity basics) Also referred to as ‘electric current,’ ‘electrical current,’ and ‘normal current.’
(Ohm’s Law) CURRENT = VOLTAGE
RESISTANCE
60 hertz = current alternating at 60 times per second
Alternating Current (AC): 120-volt or 240-volt electrical current that travels to the main electrical service box of a home which then routes it to the electrical “circuits” in the home. (Chiras, 173) In an AC “circuit” current flows in two directions. (LeDue, 9/19/09) Current that reverses its direction of flow at regular intervals. Flows in any circuit connected to a power supply producing an AC “voltage.” The flow of electrons in a “conductor” carrying AC is from the “negative terminal” to the “positive terminal.” (Shultz, 22) ‘Alternating’ implies frequent change of direction. Normally assumed to imply a simple ‘sine wave’ variation. (Chapple, 9) Early on, AC power had many advantages (over DC power), including safer connections and disconnections without arcing, and the ability to transmit power at high voltage over hundreds of miles with relatively small (line) losses. (Dunlop, 205)
Single Phase AC Power: one leg of power. Most homes use this form. (LeDue, 9/21/09)
Three-Phase AC Power: includes three separate “voltage” and “current” waveforms occurring simultaneously 120o apart. Commonly used for motors. Many large PV “inverters” are designed to produce three-phase AC outputs. (Dunlop, 206) Found with systems of big industrial power users. (LeDue, 9/21/09)
Ampacity: see “conductors:conductor characteristics.”
Amperage: strength of an electrical current measured in”amperes.” The rated current of a “fuse” or other electrical component. (Oxford)
Direct Current (DC): electricity consisting of electrons flowing in wires in a single, fixed direction. (Chiras, 172) Electrical current that flows in one direction, either positive or negative. (Dunlop, 204) The “polarity” of current flow is from the “negative terminal” of the power source toward the “positive terminal” of the power source. (Shultz, 388) Direct current flows in any circuit connected to a power supply producing a DC “voltage.” (Shultz, 22) The DC electricity produced by a solar “array” is carried away by wires that lead into the home. In order for the DC current produced by “solar PV cells” to power homes, it must be converted into “AC” current. This task is relegated to a component of the “solar electric” system known as an “inverter.” (Chiras, 172) If voltage and current signals are either always positive or always negative, they are DC waveforms. If the signals switch between positive and negative, they are AC waveforms. (Dunlop, 204)
Fault Current: see “grounding.”
Impedance: In an AC circuit, the total opposition to current is the total of three components - ‘inductance,’ ‘capacitance,’ and “resistance” added together. Minimizing the amount of opposition to current in the grounding and bonding circuits of electrical systems is very important. (Soares, 13-14)
Nominal: functioning acceptably, normal. (Oxford)
Nominal Operating Cell Temperature (NOCT): a reference temperature of an ‘open-circuited’ module based on an “irradiance” level of 800 watts per meter squared, ‘ambient temperature’ of 20o C, and wind speed of 1 meter per second. (Dunlop, 456)
Nominal Operating Conditions (NOC): a set of reference conditions that rates “module” performance at a “irradiance” of 800 watts per meter squared, spectral conditions of “AM” 1.5, and at nominal operating ell temperature. (Dunlop, 456)
Nominal Value: normal value, ‘face value.’ (Oxford)
Power: the rate of doing work or using energy. (Shultz, 30) The rate of energy transfer. It is a “scalar” quantity. The “SI” unit of power is the “watt.” (Chapple, 187) The amount of electric “current” flowing due to an applied “voltage.” The rate at which electricity is produced or consumed. The amount of electricity required to start or operate a “load” for one second and is measured in “watts” or “kilowatts.” A measure of the rate of doing work or the rate at which energy is converted. (Hall, 9/19/09) The capacity of an electrical device as indicated on its nameplate. The capacity of an electrical device to either produce electricity or consume electricity. (Saturn, Basic Building Science) The human brain runs on only about 20 watts of power. (Fox, 60) The rate at which work is performed. Power is the amount of work performed divided by the time it took to complete the task. Calculated using the same equation used to determine “mechanical energy.” Also referred to as ‘electric power’ or ‘electrical power.’ (Chiras, 26-27)
POWER = WORK
TIME
= “FORCE” x DISTANCE
TIME
Apparent Power: A combination of true and reactive power. Expressed in units of volt-amps. (Dunlop, 210) The product of the voltage and current in an electrical circuit calculated without considering the “phase shift” that may be present between the voltage and current in the circuit. (Shultz, 31-32)
APPARENT POWER = VOLTAGE x CURRENT
Power Factor: the ratio of true power to apparent power. (Dunlop, 210)
True Power: the actual power used in an “electrical circuit.” True power is always less than apparent power in any circuit in which there is a phase shift between voltage and current. (Shultz, 31) The product of ‘in-phase’ (normal) voltage and (normal) current waveforms. Produces useful work. (Dunlop, 209)
TRUE POWER = CURRENT2 x RESISTANCE
Power Quality: a measure of how closely the power in an “electrical circuit” matches the “nominal values” for parameters such as voltage, current, “harmonics,” and ‘power factor.’ Excessive variations in circuit parameters can cause damage to loads and distribution equipment. (Dunlop, 207)
Voltage Variations: variation is typically acceptable within the range of +5% to -10% of normal range. Small voltage fluctuations typically do not affect equipment performance. (Dunlop, 208)
Voltage Drop: the loss of voltage due to a wire’s “resistance” and length. A PV system’s efficiency can be improved when using properly sized wire. This reduces the ‘line loss’ of the wire. A function of wire gauge, length of wire, and current flow in the wire. Using a larger wire size, decreasing the current flow, or decreasing the length of wire are all solutions to reduce voltage drop. (SEI, 96) The amount of voltage consumed by a “device” or component as current passes through it. (Shultz, 201) Excessive voltage drop can affect “charge controllers,” “batteries,” “inverters,” “loads,” and other devices that require certain voltages to operate properly. NEC does recommend a maximum voltage drop of 3% (Dunlop, 294) “Conductors” are sized large enough to prevent no more than a 3% voltage drop during the total round-trip distance that current travels in an electric circuit from the farthest point in the circuit. (LeDue, 9/21/09) (NEC, 210.19 FPM No. 4)
Voltage Sags: commonly caused by overloaded transformers, undersized conductors, conductor runs that are too long, too many loads on a circuit, brownouts, and high-current loads being turned on. Voltage sags are often followed by voltage swells as ‘voltage regulators’ overcompensate. (Dunlop, 208)
Voltage Swells: caused by loads near the beginning of a power distribution system. Not as common as voltage sags, but more damaging to electrical equipment. (Dunlop, 208)
Voltage Unbalance: the unbalance that occurs when the voltages of a three-phase power supply are not equal. Also results in a current unbalance. Should not be more than 1%. (Dunlop, 208)
Current Unbalance: the unbalance that occurs when current is not equal on the three power lines of a “three-phase” system. Current unbalances should never exceed 10%. (Dunlop, 209)
Phase Unbalance: the unbalance that occurs when three-phase power lines are more or less than 120o out of phase. (Dunlop, 209)
Reactive Power: the product of out-of-phase voltage and current waveforms. Results in no net power flow. (Dunlop, 210)
Resistance (R): the name given to the opposition to current, offered by the internal structure of the particular conductive material, to the movement of electricity through it. This opposition results in the conversion of “electrical energy” into “heat energy.” (Soares, 12) Resistance is measure in “ohms.” The Greek symbol ‘omega’ is used to represent ohms. Resistance limits the flow of electrons in an electrical “circuit.” Resistances can be used in an electrical circuit for protection, operation, or current control, or in combination with other circuit components. The higher the resistance, the lower the flow of electrons. Likewise, the lower the resistance, the higher the flow of electrons. (Shultz, 25) The ratio of the ‘potential difference’ (“voltage”) across a “conductor” to the “current” it carries. A property of a circuit component, typically a wire. Any “circuit” component or circuit has resistance calculated from the equation below. (Chapple, 205) The total opposition to current in a “DC” circuit. In an “AC” circuit, the total opposition to current is referred to as “impedance.” (Soares, 13) Factors that affect the resistance of “conductors” are the area, length, material, and temperature. (Shultz, 4) Also, any force that tends to hinder the movement of an object. (Shultz, 743) (‘resistive’ - adjective)
RESISTANCE = VOLTAGE
CURRENT
HIGHER GAUGE ---------------------> GREATER RESISTANCE
LOWER DIAMETER -------------------> GREATER RESISTANCE
LONGER CONDUCTOR RUN ---------> GREATER RESISTANCE
LOWER CROSS SECTIONAL AREA --> GREATER RESISTANCE
HIGHER MATERIAL TEMPERATURE -> GREATER RESISTANCE
Voltage (V): a measure of the force or difference in potential that tends to give rise to an electric current. Expressed in volts. (Oxford) The electrical pressure that causes electrons to flow through a wire. (SEI, 10) Voltage will push current through a resistance. (Soares, 12) The amount of electrical pressure in a “circuit.” All sources of power produce a set voltage level or voltage range. (Shultz, 23) Also referred to as ‘electromotive force’ and ‘potential difference.’
AC Voltage: used in residential, commercial, and industrial lighting and power distribution systems. (Shultz, 23)
Clamping Voltage: see “solar PV system circuit.”
DC Voltage: produced by batteries thermocouples,’ and ‘photocells.’ Typically used in portable equipment (automobiles, golf carts, flashlights, cameras, etc.) (Shultz, 23)
Line Voltage: that from an AC circuit. usually 120 volts. (LeDue, 9/23/09)
Low Voltage: Typically 12 volts or less. Example uses - pup, controller.
Open Circuit Voltage (VOC): see “IV curve parameters.”
Photovoltaic System Voltage: see “solar PV system circuit.”
Short Circuit Voltage (ISC): see “IV curve parameters.”
Waveform: the shape of an electrical signal that varies over time. Waveforms are used to represent changing “electrical current” and “voltage.” Includes ‘periodic waveform,’ ‘sine wave,’ ‘square wave,’ and ‘modified square wave.’ AC waveforms can take a variety of shapes. To view the shape of a waveform, the time-varying values (voltage or current) must be plotted against time. (Dunlop, 204-205)
Cycle: interval of time between the beginnings of each waveform pattern. (Dunlop, 204) Also, a battery discharge followed by a charge. (Dunlop, 453)
Frequency: the number of cycles in one second. Commonly expressed in equivalent units of Hertz (Hz). The frequency of the U.S. electric grid is maintained at 60 Hz. Frequency establishes the speed of motors, generators, and some clocks and is one of the most important parameters in ‘synchronizing’ AC electrical systems (Dunlop, 206)
Harmonic: a waveform component at an integer multiple of the fundamental waveform frequency. For example, the second harmonic frequency of a 60Hz sine wave is 120 Hz, the third is 180 Hz. Higher frequency harmonic components distort the waveform. (Dunlop, 209)
Total Harmonic Distortion (THD): the ratio of the sum of all harmonic components in a waveform, to the fundamental frequency components. Expressed as a percentage. For example, a current waveform with 5% THD means that 5% of the total current is at frequencies higher than the fundamental. (Dunlop, 209) In accordance with IEEE 519 total harmonic distortion shall not exceed 5% and any individual harmonic shall not exceed 3%. Interactive inverters are required to de-energize from the grid if these limits are exceeded. (Dunlop, 224)
Magnitude: “Peak,” “RMS,” and average values of the waveform can be calculated from one another with simple formulas. (Dunlop, 207)
Peak: the maximum absolute value of an AC voltage waveform. (Dunlop, 206) Also referred to as ‘amplitude.’
Peak to Peak: a measure of the difference between positive and negative maximum values of a waveform. (Dunlop, 209)
Root-Mean-Square (RMS): a statistical parameter representing the effective value of a waveform. Most AC voltage and current measurements are actually RMS values. For example, a typical wall outlet provides about 120 volts, which is the RMS value. The peak voltage of the (wall outlet) waveform is actually about 170 volts. (Dunlop, 206)
Period: the time it takes a periodic waveform to complete one full cycle before it repeats. Period is the inverse of frequency. For example, a frequency of 60Hz repeats 60 times per second. It has a period of 1/60 seconds. (Dunlop, 206)
Periodic Waveform: waveform that repeats the same pattern at regular intervals. (Dunlop, 204)
Phase Shift: the state in which voltage and current in an AC circuit reach their maximum “amplitudes” and zero levels at different times. (Shultz, 32)
Sine Wave: a periodic waveform the value of which varies over time. May shift in time or vary in “amplitude.” Utility grid naturally produces sine waves. (Dunlop 204) Also referred to as a ‘sinusoidal waveform.’
Square Wave: an AC waveform that switches between maximum positive and negative values every half period. Not a sine wave. Not a common inverter output. Less sophisticated “inverters” approximate a sine wave with square waves or modified square waves. (Dunlop, 205)
Modified Square Wave: a synthesized, stepped waveform that approximates a sine wave. The typical AC output of many stand-alone inverters.” Significantly better power quality than square wave inverters, including lower ‘harmonic distortion,’ higher ‘peak voltage,’ higher ‘efficiency,’ and better ‘surge current capability.’(Dunlop, 205) Also referred as a ‘modified sine wave’ and ‘quasi sine wave.’
Electricity Property Measuring Tools: electronic devices to measure electricity properties.
Clamp-On Ammeter: a device to measure current in a circuit by measuring the strength of the magnetic field around a single conductor. Conductors under test should be separated from other surrounding conductors by a few inches. (Shultz, 179)
Continuity Checker: an instrument that indicates an “open or closed circuit” in a a circuit in which all power is off. Can be used to measure the integrity of a circuit or component. (Shultz, 88)
Digital Multimeter: test tool used to measure two or more electrical properties. Commonly measure “voltage,” “current,” and “resistance.” Used during electrical equipment installations and servicing. (Shultz, 173) Used to check for “continuity” or energized circuits. (Dunlop, 65) When testing voltage from the positive to the negative terminal, an “open circuit” is created by the meter which allows Voc to be measured. (SEI, 53)
Ohmmeter: an instrument used to measure the “continuity” and “resistance of a circuit or component. These seldom exist as a single-function device, but are usually built into a multimeter. (Shultz, 89) Used to detect the continuity of an “electric circuit.” (LeDue, 9/21/09) Also referred to as a ‘Volt-Ohm Meter.’
Electricity Units:
Ampere (Amp): the unit of “current” flowing through a wire. (SEI, 11) Measure of electrical flow. (Saturn, Basic Building Science) The number of electrons passing through a given point in one second. (Shultz, 735)
AMPS = WATTS
VOLTS
= VOLTS
OHMS
Amp Hour: a quantity of electricity equivalent to a current of one amp flowing for one hour. (Oxford) One amp of current flowing for one hour. (SEI, 10)
Milliampere (mA): one thousandth of an “ampere.”
Ohm: a unit of “resistance.” The amount of resistance in a “circuit” when 1 “ampere” flows with 1 ”volt” applied. (Shultz, 741)
OHMS = VOLTS
AMPS
Volt: a unit of “voltage.” The unit of measure of ‘electromotive force.’ By international agreement 1 volt is the amount of electromotive force that will establish a current of 1 amp through a resistance of 1 ohm. (Soares, 12) Measure of electrical pressure. (Saturn, Basic Building Science) Volts are abbreviated ‘V” or sometimes as ‘e” for electrical pressure. (SEI, 10)
VOLTS = WATTS
AMPS
Watt: a unit of electrical power equivalent to the current of one amp under a pressure of one volt. Watts indicate the rate at which an appliance (or other load) uses electrical energy or the rate at which electrical energy is produced. (SEI, 10) See also “power.”
WATTS = VOLTS x AMPS
1 WATT = 0.7376 foot pounds per second
1 WATT = 1 joule per second
Kilowatt: 1000 Watts
Megawatt: 1000 Kilowatts.
Gigawatt: 1000 Megawatts.
Terawatt: 1000 Gigawatts.
Kilowatt Hour: the work done by one kilowatt in one hour. (Oxford) Kilowatt Hour (KWh): A measure of energy usage or production. (BHO, 2) The kilowatt-hour is a measure of “electrical energy.” It is the product of “power” in “watts” and the time interval in hours. For example, electricity used at a rate of one watt for 1000 hours, or 10 watts for 100 hours, or 1000 watts for one hour, is equal to one kilowatt-hour of energy. (Hall, 9/19/09)
1 kWh = 3,600,000 JOULES = 3.6 MEGAJOULES
1 kWh = 3412 BTUs
Electrification: the process of charging an object. Electrons are removed from one body and transferred to another. One body becomes negatively charged while the other becomes positively charged. (Shultz, 16)
Contact Electrification: occurs any time two objects with different levels of charge make physical contact. Example - an electric “switch.” One side of the switch is connected to a source charge, and the other side is connected to a “load.” When the switch is closed, electrons flow through the switch contacts. (Shultz, 17)
Conduction Electrification: occurs when a “conductor,” such as a copper wire, connects two objects with different charges. Electrons move from a negative object to a positive object through a conductor. The most common type of electrification. Used to transmit and distribute electrical power from power generating plants to end users. (Shultz, 17)
Induction Electrification: occurs when a negatively charged object is brought close to a neutral (charged) object. Electrons are repelled from the negatively charged object into the neutral (charged) object. The electrons on the neutral object flow to “ground” if a conduction path is present. (Shultz, 17)