Electrical Contractor Exam Glossary
Master the terminology you need to pass your electrical contractor licensing exam. Simple definitions for complex concepts.
Alternating Current (AC)
An electric current that periodically reverses direction, as opposed to direct current (DC) which flows in only one direction.
Ambient Temperature
The temperature of the surrounding environment where electrical equipment or conductors are installed.
Ampacity
The maximum amount of electric current a conductor or device can carry continuously without exceeding its temperature rating.
Ampere (Amp)
The standard unit of measurement for electric current, representing the flow of one coulomb of charge per second.
Approved
Acceptable to the authority having jurisdiction (AHJ), indicating that equipment or installations meet the required standards.
Arc Fault Circuit Interrupter (AFCI)
A circuit breaker designed to detect dangerous electrical arcs and disconnect power before a fire can start.
Authority Having Jurisdiction (AHJ)
The organization, office, or individual responsible for enforcing code requirements and approving equipment, installations, or procedures.
AWG (American Wire Gauge)
A standardized system for measuring the diameter of electrical wire, where a smaller number indicates a larger wire.
Bonding
The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and safely conducts fault current.
Box Fill Calculations
The NEC-mandated process of calculating the minimum volume required for an electrical box based on the number and size of conductors, devices, and fittings it contains.
Branch Circuit
The circuit conductors between the final overcurrent device (breaker or fuse) protecting the circuit and the outlets or loads served.
Busbar
A metallic strip or bar inside a panelboard or switchgear that serves as a common connection point for multiple circuits.
Bushing
A fitting placed on the end of a conduit to protect wires from abrasion where they exit the conduit.
Cable Tray
An open support structure used to route and support cables, commonly used in commercial and industrial installations.
Capacitor
An electrical component that stores energy in an electric field between two conductive plates, used for power factor correction, motor starting, and filtering.
Circuit Breaker
An automatically operated electrical switch designed to protect a circuit from damage caused by overcurrent, overload, or short circuit.
Color Coding
The standard system of wire insulation colors used to identify conductor function in electrical circuits.
Conductor
A material or object that allows the flow of electric current, typically a wire made of copper or aluminum.
Conduit
A tube or trough used to protect and route electrical wiring in a building or structure.
Conduit Fill
The percentage of a conduit's cross-sectional area that can be occupied by conductors, as specified by the NEC.
Continuity
An unbroken electrical path through a circuit or conductor, indicating that current can flow without interruption.
CSLB (Contractors State License Board)
The California state agency responsible for licensing and regulating the construction industry, including electrical contractors.
Dedicated Circuit
A circuit that serves only one specific appliance or piece of equipment, with no other outlets or devices connected to it.
Demand Factor
The ratio of the maximum demand on an electrical system to the total connected load, expressed as a percentage.
Derating
The reduction of a conductor's ampacity due to factors such as high ambient temperature, conduit fill with multiple conductors, or continuous loading.
Direct Current (DC)
An electric current that flows in only one direction, as produced by batteries, solar panels, and DC power supplies.
Disconnect (Disconnecting Means)
A device or group of devices used to disconnect conductors of a circuit from their source of supply.
Dwelling Unit
A single unit providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.
Electrical Metallic Tubing (EMT)
A thin-walled, unthreaded metal raceway commonly used in commercial and residential construction for protecting electrical conductors.
Electrical Plan (Blueprint)
A detailed drawing showing the layout of electrical systems in a building, including the locations of outlets, switches, panels, fixtures, and circuits.
Electromotive Force (EMF)
The electrical pressure or voltage produced by a source of energy such as a battery or generator that drives current through a circuit.
Energized
Electrically connected to or having a source of voltage, making a conductor or equipment potentially dangerous.
Equipment Grounding Conductor (EGC)
A conductor that connects non-current-carrying metal parts of equipment to the grounding system, providing a low-impedance path for fault current.
Fault Current (Available)
The maximum current that would flow through a circuit during a short circuit or ground fault condition.
Feeder
The circuit conductors between the service equipment (or the source of a separately derived system) and the final branch-circuit overcurrent device.
Flexible Metal Conduit (FMC)
A spirally wound, interlocked metal raceway used where flexibility is needed for connections to equipment that vibrates or requires movement.
Fuse
An overcurrent protection device containing a fusible element that melts and opens the circuit when current exceeds its rating.
GFCI (Ground Fault Circuit Interrupter)
A device that monitors the current flowing through hot and neutral conductors and trips the circuit if it detects a difference of 5 milliamps or more, indicating current is leaking to ground.
Ground (Earth)
A conducting connection between an electrical circuit or equipment and the earth, or to a conducting body that serves in place of the earth.
Grounding Electrode Conductor (GEC)
The conductor that connects the grounded system conductor or the equipment grounding conductor to the grounding electrode.
Impedance
The total opposition to current flow in an AC circuit, combining resistance and reactance, measured in ohms.
Interrupting Rating
The maximum fault current that an overcurrent device (breaker or fuse) can safely interrupt without being damaged or causing a hazard.
Isolated Ground Receptacle
A special receptacle with an insulated grounding terminal that provides a clean, dedicated ground path for sensitive electronic equipment.
Journeyman Electrician
A licensed, skilled tradesperson who has completed an apprenticeship program and passed a certification exam, qualified to perform electrical work under the supervision of a master electrician or contractor.
Junction Box
An enclosed box used for housing and protecting electrical connections (splices) between conductors.
Listed
Equipment, materials, or services that have been evaluated by a nationally recognized testing laboratory (NRTL) and found to meet appropriate safety standards.
Load Calculation
The process of determining the total electrical demand of a building to properly size the electrical service, feeders, and branch circuits.
Lockout/Tagout (LOTO)
A safety procedure that ensures dangerous electrical equipment is properly shut off and cannot be started up again before maintenance or servicing work is completed.
Main Breaker
The primary circuit breaker in an electrical panel that controls power to the entire panel and serves as the main disconnecting means for the building.
Megger (Insulation Resistance Tester)
A specialized test instrument that measures the insulation resistance of conductors and electrical equipment using a high DC voltage, typically 250V to 1000V.
Motor Full-Load Current (FLC)
The current that a motor draws at its rated horsepower and voltage when operating at full mechanical load, as listed in NEC tables.
Multimeter
A versatile test instrument that measures voltage (volts), current (amps), and resistance (ohms), and often includes additional functions like continuity testing and capacitance measurement.
NEC (National Electrical Code)
The widely adopted model code (NFPA 70) that sets the standard for safe electrical design, installation, and inspection in the United States.
NEMA (National Electrical Manufacturers Association)
The organization that sets standards for electrical equipment manufacturing, including enclosure ratings, motor specifications, and connector types.
Neutral Conductor
The grounded conductor in an electrical system that carries the unbalanced current back to the source and is connected to the neutral bus in the panel.
NFPA 70E
The Standard for Electrical Safety in the Workplace, published by the National Fire Protection Association, which provides guidelines for protecting workers from electrical hazards.
NM Cable (Romex)
Non-metallic sheathed cable consisting of two or more insulated conductors and a bare ground wire enclosed in a plastic sheath, commonly used in residential wiring.
Ohm
The standard unit of electrical resistance, symbolized by the Greek letter omega (Ω).
Ohm's Law
The fundamental electrical formula stating that voltage (V) equals current (I) multiplied by resistance (R): V = I × R.
OSHA (Occupational Safety and Health Administration)
The federal agency responsible for ensuring safe and healthful working conditions by enforcing safety standards, including electrical safety requirements for construction and general industry.
Overcurrent
Any current in excess of the rated current of equipment or the ampacity of a conductor, which may result from an overload, short circuit, or ground fault.
Panelboard
An assembly of buses, overcurrent devices, and enclosures that distributes power to branch circuits and feeders within a building.
Parallel Circuit
A circuit configuration where multiple loads are connected across the same voltage source, each providing a separate path for current flow.
Permit
A formal authorization from the local building department required before starting electrical work, ensuring the work will be inspected for code compliance.
Photovoltaic (PV) System
A solar electric system that converts sunlight directly into electricity using semiconductor cells, increasingly common in residential and commercial installations.
Power Factor
The ratio of real power (watts) to apparent power (volt-amperes) in an AC circuit, representing how efficiently electrical power is being used.
Pull Box
A large junction box installed in a conduit run to facilitate the pulling of conductors through long or complex runs.
Raceway
An enclosed channel designed expressly for holding wires, cables, or busbars, including conduits, wireways, and cable trays.
Receptacle
A contact device installed at an outlet for the connection of an attachment plug, commonly known as an electrical outlet or socket.
Rigid Metal Conduit (RMC)
The heaviest and most durable type of metal conduit, featuring threaded connections, suitable for severe physical damage environments and outdoor use.
Series Circuit
A circuit configuration where all components are connected end-to-end in a single path, so the same current flows through each component.
Service Drop
The overhead electrical conductors from the utility's distribution system to the point of connection at the building's service entrance.
Service Entrance
The point where the utility's power lines connect to a building's electrical system, including the service conductors, meter, and main disconnect.
Service Lateral
The underground electrical conductors from the utility's distribution system to the point of connection at the building's service entrance.
Short Circuit
An abnormal connection of very low resistance between two points of different potential in a circuit, resulting in excessive current flow.
Single-Phase Power
An AC power supply system using one phase of alternating current, providing 120V and 240V in typical residential applications.
Subpanel
A smaller distribution panel fed from the main panel, used to provide circuit protection and power distribution to a specific area of a building.
Surge Protective Device (SPD)
A device designed to protect electrical equipment from voltage spikes (surges) caused by lightning, power grid switching, or other transient events.
Tamper-Resistant Receptacle
A receptacle with built-in shutters that prevent the insertion of foreign objects into the contact openings, required in dwelling units to protect children.
Tap Rules
NEC provisions that allow conductors to be connected to a feeder without overcurrent protection at the tap point, under specific conditions regarding conductor length and termination.
Three-Phase Power
An AC power supply system using three conductors, each carrying current 120 degrees out of phase with each other, commonly used for commercial and industrial applications.
Transformer
An electrical device that transfers energy between circuits through electromagnetic induction, used to increase (step up) or decrease (step down) voltage levels.
VA (Volt-Ampere)
A unit of apparent power in an electrical circuit, equal to the product of voltage and current, used in NEC load calculations.
Volt
The standard unit of electrical potential difference (voltage) or electromotive force, representing the pressure that pushes electric current through a conductor.
Voltage Drop
The reduction in voltage along a conductor due to its inherent resistance, which increases with conductor length and current flow.
Watt
The standard unit of electrical power, equal to one volt times one ampere (P = V × I).
Weatherproof
Constructed or protected so that exposure to weather conditions such as rain, snow, and wind will not interfere with successful operation of the equipment.
Wet Location
An installation location subject to saturation with water or other liquids, including underground installations, concrete slabs in direct contact with earth, and outdoor locations exposed to weather.
Wire Nut
A twist-on wire connector used to join two or more electrical conductors together, providing an insulated and secure connection inside electrical boxes.
Wireway
A sheet-metal or nonmetallic trough with a hinged or removable cover, used for housing and protecting conductors, typically at junction points between multiple conduit runs.
Working Space
The clear space required by the NEC around electrical equipment to allow safe operation and maintenance.