Electrical Glossary

AFCI (Arc-Fault Circuit Interrupter)

An arc-fault circuit interrupter (AFCI) is a breaker or outlet that cuts power when it detects dangerous electrical arcing in wiring or cords, the kind of sparking that can start a fire inside a wall.

Alternating Current (AC)

Alternating current (AC) is electric current that regularly reverses direction, flowing one way and then the other, 60 times each second on the US power grid.

Aluminum Wiring

Aluminum wiring is house wiring that uses aluminum conductors instead of copper, and in US homes the term usually means the small aluminum branch circuits for outlets and lights installed from about 1965 to the mid-1970s.

American Wire Gauge (AWG): see Electrical Wire Gauge

Amperage

Amperage is the amount of electric current flowing through a circuit, counted in amperes (amps, A): the quantity of electric charge that passes a point each second.

Arc Fault

An arc fault is an unintended electrical arc in a circuit, where current jumps across a gap or through damaged insulation and produces intense heat at that spot.

Arc Flash

An arc flash is an electrical explosion that happens when current jumps through the air between conductors or to ground, releasing intense heat, light, pressure and molten metal in a fraction of a second.

Automatic Transfer Switch (ATS)

An automatic transfer switch (ATS) is a self-acting switch that watches utility voltage, signals a standby generator to start when the power fails, moves the home’s circuits to the generator, and moves them back after utility power returns.

Backstab Wiring

Backstab wiring is a way of connecting a receptacle or switch by pushing the stripped wire straight into a hole on the back of the device, where a small spring clip holds it, instead of wrapping it around a side screw.

Battery Energy Storage System

A battery energy storage system is a set of rechargeable batteries, an inverter and controls that stores electricity, from the grid or from solar panels, and releases it later to run a home or business, including during outages.

Branch Circuit

A branch circuit is the part of a home’s wiring that runs from the final breaker or fuse protecting it to the outlets, lights or appliances it serves.

Brownout

A brownout is a period of lower-than-normal voltage on the power supply, often from grid stress or a deliberate utility voltage cut, that dims lights and strains motors without fully cutting power.

Circuit Breaker

A circuit breaker is an automatic switch in your electrical panel that opens a circuit when too much current flows, protecting the wires from overheating and fire.

Critical Loads Panel

A critical loads panel is a separate subpanel that holds only the circuits a home wants to keep running in an outage, so a battery or generator can power those must-run circuits without trying to carry the whole house.

Dedicated Circuit

A dedicated circuit is a branch circuit that runs from its own breaker to a single appliance or outlet, so nothing else shares its capacity.

Digital Multimeter

A digital multimeter (DMM) is a handheld test instrument that measures voltage, current and resistance, and often continuity, frequency and capacitance, showing the result as a number on a digital display.

Dimmer Switch

A dimmer switch is a wall control that changes how bright a light is by reducing the power delivered to it, most often by cutting off part of each AC voltage wave so the bulb or its LED driver receives less energy.

Direct Current (DC)

Direct current (DC) is electric current that flows steadily in one direction only, from the negative side of a source to the positive side, as it does from a battery.

Duplex Outlet: see Electrical Receptacle

Electric Current: see Amperage

Electric Vehicle Supply Equipment (EVSE)

Electric vehicle supply equipment (EVSE) is the equipment that safely delivers power from a building’s wiring to an electric vehicle: the wall unit or portable cord set, its cable and connector, and the controls that switch power on only when the car is connected.

Electrical Bonding

Electrical bonding is the permanent joining of metal parts, such as boxes, panels, pipes and equipment frames, so they are electrically continuous and conductive, keeping them at the same voltage and giving fault current a low-impedance path back to the source.

Electrical Busbar

An electrical busbar is a solid metal strip inside a breaker panel that carries current from the incoming service to every breaker clipped onto it, so many circuits can share one power source.

Electrical Circuit

An electrical circuit is a complete, closed path that lets current flow from a power source, through a device that uses it, and back to the source again.

Electrical Conduit

Electrical conduit is a tube or pipe, made of metal or plastic, that holds and protects individual wires as they run between boxes, panels and equipment.

Electrical Contactor

An electrical contactor is a heavy-duty, electrically operated switch whose coil, when energized by a small control signal, pulls its contacts closed to start a large load such as a motor, air-conditioner compressor, heater or bank of lights.

Electrical Continuity Testing

Electrical continuity testing is a check, done with the power off, of whether a wire, fuse, switch or other part forms a complete, unbroken path for current, usually with a multimeter that beeps when the path is complete.

Electrical Disconnect Switch

An electrical disconnect switch is a device that opens a circuit so the conductors are cut off from their power source, letting equipment be shut down for service or an emergency.

Electrical Frequency (Hertz)

Electrical frequency is the number of times alternating current completes a full back-and-forth cycle each second, measured in hertz (Hz); the US grid runs at 60 Hz.

Electrical Fuse

An electrical fuse is a safety device with a thin metal link that melts and breaks the circuit when current rises past the fuse’s rating, stopping wires from overheating.

Electrical Grounding

Electrical grounding is the intentional connection of an electrical system, and the metal parts around it, to the earth through rods, pipes or other electrodes, so voltages stay stable and surges from lightning or utility faults have a path into the ground.

Electrical Inspection

An electrical inspection is an examination of a building’s wiring and electrical equipment to confirm it is safe and meets the adopted electrical code, done either by a government inspector to close a permit or by a qualified electrician as a condition or safety check.

Electrical Load Calculation

An electrical load calculation is the code-based estimate of how much power a home or building could draw at one time, used to size the service, panel, feeders and main breaker.

Electrical Meter Base

An electrical meter base is the weatherproof enclosure and socket, usually on an outside wall, that holds the utility’s electric meter and connects the incoming service conductors to the conductors that feed your main disconnect.

Electrical Overload

An electrical overload happens when the devices on a circuit draw more current than its wire and breaker are rated to carry, so the wiring heats up until the breaker trips or the fuse blows.

Electrical Panel

An electrical panel is the metal box where power from the utility enters a home and is divided into separate circuits, each protected by its own circuit breaker or fuse.

Electrical Panel Upgrade

An electrical panel upgrade replaces or enlarges the breaker panel, usually raising the home's service capacity (for example from 100 to 200 amps) so new loads such as an EV charger or heat pump fit safely.

Electrical Permit

An electrical permit is written approval from a state or local authority to install, alter or repair electrical wiring or equipment at a property, issued before the work and closed out only after the work passes inspection.

Electrical Power Factor

Electrical power factor is the ratio of real power, measured in kilowatts (kW), to apparent power, measured in kilovolt-amperes (kVA), and shows how much of the current a load draws is doing useful work.

Electrical Receptacle

An electrical receptacle is the device mounted in a wall, floor or box that a plug fits into, connecting a cord to the building’s branch circuit through contacts for the hot, neutral and, on three-slot types, ground wires.

Electrical Relay

An electrical relay is a switch operated by electricity, in which a small control signal energizes a coil or electronic stage that opens or closes a separate circuit, keeping the control side and the load side electrically isolated.

Electrical Resistance

Electrical resistance is the opposition a material puts up against the flow of electric current, measured in ohms (Ω), where one ohm is one volt per ampere.

Electrical Shock

An electrical shock is the passage of electric current through the body, which can cause pain, muscle spasms, burns, heart rhythm problems and death, depending on the current, its path and how long it lasts.

Electrical Surge Protector

An electrical surge protector, called a surge protective device (SPD) in codes, is a device that limits brief voltage spikes by diverting the extra energy to ground, protecting wiring and connected equipment.

Electrical Transformer

An electrical transformer is a device with two or more coils of wire around an iron core that raises or lowers the voltage of alternating current, passing power from one circuit to another through a magnetic field with no moving parts.

Electrical Wire Gauge

Electrical wire gauge is the size of a metal conductor, stated in the US as an American Wire Gauge (AWG) number, where a smaller number means a thicker wire that can carry more current safely.

Electrical Working Clearance

Electrical working clearance is the open space that must be kept in front of electrical equipment such as panels, so a person can safely operate, inspect and service it and get away quickly if something goes wrong.

Electricity

Electricity is the movement of electrons from atom to atom, and the energy that movement carries through a wire to light, heat and run the things you plug in.

Electrocution: see Electrical Shock

EMT Conduit

EMT conduit, short for electrical metallic tubing, is a thin-wall, unthreaded steel tube used to protect and route individual wires, joined with set-screw or compression fittings instead of threads.

Equipment Grounding Conductor

An equipment grounding conductor (EGC) is the bare, green or green-and-yellow wire, or approved metal raceway or cable armor, that connects the metal parts of outlets, boxes and appliances back to the panel, giving fault current a low-impedance path so the breaker trips.

EV Charger Circuit: see Level 2 EV Charging

EV Charging Load Management

EV charging load management is any control that limits or shifts how much current an electric vehicle charger draws, so the charging load stays within what a home’s service, panel or circuit can safely supply.

Four-Way Switch

A four-way switch is a light switch with four traveler terminals that is installed between two three-way switches, letting one light be turned on and off from three or more locations.

Generator Interlock Kit

A generator interlock kit is a metal plate or slide fitted to the front of a main electrical panel that physically blocks the main breaker and a generator back-feed breaker from being switched on at the same time.

GFCI (Ground-Fault Circuit Interrupter)

A ground-fault circuit interrupter (GFCI) is a safety device that shuts off power in a fraction of a second when it senses current leaking out of a circuit, such as through a person to ground.

GFCI Outlet: see GFCI (Ground-Fault Circuit Interrupter)

Ground Fault

A ground fault is an unintended electrical path between a live conductor and the ground or a grounded surface, so current leaves its normal circuit and flows through metal, water or a person instead.

Heat Pump Electrical Circuit

A heat pump electrical circuit is the dedicated branch circuit, usually 240 volts, that powers a heat pump’s outdoor unit, sized from the unit’s nameplate minimum circuit ampacity (MCA) and maximum overcurrent protection (MOCP).

Home Electrification Upgrade

A home electrification upgrade is a project that replaces fuel-burning equipment, such as a gas furnace, water heater, range or car, with electric versions, plus any wiring, panel or service work needed to power them.

Hot Wire

A hot wire is the ungrounded conductor in a circuit that carries voltage from the panel to a light, outlet or appliance; in US homes it sits at 120 volts to ground and is usually black or red, though any color except white, gray or green is allowed.

Journeyman Electrician

A journeyman electrician is an electrician who has completed the required supervised training hours, usually through an apprenticeship, and passed a state or local exam, allowing them to do electrical work without direct supervision.

Junction Box

A junction box is a metal or plastic enclosure that holds wire splices and connections, keeping them covered, supported and away from building materials that could catch fire.

Kilowatt-Hour (kWh)

A kilowatt-hour (kWh) is a unit of energy equal to 1,000 watts of power used for one hour, and it is the unit utilities use to bill you for electricity.

LED Driver

An LED driver is the electronic power supply that converts household alternating current into the regulated direct current an LED light needs, holding either the current or the voltage steady so the LEDs run at the right brightness without overheating.

Level 1 EV Charging

Level 1 EV charging is charging an electric vehicle from an ordinary 120-volt household outlet, usually with the portable cord set that comes with the car.

Level 2 EV Charging

Level 2 EV charging is alternating-current charging at 240 volts in a home (or 208 volts in commercial buildings), delivered through a wall-mounted or plug-in charging unit on its own circuit.

Licensed Electrician

A licensed electrician is a person who holds a current license or certificate from a state or local authority allowing them to install, repair or maintain electrical wiring, usually after supervised work hours and a code exam.

Load Center: see Electrical Panel

Lockout/Tagout

Lockout/tagout (LOTO) is a safety procedure that shuts off machines or circuits, isolates their energy sources, and secures them with locks or warning tags so they cannot be turned on while someone works on them.

Main Breaker

A main breaker is the single large circuit breaker that controls all the power coming into a home's electrical panel, so switching it off cuts power to every branch circuit at once.

Manual Transfer Switch: see Transfer Switch

Master Electrician

A master electrician is an electrician who holds the highest individual license in a state’s system, earned after years as a journeyman and usually another exam, which lets them plan electrical work, supervise others and, in many states, pull permits or qualify a contracting business.

National Electrical Code (NEC)

The National Electrical Code (NEC), published by the National Fire Protection Association as NFPA 70, is the U.S.

Neutral Wire

A neutral wire is the circuit conductor, usually white or gray, that carries current back from lights and appliances to the panel and the utility transformer, and is connected to earth at the service so it stays near zero volts to ground.

NFPA 70: see National Electrical Code (NEC)

NM-B Cable (Romex)

NM-B cable (Romex) is nonmetallic sheathed cable: two or three insulated copper wires plus a bare ground, wrapped together in a plastic jacket, and it is the most common wiring inside the walls of US homes.

Non-Contact Voltage Tester

A non-contact voltage tester (NCVT) is a pen-shaped tool that lights up or beeps when its tip is near a live AC conductor, sensing the electric field around the wire without touching bare metal.

Open Neutral

An open neutral is a break or failed connection in the neutral conductor, the return path for current, which lets voltage on a home's two 120-volt legs swing apart so some circuits get too much voltage and others too little.

Portable Generator

A portable generator is a small engine-driven power plant, usually on wheels or a frame, that burns gasoline, propane or diesel to make electricity you can use away from the grid or during an outage.

Power Surge

A power surge is a short burst of voltage well above the normal level on a circuit, lasting from millionths to a few thousandths of a second, that can stress or destroy electronics and appliances.

Service Entrance Conductor

A service entrance conductor is one of the heavy wires that carry electricity from the point where the utility’s service drop or lateral connects to your building, through the meter, to the terminals of your main service disconnect.

Short Circuit

A short circuit is a fault where current takes a low-resistance shortcut between conductors, such as hot touching neutral, skipping the device it should power and surging far above normal.

Smart Light Switch

A smart light switch is an in-wall switch with built-in electronics and a radio that lets you control a light from a phone app, voice assistant, schedule or sensor, as well as by pressing the switch itself.

Solar Inverter

A solar inverter is the device that converts the direct current (DC) made by solar panels into the alternating current (AC) used by a home’s outlets and the utility grid, while matching the grid’s voltage and frequency.

Standby Generator

A standby generator is a permanently installed engine generator, usually fed by natural gas or propane, that starts on its own and powers a home through an automatic transfer switch when utility power fails.

Subpanel

A subpanel is a smaller breaker panel that gets its power from a breaker in the main electrical panel, adding circuit spaces in a new spot such as a garage, addition or detached workshop.

Tamper-Resistant Receptacle

A tamper-resistant receptacle is a wall outlet with built-in spring shutters that keep the slots closed unless two plug blades push in at the same time, so a child cannot insert a key or hairpin into a live slot.

Tandem Circuit Breaker

A tandem circuit breaker is a single-width breaker that holds two separate breakers in one body, so two 120-volt circuits share one panel space on the same bus leg.

THHN Wire

THHN wire is a single insulated conductor, usually copper, with thermoplastic insulation and a thin nylon outer layer, rated for 600 volts and built to be pulled through conduit.

Three-Way Switch

A three-way switch is a light switch with three terminals, used in pairs so one light or group of lights can be turned on and off from two separate locations, such as the top and bottom of a staircase.

Transfer Switch

A transfer switch is a device that moves a home’s circuits from utility power to a backup source, such as a generator, and back again, while making sure the two sources can never be connected at the same time.

Uninterruptible Power Supply (UPS)

An uninterruptible power supply, or UPS, is a battery-backed device that sits between the wall outlet and your equipment and keeps that equipment powered, with no visible gap, when utility power drops or fails.

USB Electrical Outlet

A USB electrical outlet is a wall receptacle with built-in USB charging ports, which turn the 120-volt household supply into low-voltage direct current so phones and tablets can charge without a separate plug-in adapter.

Voltage

Voltage is the electrical pressure between two points that pushes current through a circuit, measured in volts (V).

Voltage Drop

Voltage drop is the voltage a circuit loses along its wires because the wire itself has resistance, so the device at the far end gets slightly less voltage than the panel sends out.

Watt

A watt (W) is the unit of power: the rate at which electrical energy is used or produced at any moment, equal to one volt times one amp.

Wire Connector

A wire connector is a listed device that joins two or more electrical wires into one solid, insulated splice, such as a twist-on wire nut, a lever or push-in connector, or a crimp sleeve.