Chapter 36: Glossary

Every term in this book, defined plainly. Alphabetical. The shorter version of "what does this electrician word actually mean?"

A

AFCI (Arc-Fault Circuit Interrupter). A breaker or outlet that detects the electrical signature of an arc (an unwanted spark caused by damaged or loose wiring) and trips. Required in most living areas in homes built or rewired under modern code. Different from GFCI, but they can be combined into "dual-function" devices.

Ampacity. The maximum current a wire can safely carry without overheating. Depends on wire size, insulation type, and ambient conditions. A 12 AWG copper NM cable in normal residential use has an ampacity of 20A.

Amperage (Amps, A). The measure of electrical current. How much electricity is flowing. Like the volume of water in a pipe.

Arc. An unwanted electrical discharge through air. Can occur at loose connections, damaged insulation, or where a wire is being abraded. Arcs are extremely hot and can ignite nearby materials. Causing arcs is bad. AFCIs detect them.

AWG (American Wire Gauge). The standard size system for electrical conductors in North America. Lower numbers mean thicker wires (counter-intuitively). 14 AWG is small (lighting circuits), 6 AWG is medium (sub-panels and big appliances), 4/0 AWG is large (service entrance).

B

Backstab. A push-in connection on the back of an outlet or switch where you stick the wire into a hole and an internal spring clip holds it. Quick to install, unreliable long-term. Avoid in new work.

Bonding. Connecting metal parts together (and to ground) so they're all at the same electrical potential. Prevents shock from stray voltage. The water pipe in your house should be bonded to your panel ground, for example.

Box. An enclosed metal or plastic housing that contains wire connections, outlets, switches, or fixtures. Required at every connection point in a residential electrical system. Comes in many sizes and shapes.

Box Fill. The amount of "space" used in a box, calculated by counting the conductors, devices, and clamps inside. NEC sets minimums to prevent overcrowding.

Branch Circuit. A circuit that runs from a breaker in your panel out to outlets, switches, and lights. Most circuits in your house are branch circuits.

Breaker (Circuit Breaker). A safety device in your panel that automatically trips (turns off) when current exceeds its rating. Replaceable; resets after tripping.

Bus Bar. A large solid copper or aluminum strip in your panel that distributes power from the main breaker to all the branch circuit breakers. There's a hot bus (or two, for a 240V panel) and a neutral bus.

C

Cable. A bundled assembly of multiple insulated conductors. NM cable (Romex) has 2 or 3 insulated wires plus a bare ground, all wrapped in a paper or plastic jacket.

Circuit. A complete path for electricity to flow from the source, through a load, and back. If the path breaks anywhere, the circuit is "open" and no current flows.

Conductor. A wire that carries electricity. Usually copper or aluminum.

Continuity. A measure of whether a circuit is intact (closed). Tested with a multimeter or continuity tester.

Continuous Load. A load that operates at maximum capacity for 3 hours or longer. Examples: EV chargers, electric heaters, large lighting circuits. Continuous loads require 25% extra capacity in the breaker and wire (so a 40A continuous load needs a 50A breaker and 8 AWG wire).

D

Dedicated Circuit. A circuit that serves only one outlet or one appliance. Required for some equipment (microwaves, dishwashers, refrigerators in many cases). Recommended for any high-draw or sensitive load.

Dimmer. A switch that controls the brightness of a light. Old dimmers were resistive (rheostats). Modern dimmers are electronic and need to be matched to the bulb type (LED, incandescent, halogen).

E

EMT (Electrical Metallic Tubing). Thin-walled steel conduit used for protecting wires. Common in commercial work, sometimes in garages and basements.

EV Charger (Level 2). A 240V car charger that's much faster than the Level 1 (120V) charger that comes with the car. Typically 32–48A continuous draw.

F

Feeder. A cable that runs from one panel to another (typically from a main panel to a sub-panel). Distinguished from a branch circuit, which runs from a panel to loads.

Fish Tape. A flexible steel or fiberglass tape used to pull wires through walls, ceilings, or conduit.

Fixture. A permanent lighting installation (chandelier, recessed can, ceiling fan with light, etc.).

G

GFCI (Ground-Fault Circuit Interrupter). A breaker or outlet that detects current leaking to ground (typically through a person) and trips in milliseconds. Required in wet/damp areas and around water. Saves lives.

Ground. A safety conductor that provides a path back to earth in case of a fault. The bare or green wire in a circuit. Different from neutral, even though both are "grounded" in the panel.

Ground Fault. Current flowing from a hot conductor to ground unintentionally. A leak. Usually caused by damaged insulation, water intrusion, or contact with a person.

Ground Rod. A metal rod (typically copper-clad steel, 8 feet long) driven into the earth to provide a low-resistance path to ground. Connected to the panel via a grounding electrode conductor.

Grounding Electrode Conductor. The wire from your panel to your grounding electrodes (ground rods, water pipe, Ufer ground). Connects the entire electrical system to earth.

H

Hardwire. To connect an appliance directly to wiring (rather than plugging it in with a cord).

Hot. A wire or terminal carrying power. Usually black or red. Or for service entrance, the two service hots.

I

Inrush Current. The brief surge of current that occurs when a motor, transformer, or other inductive load first turns on. Can be 5–10x the running current. Why some breakers are sized for the inrush rather than the running load.

J

Junction Box. A box where multiple cables come together and are spliced. Must remain accessible (not buried in walls).

K

kVA (Kilovolt-Amperes). A unit of apparent power. Like kilowatts but for non-resistive loads.

kW (Kilowatts). A unit of real power. 1 kW = 1000 watts.

L

LED (Light Emitting Diode). A semiconductor light source. More efficient than incandescent bulbs. Comes in many "color temperatures" (warm white, daylight, etc.). Sometimes finicky with old dimmers.

Line Side. The side of a switch or outlet that's connected to incoming power. The supply side. Distinguished from "load side."

Live. A conductor that has voltage on it. "Hot" is more common, but "live" is also used.

Load. Anything that consumes electricity. A light, an appliance, an outlet (when something is plugged into it).

Load Side. The side of a switch or outlet that's connected to whatever the device controls. The output side.

M

Main Breaker. The largest breaker in your panel, located at the top. Disconnects all power to the house when turned off. Usually rated 100A, 150A, or 200A in residential.

Mechanical Connection. A connection made with screws, lugs, or other physical clamps. Distinguished from a soldered or crimped connection.

Megger. A specialized meter that measures insulation resistance using high voltage (typically 500V or 1000V). Used to find subtle insulation faults that a regular ohmmeter can't detect.

Multimeter. A meter that measures voltage, current, resistance, and continuity. Indispensable.

Multi-Wire Branch Circuit (MWBC). A circuit that uses two hot conductors (one from each phase) sharing a single neutral. Common in older construction. Has specific requirements under modern code (handle-tied breakers).

N

Neutral. The grounded conductor that completes the circuit back to the source. White wire. Carries current under normal operation.

Newer Construction (post-2014). Houses built or rewired under NEC 2014 or later have AFCI requirements that older houses don't. Many older houses are grandfathered in (you don't have to retrofit AFCIs unless you're doing a major renovation).

NEC (National Electrical Code). The US standard for electrical installation, published every three years by NFPA. NEC 2023 is currently adopted in Oklahoma.

NM Cable (Non-Metallic Cable, "Romex"). The most common cable type in residential work. A jacket of plastic with 2 or 3 insulated conductors plus a bare ground inside.

O

OCPD (Overcurrent Protective Device). Fancy term for a breaker or fuse.

OG&E (Oklahoma Gas and Electric). The local utility for most of the OKC metro area. Their crews handle anything from the meter outward.

Outlet. Where you plug things in. A "duplex outlet" has two receptacles. A "simplex outlet" has one. Sometimes called a receptacle.

Overcurrent. More current than the wire is rated for. Causes overheating, then either a tripped breaker or a fire (depending on whether you have working overcurrent protection).

Overload. A specific kind of overcurrent caused by drawing more current than the circuit was designed for. The breaker's job is to trip on overload before the wire gets hot enough to ignite.

P

Panel (Load Center, Breaker Box). The cabinet that contains the main breaker and the branch circuit breakers. Where electricity is distributed throughout the house.

Panelboard. The technical term for the panel.

Permit. Authorization from the local building department to perform electrical work. Required for most electrical work beyond like-for-like device replacement.

Phase. In residential, you have two "phases" or "legs" of 120V power, each 180 degrees from the other. Together they make 240V for big appliances. (This is sometimes called "single-phase" because it's one phase from the utility's three-phase system, just split into two.)

Pigtail. A short piece of wire that connects multiple wires to a single terminal, all joined together with a wire nut. Used to avoid stuffing too many wires under one screw.

PVC Conduit. Plastic conduit. Common for outdoor and underground work. Cheaper and easier to work with than steel conduit.

R

Receptacle. Another word for outlet.

Resistance. Opposition to current flow. Measured in ohms. Like friction in water flowing through a pipe.

Romex. Brand name (now generic) for NM-B cable, the most common residential wiring.

S

Service. The connection from the utility to your house. Includes the meter, service drop or service lateral, service entrance conductors, and main breaker.

Service Drop. Overhead wires from the utility pole to your house. Distinguished from a service lateral, which is buried.

Service Lateral. Underground service feed. Buried from the transformer or pole to your meter.

Short Circuit. A direct connection between hot and neutral (or hot and ground), causing massive current flow. Trips the breaker instantly. Requires investigation to find the fault.

SPDT (Single-Pole Double-Throw). A switch type used for 3-way wiring. Has a common terminal and two travelers.

Stab-In/Backstab. See "Backstab."

Sub-Panel. A secondary panel fed from the main panel, located in another part of the house (garage, workshop, addition).

Surge. A short voltage spike, often caused by lightning or utility events. Can damage electronics. Surge protectors absorb or divert the energy.

Switch. A device that opens or closes a circuit, controlling whether power reaches a load. Single-pole, 3-way, 4-way, dimmer, smart, etc.

T

Tamper-Resistant Outlet. An outlet with internal shutters that prevent objects from being inserted into a single slot. Required in homes for almost all outlets.

Terminal. The connection point on a device (the screw or the push-in hole).

THHN/THWN. Common insulation types for individual conductors run through conduit. THWN is rated for wet locations.

Three-Way Switch. A pair of switches used together to control a single light from two locations. Each is an SPDT switch with a common and two travelers.

Torque. The rotational force applied to a screw or bolt. Specified for breaker terminals, panel lugs, and many other connections. Too loose causes high resistance; too tight can damage threads.

Traveler. One of the two wires connecting a pair of 3-way switches.

Trip. When a breaker or GFCI senses a fault and shuts off power.

Tripping Curve. How quickly a breaker trips at various overcurrent levels. Most residential breakers are "thermal-magnetic" and have a defined curve.

U

Ufer Ground. A grounding electrode formed by a copper wire or rebar embedded in the concrete of the house's foundation. Excellent ground because of the moisture in concrete.

V

Voltage (V). The "pressure" of electricity. The push that makes current flow. 120V at residential outlets, 240V across both legs.

Voltage Drop. The reduction in voltage along a wire due to its resistance. Worse on long runs and small wires. Should be limited to 3–5% in residential circuits.

W

Watts. The measure of power consumption. Watts = volts × amps. A 100W bulb at 120V draws 0.83A.

Wire Nut. A plastic-and-metal connector that joins wires together. Twisted on, no soldering.

Whole-House Surge Protector. A surge protection device installed at the panel. Protects all circuits from surge events. Highly recommended in storm-prone areas like Oklahoma.