Electrical terms, in plain language

A breaker or outlet designed to turn off power when it detects electrical arcing that could start a fire. It protects against a different problem from a GFCI.

A measure of electrical current. A breaker’s amp rating, often 15A or 20A, is printed on its handle and is roughly how much the circuit can draw before the breaker trips. The rating is not a measurement of how much power the circuit is using right now.

Any of the numbered breakers in a panel, each feeding one circuit. The name sets them apart from the main breaker, which feeds the whole panel. When Circuit Mapper or this glossary says breaker with nothing in front of it, it means one of these.

A switch in the panel that controls a circuit and can turn itself off, or trip, when it detects certain problems such as an overload or short circuit.

See Breaker panel (electrical panel).

The record of which breaker controls each outlet, light, switch and fixed appliance in a home. Circuit Mapper keeps this record searchable by both room and breaker.

The metal enclosure that holds the breakers distributing power through a home. Mapping only requires using the switches on the closed panel; do not remove its cover.

A connected path of wiring, outlets, lights and other equipment supplied through a breaker. One circuit may cross several rooms rather than following the layout of the house.

See Panel schedule.

A tool with a transmitter that connects to an outlet and a handheld receiver used at the panel to identify its breaker. It finds a circuit; it does not keep the finished map.

Circuit Mapper’s general word for something worth locating and mapping: an outlet, light, switch, fixed appliance or other electrical item.

A breaker that spans two panel slots and switches two live conductors together. It is commonly used for 240-volt equipment and is not the same as a tandem breaker.

A breaker or outlet that combines AFCI and GFCI protection in one device. Circuit Mapper records this as dual-function or DFCI protection.

A duplex outlet is the ordinary wall fitting with two places to plug in. A single has one, and a quad has four, usually two duplexes side by side in one box. Circuit Mapper asks which kind so the map records how many things can plug in there. A duplex above a kitchen counter may be split-wired, with its two halves on different breakers: see Split-wired outlet.

See Spare or empty slot.

A breaker or outlet designed to turn off power quickly when it detects current leaking from its intended path, reducing the risk of electric shock. GFCI outlets usually have TEST and RESET buttons.

See GFCI (ground-fault circuit interrupter).

A physical connector joining the handles of separate breakers so they can be switched off together. Circuit Mapper can record which breakers are tied.

Equipment connected directly to the home’s wiring instead of through an ordinary plug. Furnaces, some dishwashers and many ceiling fans are common examples.

When using Circuit Mapper in two-person mode: a temporary link for the person staying at the panel. It gives them one breaker instruction at a time while the person holding the map walks the house and records results.

The trade word for something that uses electrical power, such as a light, heater or appliance. Circuit Mapper usually calls it a device instead.

See Breaker panel (electrical panel).

One round of turning off a breaker and checking which devices lose power. The app records what stayed on, what went off and what could not be confirmed.

The large switch that cuts power to every circuit in the panel. The wires feeding the panel stay live above it, which is one reason never to remove the cover. It is separate from the numbered branch breakers and may span both columns of the panel.

A group of checks limited to one kind of device and one area, such as the lights on one floor. Passes keep a solo mapping session short enough to complete without losing your place.

Two circuits that share a neutral wire. Their breakers are arranged so both circuits can be disconnected together, often with a handle tie. Record what is visible and ask an electrician if the arrangement is unclear.

Circuit Mapper uses outlet for the wall fitting where you plug something in. Receptacle is the trade term; socket is sometimes used for each individual place that accepts a plug.

A plug-in outlet tester shows a pattern of lights that reads the wiring in that socket. One pattern means correct. The others have names: open ground, open neutral, open hot, hot and neutral reversed, hot and ground reversed. Circuit Mapper lets you record the reading against the outlet during a tester pass. Record it and move on: a tester can miss faults it was not built to find, and deciding what a reading means and putting it right is an electrician’s job.

See Panel schedule.

Two different things. The door is the hinged flap on the outside. Open it and you see the breaker handles and the card, and nothing live is exposed. The cover, sometimes called the deadfront, is the metal plate behind the door, held on by screws, with the handles poking through it. Behind the cover are live parts. Circuit Mapper is used with the door open and the cover on. Never remove the cover.

The numbered list inside or beside a panel that describes what each breaker controls. Circuit Mapper can produce a clean printable version from the saved map.

See Breaker panel (electrical panel).

A small tool plugged directly into an outlet. Its lights show whether power is present, and their pattern can identify several common wiring problems. It does not detect every problem or certify that an outlet is safe.

The number of live conductors a breaker switches. A single-pole breaker switches one; a double-pole breaker switches two together.

A breaker assembly that fits four breaker handles into the space normally used by two full-width breakers. Its internal arrangement varies, so copy the markings you can see rather than guessing.

See Outlet, receptacle and socket.

A breaker that switches one live conductor and normally occupies one panel slot. It commonly supplies a 120-volt household circuit.

See Outlet, receptacle and socket.

A numbered physical position in a panel. Empty positions still have numbers. A tandem places two breakers in one slot, while a double-pole breaker spans two slots.

A position in the panel with nothing on it, on purpose: either an empty slot with no breaker fitted, or a breaker installed with nothing wired to it, kept for a future circuit. Circuit Mapper has one mark for both. Use it so the position does not count as unmapped and does not get walked. A breaker marked spare that turns out to control something is worth a second look: either it was never really spare, or something has been connected to it since.

An outlet whose top and bottom sockets are supplied by different circuits. Common above kitchen counters, where some electrical codes require it. The two halves must be tested and mapped separately.

A second breaker panel supplied from another panel. It distributes power to its own group of circuits, but its shutoff may be located at the panel feeding it.

A single-pole switch controls a light from one place. A 3-way pair controls one light from two places, such as both ends of a hallway, and a 4-way adds a third. A dimmer or a smart switch does the same job and also draws a little power of its own. Circuit Mapper asks which kind so a switch can be recorded as its own device when it sits on a different breaker from the light it controls, which any of these can. Not the same thing as a single-pole breaker, which shares the name and nothing else.

Two separate breakers fitted into one numbered panel slot. Each controls its own circuit. A tandem is not the same as a double-pole breaker, which spans two slots and switches two conductors together.

Anything that shows you whether an outlet has power. Your phone on its charger is the most basic one, since you already have both: if it starts charging, the socket is live. A plug-in nightlight or a small lamp can work well if you have them already. An outlet tester is a $10 upgrade that lets you confirm socket wiring at the same time. Confirm that whatever you use works before turning off a breaker.

A breaker that has turned itself off after detecting a problem. Its handle may sit between ON and OFF. Repeated trips need attention from an electrician.

See Double-pole breaker.

How hard the electricity pushes, in volts. Nearly everything in a North American home runs on 120 volts from a single-pole breaker. Large heat-producing equipment such as a range, a dryer, a water heater, a hot tub or an EV charger runs on 240 volts from a double-pole breaker that spans two slots. Circuit Mapper asks which one a device uses because it tells you what kind of breaker to look for.