Electrical glossary
69 terms in plain words. The ones an electrician says on a job and the ones printed on a quote.
A
| AFCI | Arc fault circuit interrupter. A breaker that listens for the electrical noise of arcing and cuts power before it can start a fire. |
| Ampacity | How much current a conductor can carry continuously without overheating. It depends on the wire, the insulation, the temperature and how many wires run together. |
| Ampere | The unit of electrical current, shortened to amp. It measures how much charge is flowing. |
| Apprentice | A person learning the trade through paid supervised work plus classroom hours. Most programs run four to five years. |
| Arc flash | An explosive release of energy when a fault occurs inside energized equipment. It produces extreme heat and pressure and is the reason rated protective clothing exists. |
B
| Backstab | Wiring a device by pushing the wire into a hole in the back instead of wrapping it around the screw. It loosens over time and is a common cause of dead outlets. |
| Bond | Connecting metal parts together so they stay at the same potential and fault current has a clear path back. Bonding and grounding are related and are not the same thing. |
| Box fill | The calculation that limits how many conductors and devices fit in an electrical box. Overfilled boxes trap heat and damage insulation. |
| Branch circuit | The wiring from the last breaker out to the outlets, lights or appliance it serves. |
| Breaker | A switch that opens automatically when current exceeds its rating. It protects the wire, not the appliance plugged into it. |
| Bus bar | The metal bar inside a panel that breakers clip onto. Each of the two hot bars carries one leg of the service. |
| BX | A common name for armored cable, which is conductors inside a flexible metal jacket. Older installations use it widely. |
C
| C 10 | The California contractor license classification for electrical work. Every legitimate electrical contractor in the state holds one. |
| Circuit | A complete loop that current travels, out on the hot conductor and back on the neutral. |
| Conductor | The metal that carries current, normally copper or aluminum. In everyday speech, the wire. |
| Conduit | Pipe that protects and routes conductors. It comes in rigid metal, intermediate metal, thin wall and several plastic types. |
| Conduit fill | The limit on how many conductors can go in a given size of pipe, so heat can escape and wire can be pulled without damage. |
| Continuous load | A load expected to run for three hours or more. Circuits are sized to 125 percent of it, which is why a 40 amp charger wants a 50 amp circuit. |
D
| Demand factor | A code allowance recognizing that not everything in a building runs at once. It keeps service sizing realistic instead of enormous. |
| Device | A part that carries or controls electricity but does not consume it, such as a switch or a receptacle. |
| Disconnect | A switch that cuts power to equipment, placed where a worker can see it while working on that equipment. |
| Double tap | Two wires under one breaker screw where only one is allowed. A frequent inspection finding and an easy fix. |
| Drop | The overhead wires running from the utility pole to the house. It belongs to the utility up to the connection point. |
E
| EMT | Electrical metallic tubing, the thin wall steel conduit used in most commercial work and in garages. |
F
| Feeder | The conductors between the main service and a subpanel. Larger than a branch circuit and smaller than the service. |
| Fish tape | A stiff flat wire on a reel used to pull conductors through conduit or inside a finished wall. |
| Fuse | A one time overcurrent device with a metal link that melts. Replaced by breakers in modern panels and still found in older homes. |
G
| GFCI | Ground fault circuit interrupter. It compares current out against current back and cuts power when the difference says current is leaking, which protects people. |
| Ground | The conductor that gives fault current a path back to the source so a breaker trips. It carries nothing during normal operation. |
| Ground rod | A copper coated rod driven into the earth and bonded to the electrical system. Most services need two unless resistance is tested. |
H
| Hard wired | Connected permanently to the wiring rather than plugged in. |
| Home run | The cable running from the panel to the first box on a circuit. |
J
| Journeyman | An electrician who has completed an apprenticeship and passed the exam, qualified to work without direct supervision. |
| Junction box | An enclosure where conductors are spliced. It must stay permanently accessible, never buried in a wall. |
K
| Kilowatt hour | A thousand watts used for one hour. It is the unit the utility bills you in. |
| Knob and tube | Pre war wiring with separate hot and neutral conductors on ceramic knobs. It has no ground and cannot be extended. |
L
| Leg | One of the two hot conductors of a residential service. Each measures 120 volts to neutral and 240 volts to the other leg. |
| Load calculation | Adding up the connected load with code demand factors to find the service size a building actually needs. |
| Lockout tagout | Locking a disconnect open and tagging it with your name so nobody can energize the circuit you are working on. |
| Lug | The terminal that a large conductor bolts into, found at the main breaker and the neutral bar. |
M
| Main | The largest breaker in a panel, which controls everything downstream of it. Its rating is the service size. |
| Mast | The pipe carrying service conductors up through the roof to the overhead drop. |
| Master electrician | A license above journeyman in many states, usually required to pull permits or supervise other electricians. |
| Meter | The utility device that measures what you use. The dividing line between their equipment and yours. |
| MWBC | Multi wire branch circuit. Two hot conductors from opposite legs sharing one neutral. The breakers must be tied so both open together. |
N
| NEC | The National Electrical Code, revised every three years. It becomes law when a state or city adopts it. |
| Neutral | The conductor that carries current back to the source. It is bonded to ground at the main panel and only there. |
| NM cable | Non metallic sheathed cable, the flat plastic jacketed cable used in most house wiring. Often called by the trade name Romex. |
O
| Ohm | The unit of resistance. Volts equal amps times ohms, which is the relationship the whole trade rests on. |
| Overcurrent | Current above what a conductor or device is rated for, from an overload, a short circuit or a ground fault. |
P
| Panel | The enclosure holding the main breaker and the branch breakers. Also called a load center or a breaker box. |
| Pigtail | A short length of wire spliced to join several conductors to one terminal, so devices are not used to carry current through. |
R
| Receptacle | The proper name for an outlet, the device you plug into. |
| Rough in | All the wiring done before walls are closed, inspected before insulation goes in. |
S
| Service | The conductors and equipment delivering power from the utility to a building. |
| Service upgrade | Increasing the amperage a building receives, which requires the utility to change what feeds it. |
| Short circuit | A hot conductor touching a neutral or a ground, which makes current jump instantly and trips the breaker at once. |
| Single phase | The standard residential service with two hot legs and a neutral, delivering 120 and 240 volts. |
| Subpanel | A smaller panel fed from the main. Its neutrals and grounds must stay separate, unlike in the main panel. |
T
| Tandem breaker | A thin breaker that puts two circuits in one slot. Allowed only in panels rated for it. |
| Three phase | A commercial service with three hot legs. It runs large motors more efficiently than single phase. |
| Trainee | In California, a registered uncertified worker who must be enrolled in an approved school while working under supervision. |
| Transfer switch | Equipment that connects a building to a generator while isolating the utility, so power cannot feed back onto the line. |
| Transformer | Equipment that changes voltage from one level to another. The can on the pole outside drops utility voltage to house voltage. |
V
| Volt | The unit of electrical pressure. Think of it as what pushes current through a circuit. |
| Voltage drop | The loss of voltage along a long conductor. Kept under about three percent on a branch circuit, usually by using larger wire. |
W
| Watt | The unit of power, equal to volts times amps. It is the actual work being done. |
| Wire gauge | The thickness of a conductor, counted so that a smaller number means a thicker wire. Fourteen gauge is thinner than twelve. |
| Wire nut | A twist on connector that joins conductors inside a box. Sized by how many and what gauge it holds. |