Plain-language glossary

The words nobody stops to define for you in your first week, explained the way I'd explain them on the job. These are the ideas — where a term is really governed by the code (colours, ampacity figures, fill), the entry says so and points you at the book rather than pretending the number lives here.

Some of these have a page of their own — the ones people actually search for, written out at length. Follow the "read more" link on the entry. And where a term is really about a physical thing, the fittings index and symbols index show you what it looks like.

Common (switch terminal): The odd terminal on a 3-way switch — the one that connects to either traveller depending on which way the blade is thrown. On the first switch it takes the incoming hot; on the last switch it becomes the switched hot to the load.
Traveller: One of the two conductors running between the switches in a 3-way or 4-way circuit. The switches choose which traveller is live; the light is on when the whole run agrees on one. Also spelled "traveler".
SPDT (single-pole double-throw): A switch with one input that connects to one of two outputs — never both, never neither. A 3-way switch is an SPDT: one common, two travellers.
Shrink: When you put a bend in a pipe, the pipe no longer reaches as far as it would straight — the bend "eats" length. Shrink is how much shorter the run gets, and you add it back when you measure so the fitting lands where you wanted it.
Gain: The opposite bookkeeping to shrink, for a 90° bend: the curve of the bend is shorter than going out to the corner and back, so the bend gains you a little length. You subtract the gain so the pipe is not long.
Take-up (deduct): On a 90° stub, the distance from the back of the bend to the end of the pipe. It is a property of the bender and the pipe size and is stamped on the tool — you read it off the bender, you do not look it up in a code book.
Developed length: The true length of pipe consumed by a bend measured along the centre of the pipe as it curves, rather than the straight-line distance between where it starts and stops bending. It is what you actually cut, and it is always more than the straight measurement.
Springback: Steel is elastic before it is plastic, so a pipe you bend to an angle relaxes back a few degrees when you let go. You over-bend slightly to land on the angle you want. How much depends on the material and the size.
Kick: A single bend put in a pipe to nudge it over to one side — the offset done with one bend instead of two, usually to line a stub up with a box. A deliberate, controlled version of what a dog leg is by accident.
Dog leg: A pipe run that wanders off the straight line because the bends do not share a plane — the offset twisted, or a second bend was rolled without meaning to. It is a mistake, not a technique, and it is why you level your bends.
Derating: Reducing the current you allow a conductor to carry because conditions make it run hotter than the ideal — high ambient temperature, or several current-carrying conductors bundled together sharing their heat. It is a multiplication you apply to a starting value; the starting values and the factors themselves come from your code book, not from here.
Ampacity: The current a conductor can carry continuously without its insulation getting hotter than it is rated for. It is a temperature limit expressed as a current. The actual figures for a given conductor and insulation are code-book and manufacturer data — look them up there. Read more →
Bonding vs grounding: Grounding connects a system to the earth, mainly to hold it at a stable reference and handle things like lightning and line surges. Bonding ties all the metal that could become energized together so it is at the same potential and a fault has a low-resistance path back to the source that trips the breaker. People use the words loosely; they are not the same job. Read more →
Neutral vs identified conductor: The neutral is the grounded circuit conductor that carries the unbalanced return current. "Identified" means it is marked so anyone can tell it apart from the ungrounded conductors — the specific marking and colour are set by code. Not every white-looking wire is a neutral, and not every neutral is only a neutral, which is exactly why the identification rules exist.
Wye and delta: Two ways to connect a three-phase set of windings. Wye ties one end of each of the three together at a common point (which can give you a neutral); delta connects them end to end in a loop (no neutral from the windings themselves). The choice changes the voltage relationships you see between lines and to neutral. Read more →
Power factor: The fraction of the current that is actually doing work. Motors and other inductive loads pull current that swings out of step with the voltage; that out-of-step part moves energy back and forth without doing useful work but still has to be carried. Power factor is the ratio of real power to the total, between 0 and 1. Read more →
Inrush: The brief, large current a load draws in the first instant it is switched on — a motor starting, a transformer energizing, a bank of lamps lighting cold. It can be many times the running current and dies away in a fraction of a second, which is why protection has to tolerate a short spike without tripping.
AFCI vs GFCI: A GFCI watches for current leaking off the circuit — going somewhere other than back on the neutral, such as through a person — and opens fast. An AFCI watches for the electrical signature of arcing, the sputtering fault that starts fires in damaged wiring. One is about shock, the other about fire; some devices do both. Read more →
Home run: The cable or conductors that run from the panel to the first box of a circuit, before the circuit branches out to the rest of its devices. The "run home" to the panel.
Dead leg: A length of conductor or a tap that is not carrying current in the present configuration — either spare, isolated, or fed from a source that is off. Worth naming because "dead" is a claim you verify with a meter, never an assumption.
Mule tape: A flat woven pulling tape, marked with its rated strength and often with footage, used to pull conductors into conduit. Flat so it does not dig in, strong so it does not snap mid-pull, and low-stretch so you know how much you are actually pulling.
LB and C bodies (condulets): Cast fittings with a removable cover that give you access to pull or turn conductors in a rigid run. The letter describes the shape: an LB turns the run back at a right angle (the opening faces the "back"), a C body is a straight-through pull point. There are also LL, LR and T shapes for other directions.

A few of these — shrink, take-up, developed length, kick — are bending terms. If you want the actual bending math worked out, that is what bentright.com is for.

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