How to Wire a Switch Box
An electrician walks you through step-by-step on how to wire a switch box.
Part of my job as a professional electrician is keeping my work neat and organized. A tidy work box makes it easier to install lights, switches, and outlets, and it helps future electricians to see what’s going on inside the box. Inspectors look for tidiness, too, because neat wiring makes short circuits and arcing less likely.
For me, part of being organized is maintaining some conventions with regard to how I run the cables into a switch box. When possible, I run the cable that’s feeding power into the box through a bottom knockout. Cables going to lights or receptacles down line go through knockouts in the top. If there’s an exterior light and an interior light in the same switch box (a common scenario at exterior doors), the cable closer to the door goes to the outside light; a cable farther from the door feeds the interior light.
Nothing in the code says you have to run specific cables through specific knockouts, and never assume that somebody else’s wiring follows your conventions. Using your own conventions is simply a way to know what wires go where when you’re looking at your own work, which is handy when you have to make changes or troubleshoot down the road.
Finally, always check with a voltage tester to make sure power is off to each switch (see “Make Sure the Power Is Off,” FHB #196). Some boxes contain more than one circuit.
Online Extra: Watch the companion video series
Step by Step
9. Fold the wires inside. Each single-pole switch will have a pair (line and load) of black wires. Near exterior doors, put the black wire feeding outdoor light fixtures closest to the door. Carefully fold the wires into the box without tangling them. Push the wires to the back of the box so that they’re not damaged during drywalling. When it’s time to install the switches, pull out the black and ground wires, and connect them to their respective switch terminals.
Tools of the Trade
From Fine Homebuilding #228
Cable stripper with insulation cutter
Side-cutting pliers with crimping jaw