Pick where power enters, then flip the switch on the diagram to see exactly which wires carry power. Every setup below is checked by a circuit simulator, not just drawn.
Tap a switch, button or GFCI on the diagram. Glowing wires are carrying power right now. On a small screen, scroll the diagram sideways.
Black: hot
White: neutral
Red: hot / traveler
White + black tape: hot
Bare copper: ground
Wire nut
Glow: carrying power now
The two brass screws on a standard single-pole switch are interchangeable. Only the green screw is special.
Step 3 of 3
Wire it box by box
Safety first. Turn off the breaker and confirm the power is off with a non-contact voltage tester before touching any wire. Follow your local electrical code; some areas require a licensed electrician or a permit. If you find aluminum wiring, cloth-covered wiring, scorched insulation or more than one circuit in a box, stop and call an electrician.
Switch box
Light box
Guide
How a single-pole switch works
A single-pole switch interrupts the hot wire going to a light. It has two brass screws and a green ground screw. The incoming hot goes to one brass screw and the wire to the light goes to the other. Neutral (white) wires never connect to a standard switch: they are spliced together in the back of the box and continue to the light.
Which setup do you have?
Two cables in the switch box with a bundle of white wires: power at the switch.
A 14/3 cable (black, red, white) with a capped white wire: power at the light with a modern switch loop.
One cable with its white wire on the switch: an old 2-wire switch loop. That white wire is a hot, not a neutral.
Wire size
Match the existing wire. 14 AWG copper belongs on a 15 A breaker, and 12 AWG on a 20 A breaker. Never connect 14 AWG wire to a 20 A circuit.
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Frequently asked questions
Does it matter which screw the black wire goes on?
Not on a standard single-pole switch: the two brass screws are interchangeable. Smart switches and some dimmers are different and label their LINE and LOAD wires.
Why is a white wire connected to my light switch?
It is an old-style switch loop. Power runs to the light first, and the white wire brings constant hot down to the switch. It should be wrapped in black tape, and it is not a neutral.
Can I use the push-in holes on the back of a switch?
Screw terminals are more reliable. Push-in (backstab) holes usually only accept 14 AWG wire and are a common cause of loose connections.
How do I know if my switch box has a neutral?
Look for white wires bundled together in the back of the box and not connected to the switch. Use our neutral wire checker.
