Breaker Off / Light switches
Light switches
Pick the box that matches yours. The deciding question is where the power comes in: at the switch (two cables in the switch box) or at the light (one cable at the switch).
- 01Light switch wiring, power at the switch Two cables in the switch box (one from the panel, one up to the light) and one cable in the light box.
- 03Light switch wiring, power at the light One cable in the switch box with a black and a white wire (the white should have black tape on it), and two cables in the light box.
- 05Switch loop with a neutral, power at the light One 3-wire cable in the switch box (black, red, white and bare), and two cables in the light box.
- 07Dimmer switch wiring, power at the switch Two cables in the switch box (one from the panel, one up to the light) and one cable in the light box.
- 09Dimmer switch wiring, power at the light One cable in the switch box with a black and a white wire (the white should have black tape on it), and two cables in the light box.
- 11Smart switch wiring with a neutral wire Two cables in the switch box (one from the panel, one up to the light) and one cable in the light box.
- 13Smart switch wiring with no neutral wire One cable in the switch box with a black and a white wire (the white should have black tape on it), and two cables in the light box.
- 15Smart switch on a switch loop with a neutral One 3-wire cable in the switch box (black, red, white and bare), and two cables in the light box.
Questions people ask at the box
Which wire is line on a light switch?
On an ordinary single-pole switch either brass screw can take either wire. Dimmers with two black leads are the same. Smart switches mark LINE and LOAD and only work one way round: with the breaker on, the wire your tester lights on is LINE. Turn the breaker off again before you connect anything.
Why is there a white wire on my switch?
That is a switch loop: power reaches the light first and the white wire carries it down to the switch. It is hot, not neutral, and should be wrapped with black tape at both ends.
Do I need a neutral for a smart switch?
Most smart switches need one. Since 2011 the National Electrical Code (404.2(C)) has required a neutral at most new switch locations, so newer homes usually have a bundle of whites in the back of the box. Older switch loops do not, and need a smart switch made for no-neutral boxes.
Can I replace a light switch myself?
Many places let homeowners replace a switch in their own home; some require a permit or a licensed electrician. Check with your local building department, and always turn the breaker off and test first.