Will a light switch work with no ground wire? Usually. Here’s why you normally want a ground, and what your options are for a light switch without ground.
For a normal light switch, the ground is a safety feature, not necessary for operation. You can leave that screw unconnected if you don’t have a ground wire, or if you have the wire but no screw on the switch, you can ground the switch another way.
The purpose of a ground wire on a light switch
Some occupancy-sensing automatic light switches need a ground wire, but traditional toggle-type switches do not. They can do their job just fine with or without it.
With an ordinary toggle switch like the ones on the right, the ground wire is strictly a safety feature. If you flip a switch with wet hands, having a ground connection reduces the chance of you shocking yourself. It doesn’t guarantee it, but it does reduce the chances. That’s why a light switch without ground isn’t the best idea, but it can still work.
Going without a ground wire
If the light switch has a screw for a bare ground wire but your electrical box doesn’t have one, you’re OK just leaving that screw empty and connecting your other wires to the hot screws.
In many cases, especially in older houses with metal boxes, the metal box may be grounded even if you don’t have the wire. When you screw the light switch in, it will make contact with the box, and as long as the box is grounded, it will pick up ground that way. If the box isn’t grounded, the switch will still work. Just be sure to remember your mother telling you to dry your hands before turning off the lights.
What about the persistent rumor that if you open an outlet and find no ground, you have to ground it? I have good news. The rumor isn’t true. You can replace an older light switch with a new one without turning a 75-cent project into a $750 project.
Connecting a ground wire to a switch without a ground screw
What if you have a really old light switch that doesn’t have a ground screw, but you do have a ground wire? It would be a good idea to just replace the switch with a newer one that does. A modern residential light switch costs less than $1.
If you can’t, connect the ground wire to the electrical box instead, assuming it’s a metal electrical box. If you can’t do that, or if your box is plastic, wrap one turn of the ground wire around one of the screws that secures the switch to the box. As long as the switch’s bare metal frame makes metal-to-metal contact with ground somehow, your light switch is grounded for safety. It’s not the most elegant solution and it’s probably not code, but it’s better than no ground at all.