Adding a Switch to an Electrical Outlet
Why Add A Switch To An Electrical Outlet?
There are two main reasons that most people would add a switch to an electrical outlet; to either switch that outlet (or half of it anyway) or to add a light somewhere. This article will assume that the first is the reason you are reading this; you want to switch that outlet on and off.
Switched outlets are very common in modern construction of new homes - it is much cheaper for the builder to add a switch than it is to add a switch plus a ceiling electrical box plus a light fixture. The new owner is expected to use a lamp to light the room rather than a ceiling light.
Switching an outlet yourself will do that as well; allow the homeowner to switch a lamp from a convenient location rather than unplugging it or switching it off at the lamp. It is also possible to plug such things as TV sets, computer or other "vampire" appliances into that switched outlet, saving electricity over time by turning those appliances completely off. Not a bad idea, plus it protects sensitive electronics from voltage spikes due to lightning or utility problems.
Materials For Adding A Switch
The first consideration in gathering materials is that you must know the size of the circuit breaker or fuse protecting the outlet. Plug in a lamp or radio and turn off breakers or remove fuses until you find the one that shuts off the power to the outlet. It will be marked with the ampacity of the circuit, either a 15 amp or 20 amp circuit. That number will determine the rating of both the switch and the wire to be used. The switch must never be rated for less than the circuit; a 20 amp circuit must have a 20 amp switch while a 15 amp circuit may use either a 15 or 20 amp switch.
Similarly, a 20 amp circuit requires #12 wire while a 15 amp circuit may use either #14 or #12 wire (although #14 is cheaper and easier to use). You will need 3 conductor wire, typically labeled either 14/3 or 12/3 depending on size; it will have 3 insulated wires plus a bare grounding wire. Make sure that you have enough wire to reach to either the attic or crawl space, across to the wall where the new switch is to be located and down to the switch. Measure carefully and add ten feet or so; better to have too much than too little.
You will need an "old work" box for the switch and almost certainly another one to replace the one the outlet is in, along with a small handful of wire staples to fasten the wire to rafters or joists with. A few wire nuts will be useful, and you will need a cover plate for the new switch.
Before any work is done, make absolutely sure the power is turned OFF. One of the best methods is to use a non contact voltage detectors such as is shown in this photo. Inexpensive and easy to use, these testers are a must for anyone doing electrical work.
Running The Wire For The New Switch
This is the most labor intensive part of the job and will require the most work. Wire must be run from the outlet to the new switch and that isn't always easy. Holes must be drilled inside the stud bay, either through the floor into the crawl space or through the top plate into the attic, at both the existing outlet and the new switch.
Wire must then be fed through the hole, across the space and into the wall with the switch. It must then be inserted in the respective electrical boxes, along with any existing wire.
It is beyond the scope of this short article to detail how this is to be done, but a second article on adding an outlet to an existing outlet does. If you're having any trouble, please reference that article on how to run wire between an existing outlet and a new outlet or switch.
Wiring The New Switch
The existing outlet will have a black and white wires attached to it, and probably a third, ground, wire that is either green in color or bare of any insulation. Remove the black wire from the outlet and, using a wire nut, splice it to the black wire in the new cable you have run.
If the existing white wire is spliced to other white wires, add the new white wire to the wire nut. If it is not, cut a short, 6" piece of white wire, remove the white wire from the outlet and splice the short piece, the existing white wire and the new white wire all together. Terminate the short piece back to where the white wire came from. Do the same for the ground wire - that wire that is either green or bare of insulation.
If the outlet is to be completely switched (both plug in spots) terminate the red wire in the new cable to where the black wire used to be. If the outlet is to be a half hot outlet, half of it permanently powered and half of it switched, break the small tab between the two brass colored screws off. Do not break the tab between the silver colored screws, just the one between brass screws. A small 6" piece of wire must be added to the splice of the two black wires and terminated on one of the brass screws (normally the bottom one). The red wire in the new cable is terminated on the upper brass screw. Please note that one of these two screws is where the original black wire used to be terminated - the small tab between the screws used to power both plug in spaces from one screw, but a wire to each one is now required. To terminate a wire onto a screw, strip the insulation from the last ½" of wire and bend it into a loop. Wrap it around the screw in a clockwise direction and tighten the screw.
The new switch is wired by attaching the black wire to one screw, the red to a second screw and the ground wire to the ground screw located near one end of the switch. While it doesn't make any difference which brass screw is chosen for which colored wire, make sure that the ground screw attaches to the ground screw.
Install the switch into the new electrical box and fit the cover plate to it with the two small screws that came with the cover plate. You're finished!
Questions & Answers
I ran a new wire from a light switch to an overhead light. The area overhead above the ceiling joist is very close together. Should the wires be stapled to the ceiling joist? The wire is going across the top of the joist.
© 2012 Dan Harmon