An Electrician Explains How to Wire a Switched (Half-Hot) Outlet
What Is a Half-Hot Outlet?
Most of the outlets in your home are of the duplex variety—that is, you can plug two devices into them at one time. A half-hot (or switched) outlet is a duplex outlet that has one half permanently "on" or ready to provide electricity while the other half can be turned off and an via an ordinary wall switch.
While the entire duplex outlet could be turned on via a wall switch, only one of the two plug-ins is usually switched; this leaves the other half permanently powered for other uses.
This kind of outlet is quite common in modern construction. If you plug a lamp into the switched side, you can turn the light off and on via the wall switch. Half-hot outlets are most frequently found in living rooms, but can be put into any location.
Learning how to wire a switched outlet is not difficult. It is similar to wiring a regular light fixture. Find out how below.
Note: If you are installing a new outlet or pulling additional wire to an existing one, please check this article about adding an outlet; it contains tips and suggestions for pulling wire to both new and existing outlets.
A half-hot (or switched) outlet is a double outlet that has one half permanently on (ready to provide electricity) while the other half can be turned on and off via an ordinary wall switch.
Preparing the Switched Outlet for Wiring
- If you are modifying an existing outlet, it is almost certain that the old outlet won't need to be replaced, although if it is more than a few years old it should probably be replaced anyway.
- Either the square, Decora style switch or the more common semi-round type may be used as a half-hot outlet. You may not, however, use a GFI outlet (it is not possible to modify one so that only half of it is switched), but the entire outlet could be switched.
- If you are purchasing a new outlet, make sure that you match the outlet's ampacity (amps) to that provided by the circuit breaker for that circuit; a 15 amp breaker requires a 15 amp outlet and a 20 amp breaker should have a 20 amp outlet.
- After you've taken off the faceplate, on the side of the outlet, there is a small tab connecting the two brass screw-plates together. This tab allows one wire to be used to power both halves. This tab has a slot in it so a small screwdriver can be inserted to break it off. To modify the outlet for use as half-hot, use a screwdriver or a pair of needle-nose pliers to twist and break that small connecting tab. Break only the tab on the side with the brass-colored screws; the one connecting the two silver screws needs to remain intact. See photos for details.
- With the tab broken, the outlet is ready for use.
Turn the Power Off First!
Breaking the Tab for a Half-Hot Outlet
What Kind of Wiring Do You Need for a Switched Outlet?
- The National Electric Code requires that all lighting switch boxes contain a "neutral", which is an electrical term for a grounded conductor (not to be confused with a ground wire). In your outlet, it is the white wire that terminates on the outlet. Whether or not a half-hot outlet is for lighting is debatable, but you must still have a neutral in the switch box.
- There are two possibilities for the location of the incoming power: either in the outlet box or in the switch box. Either way, you will need what is called "3-wire cable" (black, red, white, and green OR metal all sheathed together: yes I know that makes 4 wires, but that's what it's called!) to connect the two boxes.
- Check the breaker that turns the circuit off; if it is a 20 amp breaker or fuse, you will need 12-3 wire (12 gauge, 3-wire, plus ground). If it is a 15 amp breaker, you will need either that same 12-3 or 14-3 wire (14 gauge, 3-wire, plus ground). You will find that the 14 gauge wire is cheaper and a little easier to handle.
- The Romex (NMC) wire you will be using is generally available in 25', 50', 100', and 250' rolls.
- Make sure you purchase enough wire, as the job will usually require more than you think. To be safe, add about 20% to your best estimate.
There Are 4 Wires in a Romex 3-Wire Cable! What Do the Colors of the Wires Indicate?
- White: the neutral. See warning below!
- Green or bare copper without insulation: the ground wire.
- Red: hot.
- Black: hot.
These will all be cabled together in a sheath. Romex wire is usually used in houses.
The White Wire: A Word of Caution
Switch boxes in older homes usually used the white wire as a power wire, not a neutral. So when the white wires in a switch box are spliced together, any that go to a switch should be ignored and left right where they are.
Do not splice those white wires already on a switch to any other white wires, and especially not to the new white wire that is a part of your new 3-wire cable.
It wasn't until 2011 that the National Electric Code ruled that a white wire being used as a neutral was required in the switch box. Prior to that, it was acceptable to use the white as the switched "hot" wire, although a conscientious electrician would color it to something else (using magic marker, black tape, etc.).
So if you are replacing an older, existing switched outlet, and if it has 2-wire cable between the outlet and the switch, then the white wire is being used as either a permanent hot or as the switched power and IS NOT neutral. Care must be taken to keep it separate from other white wires.
How to Wire a Half-Hot Switched Outlet
Before you do anything, TURN OFF THE POWER! A non-contact voltage detector can be invaluable here for detecting power through the insulation of the wire. Make sure that the power is off. A nasty shock is the least desirable outcome of your project.
As noted above, there are two possibilities for the incoming power: either in the switch box or in the outlet box. These will be treated separately below.
As a professional electrician, I always keep one of these testers in my pocket and a backup in my toolbox. Safety is paramount when working with electricity and this tester is a great place to start.
How to Wire a Switched Half-Hot Outlet That Gets Its Power From the Outlet Box
This is the preferred method of wiring a half-hot switched outlet, because if the power is coming from the switch, it is most likely a lighting circuit that is intended to operate lights, not outlets. Yes, you will probably have a lamp plugged in, but the other half of the outlet could run anything. It is best if this outlet is on a circuit intended for outlets. So if there is an option, use the power already in the outlet box.
- In order for the outlet box to work, it must already contain one or more cables made up of black, white, and green/bare ground wires all cabled together. In order to add the switch, you will be adding a Romex 3-wire cable to the box.
- Cut a short 6" piece of cable and remove the outer sheath. This gives you four different colored wires to splice in with the matching wires in the box. These 6" pieces (or "pigtails") will attach to the outlet. Strip off the last 1/2 inch of colored plastic coating on each end of each wire.
- Next, you will splice all of the grounds (green or bare wires) together with that additional green/bare 6" piece. Splicing is when you twist all the bare metal wires together so that they're in contact. You should pull them into a neat bundle with the stripped ends all together, twist them into one, put a plastic twist-on wire nut over them, and screw it down tightly as if it were a bolt head. Hold the wire nut in one hand and tug firmly on each individual wire to make sure it doesn't come loose. Pull fairly hard to test the connection; better that it comes apart now than later.
- Do the same with all the black wires (and the additional 6" piece of black wire you cut in step 2).
- Splice all the white wires together, again with the 6" additional white piece.
- The loose end of the 6" ground wire will terminate on the green ground screw of the outlet. The black 6" wire will terminate on one of the brass-colored screws, the red one on the other brass screw, and the white one on the silver-colored screw. It is most common to put the red wire on the bottom screw, since that will make the top plug-in "hot" at all times and will be a little easier to plug things into it.
- To terminate (affix or connect) the wires, bend a hook in the wire, loop it around the screw in a clockwise direction, and tighten the screw firmly. If the wire tends to come out from under the screw while tightening, you have looped it the wrong direction. Alternatively, many home grade outlets have small holes in the rear of the outlet where the wires can be simply pushed in instead of wrapping around the screw.
- At the switch, put a wire nut on the white wire, capping it off, and tuck it into the back of the box. It will not be used. Splice all ground wires in the box together (if multiple switches or other wires are in the box), again with an additional 6" green/bare piece to go to the switch. Terminate the ground wire on the green ground screw of the switch.
- Terminate the black wire from your new 3-wire cable on one of the screws on the side of the switch, and the red on the other. It doesn't matter which one goes where.
How to Splice Electrical Wire (the Electrical Tape Is Optional):
How to Wire a Switched Outlet That Gets Its Power From the Switch Box
- First, locate the cable that is bringing power into the box. You will see at least one 2-wire cable and the added Romex 3-wire cable that you're connecting to the outlet. If this is a multiple switch location (with more than one switch in the box), there will be other cables, too. The power cable will almost certainly have multiple short wires spliced to it, one wire for each switch.
- Cut a short 6" piece of cable and remove the outer sheath. This gives you four different colored wires to splice in with the matching wires in the box. Strip off the last 1/2 inch of colored plastic coating on each end of each of these 6" pieces (or "pigtails").
- Splice all the ground wires together, with an extra 6" pigtail piece of ground wire added.
- Splice the black power wire and the new black wire from the new 3-wire cable together, with a black pigtail added.
- Splice all neutral wires together, but without a pigtail. The black pigtail will terminate on one of the switch screws and the red wire on the other.
- The ground pigtail goes to the green ground screw on the switch.
- At the outlet box, if there are cables other than the new 3-wire you are using to connect the outlet to the switch, splice them together by color: Black wires together, white wires together, and all ground wires (including the one in the 3-wire cable) together, all with like-colored pigtails.
- At the outlet box, neither the existing black or white wires will be used for the outlet, but may be powering other outlets on the circuit if this is not a new outlet.
- The ground wire goes to the green ground screw on the outlet, the white wire goes to a silver screw, the black wire to one of the brass screws, and the red wire to the other brass screw. All of these wires (except for the ground wire if there are other cables in the box) come only from the new 3-wire cable.
Finishing the Job
- After wiring the outlet and switch, fold the wires back into the boxes as neatly as possible and mount the outlet and switch into the box.
- Attach the cover plates.
- If you have any trouble here, additional instructions on changing light switches or installing electrical outlets can be found in these links. You'll also find tips on removing existing outlets and switches in these articles.
- Turn the breaker back on and check operation. One half of the outlet should be on at all times, with the wall switch controlling the other half.
© 2012 Dan Harmon