Home Wiring Guide - 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 of it permanently "hot" while the other half is switched via an ordinary wall switch. Learning how to wire a switched outlet is not difficult; it is similar to wiring a regular light fixture.
This method of wiring outlets is quite common in modern construction; a switched outlet is provided to plug a lamp into rather than providing a ceiling light fixture. They are most frequently found in living rooms, but can be put into any location where there is an outlet.
While the entire duplex outlet could be switched, only one of the two places to plug a device into is usually switched; this leaves the other half permanently powered for other uses. 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.
Preparing The Switched Outlet For Wiring
Either the square, "Decora" style or the more common semi-round may be used as a half hot outlet. You may not, however, use a GFI outlet as a half hot, although the entire outlet could be switched. It is not possible to modify the GFI so that only half of it is switched.
On the side of the outlet there is a small plate connecting the two brass screws where the wires go. This plate allows one wire to be used to power up both halves. To modify the outlet for use as a half hot, use a pair of needle nose pliers to twist and break that small plate. Break only the plate on the side with the brass colored screws; the plate connecting the two silver colored screws needs to remain intact. The pictures to the right show the detail for this.
With the plate broken, the outlet is ready for use. If you are modifying an existing installation, it is almost certain that the old outlet will serve, although if it is more than a few years old it should probably be replaced anyway. If you are purchasing a new outlet, make sure that you match the outlet 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.
Breaking the Tab for a Half Hot Outlet
What Kind Of Wire?
The National Electric Code requires that all lighting switch boxes contain a neutral. Whether or not a half hot outlet is for lighting could be up for discussion; it is probably wise to make arrangements to have that neutral in the switch box. A word of caution, however; if you are replacing an existing switched outlet, it most likely has a 2 wire cable between the outlet and the switch. In this case the white wire is being used as either a permanent hot or as the switched power and is not a neutral wire. It should be colored (magic marker, tape, etc) but often is not, and care must be taken to keep it separate from other white wires.
There are two possibilities for the incoming power; either in the outlet box or in the switch box. Either way, you will need a 3 wire cable to connect the two boxes. This cable will have a black, white, red and a bare, ground, wire in it.
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.
Make sure you purchase enough wire - it will usually take more than you think. A good measure is to add about 20% to your best estimate. The Romex (NMC) wire you will be using is generally available in 25', 50', 100' and 250' rolls.
Wiring The Half Hot Switched Outlet
Before any work is done TURN OFF THE POWER! A non contact voltage detector can be invaluable here; it can detect power through the insulation of the wire. Make sure that the power is off - a nasty shock is not the most 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.
Voltage Testers from Amazon
Power in The Outlet Box
This is the preferred method of wiring a half hot switched outlet. If power is coming from the switch it is most likely a lighting circuit, intended to operate lights, not outlets. Yes, you will probably have a lamp plugged in, and yes that is a light, but the other half of the outlet could run anything. 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.
Whether you are installing a completely new outlet or replacing an existing one, the box will contain one or more 2 wire cables with a black, white and ground in addition to the 3 wire cable you have added. Cut a short, 6" piece of additional cable and remove the outer sheath. Splice all of the grounds together, with an additional 6" piece to go to the outlet. Splice all the black wires together with an additional 6" piece of black wire. Splice all the white wires together, again with a 6" additional piece.
Splicing is accomplished by stripping about ½" of insulation from each wire and twisting a wire nut onto the bundle of wires, fastening them all together. Holding the wire nut in one hand, tug firmly on each individual wire to make sure it isn't loose in the wire nut. Pull fairly hard to test the wire nut; better that it come apart now than later.
The ground wire will terminate on the green ground screw of the outlet. The black wire will terminate on one of the brass colored screws, the red wire on the other brass screw and the white wire on the silver colored screw. Most common is to put the red wire on the bottom screw; that will leave the top plug in "hot" at all times and be a little easier to plug things into it. To terminate the wires, strip about ½" of insulation and 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 a "pigtail" 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.
Wiring Diagrams for a Half Hot Switched Outlet
Power In The Switch Box
There will again be at least one 2 wire cable plus the new 3 wire cable you have installed. If this is a multiple switch location (more than one switch in one box) there will be other cables, and the cable that is bringing power into the box must be located. This cable will almost certainly have multiple short wires spliced to it, one wire for each switch.
Splice all ground wires together, with a pigtail added. Splice the black power wire and the 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 have added, splice them together by color. Black wires together, white wires together and all ground wires (including the one in the 3 wire cable) together with a pigtail. 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.
Wiring Diagram For Power In The Switch Box
Finishing The Job
With the outlet and switch wired, fold the wires back into the boxes as neatly as possible and mount the outlet and switch into the box. Attach the cover plate. If you have any trouble here, additional instructions on changing light switches or installing electrical outlets in general can be found in these links. Tips on removing existing outlets and switches are also in those 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
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