Adding Electrical Outlets: How To Wire An Outlet To An Existing One
Adding and Wiring New Outlets
All too often it becomes necessary to add a new electrical outlet and wire it into an existing circuit. No one wants extension cords snaking over the floor, and they are usually a fire hazard as well as being very attractive to small children.
Maybe you are changing the location of the TV, maybe you are installing an over-the-range microwave, or maybe you bought a new computer desk. Whatever the reason, there isn't a handy outlet for the equipment and you need to install a new outlet and wire it into the system.
This article will walk the homeowner through not only the mechanics of putting a new electrical outlet into the wall, but also running the wire from an existing outlet to the new location and wiring the new outlet into the existing circuit. Both the tools and materials will be discussed as well as the procedures and tips for accomplishing the work in the easiest manner.
While the task will take some work, often involving crawling through attics or crawl spaces, it is not particularly esoteric or difficult to understand.
Tools Necessary to Add and Wire a New Outlet
Most of the tools you will need for wiring the new outlet and for running the wire are, or should be, found in the homeowner's tool kit, but some are a little more specialized. Many also have options: several different tools might be used to do the job. Take a look at the list and decide what you already have, or can use, and what you might need to purchase.
- Drill. Some form of drill will be necessary, capable of drilling through about five inches of wood. A drill bit of about ¾" will do this. A spade bit is fine here. A second, smaller bit can be very useful, around 1/8 inch. A cordless drill is ideal. If your drill has a cord, you will need an extension cord as well.
- Saw. A square hole the size of an electrical box will need to be cut into the wall where the new outlet is to be installed. To cut the wall, you could use a razor knife (box cutter), a, or a jigsaw for paneling (or drywall). It will be very handy to have a metal-cutting blade for a jigsaw, or some other saw blade that will cut nails—even a plain hacksaw blade will do. jab saw for drywall
- Wire cutters. You will need a way to cut wire and strip insulation off it. are the preferred tool, but many tools will do. Wire strippersElectrician's diagonal wire cutters will be useful.
- Tape measure. You need a way to measure, because locating the hole to cut into the wall or the hole to be drilled must be done with some precision.
- Screwdriver. You will need a Phillips-tip screwdriver, and a flat blade can be handy as well.
- Pliers. A pair of needle-nose pliers will be very handy to have.
- Flashlight. You will be working in either an attic or crawl space where it is dark, and you will need some light to work by.
- Voltage detector. A non-contact voltage detector is always a very nice tool to have when doing electrical work. Although not strictly necessary, it is a wonderful addition to your toolbox and can protect you from many shock hazards.
Before rushing out to purchase all of these, please read through this article, see what will be necessary, and check your list off against what tools you already have. If the new outlet is in the right location compared to the existing one, for instance, it may not be necessary to cut nails or drill holes. It will be more difficult to cut two nails with a simple hacksaw blade rather than buying a new cordless sawzall, but it's also lots cheaper. Some of these tools are nice to have and use, but are not absolutely necessary and it doesn't always make sense to spend $50 for a new tool to save ten minutes of work (unless, of course, that is the only way to get that new tool passed by your spouse!).
Materials for Wiring the New Outlet
Materials will be minimal: two new plastic "old work" or "cut in" boxes, some wire, and a new outlet.
Boxes. One of the old work boxes needs to match the existing box. If the existing box has two outlets in it (four places to plug into), a "two-gang" box will be necessary. Most outlets are single, though, meaning they have just two places to plug into),and a single gang box will be necessary. The second box needs to be a single gang as well. Try not to buy very shallow boxes in either case. A 3-inch-deep box is far preferable to one that is only a couple of inches deep.
Wire. Before purchasing wire, locate the circuit breaker that feeds the existing outlet. It will have either a 15 or a 20 stamped on it; this refers to the amps available on that circuit. A 15-amp circuit breaker will require (with ground), while a 20 amp circuit breaker will need 14-2 NM (Romex) wire, also with a ground. To estimate how much wire you need, you will want to decide whether the new wire will be run overhead in the attic or below the floor in the crawl space. Measure how far it is from the existing to the new outlet and add enough to get to the attic or crawl space twice (once up from the existing outlet, once down to the new outlet). Add around 20% to that total for a final estimate; it always takes more wire than you think. NM wire is commonly sold in 25-, 50-, 100- and 250-foot rolls; choose the roll that is the next larger size from your estimate. 12-2 wire
Non-GFCI 15-Amp Outlet
New Outlet(s). Outlets are available in 15- or 20-amp capacity; choose one that matches the breaker on the circuit, just as you did for the wire. Various colors are available, the plug connectors can be square or semi-round, and new cover plates offer dozens of options for color, shape, size, and material. All but the ampacity are personal choices.
A note of caution, though, on the outlet itself. If the existing outlet does not accept a three-prong cord, the new outlet must be a GFCI type. The instructions further down will guide you through the installation, replacing the existing outlet with a GFCI and adding a new outlet. While GFCI outlets are considerably more expensive, don't skimp here. The National Electric Code requires that any outlet without a ground must be a GFCI, and for good reason: without a ground wire the shock hazard increases dramatically. The GFCI outlet is designed to eliminate that hazard.
15-Amp Compared to 20-Amp Outlet
Removing the Old Outlet and Box
Turn off the power! Please don't begin your work by getting a nasty shock - turn off the power to the existing outlet you will be working with. Tape the breaker off so that no one else will turn it back on. Make sure that you are working safely; test that the outlet is dead by either plugging a radio or lamp into it or test it with a voltmeter or non-contact voltage detector. Don't turn it back on until the job is complete; this author, an electrician by trade, has been shocked too many times from "temporarily" making the work safe by capping off wires, turning the power on "for just a minute" and forgetting to turn it back off. Don't let it happen to you!
You need to choose the existing outlet you will wire the new outlet into. The best choice of location is almost (but not quite) directly through the wall from an existing outlet. Next would be an outlet on the same or different interior wall: preferably one without insulation (it is much easier to get new wire through an empty wall than one filled with insulation).
With the power safely off, remove the cover plate on the old outlet and set it and the single screw that holds it aside for re-installation later. Remove the two screws holding the outlet to the box behind it.
The wires to the old outlet now to be need removed as well. Make careful note of which wire goes where; the black wire should go to the brass-colored screws, the white wire to the silver-colored screws and the wire bare of insulation (the ground) to the green ground screw. There may be other wires in the box that are spliced together with wire nuts or terminate on the outlet as well; take note of where each goes and mark them or draw a picture for future reference. The old outlet could have a red wire as well: if so, this article on wiring a half-hot outlet has more information on this specialty application.
A common practice in wiring houses is to plug the wires into the back of the outlet instead of attaching them to the screws on the side. If you have this kind of outlet, there is a small slot on the back of the outlet where a very small screwdriver or other tool can be inserted; this will release the spring tension on the electrical wire and allow it to be pulled out of the hole. Alternatively, the wires can simply be cut off if they are long enough and the outlet is to be replaced.
Now, unless the new outlet is almost directly through the wall from the old outlet, you need to remove the old box. Most home boxes are fastened via two nails, just above and below the box, that are driven into the stud just to one side. The best way to remove the box from the wall is to reach just alongside with a metal cutting saw blade; a sawzall, jigsaw or even a bare hacksaw blade will do the trick. Cut the nails holding the box to the wall, but be aware that the wires entering the box are fastened to the same stud just above or below the box - make sure that you don't damage those wires, as such damage will likely require an electrician to re-wire that section of the house.
If you don't care to cut the nails holding the old box, you can take the box out in pieces, since you won't be re-using it. Use a pair of pliers, diagonal cutters, a hammer and screwdriver—whatever it takes—to tear apart and remove the plastic box. Just tear it into little pieces and get it out of the wall. Again: don't damage the wire! Bend the nails that used to hold as best you can; the objective is to make sure they don't interfere with the little arms on the new box that need to be attached to the wall.
As you draw the box out of the wall, the wire(s) in it will need to pass through the slots in the rear of the box and exit the box. Different boxes have different methods of holding those wires; take a good look at what you will have to do to let them exit the box. Loosen a screw, perhaps, or simply work them gently out of slots in the back.
Running the Wire for the New Outlet
Start cutting a hole for the new plastic box at the new location. Make sure not to cut too large a hole, because the "ears" on the box must remain outside the wall; if they fit through the hole the box will not clamp to the wall but simply fall inside it.
If the new location is through the wall from another existing outlet, be sure they don't exactly line up, because there is not enough room in the wall for two boxes to fit back to back. Move the new one a few inches to one side. This is absolutely the preferred location for a new outlet: through the wall and not absolutely back to back, but between the same pair of studs from an existing outlet. It makes running the wire a very easy task (you won't be crawling the attic after all!) and removal of the existing box probably won't be necessary.
If you can reach into the hole where the new box goes and touch the existing box, you can skip all the hard work of running new wire through the attic; simply take one end of the new wire, reach inside the wall ,and push it into the old box alongside the other wires. Push in about a foot of wire; you will cut off to a more reasonable length when wiring the outlet. Cut the other end off a foot outside the wall, leaving a good sized loop inside the wall to go up and back down into the top of the new box.
If the two boxes aren't so conveniently located, however, it is time to begin pulling wire between the two outlets. You are strongly advised to have a helper for this operation. A ¾" hole needs to be drilled, either up from the crawl space or down from the attic, into the center of the wall directly above or below the new outlet location. Begin by locating the wall as nearly as possible; drill a very small hole through the floor or ceiling right at the edge of the wall and in line with the new outlet location. Push a stiff wire (like a straightened clothes hanger) through it, so that the wire is visible in the crawl space or attic. If necessary, remove a section of baseboard or shoe molding on the floor, so that when it is replaced the small hole will be covered. Be aware that a spinning drill bit can and will "grab" carpet and unravel it; take extreme care here. A very small hole in a ceiling can be covered with toothpaste to repair it.
With your stiff wire poking into the crawl space, carefully orient yourself in the crawl space. To determine where the wall is, measure 2½ inches over and drill a small hole up into the wall; if the hole does not come through the floor into the living area you are inside the wall. If your hole went into the wall, replace the small drill bit with a ¾" bit and drill again in the same place. The procedure is the same if you are working in the attic. From the attic you should be able to see the top of the wall; the 2X4 running along the top of the wall is generally visible under the attic insulation. Either way, repeat the procedure at the existing outlet location.
Push one end of the new wire into the hole until it can be reached from the outlet location, and pull about a foot of wire out of the wall at that point. String the wire across to the next hole and estimate how much more wire will be needed to get it through the wall and pulled out. Cut off the length needed and push it into the drilled hole until it can be reached. Do not short what you need; far better to waste an extra five feet of electrical wire here than to waste all that you have strung across the house because you cut it short.
Staple the wire to convenient rafters or floor joists every 4 feet or so with staples made for NM cable. These staples do not use a staple gun, but are hammered in. Do not pinch the wire; drive the staples just far enough to hold the wire fairly firmly.
If the wall has insulation it will be virtually impossible to push the wire down from the attic, although you can probably push it up from the crawl space far enough to reach in the outlet hole and find it. A long (10 foot) piece of stiff wire or an electrician's "fish tape" can be invaluable as it is stiff enough to penetrate the insulation with a little effort and several tries. With the stiff wire through the wall from the attic to the outlet location, tie or tape the electrical wire to it and, using a helper, pull it down into the room. This procedure will take some time and most likely several tries, but it does work. It is also about the only way to get that electrical wire through an insulated wall without tearing the entire wall apart.
Wiring the New Outlet
Carefully score the soft outer sheath on the new wire about 6 inches from the end and pull the sheath just enough so that it tears and comes apart at the score. Try not to pull it off; just make sure that it will come off when you try, although it is not the end of the world if you do pull it off. Take a great deal of care not to cut into the individual wire insulation as this will ruin the wire.
Push the cable into the slots at the back of the box so that the uncut sheath is just inside the box. At the existing location, push all the wires there into the box in the same way; the sheath is obviously already gone so cutting it isn't necessary. Work the box into the wall and turn the screws to clamp it onto the wall.
The existing outlet may well have three or even more cables in the box that must be spliced together. Cut 6" pieces of additional black, white, and ground wire (remember that uninsulated wire in the cable is the ground wire) and strip one end. Remove the sheath from the new wire and any paper wrapping on the wire. Strip the end of each wire about ½" (there is a strip gauge on the back of the outlet). Splice all ground wires together, with that 6" piece you cut added in, using a wire nut. Holding the nut in one hand, pull firmly on each individual wire to make sure it is held well—better that a loose connection come out of the nut now than later. Repeat for the black wires and repeat again for the white wires. Fold the wires and wire nuts back neatly back into the box; this is where a deeper box is very nice as it gives more room for all the wires.
The ground wire is to be terminated on the outlet on the green screw, the black wire on a brass-colored screw (same side as the smaller of the slots to plug things into), and the white wire on a silver-colored screw. Terminations can be made by bending a loop in the stripped wire, hooking it around the termination screw, and tightening the screw. Alternatively, most 15-amp outlets and some 20-amp outlets have the hole in the back of the outlet where the wire can be simply pushed into; a spring affair there grabs it and prevents it from falling out.
Again folding the wires as you do, push the outlet into the box and attach it with the two screws provided. Install a new cover plate. Repeat the entire process for the new outlet as well.
No Ground on the Existing Outlet?
If there is no ground wire in the old, existing box, the outlet should be replaced with a GFCI type. If it is not, the new outlet must be a GFCI so you might as well replace the old outlet too, and have two protected outlets instead of just one.
Splice all the existing wires together just as instructed above, but do not include the new black or white wires you have just installed. The 6-inch "pigtails" you added to the splices will terminate on the "line" terminals of the GFCI outlet; this is marked on the back of the outlet and there is usually a piece of tape covering the "load" terminals.
The new wire is terminated on the "load" terminals of the GFCI outlet. Install the GFCI outlet into the box, along with its cover plate. The new outlet is wired normally, just as indicated in the previous section. There will be stickers in the box with the GFCI outlet indicating that the new outlet you have wired in is GFCI protected and that it has no ground. These need to be attached to that new outlet. Remember, though, that if the new outlet suddenly goes dead, you need to check the GFCI and see if it has been tripped.
Congratulations! You now understand how to add a new outlet, pull the wire for it and wire the outlet into an existing circuit. You also have a brand new outlet right where you need it!
GFCI Outlets Can Be Added
© 2012 Dan Harmon
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