Dan has been a licensed journey-level electrician for 17 years. He has extensive experience in most areas of the electrical trade.
Buying and Installing Electrical Outlets
Installing an electrical outlet, even a GFCI outlet, is not a difficult task—the hardest part may be deciding which one to buy! There are literally dozens and dozens of possibilities, but only one or two are correct for any given application.
- This article will walk the homeowner through not only how to install electrical outlets, but how to purchase, as well.
- It is not intended to cover all the possibilities of receptacles to be installed and wired, only the normal, common types of outlets found in residential homes.
- The duplex outlet (which has two spots to plug a cord into) in both 15 amp and 20 amp ratings, as well as the GFCI (or GFI as it is often called) outlets, will be discussed.
- Simplex outlets (one spot to plug into) are wired the same as the duplex outlet.
Choosing a New Plug-In or Receptacle Outlet
While there are many choices of new outlets, there will only be one or two that are a good choice for your given location. Primary considerations include the following:
- Amperage. When installing a new electrical outlet, the amperage must be considered. A 15 amp circuit should have only a 15 amp outlet on it. A 15 amp outlet may be placed on a 20 amp circuit as well, but 20 amp appliances will not plug into it and the value of the greater circuit ampacity is, to a large degree, lost. Never, never install a 20 amp outlet onto a 15 amp circuit—20 amp appliances will trip the circuit breaker or fuse and could cause fires. A good way to check the circuit ampacity is to inspect existing outlets (the picture below indicates the difference in outlets), but a better method is to look at the circuit breaker or fuse that is feeding that circuit. Each will have the ampacity of the circuit stamped on it.
- GFCI outlet. These are more square-looking outlets that have two small buttons on the front to test and reset the shock protection they offer. Any outlet installed within 6 feet of a water outlet such as a sink or tub must be GFCI protected, as must outlets installed in garages, outdoors or other "non-living" spaces. A possibility to look out for here is that the outlet being changed is protected by a GFCI outlet "upline" from it. If a different GFCI outlet that trips off also shuts off the outlet being replaced it is already protected and a normal outlet may be installed. GFCI outlets cost considerably more, but how much is your safety or life worth? Use one if necessary, and always replace a GFCI outlet with the same thing. In addition, any outlet being replaced that does not have a ground wire (either bare or green) connected to it must be replaced with the GFCI variety with a sticker attached indicating that there is no ground wire (stickers come with the new outlet).
- Color. A purely personal choice, of course, and not a requirement. There are many colors commonly available including ivory, white, gray and black, but more are available by special order. Cover plates are also available to match the outlet color.
- Style. Both regular and "decora" styles are commonly available. The decora designation refers to switches and receptacles of the square appearance (a GFCI looks similar, with buttons added to test and reset it).
Electrical Outlets (Receptacles)
How to Remove an Old Electrical Outlet That Is Being Replaced
- If the task involves replacing an old outlet, that outlet must be removed first. Turn the power off before doing any work! A loud radio plugged into the outlet in question may help if the circuit breakers are not labeled properly.
- After turning the power off, check the outlet again, preferably with a plug tester or noncontact voltage detector. Make sure it is off! Being shocked is no fun, but there is no reason to suffer that indignity if you are careful about removing power before working on it. The picture below shows an outlet pulled from a pegboard wall that is still powered on.
- Remove the cover plate and the two screws, top and bottom, that hold the outlet in place and gently pull the outlet out from the wall.
- If a voltage detector is available, now is a good time to check once more for the presence of voltage on the wires.
- If the outlet is switched, and particularly if a switch controls only half of it, make careful note of which wire goes where. Label them with a piece of tape or other method and make a drawing of which wire goes where.
- Also label the wires to any GFCI that has more than one each of white, black, and green wires attached to it. Wires to a GFCI outlet must go to the "line" and "load" terminals, so if there is more than one set of wires, label which set (white and black) is "line" and which is "load".
- Take note of whether or not the existing outlet has a ground wire (bare copper or with green insulation) connected to it. If not, and there is no ground wire in the box, a GFCI outlet must be installed (this is assuming that an "upline" existing GFCI outlet does not already protect it—as noted above, that should have already been checked for).
- If wires are connected to the screws on the side of the outlet, loosen the screws (they should not come completely out) and remove the wires. If the wires are plugged into the back of the outlet, there will be a small slot or hole next to the wire: Insert a small screwdriver or other tools into the hole and while pressing in pull the wire out of its hole. It may take a little pressure with the screwdriver to do this. If the wire can't be removed by this method, simply cut it off with wire cutters and strip about ½" of insulation so that once again the end of the wire is bare of insulation.
- Remove and discard the old outlet.
Removing the Old Outlet
Testers From Amazon
Shown is a non-contact voltage tester from Amazon. As a professional electrician one of these testers is in my pocket any time I'm on the job, with another backup tester in my toolbox. Safety is paramount when working with electricity and this tester is a great place to start.
How to Install and Wire a New Electrical Outlet
- If the old outlet was switched on just the top or bottom half, the new outlet must be prepared for that function as well. On the side of the outlet, between the two wiring screws, is a small tab connecting the two screws. The picture below shows such an arrangement, with a small screwdriver resting on the tab. Break the tab off so that the two screws are no longer connected. Normally, only the tab between the brass screws is broken off—the tab between white screws is left alone. Check the original outlet and prepare the new one the same way.
- Connect the wires to the new outlet. The ground wire (bare or insulated with a green color) goes to the green screw, usually near the bottom of the outlet. If by chance there is a ground wire in the box but it was never connected to the old outlet, it must now be connected. An additional 6" piece of wire may be necessary to connect between two or more ground wires already in the box and the outlet. If so, add it by removing the wire nut holding the two existing ground wires together, adding the new "pigtail" and replacing the wire nut. Bend a small hook in the stripped wire and wrap it around the screw in a clockwise direction. If wrapped in the wrong direction it may tend to come off when tightening the screw. Tighten the screw firmly.
- The white wires go to the white-colored screws, or can be plugged into the back of a 15 amp outlet. Make sure they are plugged into the holes nearest the white screws. Black or other colored wires go to the more brass-colored screws (or holes) on the other side. If you are looking at the front of the outlet, black wires go to the right side. If the outlet was switched on either the top or bottom the black wires still go to the same side, making sure that the labels previously applied to the wires go to the same place. If labels have come off, the worst that can happen is the switched part will reverse from top to bottom or vice versa, so don't worry too much about it.
Wiring the New Outlet
Wiring a GFCI Outlet
The backside of the GFCI outlet has two sets of screws or holes to use. One set is for the "line" side and one for the "load side."
Line side screws are for GFCI outlets that are stand-alone outlets; they do not protect any "downstream" outlets. If you are replacing an old outlet without a ground wire and have more than two white or two black wires in the box, these wires will have to be "pigtailed" to the new GFCI outlet.
Read More From Dengarden
- To do this, both white wires need to be connected together using a wire nut, along with a new 6" piece of white wire. All three white wires will be fastened together with the wire nut.
- The same thing must be done with the black wires.
- The new pigtails are now connected to the "line" side of the GFCI outlet with the white wires going to the white screws and the black wires going to the brass-colored screws.
- Short lengths of wire are usually available to home improvement stores such as Home Depot.
Alternatively, the new GFCI may be used to protect "downstream" outlets as well as itself; this is the preferred option.
- To accomplish this, a tester, preferably a noncontact voltage detector, will be necessary, as will some wire nuts.
- Separate all the wires in the box from each other if they aren't already separated and put a wire nut on each individual wire to cover any exposed copper wire.
- Turn on the power once more and check to see which wire is "hot"—that is, which wire is now powered. Mark that wire, being careful not to dislodge the wire nut; that wire will be the "line" side of the GFCI outlet.
- Turn the power back off and verify with the tester that it is off.
- Trace the marked, black, wire into the box to find which white wire goes with it. Most houses use wiring in cables that have one white and one black wire; you are looking for the white wire that is cabled with the marked black wire. That white wire is also the "line" side of the new GFCI and will be connected to the white screw marked "line" on the GFCI outlet. The marked black wire will be attached to the brass screw marked "line" as well.
- The remaining white and black wires are connected to the "load" end of the GFCI outlet (these screws are normally covered with a caution tape from the factory and such tape must be removed, but the outlet is also stamped with the words "line" and "load").
- Electrical code requires that all outlets now protected by the new GFCI be labeled as such; stickers should have come with the new outlet. If there is no ground in the box, all the outlets must also be labeled with a "no ground" sticker.
Wiring a GFCI Outlet
Complete the Job
Fold the wires neatly back into the box and push the electrical outlet into the box as well. The outlet is attached with two screws, one each at top and bottom - very occasionally the plastic boxes used in residential wiring will have the threads stripped out of the screw holes. Not to panic - a 1" long #8 sheet metal screw will work too, although it cannot be repeatedly removed and put back without again stripping out the hole.
Attach the cover plate and turn on the power. It is best to check the new outlet with an outlet tester - these are small inexpensive testers made just for testing to see if an outlet is wired correctly.
Congratulations: you have learned how to wire and install a new electrical outlet and done it yourself! Another home repair task completed with a minimum of fuss or bother.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Is a 20 amp breaker suppose to have 12/2 w gr?
Question: When I use a screwdriver to remove my metal outlet covers I feel a light shock, is this the ground wire doing its job?
Answer: It is the ground wire NOT doing it's job. You should not be able to feel any shock unless you touch the wires on the terminals. Never from a metal cover plate.
Question: What do I do when I have two blk wires and only one screw on the new outlet? I am replacing a 15 amp plug with a new 15 amp plug that has two USB ports. The old plug has a bare copper wire (ground) one white wire, and two black wires. Like the plugs you’ve shown, there are two screws on each side and a ground screw at the bottom of the plug. My new outlet has one screw on each side and a ground screw at the bottom. I’m not sure what to do with the two black wires or how to reduce them to one.
Answer: Using a wire nut, fasten the two black wires together, along with a third piece about 6" long. That "pigtail" can then go to the single terminal on the new outlet.
Question: The black wire is too short to connect to terminals on the new outlet. What can I do?
Answer: You will need another short (6") piece of additional wire, preferably black, and a wire nut. Make sure the wire is the proper size; if the outlet is on a 15 amp breaker it must be at least 14 gauge wire or larger; if it is a 20 amp breaker it must be at least a 12 gauge wire. If in doubt, purchase 12 gauge.
Strip 1/2" of insulation from the new wire and use the wire nut to splice it to the existing wire. That will produce enough to terminate it on the new outlet.
Question: I have an old receptacle has no tab. Two black and two white wires. I think the receptacle is in series and I should not remove the tab on the new one. Right?
Answer: Yes. If you are simply replacing the outlet, wire the new one exactly the same, without breaking the tab. Hopefully, there is a ground in the box that can be put on the new outlet, but if not the new one should be a GFCI outlet. If it is, both blacks need to be spliced together with a third, 6" piece added in; that short 6" piece goes to the "load" side of the GFCI. The white wires are treated the same, with an additional "pigtail" added to terminate on the new GFCI outlet. Do not replace an old, ungrounded outlet with a new one with a grounded outlet without having a ground wire to put on it.
Question: If one wire isn’t hooked up to the screw, can that be the reason I’m not getting any electricity downstairs in my room?
Answer: If there is a wire in the box that is stripped of insulation, and without a wire nut or other protection, it is very likely the cause.
Question: This question is about replacing plugs. The wire that goes into the hole behind/beside the screw connection to get it out, I tried pulling. I saw somewhere that a person said to use a screwdriver 'beside' - where beside? Or must you simply cut the wire as once it is inserted into the hole, it won't come out?
Answer: There is a small slot right next to the hole on the back of the outlet where the wire goes in. A tiny screwdriver can be pushed into the slot, which releases the spring holding the wire and the wire thus removed.
Question: We get electricity everywhere in the house besides downstairs, in my room and in the bathroom. Why is this?
Answer: My best guess is that a GFCI in a bathroom or somewhere (perhaps outside) has tripped. Very often, a single GFCI is used to protect multiple bathrooms or other locations, and will shut them all down when it trips.
Question: I have a 2 wire 15 amp receptacle with no ground wire. Why am I not getting 120 vac when all other outlets are?
Answer: It's possible a GFCI somewhere is tripped, removing power from both it and the outlet you're referring to. Other than that, it is most likely a bad connection somewhere, either on that outlet or a different one.
Question: The wire from my old plug won’t go in the hole of new plug. The wire is to big for the hole. What is wrong?
Answer: It sounds like you are trying to use a 15 amp outlet on a 20 amp circuit - 20 amp circuits require a #12 wire, rather than a #14, and is larger in size. Check the breaker, and if it has a "20" stamped on it you will need a 20 amp outlet. If it has a "15", then a 15 amp outlet is fine (there is a picture showing the difference in the two in the article) and you can put the wire under the screws on the side of the new outlet.
Question: An outlet is on a switch to turn on and off a trash compactor. Can I use a gfci?
Answer: At worst you will have to change it out. Many motors will trip a GFCI (a common problem with freezers in a garage), and a trash compactor is a fairly large one.
Question: Can I run the orange 10/2 on a 20 amp single pole breaker for things inside my home? And what is the range of what could (if at all) could be wired with ten gauge CU THHN wire? I have green, black, and white individual spools of those with 400+ ft left. What do I pipe or insulate them with?
Answer: #10 wire will work fine on a 20 amp breaker - it is rated for a 30 amp so anything less is fine. It can be put in EMT or, if outdoors, rigid PVC conduit. Do not use rigid PVC indoors; in case of fire, the fumes from it are quite toxic. You can even use liquid-tight flexible tubing although it is expensive and not generally used for long runs. Flexible conduit, either metallic or non-metallic, is acceptable but care must be taken to limit the bends used or it will difficult to impossible to pull the wire through. For three #10 wires (black, white and green) a 1/2" conduit is acceptable.
Question: Can I use 20 amp breaker with 12 wire to an outlet? Can I run a 14 wire to a switch then to an overhead light?
Answer: Number 12 wire is the correct size for a 20 amp breaker. It is not required, but you really should use a 20 amp outlet as well even though a 15 amp outlet is legal and acceptable. You may run 14 gauge wire to a switch and then to a light, but ONLY if the circuit is on a 15 amp breaker. You may NOT use #14 wire to go from that outlet on a 20 amp breaker to anywhere at all.
The circuit breaker size determines what size wire to use, not where that wire originates.
© 2010 Dan Harmon
Dan Harmon (author) from Boise, Idaho on November 23, 2019:
It doesn't matter one bit whether they are in line or not; feel free to run two different directions from one outlet. As you say, simply pigtail a short wire from the spliced connection to the existing outlet.
Be careful, though, in that there are rules on box fill and don't stuff that box so full of wire that it takes a bulldozer to get the outlet back into it. You might want to replace the existing box with a deeper one if it is a shallow box.
Congratulations on getting rid of extension cords: they are a fire hazard and you've picked a perfect solution in adding more outlets.
Chris on November 23, 2019:
I am wiring in 2 more outlets to one 15 AMP outlet so I don’t have to run extension cords any longer. Currently the wall is down for some retiling. Each new receptacle is in different directions from the current one. Can I run two receptacles off the one by doing a 6 inch extension connected to the receptacle and then the two 14 AWG wires attached to go the different direction? Or do I need to run them all together in sequence?
Dan Harmon (author) from Boise, Idaho on April 27, 2019:
@Ken: Best guess is a poor connection in either the outlet that works or the next one in line. Unfortunately, the "next one in line" could be any of the others - if you go searching, start with the closest one and go from there.
In a house built in 1900 there is also a good chance it is all knob and tube wiring; if that is the case there could be a problem anywhere in the room and the entire room require re-wiring. Unlikely, but possible.
Ken on April 27, 2019:
Got power to light switch and outlet beside it. All others in bed rm is dead. What gives
Old 1900 home
Dan Harmon (author) from Boise, Idaho on December 20, 2018:
@ Robert: yes, tie them all together as you say, adding a short piece about 6" long to go to the outlet itself. The whites together, the blacks together and the bare grounds together, with additional jumpers to put on the outlet. Preferably jumpers of the same color; colored tape or even markers can be used to color the wires if you don't have wires of the proper colors.
robert on December 20, 2018:
What to do I have 3 white and 3 black wires coming out of the box, do i tide, all white together and all black together, as shown for 2 wires only?
Dan Harmon (author) from Boise, Idaho on March 11, 2018:
The connection to the switched wire has been lost. I'm going to assume that the switched wire is spliced in each outlet box - one of those splices has failed. Probably pulled out of the wire nut when you disturbed the wires.
I'd make a guess at how the wire is physically run and check the second and third outlets in terms of distance from the switch. If the problem isn't there, keep checking until it is found.
Nancy on March 11, 2018:
Excellent tutorial. I just replaced 5 half switch receptacles. The first two that I did worked great with the switch. Then I did the next three and now there’s no power to the switched plate but there is power to the full one. What do you think is the problem?
Dan Harmon (author) from Boise, Idaho on March 11, 2017:
Sounds like a 240 volt outlet. Some uses might be a dryer, a range, a hot tub or perhaps a power tool like a large air compressor. As it's on a patio, best guess is a hot tub: you might find the breaker and check if it is a GFI style of circuit breaker. Hot tubs require such a breaker now, but very little else does so that might be an indication.
LJ0810 on March 11, 2017:
On the patio I have a electrical outlet that receives a 4 prong plug what could this be used for? The is a home I am purchasing the current owner has no idea. there is a GFI on the same exterior wall about a foot away.
Dan Harmon (author) from Boise, Idaho on May 07, 2012:
Thanks, cablez. We all have outlets in our homes; it can pay dividends to understand a little about them.
cablez1122 on May 07, 2012:
Useful information and a must for everyone to know about these electrical outlet
Dan Harmon (author) from Boise, Idaho on January 31, 2012:
Perhaps I misunderstand; if there is a wall switch you can disable it removing the wires from it and splicing them together. This will leave the light on at all times, but a pull chain could be added at the light to turn it on and off. It will also provide a constant hot at the light box that could be used to power an outlet as well as the light with a pull chain. The now disabled switch can stay in the wall for appearance sake, but it will not control anything.
What you cannot do is use the wire between the switch and the light to provide BOTH a switched and constant hot wire. That takes three wires; a neutral (which you have), a switched wire (which you have) and a third, unswitched, wire (which you do not have).
Brian on January 31, 2012:
Thanks for all your help on this. I don't want to remove the switch...I was wondering if there is a way to use the current wire that is there to run a constant hot line for the outlet and light switch in the ceiling area by pigtailing at the switch...so that I would have the best of both worlds, but running another wire back to the switch area is out of the question. I'm probably trying to do the impossible, but thanks for your help.
Dan Harmon (author) from Boise, Idaho on January 31, 2012:
If you run your new wire into the switch, you may get power there as mentioned in my earlier post. If you must run the wire into the light, you can go into the switch and take the wires off the switch and splice them together, although this will disable the switch and turn the light on all the time. Maybe install a fan/light combo with a remote control? Or a cheap ceramic fixture with a pull chain?
And yes, if you disable this switch this way you sill simply tie all the blacks at the light together, all the whites together and all the grounds together.
Brian on January 30, 2012:
There is only one wire in the light box, so I guess it will always be switched, if I tap in there. I kind of have to use that power source ( at the light) - I did it over the holidays for a 'village' power source, and just unscrewed the lightbulb and put tape over the switch to keep it 'on'.
If I go into the switch, is there a way I could use the wire that goes to the light as a 'hot' wire to power both? Would a pigtail at the switch do the trick? How would I wire that? Then at the light - I would just tieall 3 blacks together, all 3 whites together and all 3 grounds together, correct?
Dan Harmon (author) from Boise, Idaho on January 30, 2012:
I understand - you have the reverse of the same problem that Carly has.
It sounds as if you have wired the new outlet to the same wires that the light fixture uses; the "hot" wire is switched and this will turn off the outlet every time the light goes off.
If there is only one cable in the light box you are out of luck; the "power" cable is going to the switch first and the only thing available at the light is going to be a switched wire.
If there are 2 cables in the light box (2 blacks, 2 whites) you may be all right (assuming there aren't two light fixtures operating off of the one switch and the other cable simply feeds the other fixture). One of those cables will be "hot" at all times.
If this is the case, one of the black wires will be spliced, probably with a wire nut, to either another white or black wire (it will not go to the light) from the second cable. The white wire from the same (first) cable will go to the light. This is the black wire you want; splice your new black wire going to the outlet into the same wire nut. The white wire to the outlet will go to the same white wire that goes to the light fixture. Be sure all the ground wires are spliced together.
If this is not possible you will have to get power either from the switch or from another outlet. If there is only one switch in the switch box (it isn't a set of several switches all in one box) this is quite possible. In the switch box you should find two cables, each with a black and white. The whites should splice together and not terminate on the switch. Each of the black wires will go to the switch: one is hot all the time, one is switched and goes to the light. You will either have to test this with a voltmeter or simply use trial and error. To use the hot wire in the switch box, run the new outlet cable to the switch box, cut an additional 6" piece of black wire and splice the new black wire, the permanent hot black wire and the six inch piece all together. The other end of that 6" piece goes to the switch where the permanent hot was. All the whites splice together. Another article,
gives tips on running new wire into existing boxes, whether they are switch boxes or outlet boxes.
Brian on January 30, 2012:
I have a similar situation to the one about 4 months ago:
"You will have to run the outlet from the ceiling light (or another outlet), using the white that also feeds the light fixture. The cable going to the switch will contain a wire to the light fixture as well; the black you need for the outlet will be the other wire to the switch."
The wiring direction is not clear to me. I want to run an outlet off a ceiling light with a switch on it. The problem is that my first attempt would turn the electric off to the outlet AND the light (I want to leave the outlet 'hot')
Dan Harmon (author) from Boise, Idaho on January 14, 2012:
Sounds like one of three things. Either that plug is being protected by a GFI outlet somewhere "upstream" (closer electrically to the breaker panel) and that GFI is tripped, the outlet is switched and you haven't found the switch, or there is bad "makeup" upstream.
GFI breakers are commonly used in kitchens, bathrooms and garages. Is this one of those, or perhaps a converted garage? Is it in a room that used to be a porch (outside outlets must also be protected by a GFI)?
How about a switch you haven't found? Switched outlets are common in living rooms or perhaps family rooms.
Finally, there is a bad connection either buried in the box behind the outlet or in one "upstream". Check that there is indeed no power to the outlet with a non-contact voltage detector or a voltmeter. Turn off the breaker that provides power to the rest of the outlets in that room and check that each and every wire in each box is spliced correctly, either with a wire nut of with two wires going to the same place on the other outlets. Any one of them could be loose, causing that "downstream" outlet to go dead.
If none of this works, please email me with more particulars - what room is it in, about how old is the house, is there power in the box (very rare, but a brand new outlet could be bad), has it been remodeled, are there other outlets on the same wall, etc. and I will give it another try.
Jennifer on January 13, 2012:
Hi I have a fairly new home. Did some rearranging in a room and when I went to use an outlet, I discovered it did not work. It is the only one in the house doing this. I went to replace the receptacle which only has one black, one white, and the ground wire. Even after replacing it it still does not work. Any thing I can do?
Dan Harmon (author) from Boise, Idaho on January 08, 2012:
These are very common, inexpensive outlets often used in homes. To remove the wire from the outlet, look for either a slotted or round hole in the back of the outlet. Insert a small screwdriver or a piece of stiff wire into the hole; it will release the catch holding the electrical wire and you can simply pull the electrical wire out.
If all else fails and you simply can't get the wires out of the old outlet, simply cut them off and strip the insulation from the last 1/2 or 3/4 inch. You SHOULD still have plenty of wire to terminate on a new outlet. If not, an additional 6" piece of wire may be connected to the original wire using a wire nut and will provide plenty to hook to a new outlet. It won't be real easy, but it can be done with only a couple of inches of old wire way back in the box. Just be very sure to tug firmly on each wire in the wire nut, trying to pull it out of the wire nut, before mounting the outlet to the box. The object here is to make SURE that the wire nut has a good hold on all the wires in it.
Whitney on January 08, 2012:
I'm changing out worn receptacles in my parents new house. When I pulled out the receptacles in a basement bedroom, I found the hot and neutral wires plugged directly into the back of the unit rather than connected to the sides with screws. I haven't managed to figure out how to disconnect the wires from that box without destroying something and I can't find any reference online for this type of box. The house was built in 1986 but we don't know when the basement was finished. What is this receptacle and how do I change it?
Dan Harmon (author) from Boise, Idaho on November 13, 2011:
If I'm understanding your question, the acceptable method is to bring the incoming power into the box with two duplex (common) receptacles. At that point splice two more small lengths of ground wire onto the ground on the incoming cable, and run one of the spliced pieces to the ground terminal on each receptacle.
If you are using a metal box and romex (common house wiring) or MC cable you are also required to add a third ground to the pair you spliced on and terminate it on the box itself. Even if the box is screwed to metal framing in a barn or other metal structure it is not considered to be grounded until the incoming ground is screwed to it - there is a threaded hole in the box for that purpose. A plastic box will not, of course, require a ground wire to the box, just to the receptacles.