How to Hide a Wall Wart Transformer




In the last 20 years our homes have become inundated with "wall warts," the small to not-so-small electric transformers for everything from powering our computer printers to recharging our iPads. Behind our TV, there are at least four of them attached to devices such as the cable box or my wireless stereo headphones. Because some of these ubiquitous devices are inside a cabinet or behind the appliance they power, they are out of sight and out of mind. However, many of these byproducts of the electronic age create a blight on the visual harmony of our home. A case in point:

In our kitchen, the hub of activity in our house, the cordless phone system’s mother ship was mounted on a wall over a countertop (see photo). However, like many modern phones, it required a fairly large transformer to power it. The good news was there was a duplex electric outlet right next to the phone; the bad news was that this wall wart was unsightly. The situation begged for a hidden remote electric outlet. So I decided to make an extension to the wall mounted duplex outlet next to the phone by dropping below the countertop, installing the new outlet inside the cabinet below and, most importantly, placing it out of sight.

Here is how to do that...

Step 1: Turn Off the Power

Turn off the electric power to this circuit at your circuit breaker box. Verify with a circuit tester, a voltage detector, or a voltmeter that the circuit is offline. Any of these 3 tools can tell you if the power is shut off. None of them is foolproof. I usually check a nearby circuit that I know is hot with the voltage detector to prove it is working and then check the duplex outlet I will be working on. To be on the safe side I will also plug in the circuit tester. My least favorite tool for this job is the voltmeter. Too many times I have seen the probe not make contact with the element in the socket until I moved it around a bit.

Step 2: Pull Out the Duplex Socket

Before starting anything, put on some eye protection even if it is just your regular glasses. The wires and the tools you will deal with can injure your eyes when you least expect it.

Take the plastic cover off of the duplex socket, remove the attachment screws, and pull out the socket itself. I often wear some work gloves when doing this because a lot of the edges of these sockets and the wire ends are sharp. Usually the wires in an older outlet box are stiff and some effort is required to pull the socket out far enough to get to the lug screws. You will now be able to look inside the outlet box that housed the socket.

Step 3: Remove a "Knock-Out" Slug in the Bottom of the Outlet Box

Unless there is an unused opening in the bottom of this outlet box already, you will need to remove a knock-out slug in the bottom of a metal box so that you can pass a piece of Romex electrical cable through that opening. These pre-punched disks push inward to create additional openings in electric boxes. In a new construction situation an electrician would knock out the disk with a screwdriver and the heal of his hand from the outside. But you will be approaching the box from the inside. In this situation it is usually easier to use a small blade screwdriver and get it into the pre-punched slot and pry up on the disk until the slot gets bigger. Then you can insert a bigger screwdriver to push it up enough until you can grasp the K-O slug with some needle nose pliers and bend it up and down until it breaks off.

Step 4: Probe Down Through the Inner Wall Space With a "Fish"

Probe downward through the new opening in the outlet box with a wire fish (a piece of semi-rigid wire rod with a small loop in one end) into the inner wall space to make sure there is not a noggin, a horizontal 2 X 4 cross member, inside the wall between the studs. Although this would not be a show-stopper, it would definitely require a decision on your part. At this point, you would either have to figure out how to drill at least a 1/2" hole through the noggin or look elsewhere for another location for the wall wart, such as in a cabinet above the counter top. The latter choice would usually be the better option. The process would be virtually identical for putting the new hidden outlet in the cabinet below the counter top except you would run the wiring upward through the wall instead of down.

It is likely that this outlet box in the wall is attached to a stud. Be mindful of this since the hole in the sheetrock you will make below must be on the same side of the stud as this box. Note- in the photo above the fish is protruding from the hole in the bottom of the outlet box.

Step 5: Decide Where You Want the Duplex Outlet in the Cabinet Below

Figure out where you want the duplex outlet to be in the cabinet below. Normally it should be located directly below the outlet you are connecting to. On the rear wall of the cabinet, draw the outline or the footprint of the old work electric box. Place masking tape on the outsides of the lines to help prevent the sheetrock from splitting or crumbling when you are sawing the opening.

Step 6: Cut the Opening in the Sheetrock

Drill a one-inch hole through the sheetrock or wood panel in one corner of that outline. Use a hole saw or jigsaw to cut a rectangular opening in the rear wall. Remember that there may be wires inside the wall into which you are drilling/cutting and you don't want to damage it. The sheetrock in the back of my cabinet was old and very friable and did not make sharp edges.

Step 7: Measure Your Wall Space

Insert a ruler into the new opening to measure how much room there is between the inside surface of the sheetrock and the outer wall. That is to say, will the wall space accommodate a full depth old work (push-in type) outlet box or will you need a shallow depth version? Note- The term old work means the type of electric box that is added to an existing house and is generally pushed into to newly created opening in a wall.

Step 8: Pull the Fish Out of the Wall Opening

Using the fish, go down from the opening in the bottom of the outlet box and feed it downward through the wall space until it appears in the opening that you have just made in the cabinet below. Pull the end of the fish slightly out of that hole (see photo).

Step 9: Estimate How Much Romex You Will Need

Estimate how much 12-gauge Romex wire you will need to connect the top and bottom boxes. Then cut at least a foot more to give yourself some some extra wire for a service loop in the back of each box, i.e., some slack in the Romex to allow you to easily connect the wiring to the sockets and to permit trouble-free access if you have to work on these sockets again in the future.

Step 10: Prepare the New Outlet Box

1. Push one end of the Romex cable through an opening in the top of the old work outlet box.

2. Strip back approx 6 inches of the outer insulation covering on both ends of the Romex and then strip the insulation off the black and white wires on both ends sufficient to make C shaped bends in the wire. This will render it easier to attach these wires to the sockets (see photo).

3. On the end of the Romex you pushed into the outlet box, attach the three wires (hot, common, and ground) to the appropriate lugs on the new duplex socket. It is much easier to do this out on a workbench or a countertop rather than trying to work up inside the cabinet.

Step 11: Bring the Romex Up Through the Top Opening

1. Tape the loose end of the Romex to the small loop in the end of the fish that is protruding from the hole in the wall.

2. From the wall opening above the countertop, pull the fish wire up through the wall and bring the loose end of the Romex out of the hole in the bottom of the outlet box (see photo).

3. Remove the tape and free up the ends of the Romex wire.

Step 12: Connect the Wires to the Top Socket

Connect the two insulated Romex wires to the appropriate lug screws on the sides of the duplex socket in the top outlet. The black wire goes to the brass colored lug, the white wire goes to the silver lug, and the bare copper ground wire connects to the bundle of ground wires in the back of the outlet box by way of a wire nut.

Step 13: Fish the Transformer Wire Up Through the Wall

1. If you are trying to hide the transformer and its cord, you should first remove the phone from its attachment plate. Then pass the fish wire through the hole in the plate and through the wall space down to the opening in the cabinet below. In my case I had to remove the mounting plate from the wall because the hole in the plate was too small for the fish to make the bend downward.

2. If the phone cord is not attached to the mounting plate, tie a piece of string around that cord so you don't lose it down in the wall.

3. This time, you will bring the fish out of the opening below, tape the wall wart's plug to the fish wire, and pull it up through the phone's wall opening, leaving the transformer in the cabinet below just outside of the wall opening.

4. Pass both the transformer cord and the telephone cord through the hole in the phone mounting plate and re-attach the plate to the wall.

5. Plug the phone cord and the transformer cord into the back of the phone and then replace the phone on its attachment bracket (see photo).

Step 14: Turn the Power Back on Temporarily

1. Turn the power back on. Use the circuit tester on both upper and lower duplex sockets to insure that all leads, including ground wires are hooked up properly.

2. Turn the power off and push the sockets back into their respective outlet boxes and re-install the screws that hold them in. Put the socket covers on over both the sockets. In the cabinet, the wall wart will remain outside the wall and its cord will pass just under the lip of the outlet cover.

3. Turn the power back on one more time. Plug the wall wart into its new socket in the cabinet and check to see if the phone is operating properly (see photo).

Step 15: The Wall Wart Is Gone

The results were more that worth the effort. I probably did not spend $10 on the parts. And my wife was very happy to see the wall wart disappear.

Step 16: The Tools & Materials Needed for the Project

This is a list of the tools and materials needed for this project:

1. About 3 feet of Romex 12/2 cable. This electrical cable has two solid 12 gauge insulated copper wires- one black and one white, plus a single bare copper ground wire, all inside of a plastic insulated sheath. Although I show a 15 ft package of Romex (for the sake of the photo), you can buy this wire by the foot at Lowe's or Home Depot.

2. One old work electric outlet box

3. One duplex electric socket

4. One duplex socket cover

5. Some masking tape

6. Wire fish- although you can buy these commercially made up in various lengths, I made a couple several years ago out of some 1/8-inch diameter steel rod from a hardware store. The rod is stiff enough to be pushed through wall spaces and insulation, but yet flexible enough to bend when you put it in an outlet hole in the sheetrock. For a small job like this one, some coat hanger wire would likely do the job.

7. Circuit tester- this device plugs into a wall socket and is mandatory when installing a new outlet. It has lights on it that will tell you whether a circuit is wired correctly and if the ground is connected.

8. Voltage detector- very nice to have and gives you some backup for the circuit tester as to whether there is some unexpected current in one of the wires in an outlet box. It happens.

9. Voltmeter- OK for testing the amount of voltage in a circuit, but not my favorite "failsafe" mechanism when working around live electrical wiring.

10. Wire strippers or a pocket knife for removing insulation. The strippers are nice to have, but the knife will strip wire and split the outer covering on Romex, which the wire strippers will not.

11. Pair of needle nose pliers

12. Flat blade screwdriver or two and possibly a #2 Phillips screwdriver depending on the kind of screws you encounter

13. Pair of wire cutters

Step 17: Epilog

I installed this out-of sight duplex outlet about 2 1/2 years ago. At the time I had not considered that the socket in the cabinet might be used for anything else. But, about 6 months later I decided to install a 4-gallon point of use water heater in the adjacent sink cabinet. I quickly determined that the electric outlet in the under-sink cabinet was not what electricians call a half-hot outlet. Some brief background information is in order.

The under-sink cabinets in most homes have a duplex electric outlet on the rear wall intended to power the garbage disposal. Some are wired so that both sockets are connected to the disposal wall switch next the sink, while others have one of the sockets always hot (the aforementioned half-hot outlet). If the latter is the case under your sink, you may be able to use the always hot socket in the outlet to power a small water heater. If you have the former arrangement, as I did, then you will need to find an uninterrupted power source elsewhere.

In my water heater project, I was fortunate to be able to drill a one-inch hole in the common wall with the adjoining cabinet where I had, a few months before, already installed a duplex electric wall outlet to hide my wall wart. I am always amazed at how two fairly different projects come together in a kind of unplanned synergy. Did the wall wart project unconsciously influence my thinking on the water heater installation? This much I do know; having that hidden duplex outlet in the cabinet next to the sink certainly saved me some time providing another source of electricity.

Step 18: The Disclaimer

It is beyond the scope of this tutorial to address the legalities of doing these types of repairs. However, I will say that in most municipalities, the homeowner is allowed to make minor modifications in the electric system of his own home. Some towns will allow you to simply go online to apply for a permit, if one is needed, and describe what you are going to do. In the city where I live, one can obtain a homeowner’s electrician license just for his domicile, i.e., while he may do electrical work in his own home, he is not authorized to do so elsewhere. I passed a written test and got such a license a couple of years ago. With it, I am permitted to install up to 3 new circuits and do some other things. By the way, adding these branch outlet extensions is not considered adding new circuits; this project falls under the category of a minor electrical repair.

I realize that ordinances vary from city to city. In our town they use the NEC 2008 Manual, with some minor exceptions, as their electrical code. This project totally complies with that code and I have verified that not once but twice with code compliance electrical inspectors. They also said that a small electrical repair such as this would not require a permit nor an inspection. I will leave it up to you, the reader, to make certain that this project complies with your local code.

Most electrical repairs such as these extensions are quite easy to perform and should be good confidence builders. However, if you have doubts or are uncomfortable doing these projects, by all means, get some expert help- and learn from it. This is not rocket science, but there is an element of danger in working around electrical wiring, especially if you do not follow some basic safety rules.



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    125 Discussions


    1 year ago

    While my home was wired with category 5 (4 pairs, 8 conductors), even older homes have 4-wire (2-pair) voice cable. Home lines only use 2 of these wires, the other 2 (or 6) are for extra lines, data, and yes! Low Voltage DC. In my situation, the phone line enters the basement where it is connected to a "punch block" and the lines to the individual rooms go there separate ways. I used a spare pair from the kitchen and cut the cable to the wall wart. I plugged the wall wart in in a basement electrical outlet, soldered the 2 wires to an unused pair and connected the plug that goes in to the phone to the other end. You will probably want a volt meter to do this to ensure correct polarity, but if it's do-able for you it's a lot less work that adding an extra 110 volt outlet. BTW, I worked for one of the "Baby Bells" back in the 1980s and I'm quite certain that this approach is legal and to code. I have also installed electrical outlets via the "cut-in" method on too many occasions to count. If you can use the phone cable it's a lot less cutting and cable fishing.


    Reply 3 years ago

    That said i could see a use for this with fax machines and printers


    Reply 2 years ago

    Certain non-telco payphones use the phone line to charge the battery. Payphones are going out of style now, so it isn't common.


    Reply 2 years ago

    I do. I don't have to carry a cell phone from room to room, as I have phones in most rooms and I can hear the landline ring anywhere in the house. I don't need to recharge it either.


    Reply 2 years ago

    I do....I don't like talking on a small phone. When I use my land line, I can perch it on my shoulder and do something while I am talking on the phone. You can not do that when you use the little cell phone.


    Reply 2 years ago

    I do for over 40 years! The phone company supplies 48 VDC battery power with its own UPS and generators. So if there is a general power failure, your home phone will still operate, but your cellphone may not! Besides, without power, how can you keep your cellphone charged?


    Reply 2 years ago

    It just occurred to me that maybe that 48 VDC current could be used to power a few things around the house in case of an outage or emergency.. maybe to charge a smartphone or rechargeable flashlight? I bet one could probably even get a laptop to stay charged if they left it plugged in long enough.. [disclaimer:] I don't really know anything about electricity ... well not enough to know how much it would take to charge something off the phone line.


    Reply 2 years ago

    No, you cannot use the phone company's power to charge your devices. It is limited to several milliamps (mA) and they can measure that consumption, indicating an "off-hook" condition as if you were activating a phone. And if the limit is exceeded, they can do a "disconnect" and you are left without phone service. Don't tryit unless you wish to pay for a line reconnection at the CO (Central Office). If you wish to know more, you can ask the phone company or just search the Web.


    2 years ago

    The variances in electrical codes are fascinating. I had a lift motor installed on a dock recently in Jacksonville, Florida, and noticed a wire running from the motor into the river attached to a piece of metal. In response to my question, the installer indicated that it was required by code. Both the installer and myself knew that the wire would corrode off the metal within a few weeks, and it did. Sad to say, I had to change out a GFCI outlet in my garage for a non-GFCI because I had a freezer on that outlet, and it would 'pop' every now and again for no identifiable reason, and there's been numerous instances of outside mounted GFCI's just failing over time. I'm just saying that I'm sure the people writing these codes are trying to make everyone safe, but sometimes you just want something to work, as well.

    3 replies

    Reply 2 years ago

    Thanks for your informative reply. Evidently the professional, and experienced electrician did not know of this variance. His point was every outlet in a garage has to be GFCI protected because the garage is regarded as 'being outside' as far as code goes, and the need to protect people from potential electrocution. I really don't understand the thinking on that one. There are plenty of houses with exposed concrete floors these days, so I guess that has to be considered 'outside' as well. I guess this is a part of the overall problem of their being so many rules and regs. these days that we are all just drowning in a sea of words.
    As an aside, in the thread about potential food poisoning after fridges have been turned off by a tripped GFCI, someone suggested that the chef should know if the food is spoiled or not. As a retired physician, I can assure you that is completely false. The reason food poisoning exists at all, is that the food appears normal to all inspections. The toxins produced by the bacteria are in many cases, heat stable, meaning that they are not effected by cooking, and will poison you anyway. It seems it is time for all refrigerator/freezers to come with a big warning sticker advising the owner to NOT plug them into a GFCI protected circuit.


    Reply 2 years ago

    "every outlet in a garage has to be GFCI protected because the garage is regarded as 'being outside' as far as code goes"

    is not the same as:

    "There are plenty of houses with exposed concrete floors these days, so I guess that has to be considered 'outside' as well"

    A concrete floor has nothing to do with the code.

    I do not know the exact reasoning but a garage is not generally used in the same manner as the interior of a home. People can and do wash their garage floors with hoses, pressure washers etc.. among other things. They also use the outlets with extension cords for outside work. There are plenty of examples on how people can and do use their garage as an "outside" space.

    A garage is not an extra room in your home.

    Building and electrical codes are not something we as a society just guess at. They are created for maximum safety level with the materials and building techniques available. They can be super frustrating, but in the end, they make us all safer from ourselves.


    2 years ago

    I like your idea and project, I have done something similar some years ago - the wall wart is on the other side of the dry wall in a closet.

    I am not concerned about the electrical safety of your project, but rather concerned about a fire hazard, keeping the wallwart in a small hidden volume inside the wall. I see a risk of overheating and smoldering which could go quite some time unnoticed...

    1 reply

    Reply 2 years ago

    Thanks for compliment. Lay your fears to rest. The cabinet is quite large and is opened 2-3 times a day. It has been in there for over 2 yrs and I have never felt the wall wart even warm. Just to re-affirm my findings, I just went into the kitchen and felt it again. The plastic case was actually COOL. Go figure. It must not draw much current.

    I may have mentioned this in the instructable, but when I asked the electrical inspector at my local city hall about this project before I did it, he said that he, himself, had done this kind of thing in his own house- and saw nothing wrong with it and had never seen a problem with it.


    3 years ago

    Great instructable, however, does not meet code in many ways. 1) share path for power and signal, 2), non CL/in-wall rated cable for the transformer, 3) no GFCI outlet.

    2 replies

    Reply 3 years ago

    I think most people would agree with me In saying that your complaints do not make sense. What is the shared path for power and signal? There is only voltage It being supplied to the Transformer and then The power for the base station of the mobile phone.I'm not sure what the second Issue is. As far as your third concern If there is no GFCI receptacle present there doesn't need to be one added. The National Electric Code has never been retroactive.


    Reply 3 years ago

    1) Shared path is the power to the phone run through the same opening as the phone lines (signal). 2) The wall wart transformer cord ran back under the face plate into the wall traveling up in the wall to the phone. Means it's not supposed to be installed in the wall. 3) If you modify any existing electrical it has to be brought up to current code.