Dear Mr. Electrician: How do I add a dimmer switch next to an existing wall switch? I want to hang a light fixture where there is currently no wiring.
Answer: The methods used to achieve this type of installation will vary according to your building structure and the location of the switches and light fixtures. Below are photos of a simple dimmer and ceiling light installation in a two story condominium. NOTE: Text links go to applicable products on Amazon and EBay.
DIMMER SWITCH INSTALLED IN EXISTING WALL
You need to determine where you will be getting power from and where do you want the wall switch to be located. In the example on this page I was lucky to find power in an existing wall switch where the client wanted the additional switch located. Not all wall switches have a hot and a neutral. Some just have a hot and a switch leg which cannot be used to feed something else.
I used a long thin screwdriver inserted along side of the switch box to feel for any obstacles such as pipes or wood studs. A short piece of fish tape can also be used for probing into a wall.
I removed the existing one gang plastic switch box and cut a hole for a new two gang plastic old work switch box.
The existing black switch leg wire was temporarily identified with green electrical tape. The other black wires get spliced together. The wood stud on the left side of this wall opening is perfect for attaching the new two gang plastic old work electrical box for additional support.
INSTALLING NEW WIRING FOR A LIGHT FIXTURE
The access hole in the wall and the access hole in the ceiling were made using “The Grabowski Method” (Hold the Saw at a 45 degree angle) to facilitate the installation of a new wire to feed the new light fixture.
I had to drill inside the wall to avoid damaging the crown molding around the ceiling. A large hole was needed to fit the Milwaukee right angle drill into the wall to drill up into the top support plate.
I did have to cut holes in the ceiling and the wall to facilitate the installation of a new 14/2 Romex cable to the new light fixture location. I cut the holes at a 45 degree angle inward to make it easy for patching later.
This hole was made using “The Grabowski Method” of cutting holes in drywall. You simply hold your compass saw at a forty five degree angle inward when cutting to give you a beveled edge. This makes it much easier to patch the hole using the same piece of cut out drywall and some joint compound. Lately I have been using my Milwaukee Cordless Multi-Oscillating Tool to cut such holes.
The above view is the inside of the wall through the hole in the previous photo. The big hole in the wall was needed to accommodate the big angle drill and a long auger drill bit.
I had to drill a hole using my angle drill to penetrate the top supporting plate in the wall to get the new Romex cable into the ceiling.
After the new Romex cable was installed up to the ceiling, I caulked the hole through the wood top plate with a fire rated caulk. This is done to prevent the flow of air which would help support a fire.
The hole above is for the new octagonal electrical box that will support the light fixture where the customer wanted it. The existing cables in the ceiling are set back far enough to provide clearance for the new box. You can see the side of the laminated beam on the bottom edge of the hole.
Because this ceiling was supported by trusses instead of solid wood joists I was able to get my fish tape through very easily after the holes were made.
I have several pieces of short fish tape which had broken off of my longer fish tapes. The short fish tapes come in handy for small jobs like this. See my post about wire pulling in walls for more information.
Sometimes it is easier to work with two or more short fish tapes than one long one.
When I cut open the ceiling to fish the wire in the above photo, I was delighted to see that a hole in the laminated beam was already drilled.
The fender washer allows for a little adjustment to get the box positioned correctly. The other screws lock it in place. Note the copper ground wire attached with a 10/32 screw. I had originally planned to install an adjustable retrofit fan brace and box, but the joists were too close together to fit it in.
In most cases I would have used a fan rated ceiling box and installed a 14/3 cable for future fan use. However this light fixture installation was in a small nook next to the dining room. It was not likely that a ceiling fan would ever be wanted there.
HANGING A CEILING LIGHT FIXTURE
Everything metal must be grounded. Because I used a metal box and grounded it, the round fixture mounting bracket is grounded by being physically attached to the ceiling box. If the ceiling box was plastic it would have been necessary to install a ground wire onto the green screw on the mounting bracket. The light fixture ground wire will connect to the ground wire in the ceiling electrical box.