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Calculating Box Sizes
To figure the minimum box size required by the National Electrical Code, add: 1 for each hot and neutral wire entering the box, 1 for all the ground wires combined, 1 for all the clamps combined, and 2 for each device (switch or receptacle, but usually not light fixtures) installed in the box. Multiply this figure by 2 for 14-gauge wire and 2.25 for 12-gauge wire to get the minimum box volume in cubic inches. Plastic boxes have the volume stamped inside.
Remove the Old Box
Whether you choose a switch or outlet to provide power, replace the existing electrical box with a new one. With the old box out of the way, you’ll be able to use the hole to fish in the new cable. Then determine the box size required (see “Calculating Box Sizes” above) and install a new remodeling box that’s large enough to safely hold all the wires. We used a 20-cu.-in. plastic box. Make sure the new box has built-in cable clamps.
Cut a Slot for Easy Access
Now that you’ve located a source of power and have a plan showing your recessed light and switch locations, it’s time to figure out how you’ll run the cables. Start by locating the ceiling framing members (joists) with a stud finder and determining which direction they run. They’re usually spaced 16 in. or 24 in. on center. Sketch the joist locations onto your lighting plan. Now draw in the cable route. We installed a standard recessed light housing in the slot where we had access to the ceiling framing. In other areas, we installed remodeling housings that mount in a hole cut in the drywall.
Figure A shows how we ran the cables for our lights. Make sure the junction boxes on the remodeling housings are listed for “through branch circuit wiring” so you can run at least one cable in and one out to the next fixture. Check the labeling on the housing to be sure. Some recessed light junction boxes allow more than two cables.
If you don’t have access to the joist spaces from the attic, remove a 12- to 16-in. wide piece of drywall from the ceiling. Cut the slot perpendicular to the joists about 6 in. out from the wall and make it long enough to include all the joist spaces that will contain a recessed fixture and the power source. Ideally, the opening will be in line with the switch and power source so you can use it to drill down through the top plate. If not, you may have to cut another opening.
Before you cut any holes, make a small hole and measure the depth of the joists to make sure your recessed light housings will fit. Most housings require about 7 in. Look through the slot with a flashlight to check each joist space for obstructions. Then measure and mark the center of each recessed light according to your plan, adjusting the position as needed to avoid joists and other obstacles. Finally, mark and cut the holes for the housings.
CAUTION:
Some insulating materials, ceiling spray textures, plaster and joint compounds made before 1979 contain asbestos. Breathing asbestos can cause cancer and other health problems. Call your local health department for information on testing for asbestos.
Fish the Cable
Select cable according to the circuit rating—14-gauge for 15-amp and 12- gauge for 20-amp.
Figure B: Switch wiring
Here Are a Few Tips:
Uncoil, cut off and straighten a length of cable at least 15 percent longer than you think you’ll need before fishing it through the framing.
Leave about 2 ft. of extra cable at each opening.
Staple the cable to the joists where you have access.
Run only one or two cables through each 3/4-in. hole you’ve drilled. Keep holes at least 2 in. from the top and bottom of the joists.
Strip 12 in. of sheathing from the cable before sliding the cable into the electrical box. The sheathing should extend 1/4 in. beyond the clamp.
When you’re through running cables, make final connections at the lights, switch and receptacle (Figure B) and install the remodel housings in the ceiling. If you’re using low-voltage lights like ours and want to dim them, install a special magnetic dimmer. Replace the ceiling drywall and patch the ceiling after the electrical inspector has approved the work. Then paint the ceiling and finally install the recessed light trim and lamps. Follow the instructions included with your recessed light for exact installation procedures.
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