In the January 2018 issue, I wrote “Rough-In Wiring,” a feature about doing the preliminary work to install the electrical system in a home. Although that article covered the basics, there was not enough space for every single detail involved in the rough-in process. One thing I had to leave out was how to rough in a ceiling can.

Ceiling cans are the most ubiquitous permanent lighting fixtures in a house. These fixtures have a place for lighting in every room, from closets to kitchens. And with the wide variety of trim rings available to finish off the fixtures, they can serve myriad lighting duties, from ambient lighting to task and spot lighting.

THE RIGHT CAN FOR THE JOB

For every ceiling-can fixture I install, the first thing I need to determine is the type of can required for the location. The light for this project was being installed in a shower ceiling located directly below an unconditioned attic space. Because of the insulation that would be installed in the ceiling, I chose an IC (insulation contact) rated fixture.

I also chose a fixture outfitted with a gasket that blocks the flow of warm, moist air from the shower into the attic. From a design standpoint, the owners had specified a small, 4-inch-diameter fixture, which would provide plenty of light for the shower.

From an installation perspective, I wanted a fixture that was quick and easy to install. I also wanted a fixture that was adjustable in all directions, vertically as well as horizontally, and that I could lock in place after positioning it.

The first step when roughing in a ceiling can is marking out the location. For this shower light, the author first marked the centerline between the back wall and the showerhead.
The first step when roughing in a ceiling can is marking out the location. For this shower light, the author first marked the centerline between the back wall and the showerhead.
Next, he marked the centerline of the width of the shower.
Next, he marked the centerline of the width of the shower.

MARK THE LOCATION

Installation always starts with laying out the placement of the light. Specifications called for the fixture to be centered in one direction between the back wall of the shower and the shower head, and centered in the other direction on the width of the shower. I measured and marked the location of the can in both directions. Many electricians opt to install the fixture first and then make all the electrical connections, but I find it easier to make the connections before installing the box.

HOOK UP THE CONDUCTORS

The crew had left a single cable (called a switch leg) leading from the switch for connecting the can, so the wiring would be straightforward. I stripped back the outer jacket of the cable about 8 inches, exposing the conductors.

To prep the can, I used a slotted screwdriver to remove a single knockout from the corner of the metal electrical box that was mounted on the side of the fixture. On this particular fixture, the corner knockouts were equipped with spring-loaded cable clamps. I fed the cable into the box, letting the jacketed part of the cable extend about an inch past the spring clamp.

A slotted screwdriver removes the knockout for the switch leg.
A slotted screwdriver removes the knockout for the switch leg.
After stripping back the outer jacket of the switch leg, the author feeds the cable into the box where a spring-loaded cable clamp secures it in place.
After stripping back the outer jacket of the switch leg, the author feeds the cable into the box where a spring-loaded cable clamp secures it in place.

The fixture came equipped with three wires inside the metal box: a white, a black, and a green (ground). As with most fixtures such as this, the factory-installed conductors were braided wire. The fixture conductors were already stripped and twisted with about 3/4 inch of bare wire exposed.

With the switch leg fed inside the fixture’s electrical box, the first connection I made was the ground. The ground for this fixture was riveted to the metal housing, so no additional grounding screw was necessary. I simply lined up the end of the green fixture wire with the bare conductor from the switch leg and twisted the two together with the appropriate-size wire nut.

The author twists the green ground from the fixture with the bare conductor of the switch leg.
The author twists the green ground from the fixture with the bare conductor of the switch leg.
Next, he strips about 1/2 inch of insulation from the white and black conductors of the switch leg.
Next, he strips about 1/2 inch of insulation from the white and black conductors of the switch leg.
Leave the braided fixture wires longer than the solid switch-leg conductors.
Leave the braided fixture wires longer than the solid switch-leg conductors.

Next, I stripped back the insulation on the black and white conductors of the switch leg, removing about 1/2 inch of insulation from each of the conductors. Because the braided wire is more flexible, it tends to wrap around the solid conductor when they are twisted together. So I made the exposed solid conductor slightly shorter than the braided conductor so that the two ended at roughly the same point when twisted together with a wire nut.

After twisting the conductors with wire nuts ...
After twisting the conductors with wire nuts ...
... he pushes the bundles into the box.
... he pushes the bundles into the box.

To join the white and black switch-leg conductors to their fixture counterparts, I held them together with the shoulders of the insulation from both conductors lined up. I twisted a wire nut onto the ends, letting the braided conductor twist around the solid conductor. When that was tight, I continued turning the wire nut a couple of more turns, so that the insulated parts of the conductors twisted together as well. When all three connections have been made, I push the bundles into the box and snap on the cover, and I’m ready to fasten the fixture in place.

INSTALLING THE FIXTURE

This fixture came with bar hangers that adjust for joist spans of 12 inches to 24 inches. I began by setting the fixture between the joists and aligning it side-to-side on the mark that I’d made earlier. Then I extended the hanger bars out to span the distance between the joists.

To install the ceiling can, the author lines it up on one of his centerline marks.
To install the ceiling can, the author lines it up on one of his centerline marks.
Metal tabs on the hanger bars set the can at the proper height.
Metal tabs on the hanger bars set the can at the proper height.

The bar hangers have attachment flanges at the ends with double-headed nails all set and ready to drive. The flanges have metal tabs that hang down to help gauge the proper height for the fixture. The ceilings in this house were strapped with 1x2 furring, so I let the tabs extend down 3/4 inch, and I drove in the nails on the ends of the hanger bars facing away from me.

Next, I drove the nails at the other end. For this part of the installation, I am working off a ladder, so rather than getting down and shifting positions to nail in the other side, I’ve gotten pretty good at hammering backwards.

He drives nails to attach the hanger bars to the framing.
He drives nails to attach the hanger bars to the framing.
He aligns the can to his other mark, and locks the can to the hanger bar with a screw.
He aligns the can to his other mark, and locks the can to the hanger bar with a screw.

After driving all four nails, I slid the fixture along the bar hangers until it lined up with my other layout mark. Then I tightened the screw on the hanger bar to lock the fixture in place.

Finally, he pulls the slack out of the switch leg and staples the cable to the joist.
Finally, he pulls the slack out of the switch leg and staples the cable to the joist.

SECURE THE CABLE

As when running cable during rough-in, I try to minimize the stress on the conductors. To secure the cable after installation, I pulled the slack out of the supply side. Then I drove a staple near the top of the joist close to the position of the box. This left a nice, relaxed loop of cable between the staple and the electrical box on the side of the fixture.

Photos by Roe Osborn