How to Install an Electric Outlet in a Concrete Floor

Installing a floor outlet is a great way to eliminate the use of extension cords, which just get in the way and are really intended only for temporary use anyway. A floor-mount electrical box goes under the surface of the floor, which makes the outlet unobtrusive and easy to access. Installation is a relatively simple job if the subfloor is wood but a somewhat more challenging one if the subfloor is concrete.

Ideally, the electrical box and conduit for a floor outlet should be installed when pouring the concrete. When you install an outlet on an existing slab, you'll need to cut a hole for the electrical box and a trench for the cable in the slab. You might think installing a surface-mount box and covering the wires with a raceway would be easier, and that's probably true, but you would need an impactproof, waterproof electrical box — which you'll have a hard time finding if there even is such a thing — and the outlet would be an obstacle. A flush-mount floor box is safer, and it's approved, so get out your concrete tools and start cutting.

First and foremost, you'll need an electrical box designed to be encased in concrete. Several manufacturers supply these, and the one offered by Leviton, which is made of PVC and includes all the fittings you need, is one of the best. Note that you have to purchase two extra parts separately: the leveling ring and cover plate. You'll also need enough 3/4- or 1-inch PVC conduit to reach the wall in which the power source is located, some PVC cement, and 12-gauge UF-B electrical cable rated for underground installation. Of course, you'll also need a tamperproof receptacle.

You need to cut a hole deep enough to accommodate the electrical box, and the one from Leviton can be cut to the height you need, so your hole doesn't need to go all the way through the slab. Mark the location of the outlet and use a concrete-cutting saw with a dry-cut diamond blade to cut a series of strips 2 to 3 inches deep and about 1/2 inch apart for a total width of about 2 inches. Break off the strips of concrete with a cold chisel and hammer to make the trench for the conduit. Go back to the beginning of the trench and widen it using a saw or cold chisel until you have enough room for the electrical box.

Follow the instructions that come with the electrical box when installing it because it has leveling pegs that raise it off the bottom of the hole so fresh concrete can get underneath it. Glue the conduit to the access port with PVC cement, route the conduit into the wall, and install an elbow pointing upward through which you can feed the electrical cable. Cut the electrical box flush with the floor using a hand saw or oscillating tool and then install the leveling ring according to the product directions. Now you can backfill the hole and trench with fresh concrete and cut the electrical box flush with the floor when the concrete hardens.

Feed enough electrical cable into the conduit to give yourself plenty of slack at the box for connecting the receptacle. Locate a power source (which might be another outlet), turn off the breaker for that circuit, and connect the cable to it. Be sure to secure the cable to the wall studs with staples.

When installing the new outlet, you may have to clip off the metal tabs on the ends to get it to fit. The leveling ring has a push-on grounding connector, so insert the ground wire from the power cable into the appropriate slot and push. Wire the outlet just as you would wire any outlet — black wire on a brass terminal and white wire on the corresponding chrome one — and then screw the outlet to the box. Finish by installing a moistureproof gasket and cover plate according to the directions supplied with the cover plate. Finally, turn on the power and test the outlet.