How to Install an Electric Box in a Retaining Wall

Mark the location on the wall with a piece of chalk where you will mount the electrical box. If possible, select a somewhat protected location, such as by a tree or large bush. Use spray paint to indicate the electrical cable's path from the power source to the electrical box.

Call your local municipality and ask if underground electrical cables must be protected by conduit. If conduit is required, make the trench at least 12 inches deep to allow enough room. Dig a trench along the spray paint line.

Set the electrical box against the retaining wall. Mark the screw hole locations of the box onto the wall and set the box aside. Drill pilot holes through each screw hole mark with a hammer drill and 5/32-inch masonry bit. Make the pilot holes about a half-inch deeper than the masonry screws you will be using.

Hold a screwdriver against a knockout hole and hit the handle with a hammer until you loosen the knockout. Twist the knockout free and throw it away. Insert an offset screw connector into the knockout hole.

Line up the electrical box's screw holes with the retaining wall's pilot holes. Drive a masonry screw through each hole to secure the box to the wall.

Bend conduit with a conduit bender so it follows the trench you dug from the power source to the electrical box. Run the conduit up the retaining wall to the electrical box and into the offset screw connector.

Turn off the electricity to the power source and test the wires to ensure they are safe to handle using a circuit tester. Send a fish tape through the conduit from the retaining wall to the power source. Wrap a 12 or 14-gauge electrical cable around the fish tape's hook and reel it in to the electrical box. Extend the cable 6 inches into the box. Cut off the outer and inner insulation with a utility knife and separate the three wires.

Strip a half-inch of insulation off the end of each wire with wire strippers. Bend the stripped wires into a hook. Wrap the black wire's hook around the GFCI outlet's top brass screw terminal and tighten the screw. Wrap the white wire's hook around the top silver screw terminal and tighten the screw. Wrap the green wire's hook around the green screw terminal and tighten the screw.

Push the wiring and GFCI outlet into the electrical box. Secure the outlet in place with the provided screws using a flat-head screwdriver. Place the provided watertight cover over the electrical box. Secure the cover to the box with the provided screws.