How to Install Electrical Wire in a Concrete Ceiling

Turn off power to the existing switch or outlet to which you will connect the new wiring to at the circuit breaker. Check if the existing switch or outlet is safe to work with using a circuit tester.

Remove the screws that hold the existing switch or outlet's cover in place with a flat-head screwdriver. Remove the screws that hold the switch or outlet in the electrical box. Pull the switch or outlet out of the box. Use the flat-head screwdriver to loosen the screw terminals and unwind the wire from each one.

Remove the back and top knockout hole from a surface-mount junction box by holding a screwdriver over them and tapping the screwdriver's handle with a hammer. Insert a cable connector into the back hole and an offset connector into the top hole. Feed the electrical wires coming from the wall through the cable connector and tighten the set screws. Hold the junction box flat against the wall. Drill pilot holes through the junction box's screw holes using a drill bit the same diameter as the wall anchors you will use and a hammer drill. Insert one wall anchor into each hole and secure the junction box in place with screws.

Measure the distance from the junction box on the wall to the corner where the wall meets the ceiling and subtract 5 inches. Mark this measurement on a piece of conduit. Insert the conduit into a conduit bender and line up the mark you made with the bender's arrow. Bend the conduit into a 90-degree angle.

Measure the distance from the corner where the wall meets the ceiling to the junction box mounted on the ceiling. Mark this measurement onto the conduit you just bent. Cut the conduit to length with a hacksaw. Fit each of the conduit's ends into the offset connectors installed in the two junction boxes. Tighten the connectors' set screws with a flat-head screwdriver.

Fit one or two conduit straps over the conduit running across the ceiling. Drill pilot holes through each of the straps' screw holes with a hammer drill and masonry bit. Secure the straps to the concrete ceiling with masonry screws.

Thread a new electrical cable through the conduit starting at the junction box on the wall. Extend the cable about 6 inches into the junction box on the ceiling. Cut the cable off with a wire cutters/strippers so it extends about 6 inches into the junction box on the wall.

Strip 1/2 inch of insulation off the end of each wire entering both junction boxes with a wire strippers. Bend the wires into hooks. Return to the junction box on the ceiling where you will be wiring either a new switch or outlet. Wrap the black and white wire around the switch or outlet's screw terminals. Wrap the green wire around the junction box's green grounding screw terminal. Tighten each screw terminal with a flat-head screwdriver. Push the outlet or switch into the junction box and secure it in place with the provided screws.

Move to the junction box mounted on the wall. Cut a new 6-inch piece of electrical cable. Remove the outer insulation and separate the three wires. Strip 1/2 inch off both of each wires' ends. Bend one of the ends into hooks and wrap the black and white wire around the switch or outlet's screw terminals and the green wire around the electrical box's grounding screw terminal. Tighten the screw terminals.

Hold the short wires' other ends together with the same-color wires coming from both the wall and the junction box on the ceiling; white with white, black with black, and green with green. Twist a wire nut over each wire grouping. Push the outlet or switch into the junction box and secure it in place with the screws you removed in Step 2. Restore power from the main power source.