How To Wire A Switch Leg
If you live in an older home, there is an excellent chance that ceiling mounted light fixtures are controlled by pull chain switches. The problem with fixture mounted pull chain switches is that you have to stumble through a pitch black room and fumble around the find the pull chain. It is mush easier and safer if the switch is wall mounted by the entryway. Converting from a pull chain switch to a wall mounted switch is not rocket science, but it will require running a switch leg to where the switch is to be located.
Degree of difficulty on a scale of 1 to 10 is a solid 3 (Almost any handy person can do this.)
Tools and supplies that you will need for this project
- Tape measure
- Non-contact voltage probe
- 3/8 inch battery powered drill/driver
- Spade bit set
- Portable, electric jigsaw
- 12 inch bit extension
- Cable cutters
- Wire cutters
- Wire stripper
- Needle nose pliers
- Lineman's pliers
- 12/2 w/gr Romex cable
- Cable connectors
- Romex cable staples
- “Old Work” ABS device box
- SPST light switch
- Cover plate
- Wire nuts
- Black, plastic electric tape
Before starting this project
Because you will be installing new wiring, you will need to purchase a wiring permit from your local building permits department. You will also need to have the Authority Having Jurisdiction that issued you the permit, inspect your work when you are finished. The permit and inspections are required by law and you can be fined if caught doing this job without them.
Locate the switch next to the open side of the door. Make a mark on the wall 46 inches above the finished floor. Position the “Old Work” device box against the wall so the mark is at the center of the box. Using the box as a template, draw an outline around the box. Drill ½ inch hole in the inside corners and finish removing the cutout with the portable jigsaw.
Turn off the circuit breaker to the branch circuit serving the light fixture and lower the fixture. Turn on the non-contact voltage probe and check the insulated conductors to make sure they are safe. The nice thing about using a non-contact voltage probe over a conventional circuit tester is that you do not have to make contact with bare wires or terminals for it to work. Disconnect the light fixture and set it aside.
Drill a 5/8 inch hole down through the wall's top plate into the wall space where the switch is to be located. Layout the route the cable will take from this point to the light fixture's lighting outlet box. You can run the cable through holes drilled in the joists as long as the near edge of the hole is at least 1 and ¼ inches back from the nearest edge of the joist. You may also run it along the face of the joists secured every 4 and ½ feet with cable staples. The cable must be positioned at least 1 and ¼ inches back from the nearest edge of the joist.
Starting at the lighting outlet box, run the cable over to the hole you drilled in the walls top plate. Then feed the cable down through the hole and into the wall space where you made the switch box cutout. Feed enough cable down into the wall space until it extends 12 inches into the room.
Push the end of the cable into the new “Old Work” device box until it extends 6 inches pass the front edge of the box. Shove the box through the cutout and turn the mounting wing screws in a clockwise direction, drawing the mounting wings up against the backside of the wall finish.
Remove a knock out from the side of the lighting outlet box and install a cable connector. Slide the end of the cable through the cable connector 8 or 9 inches and then tighten the clamping screws securing the cable in place.
Remove the outer jacket from both ends of the cable starting ¼ inches from where it exits the clamp. Strip ½ inch of insulation from the black and white insulated wires. Using the needle nose pliers, form loops in the end of the wires at the switch location. The finished loops should look like question mars with the opening just large enough to slip around the terminal screws on the switch. Slip the wires around the screws in a clockwise direction and tighten the screws down on the wires.
Since this is a switch loop ant the white wire will be a current-carrying conductor, re-identify it as such by wrapping its entire exposed length with black tape. Attach the black wire and the re-identified white wires to the two brass colored screws and attach the bare ground wire to the green screw.
Wrap the switch's terminal screws with tape. Push the switch into the box and secure in place with the two 6-32 “captured” screws. Install the cover plate.
If you are going to use the old light fixture, disconnect and remove the pull chain switch. Splice the black switch loop wire to the black wire bring power into the lighting outlet box. Hold the two stripped ends side by side and then twist them tightly together in a right-hand twist using the Lineman's pliers. Complete the splice by screwing on a wire nut. Splice the re-identified white, switch-loop wire, to the black fixture wire and splice the white fixture wire to the white wire coming from the circuit breaker panel. Splice the bare fixture wire to the two bare ground wires in the box.
Install the light fixture on the lighting outlet box and turn on the circuit breaker.