Adding Electrical Wiring Behind Baseboards
–Check local regulations for restrictions and permit requirements before beginning electrical work–
–Most wiring diagrams on this site include a green dot representing the integrated grounding terminal found in most metal outlet boxes. However, some older metal boxes and most plastic boxes don't have a terminal like this.
–By code, the number of conductors allowed in a box are limited depending on its size. Conductors include wires, devices like switches and receptacles, and some other metal parts. Check here to calculate the number of conductors allowed in a box before adding new wiring, etc.
If permitted, new electrical wiring may be run behind baseboards to serve a new wall receptacle, or to a switch and new ceiling light fixture. To pass the cable through the wall studs a notch is cut in the wood and a metal shield, sometimes called a nail guard, is fastened over the notch to protect the new wires from nail and screw punctures.
#1- Remove the Baseboard
Use a straight edge held flat against the top of the base cap to keep your line straight as you pull the knife through the caulk several times until it's cut cleanly.
Pry the molding off the wall working at each stud. Drive a broad chisel-type joint knife between the baseboard and wall. Pull out on the handle several times to loosen the molding enough to wedge a crowbar behind it.
Hold a piece of plywood against the wallboard at each stud and press the crowbar against it to pry the molding off. If you have two-piece baseboards, remove one piece at a time starting with the base cap and then remove the wider parts.
Scrape the old caulk off the wall and molding using a putty knife, and remove the old nails. Sand the wood lightly with 120 sandpaper and put it aside to reinstall later.
#2- Mark and Cut the Wall
Mark a straight line along the wall a few inches from the floor just below the top of the baseboard. Cut the wallboard along this line using a drywall saw for the hollow parts between the studs and a drywall knife to cut over the studs.
Try to remove the wallboard cleanly so it can be reattached when you're done. The baseboard can be reinstalled without replacing the wallboard, but this will create easy access for pest such as rodents, as well as drafts from cold air during the winter.
#3- Notch the Studs
Mark each stud for notching using one of the nail guards as a template. Use a handsaw to cut the top and bottom lines for the notch to the depth of the plate thickness.
Use a wood chisel to chip out between the two cuts, deep enough to fit the plate flush with the stud surface. Keep the plates flush with the studs to ensure the baseboard won't stick out when reinstalled.
In the center of each plate notch, cut a second, 3/4 inch notch for the cable. Make the depth about 1/2 inch to accept the cable thickness, but keep the entire notch depth to a maximum of 7/8 inch for load-bearing 2x4 studs and 1-7/16 inches for non load-bearing studs.
#4- Run the Cable
Run the new cable from the source electrical box, through the notches and into the new outlet box. Pull an extra 8-10 inches of cable into each outlet box to allow for stripping and connecting the wires.
Fit a nail guard into each notch, covering the new wires. Drive the plates down tightly making sure they are flush and not protruding from the stud surface.
#5- Reinstall the Baseboard
Reinstall the wallboard strip. Trim along the edges with a sharp drywall knife first to remove any torn paper that could created a gap behind the molding.
Apply caulk to the back of the strip and stick it to each stud. Press it down until it's flush with the wall surface. You can leave the wallboard off, but it's best to put it back in place. Caulk along the seam to seal out air drafts and then reinstall the baseboard.