Adding Electrical Wiring Behind Baseboards
by: Dale Cox
By code, the number of conductors allowed in a box are limited depending on box size and wire gauge. Calculate total conductors allowed in a box before adding new wiring, etc. Check local regulations for restrictions and permit requirements before beginning electrical work. The user of this information is responsible for following all applicable regulations and best practices when performing electrical work. If the user is unable to perform electrical work themselves, a qualified electrician should be consulted. How to Read These Diagrams
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 wallboard, 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 so it's best to put it back when you're done.
#3- Notch the Studs
Mark each stud for notching using one of the nail guards as a template. Use a handsaw to cut to the depth of the plate thickness along the top and bottom lines.
Use a wood chisel to chip out between the two cuts. Chip deep enough to fit the plate flush with the stud surface. Keeping the plates flush with the wood will ensure the baseboard won't stick out when reinstalled.
In the center of each plate notch, cut a second notch about ¾ inch wide to fit the new cable. Make the depth about 1/2 inch to accept the cable thickness but by code you need to 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 cable. 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. First, trim along the edges with a sharp drywall knife to remove any torn paper that could created a bulge behind the molding.
Apply caulk to the back of the strip at each stud and stick it down tightly at each one. Push the wallboard strip along the entire length to force it flush with the wall surface. Caulk along the seam between the two to seal out air drafts and then reinstall the baseboard to cover it.