Routing wires through a finished home can be a challenge. It requires drilling and cutting into the structure's finish to gain access to the walls, ceilings and floors. Routing wires through finished walls, floors and ceilings requires fishing the wires through wall cavities where unexpected obstructions may be encountered. Using an electronic stud finder will allow you to locate hidden obstructions and reduce some of the stress and frustrations. For the most part, residential electrical work isn't rocket science, but it can be labour-intensive, especially when it comes to routing wires through finished walls, ceilings and floors. You can't predict what problems you will encounter.
Remove the baseboards in the room where receptacle outlets are to be installed. Run a razor knife along the top of the baseboard to cut its paint seal with the wall. Remove the baseboards carefully, using the hammer and flat pry-bar. Use caution here, because old, dry wood breaks easily, and you may have trouble finding baseboard that will match what you have.
Cut a 2-inch-wide channel in the wall surface. Outline a 2-inch-high rectangle on the wall and drill 1/2-inch holes in the corners to make cutting it out easier. Set the saw's cutting depth to 1 1/2 inches. By setting your saw to a 1 1/2-inch depth, you also set the depth of the notches you will be making in the studs. The actual depth of the notches will vary with the thickness of the wall finish.
Finish notching the studs using the claw hammer and a wood chisel. You will lay the cable in these notches and then cover them with nailing plate, as required by the National Electrical Code, to protect them from damage by nails or screws. Cutting the channel before cutting the openings for the device boxes that will hold the receptacles serves the added useful purpose of actually allowing you see where the studs are inside the wall.
Route cables down, over and up or route them up, over and down when a door is encountered. Routing them down, over and up is the best way to route them when running a receptacle circuit where the receptacles are located close to the floor. Drill ½-inch holes down through the wall's sill plate, the bottom, horizontal framing member, into the basement or basement crawlspace on both side of the door. Loop the cable down through the hole on one side of the door and back up through the second hole. For cables supplying wall sconce lighting outlets, the up, over, and down method is the method of choice. Drill ½ inch holes down through the wall's top plate on both sides of the door from the attic or attic crawl space allowing you to loop the cable up, over, and down around the door.
Route the cable along the sides of floor and ceiling joists in unfinished attics and attic crawl spaces or in unfinished basements and basement crawl spaces. Where the cable has to be routed perpendicular to the face of joists or other framing members, pass it through holes drilled in the framing members so that the near edge of the hole is at least 1¼ inches from the near edge of the framing member. This is required by the NEC to protect the cables from being damaged by screws and nails.
Locate wall studs and fire stops using the electronic stud finder. Fire stops are horizontal framing members placed in the wall to slow the spreading of fires inside walls. You need to know where these fire stops are in order to route a cable down through a wall cavity. The easiest way to get around a fire stop is to cut out a small square of the wall finish and then notch the fire stop as you notched the studs behind the baseboard. After notching the fire stop, you should be able to run the fish tape down the wall cavity, hook on the cable and pull it into place.
Routing wires through a finished house can be frustrating, and it may take several attempts to get the wiring where you actually need it, but it can be done. Installing new wiring in an older home is an art form that can only be mastered with lots of practice, so allow yourself plenty of time to complete the project while you are learning these new skills. The easiest way to route wire through a home is to run it through unfinished areas like basements, basement crawl spaces, attics, or attic crawl spaces and to run it in channels cut behind baseboards. The most important thing to remember is to get a wiring permit from the Building Codes Department before under taking an actual project. When you apply for the permit they will tell you who to call to have your work inspected.