How to Run Electrical Wire Through Walls

How to Run Electrical Wiring

This demonstration shows one of the simplest and most common applications for running new wire: extending the circuit from an existing outlet to a new outlet location in a finished wall.

1. Turn Off the Power

   For safety purposes, turn off the circuit breakers that control any associated live wiring in the wall where you'll be working. Use a non-contact circuit tester on nearby outlets or switches to verify that the power is off.

   Put on your dust mask and safety glasses.
   

2. Open Up the Wall

   With finished walls, you'll need to cut through the surface layer to gain access to the studs in order to run cable through them.

   Begin by marking a pair of cutting lines across the wall, from the electrical source to the destination box. Your goal is to remove as little drywall as possible, but the removed section needs to be wide enough so to bore holes in the studs with a drill. A section about 6 to 12 inches wide is usually sufficient. After marking, use a drywall saw or similar tool to cut out a channel of drywall between studs.

   When you are running cables vertically through the wall, you'll be removing the entire vertical section of drywall between two studs. Begin by using a stud finder to locate the studs, then cut away a vertical section of drywall from the stud cavity where you want to install cable. The large removed section of drywall can be saved to use for patching the wall when the cable work is completed.

   Tip

   It can be difficult to open up walls that are made with plaster and lathe rather than drywall. One method is to use a circular saw fitted with a masonry blade set only about 3/4 inch deep. Cut horizontally along the wall surface to cut through the plaster and lathe and remove a section of the wall surface. Repairing the wall after the cable installation can be done with drywall.

3. Bore Holes for Cable

   Near the center of each stud, drill a 1/2-inch hole where the NM cable will run. According to code regulations, the holes need to be set back at least 1 1/4 inches from the front edge of the studs, or, you will need to use metal plates nailed to the fronts of the studs to protect the cables from accidental penetration from screws or nails. Many electricians follow both guidelines—both setback and protective plates.

   When drilling holes, try to follow a straight line. Any deviation from a straight line makes it harder to pull cable. To ensure straight holes, hold the drill inside the stud cavity as you drill horizontally through the studs.

   After drilling all holes, clean out the wood chips and sawdust with a shop vacuum.

4. Cut and Pull the Cable

   Measure and cut a length of cable to run from the source to the destination, allowing a full foot of excess at each end. Beginning at one end of the cable run, thread ("pull") the cable through the first stud, across the wall cavity, through the next stud, and so on.

   Before pulling long stretches of wire, unravel and straighten out the coil of cable. This will help make the pull go more smoothly.

   Tip

   Where you are running cable from an upstairs room to a downstairs room through floor plates, a drill bit extender can be useful for drilling the holes, and a fish tape is often helpful for pulling the cable. Pros often use a fish tape for long vertical pulls to avoid removing drywall altogether, except for small access holes necessary for drilling through the wall plates.

   At each end of the cable run, insert the end of the cable into the electrical box, using whatever cable clamps are necessary. Plastic boxes usually have preattached grip clamps; metal boxes may require an additional cable clamp that fits into an available knockout opening in the box.
   

5. Attach Nail Guards

   Metal nail guard plates can be placed over the edges of studs to protect the wiring against accidental penetration from nails or screws. They also serve to reinforce the strength of the stud where it has been drilled.

   Although the code does not require nail guards if the holes have been bored with the proper 1 1/4-inch setback, it's a good idea to install them as a safety measure.

   Now, attach cable staples as needed: According to the electrical code, cables must be firmly anchored within 8 inches of each electrical box and every 4 1/2 feet if they run vertically along a stud.

   On horizontal runs, if the last hole falls more than 8 inches from the electrical box, secure the cable to the stud near the point where it emerges from the box, using a plastic wire staple. A vertical cable run should also be anchored to a stud with staples spaced no more than 4 1/2 feet apart along its length.

6. Patch the Wall

   The final step is to patch the wall where it was channeled out to install the cable.

   Cut a drywall patch using a straightedge and utility knife, then insert it in the open channel and attach it to the studs with drywall screws. Where necessary, you can attach wood blocking alongside existing studs to provide a surface for attaching the edges of the wallboard patch.

   Finish the joints and screw heads with joint tape and drywall joint compound.

   Tip

   If you plan to insulate an exterior wall before patching the drywall, be sure to leave enough slack in the wiring between the studs so there is no tension when the insulation is put in. Batt Insulation is commonly sliced or peeled in half so the wiring is encased in it.