Any time your project involves extending or adding an electrical circuit, a big part of the job will involve running new wires from the power source to the end destination. "Pulling wires" through finished walls can range from running a few feet of cable, such as when you are extending a circuit to feed an additional outlet in a room, to pulling several dozen feet of cable if you are adding an entirely new circuit fed by the main service panel.
In many ways, running new wire can be the most complicated part of an electrical project, and often the most time-consuming. The most intricate work occurs if you are running cable between house levels, such as from remodeled second-story space all the way down to a basement service panel. It is much less complicated if you are simply extending the cable from an existing outlet to a new location in order to add an outlet. This simpler scenario is what is described in this demonstration project.
Although it does require that you remove and patch some drywall, one of the easier ways to run cable is to simply cut a channel in the finished wall surface, which exposes the studs so you can drill and run the cable. This is the method shown here.
Before You Begin
Running electrical wires running through finished walls is almost always done with a sheathed cable, often known as NM (non metallic) cable, or Romex (named after one of the popular brands). Not all sheathed cable is created equal, and it's important to choose the type that is right for the circuit configuration. First, the wire gauge needs to be sufficient for the amperage load of the circuit; and second, the cable needs to have the right number of conductors for the circuit configuration.
For a 15-amp circuit, 14-gauge wire is the standard, while for a 20-amp circuit, 12-gauge wire is the norm. For a simple receptacle outlet circuit, the cable will normally have two conducting wires—a white neutral and a black "hot" wire—plus a bare copper grounding wire. This cable usually carries a label like "12-2 with ground" (translation: 12-gauge wire, two conductors, plus grounding wire). But if the circuit is linking three-way switches or is being used for certain light fixture configurations, the installation may call for three conducting wires, plus ground. These three-wire cables generally have two hot wires (red and black) and a white neutral wire, plus the bare copper grounding wire.
Thus, it's critical that you have some understanding of circuits in order to choose the right cable for the installation.
When cable is being run through walls without finished surfaces (such as in an unfinished garage or attic), or when it must be mounted on the surface of the wall, the electrical code may forbid the use of NM cable. Instead, you'll need to run the wires as individual conducting wires contained inside metal or plastic conduit, or in a metal-sheathed cable known as BX cable. Those installations are not covered here, as they require different skills.
In most municipalities, any work that involves running electrical cable through walls and connecting that wire to devices will require a building permit, as well as an on-site review by an inspector before the walls are closed up. In many communities, do-it-yourself electricians are allowed to do such work, as long as it is being performed in the DIYers home. Sometimes, a short homeowner's electrical exam is required for the do-it-yourselfer to obtain a permit.
It's important not to bypass the permit and inspection process. The process exists to ensure that the work is done safely, and the inspector will check, among other things, to make sure that the wire gauge is sufficient to handle the amperage load, and that the cables are routed properly through the studs.
Cutting drywall can throw up some gypsum dust that irritates eyes and lungs, so always wear a particle mask and safety glasses when doing this work.
When to Call a Professional
While running NM cable for new or extended circuits is not a difficult job, the final hookups of outlets, switches, and especially the circuit breaker connections in the main service panel, does require some understanding and experience with electrical work. You may well want to call an electrician to make the final connections if you aren't fully confident of your DIY skills. Local codes sometimes stipulate that only a licensed electrician is allowed to do work in the service panel.
And you may want to call an electrician for very long or complicated cable runs. A professional has many tools and techniques for running ("fishing") cables through walls, floors, and ceilings without removing much if any, drywall.
Equipment / Tools
- Non-contact circuit tester
- Drywall saw
- Stud finder (if needed)
- Safety glasses
- Dust mask
- Drill with 1/2-inch bit
- Circular saw with masonry blade (for plaster walls)
- Shop vacuum
- Tape measure
- Wire cutters
- Drywall finishing tools
- NM cable
- Metal nail guards
- Cable clamps (where needed)
- Metal nail guards
- Cable staples (where needed)
- Drywall screws
- Drywall joint tape
- Drywall joint compound
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.
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 that the power is off.
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.
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.
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.
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.
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.
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.
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.
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.