Umair Gaines
Running electrical wires through finished walls can be a challenging task. While it is easy to run cables through unfinished basements or attics, running them inside finished walls is a different matter. The approach taken will depend on the scope of the job. For instance, it could involve extending a circuit from an existing outlet to a new location or installing an entirely new circuit from the main service panel. Regardless of the approach, a basic understanding of electrical work and circuits is necessary to choose the right cable and ensure a safe installation.
| Characteristics | Values |
|---|---|
| Scope of the job | Extending a circuit to a new outlet location, running a new circuit from the main service panel, or replacing old wiring |
| Approach | Depends on the scope of the job, but all retrofit wiring jobs use similar techniques |
| Cable type | NM (non-metallic) cable, Romex, or BX cable |
| Cable route | Through studs and ceiling cavities, or through floors, basements, crawl spaces, and attics |
| Cable length | A few feet to an additional outlet, or dozens of feet for a new circuit |
| Cable height | Typically 16-18 inches above the floor and in line with wall outlets |
| Wire gauge | 12-gauge for 20-amp circuits, 14-gauge for 15-amp circuits |
| Arc-fault protection | Required when extending a circuit if mandated by the National Electric Code |
| Cutting drywall | Cut as little as possible, use a drywall hand saw or oscillating multi-tool, wear a dust mask |
| Permits and inspections | Required in most municipalities, may need a homeowner's electrical exam |
| Safety | Turn off power, use a non-contact circuit tester, wear safety glasses and a dust mask |
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What You'll Learn
Know your local electric and building codes
When running electrical wires through finished walls, it is important to be aware of the local electric and building codes to ensure that your work complies with safety regulations. Here are some key points to consider:
- The National Electrical Code (NEC), published by the National Fire Protection Agency (NFPA), serves as the basis for local building codes and provides specific guidelines for installing electrical wires to prevent fire, shocks, and electrical surges. It is essential to familiarise yourself with the NEC requirements and any variations adopted by your local municipality.
- Local codes may have specific requirements for residential electric wiring, including outlets, boxes, grounding, GFCI and AFCI protection, and other electrical system components. Check with your local building department to understand the specific codes that apply to your project.
- In most municipalities, running and connecting wires requires a building permit and an on-site inspection. Some localities may allow a DIY electrician to perform the work in their own home, but a permit and inspection are typically mandatory. This process ensures the work is done safely and that the wire gauge can handle the amperage load.
- Local codes may dictate the type of electrical boxes allowed. While plastic electrical boxes are standard in the US and Canada, some localities may require the use of metal boxes. It is advisable to purchase large boxes to avoid wire congestion and ensure proper installation.
- When running wires through walls without finished surfaces or mounting them on wall surfaces, local electrical codes may prohibit the use of NM (Non-Metallic) cable. In such cases, you may need to use metal or plastic conduit or a metal-sheathed cable like BX cable.
- If you are simply extending a circuit or adding an outlet, some electricians may remove baseboard molding and notch out the drywall to drill access holes for the cables. This method avoids the need for patching and can be a straightforward way to run cables.
- When installing electrical boxes in finished walls, they should typically be placed between studs, and the standard height for electrical wires in walls is 16 to 18 inches above the floor, aligned with the wall's outlets.
- Local codes may require a licensed electrician to work on the service panel. For long or complicated cable runs or if you are unsure about your skills, it is recommended to consult a professional electrician.
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Understand the basics of circuits
To understand the basics of circuits, it is important to know the different types of wires and cables used in electrical work. A sheathed cable, often known as NM (non-metallic) cable, or Romex (a popular brand name), is designed for specific circuit configurations and amperage loads. The wire gauge must be appropriate for the amperage of the circuit. For instance, standard 120-volt branch circuits use 12-gauge wire for 20-amp circuits and 14-gauge wire for 15-amp circuits.
For a simple receptacle outlet circuit, the cable typically has two conducting wires—a white neutral wire and a black "hot" wire, along with a bare copper grounding wire. This type of cable is labelled "12-2 with ground", indicating 12-gauge wire, two conductors, and a grounding wire. However, for circuits connecting three-way switches or certain light fixture configurations, three conducting wires may be needed, with two hot wires (red and black), a white neutral wire, and a grounding wire.
When running cables through walls without finished surfaces, such as unfinished garages or attics, or when mounting on wall surfaces, NM cable may not be permitted by electrical codes. Instead, metal or plastic conduit, or metal-sheathed BX cable, must be used. It is important to consult local codes and requirements when running cables, as some areas may have specific restrictions, such as forbidding surface raceway wiring.
Additionally, when extending or adding circuits, it is crucial to turn off the circuit breakers controlling any associated live wiring in the wall. This ensures safety during work. Before beginning any electrical work, it is also essential to carefully plan the wiring route, taking into account the locations of studs and potential obstacles like pipes or previous wiring.
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Use a stud finder to check for obstructions
When running electrical wires through finished walls, it is important to first trace the electrical wires in your wall with a magnetic or electrical stud finder. Wires typically run through drilled holes in the wall's studs, and using a stud finder can help you locate these wires to ensure you do not cut into them.
To use a stud finder to check for obstructions, first ensure that the wall is free from any obstructions, such as furniture, curtains, or decorations. This will ensure accurate readings and make it easier to identify the studs. Choose the right mode on your stud finder—magnetic stud finders do not require any mode selection, but electronic and radar stud finders often have different modes for different materials, such as wood, metal, or live wire detection. If your stud finder requires calibration, place it on a wall without any studs and calibrate it according to the manufacturer's instructions.
Once your stud finder is prepared, start scanning by holding it against the wall and slowly sliding it horizontally. The stud finder will emit a signal or display a visual indication when it detects a stud. Mark the location of the stud with a pencil, and then move the stud finder vertically to locate the edges of the stud. Mark these spots as well. Repeat this process until you have located all the studs in the area you plan to work on.
It is important to double-check your findings before proceeding with any electrical work. Additionally, consider using a stud finder app or manual methods, such as knocking on the wall, to verify the location of studs.
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Cut holes in the wall with a saw
To cut holes in the wall with a saw, you will need to use a jab saw, also known as a drywall saw. It is important to never use a circular saw or other large power saw as this will generate a lot of dust and may damage something behind the wall.
First, plan your cuts and take the necessary safety precautions. Put on safety goggles and a face mask, and mark the outline of the section you want to cut out with a pencil. If you want to create a circular opening, you can trace around a round object to create a neat cut line.
Next, use your jab saw to cut along the outline by hand, or use an electric rotary tool for a quicker job. When sawing, apply more pressure on the forward motion to create a neat cut without jagged edges. Pull the blade out and rotate it 90 degrees before plunging it back in at the end of each cut line. Try to use even, controlled motions and only saw about 1/2 inch deep, which is the typical depth of drywall.
If you want to minimise the mess, you can hold a shop vac in your non-dominant hand to suck up the dust as you cut. Alternatively, you can always vacuum up the dust afterwards. To minimise dust, you can also fit the jab saw with a finer-toothed blade meant for cutting metal.
Once you have finished cutting, smooth out any irregular edges with a utility knife. If you need to reinstall the same piece of drywall, hold the jab saw at a 45-degree angle away from the centre of the section as you cut to create a bevelled cutout, making it easier to patch the piece back in.
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Seal holes with fire-resistant caulk
When running electrical wires through finished walls, it is essential to seal any holes with fire-resistant caulk to ensure safety and prevent fires from spreading. This process, known as air sealing, is a critical step in maintaining the integrity of the wall and creating a barrier against fire and air leakage.
Fire-resistant caulk, also known as fire-rated caulk, is designed to withstand extremely high temperatures and prevent the spread of fire. It is important to use a high-temperature caulk that can handle temperatures upwards of 600 degrees Fahrenheit. This type of caulk is commonly used in fire-rated wall assemblies and provides an effective barrier against fire.
When sealing holes, it is crucial to use a caulk that is compatible with all adjoining surfaces and meets the fire and air barrier specifications according to code. The caulk should be applied around the electrical wiring and penetrations to create a continuous air barrier. Be sure to caulk all holes, including those in wall-mounted electrical boxes, to ensure that there are no gaps or openings for air or fire to pass through.
In addition to fire-resistant caulk, other materials can be used in conjunction for added protection. Fire-rated spray foam or fire-resistant putty can be used to seal around electrical boxes and wires, providing an extra layer of fire protection. These materials are often used in conjunction with caulk to create a comprehensive fire-resistant barrier.
It is important to note that fire-resistant caulk is not always required for all holes. According to some sources, the use of fire caulk is typically mandated when penetrating a fire barrier, such as a fire-rated ceiling or wall. However, for interior walls that are not fire-rated, standard caulk or foam sealant may be sufficient. It is always best to consult with a professional or refer to local building codes to determine the specific requirements for your project.
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Frequently asked questions
You can do this by first locating the studs in the wall and then cutting holes in the wall to run the wires through. The wires will run through the hollow space between the studs.
You will need a stud finder, a pencil, a drill, a drywall saw, a utility knife, a screwdriver, a dust mask, safety glasses, electrical tape, and a fish tape.
You will need a sheathed cable, also known as NM (non-metallic) cable or Romex. The wire gauge will depend on the amperage of the circuit. For a 15-amp circuit, use 14-gauge wire, and for a 20-amp circuit, use 12-gauge wire.
It is recommended to call an electrician if you are not fully confident in your skills. Local code may also require a licensed electrician to conduct work on the service panel. Additionally, an electrician may be needed for long or complicated cable runs.
Before beginning any work, turn off the power to the area at the circuit breaker. Check your local electric and building codes to ensure that you are using the correct type of wiring. Obtain any necessary permits and inspections. Be careful not to inhale any drywall dust created during the process.
