Running Electrical Wires in a Finished Wall: A Comprehensive Guide
Understanding the Challenges
Adding or extending electrical circuits in finished walls can be a challenging task, especially for DIYers. Unlike unfinished basements or attics, where running cables is relatively straightforward, navigating finished walls requires a different approach. The key lies in avoiding damage to the walls and minimizing the need for major renovations.
Planning and Preparation
Before embarking on this project, it’s crucial to plan the cable routes and box locations carefully. Utilize a stud finder to locate the wall studs, ensuring that the electrical boxes are positioned between them. Outline the box openings on the wall, considering the desired height and alignment with existing outlets.
Cutting Box Openings
With the box locations marked, use a drywall saw or jigsaw to cut out the openings along the outlines. Exercise caution to avoid cutting into existing electrical wires, plumbing pipes, or other mechanicals. Ensure that the cutouts precisely fit the electrical boxes.
Drilling Holes in the Wall Plate
Once the box holes are cut, drill access holes in the wall plate at the bottom or top of the stud cavity. These holes will serve as entry points for fishing the cable into the basement, crawlspace, or attic. Insert a spade bit or auger bit into a flexible bit extension and drill through the wall plate into the desired cavity.
Locating the Drilled Hole
If your home has a crawlspace or low attic, finding the drilled hole in the wall plate can be challenging. Insert a long wire, such as a straightened coat hanger, through the hole and locate it in the attic or crawlspace.
Threading the Fish Tape
Unwind the end of an electrician’s fish tape and insert it through the drilled hole in the wall plate. Extend the blade of the fish tape until it is visible in the wall box opening, ideally protruding through the drywall hole.
Attaching the Cable to the Fish Tape
Uncoil the NM cable and strip about 6 inches of outer sheathing from one end. Hook the conducting wires and bare copper grounding wire through the loop at the end of the fish tape blade. Bend the wires over and wrap them securely with electrical tape to create a smooth head that will easily slide through the wall plate hole.
Fishing the Cable
From the attic or basement, pull steadily on the fish tape while your helper feeds the cable into the wall opening. Finesse is required as the tip of the fish tape blade passes through the drilled hole. Pull in short intervals to ensure the cable is being pulled simultaneously from both ends.
Completing the Cable Run
Run the free end of the cable to the next stud cavity location, securing it with approved methods such as drilling holes through joists or stapling the cable where necessary. Strip the end of the sheathing, attach the wires to the fish tape, and pull the cable through the wall plate and out the next wall box opening.
Additional Tips
- For switch locations, you may encounter fire blocks that obstruct the stud cavity. Cut an access hole in the drywall to drill through the fire block.
- Consider using cable lube to reduce friction and prevent tearing the sheathing.
- You can also use a string and a small weight to fish the wire instead of a fish tape.
Safety Precautions
Remember to consult local codes for requirements on running cable. Observe safety precautions, such as drilling holes through joists rather than stapling the cable to the face of the joists in exposed locations. Ensure the wire gauge is appropriate for the amperage of the circuit and consider arc-fault protection if required by code.
