How to Run Electrical Wire Through Finished Walls?

Running electrical wire through finished walls is the electrician’s version of a magic trick — no visible openings, no drywall damage, just a working switch or receptacle where none existed before. In practice it is a mix of preparation, the right tools, and knowing which shortcuts work and which lead to hours of drywall repair. This guide walks GTA homeowners through how to run electrical wire through finished walls, what tools make the job possible, and when a licensed contractor’s experience saves the day.

Short answer: use fish tape from an access hole to a target hole, pull the cable through the wall cavity

Direct answer: cut small access holes at the source and destination, use a fish tape or fish rod to push a leader through the wall cavity, connect the cable to the fish tape, and pull it back through. Patch the holes afterwards. Time: 30 minutes to 3 hours depending on wall complexity.

Tools you need

• Fish tape — flat steel or nylon tape on a reel, 15-30 m long. $30-60.
• Glow rods (fibreglass push rods) — rigid but bendable rods that push through insulation and around bends. $30-80 for a set.
• Stud finder with wire detection. Finds studs, wires, and pipes before you drill.
• Drill with long bits (auger or spade) — for boring through top or bottom plates.
• Drywall saw — for access holes.
• Old-work box — our post on cutting in an old-work box covers the destination end.
• Cable pull lubricant — makes long pulls dramatically easier.
• Electrical tape — for attaching cable to the fish tape leader.

The three common wall-fishing scenarios

• Same-bay fish (easy): new device in the same stud bay as the source. Fish tape straight down or up inside the bay. 20-40 minutes.
• Cross-bay fish (medium): new device in an adjacent bay. Requires drilling through a stud or going around it via basement/attic. 1-2 hours.
• Cross-room fish (hard): new device on a different wall or floor. Requires access through basement, attic, or multi-hop fishing. 2-4 hours or more.

Step-by-step: same-bay fish

1. Kill the source breaker. Verify with a non-contact voltage tester.
2. Locate the source (existing outlet, junction box, or switch box).
3. Find the target location. Use the stud finder to confirm the destination is in the same bay.
4. Cut the destination hole. Trace the old-work box outline, cut with drywall saw.
5. Feed fish tape into the destination hole, pushing it up or down toward the source.
6. Retrieve the fish tape at the source through the existing box opening.
7. Attach the cable using electrical tape wrapped tight over the tape hook and the cable end. Streamline for smooth pulling.
8. Pull the cable through from the destination end. Steady and firm, with a helper if the pull is stiff.
9. Terminate at both ends per code.

Getting past horizontal blocking

Direct answer: most walls have horizontal fire blocking or top/bottom plates that block a straight vertical fish. To get past, either drill through the blocking from an access hole beside it (patch after), or use flexible glow rods that can push through insulation and around a blocking plate.

The Ontario Building Code requires fire blocking in specific locations. Do not remove or modify fire blocking permanently; drill only what you need for the cable and re-seal with fire-rated caulk after the pull.

Going through the basement or attic

Direct answer: the fastest way to fish between rooms is via unfinished basement or attic. Cable runs horizontally through the joist space, then drops down or up through a drilled hole in the top or bottom plate of the target wall.

OESC Section 12 requires cable in unfinished basements and attics to be secured every 1.4 m and within 300 mm of every box. Use staples or cable clamps. In accessible attics, the cable must be secured against joists; do not lay it loose on insulation.

Common wall-fishing mistakes

• Drilling into a hidden pipe or existing wire. Always use a wire-detecting stud finder first.
• Cable snagging on insulation. Fibreglass insulation grabs cable. Use lubricant or a glow rod to push through.
• Fish tape ripping cable off the leader. Wrap tape tightly and pull steadily; sudden jerks tear the connection.
• Access hole too small. Cut generously; you can patch a larger hole more easily than fight a small one.
• No consideration for future access. Leave enough conductor in the box for future re-work.

Expert tip from our ESA-licensed electricians

In our experience fishing walls across the GTA — from Etobicoke bungalows to Vaughan two-storeys — the single detail that turns a 4-hour job into a 45-minute one is the up-front assessment. We walk the entire path before cutting anything, identifying obstacles (blocking, ductwork, existing wiring, plumbing). Homeowners who dive in and start cutting often discover a duct halfway through the run and have to open another hole. Ten minutes of planning saves hours of drywall repair. Same lesson as the pre-run photo record. If the fish looks complex, either budget the extra time or hire it out. Our post on patching drywall covers the repair side.

Related reading from ezsmart.ca

• Cut in an old-work electrical box
• Patch drywall around electrical box
• Add switch without new wire?
• Easiest way to cut and strip wire?
• Add a new circuit

Contact us

Complex wall fish in your GTA home that is turning into a bigger project than expected? Book an ESA-certified electrician. Call us at 416-838-9006 or visit our contact page — we will get back to you the same day.