How do electricians run new wires through finished walls without tearing everything apart?

Experienced electricians use a combination of fish tapes, flex drill bits, access holes at strategic points, and creative routing through attics and basements to run new wire through finished walls with minimal damage. It's one of the skills that separates a seasoned residential electrician from someone who learned on new construction, and it's especially important in Toronto's older housing stock where plaster walls and complex framing make the job more challenging.

The basic technique starts with understanding the home's structure. Your electrician identifies the path from the panel to the destination — which walls are accessible from the attic above, which can be reached from the basement below, and where the cable needs to pass through floors or cross wall cavities. In the best scenario, your electrician can access the attic and basement, drill down or up through the wall's top plate or bottom plate, and fish the NMD90 cable vertically through the wall cavity without cutting any drywall at all.

When the attic or basement route isn't possible — say you're running a new circuit to a second-floor room in a two-storey home with a finished basement — your electrician cuts small access holes at key points. A typical access hole is about 10 by 10 centimetres, just large enough to reach in with a flex drill bit and bore through the top or bottom plate of the wall. The electrician then uses a fish tape (a flexible steel or fibreglass rod) threaded through from one opening to another, attaches the cable, and pulls it through. These access holes are patched with drywall compound after the work is done — a skilled electrician makes cuts that are easy to patch cleanly.

Flex drill bits are the essential tool for this work. These are long, flexible drill bits (typically 120 to 180 centimetres) that can bend through wall cavities and bore through studs and plates at angles that a rigid bit can't reach. An electrician fishing wire through a finished wall might drill through three or four studs from a single access point, creating a path for the cable to follow.

In Toronto's pre-war homes — the century homes with plaster-and-lath walls in Cabbagetown, the Annex, and Riverdale — the process requires extra care. Plaster is harder to cut cleanly than modern drywall, and the lath strips behind the plaster can splinter unpredictably. Experienced GTA electricians who work regularly in these neighbourhoods know how to cut plaster access holes with an oscillating multi-tool for clean edges that patch neatly. The wall cavities in older homes can also contain surprises: old gas pipe stubs, abandoned plumbing, brick nogging (bricks stacked between studs for insulation), and of course, existing knob-and-tube wiring that needs to be dealt with.

For larger rewiring projects, AC90 armoured cable is sometimes used in exposed locations like unfinished basements or garages where running cable through finished walls isn't necessary. AC90's metal jacket provides mechanical protection without the need for conduit, and it can be surface-mounted along joists and walls.

The number of access holes and amount of patching needed varies enormously depending on the home's layout and the electrician's skill. When getting quotes for rewiring work, ask specifically about their approach to routing cable and how much drywall repair is included. Some electricians include basic patching in their price; others leave that to a drywall contractor. Toronto Electrical Repair can connect you with electricians who specialize in rewiring occupied homes across the GTA — professionals who understand that minimizing wall damage is just as important as the electrical work itself.