EZSMART Corporation, ESA/ECRA #7012690 , North York , Ontario
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A Toronto or GTA homeowner buying a house from the 1970s often wonders whether the original wiring is nearing the end of its usable life. The honest answer for standard copper Romex-style cable (NMD90 in Ontario) is that it lasts a long time under normal conditions, sometimes past a century. What actually kills wiring is not calendar age — it is heat, moisture, physical damage, and rodents. This guide covers real-world Romex lifespan, what shortens it, and when your Ontario home actually needs rewiring.
Modern copper Romex-style cable, called NMD90 in Ontario, has a typical useful life of 60 to 100+ years when installed to code and kept dry, cool, and undisturbed. The copper conductor itself does not wear out. What ages is the thermoplastic insulation and the outer sheath. Insulation lasts longest at low temperatures, in dry indoor spaces, and where it is not repeatedly bent, nicked, or exposed to UV. Under those conditions, wiring installed in a 1965 GTA home can still be perfectly serviceable today.
Where wiring fails early, it is almost always because of specific abuses. Heat from an overloaded circuit, moisture in a basement or attic, rodent damage, or a nail through the sheath during a renovation shortens life dramatically.
“Romex” is a trade name (originally from Southwire) that has become the generic term for non-metallic sheathed cable. In Ontario the equivalent is NMD90: 90 °C-rated non-metallic sheathed dry-location cable, the workhorse of Canadian residential wiring since the 1970s. Older homes may have earlier variants (NM, NMD, or even cloth-sheathed cable) that have different lifespans and rules. Full breakdown at what is the difference between Romex, THHN, and UF wire.
Absent these abuses, standard copper NMD90 keeps working past most homeowners’ lifetimes.
Full checklist at what are the signs that my house needs rewiring.
Any of these are inspection triggers, not necessarily whole-house rewire triggers.
Full whole-house rewires are expensive and disruptive. Partial rewires targeting the worst rooms or the most-loaded circuits are often the right answer. Consider partial when:
Consider whole-house when:
Cost context at how much does it cost to rewire a whole house.
The oldest fully functional NMD90 we routinely encounter in GTA homes is from the mid-1960s and still tests fine under load. What ages the wiring in those homes is almost never the cable itself — it is the devices at the ends of the runs. Backstabbed receptacles, loose switch terminals, and old junction connections cause 90% of the failures we replace. If you own an older Ontario home and want to extend the useful life of otherwise sound wiring, the highest-value project is not a rewire. It is a device-by-device audit: replace every backstabbed outlet with screw-terminal wiring, torque every switch terminal to spec, and pigtail rather than daisy-chain through devices. That preserves the good copper you have for another twenty or thirty years.
Typically 60 to 100+ years when kept dry, cool, and undisturbed. Copper does not wear out; insulation does.
Heat, moisture, UV exposure, rodent damage, physical damage from nails, and loose device connections.
Brittle or discoloured insulation at accessible boxes, warm outlets, burning smells, and repeated breaker trips.
Not automatically. Have a licensed contractor inspect; many older copper installations still test fine.
NMD90 in the same gauge appropriate for the circuit (14/2 for 15-amp, 12/2 for 20-amp, etc.).
Wondering if the wiring in your Toronto or GTA home has decades left or needs replacement? Call ezsmart at 416-838-9006 or use our contact page. An ESA-licensed electrician will inspect the wiring, run tests, and give you an honest answer.
Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp
