Is Knob and Tube Wiring Dangerous?

The short answer is: it depends on its condition — but the risks are serious enough that most licensed electricians and insurers treat it as a significant concern. Here’s why:

• No ground wire. Knob and tube is a two-wire system with no ground conductor. That means no protection against electrical surges, no safe path for fault current, and incompatibility with modern three-prong outlets and grounded appliances. Using adapters to plug three-prong devices into ungrounded circuits is a common — and genuinely hazardous — workaround in homes that haven’t been rewired.
• Insulation contact is a fire hazard. Knob and tube was designed to dissipate heat by running through open air. When blown-in or batt insulation was added to attics and walls over the decades — often without anyone flagging the wiring — that heat had nowhere to go. This is one of the most common causes of electrical fires in older Portland homes.
• Deteriorating insulation on the wires themselves. The cloth or rubber insulation coating on knob and tube conductors becomes brittle and cracked with age. Wires that were safe in 1940 may have exposed conductors today, particularly in attics, basements, and crawl spaces where temperature swings are severe.
• Improper modifications multiply the risk. Decades of DIY additions — junction boxes tucked in walls, mismatched wire gauges, oversized fuses — are nearly universal in homes with original knob and tube wiring. Each modification is a potential failure point, and they’re often invisible without an inspection.
• Homeowner’s insurance complications. Many Oregon insurers will not write new policies on homes with active knob and tube wiring, or will require it to be replaced as a condition of coverage. If you’re buying or selling a Portland home with knob and tube, expect it to come up in the inspection report and affect your financing or closing timeline.

Signs You May Have Knob and Tube Wiring

You don’t need to open your walls to spot the warning signs. Look for these indicators in your Portland home:

• Your home was built before 1950. If you’re in an older Portland neighborhood and your electrical system has never been fully updated, knob and tube is likely still present in some form — even if newer wiring has been added to parts of the house over the years.
• Two-prong outlets throughout the home. Ungrounded, two-slot outlets are a reliable indicator that the circuits feeding them haven’t been modernized. You may see a mix of two- and three-prong outlets if partial updates have been made.
• Visible ceramic knobs or tubes in the attic or basement. Pull-down attic stairs and unfinished basements often give a clear view of the original wiring. White or cream-colored ceramic insulators stapled to framing members are the telltale sign.
• A home inspection report flagging it. If you’ve recently purchased or are preparing to sell a pre-1950 Portland home, your inspector almost certainly noted any knob and tube they found. That report is a useful starting point for scoping a replacement project.

Our Knob and Tube Wiring Replacement Process

Rewiring a Portland home is a significant project, and we approach it with the transparency and care your home deserves. Here’s what to expect working with Smiley Electric:

1. On-Site Evaluation — $295, Credited Toward Your Project. Because knob and tube assessments are detailed, technical inspections — not a quick visual walk-through — Smiley Electric charges a $295 evaluation fee for on-site knob and tube assessments. A licensed electrician will inspect your attic, basement, crawl space, and accessible wall cavities, map the full extent of your knob and tube wiring, document any unsafe modifications, and walk you through the findings in plain language. If you accept a project quote, the $295 evaluation fee is credited in full toward the cost of the work. This is standard practice for complex rewiring projects and ensures you receive a thorough, accurate assessment rather than a rushed estimate.
2. Scoped Proposal and Permit Filing. Based on the evaluation, we provide a written proposal covering the full scope of work: circuits to be replaced, panel capacity needed, outlet upgrades, and any ancillary work required — and if a panel upgrade is needed, our panel upgrade service covers that and we’ll quote both together.Once you approve, we pull the required electrical permit through the City of Portland Bureau of Development Services before a single wire is touched.
3. Systematic Rewiring. Our crew replaces knob and tube circuits with modern NM-B (Romex) or conduit wiring run to current Oregon Electrical Specialty Code standards. We work methodically room by room, minimizing disruption and patching any drywall or plaster access points as we go. All new circuits include proper grounding.
4. Inspection, Documentation, and Walk-Through. We coordinate the final inspection with the city, provide you with a copy of the closed permit for your records, and walk through the completed work so you know exactly what was replaced and where. That documentation is valuable for your insurer and for any future buyer of your home.

Why Portland Homeowners Choose Smiley Electric

• Oregon Licensed & Fully Insured. Rewiring an older home is complex, high-stakes work. Every Smiley Electric technician holds a current Oregon electrical contractor license, and we carry full liability and workers’ comp insurance — protecting you, your home, and your existing insurance policy throughout the project.
• Permit-Ready on Every Job. We pull permits and pass inspections on every rewiring project, full stop. A permitted rewire gives you documentation your insurer can act on, protects you at resale, and ensures the work meets current code — not just the code from when the house was built.
• Thorough Evaluations, Honest Recommendations. Some contractors quote a full rewire when only targeted replacement is needed — and others underscope the job to win the bid, leaving problems behind. Our $295 evaluation is designed to give you a complete, accurate picture of your home’s wiring before any commitment is made. We tell you what we find and recommend only what’s necessary — and if you move forward, that evaluation fee comes off your invoice.
• Locally Owned, Portland Metro Based. Smiley Electric is a locally owned, owner-operated company serving Portland and the surrounding metro area. We know Portland’s older housing stock, we know the local inspection process, and we’ll be around after the job is done. Call (503) 484-7556 to talk to a real person.

Knob and Tube Wiring FAQs — Portland, OR