Amherst, N.H. – November 01, 2026 -- Homeowners and buyers of houses with knob-and-tube wiring, a system installed from about the 1880s through the 1940s, may face insurance hurdles, sale complications, and safety risks, according to electrical contractor Thomas Reilly of Amherst, New Hampshire.
Reilly's insights appear in a HelloNation article that explains how aging wiring can affect safety, insurance, and renovation plans.
Ceramic knobs and tubes rely on open air to shed heat
The system used ceramic knobs to support separate wires and ceramic tubes to protect them where they passed through wood framing. Rubber and cloth insulation covered the wires, and surrounding air released heat. The design predates today's electrical demands and grounding needs.
These systems have no ground wire. Aging insulation can also crack or fall away, leaving exposed conductors that create shock or fire risks.
Modern appliances and added insulation strain old circuits
Air conditioners, microwaves, and other appliances can place demands on wiring beyond its original purpose and overload older circuits. Insulation added around active wires can trap heat, which works against a system designed to operate in open air. The article also names improper splices and oversized replacement fuses as safety concerns.
Visible ceramic components can help identify the system in unfinished spaces. Two-prong outlets alone do not confirm it, and an electrician must determine which wiring remains active.
Insurers and buyers may ask for inspection or replacement
Active knob-and-tube wiring may complicate insurance coverage or a home sale. Requirements vary, and some insurers seek an inspection or replacement.
Replacement means installing modern grounded cable throughout affected areas. Accessibility, layout, and wall materials influence the work, and some homeowners rewire in stages. Reilly says electricians can often fish new cables through walls, with the access needed depending on the home's construction and layout.
Undisturbed wiring in good condition may keep working
Reilly says undisturbed wiring in good condition may continue working if it is not overloaded, though its condition still warrants professional evaluation.
Until replacement, the article advises avoiding overloaded circuits, keeping visible wiring clear of insulation and storage, and leaving repairs to qualified professionals.