Is Your Knob-and-Tube Wiring Still Safe?

Knob-and-tube is an early wiring method used in homes built roughly between 1900 and 1950. Single copper conductors run through ceramic knobs and tubes, with no ground wire and rubber-based insulation that becomes brittle with age.

Knob-and-tube is not automatically dangerous, but it has no ground, its insulation degrades over decades, and it was never designed for modern electrical loads. Damaged runs, buried splices and contact with insulation are the common hazards — which is why an inspection matters.

Common signs include two-prong ungrounded outlets, a fuse box instead of a breaker panel, ceramic knobs and tubes visible in the basement or attic, cloth-covered cable, and breakers or fuses that trip often. A licensed electrician can confirm during an inspection.

Not always all at once. Some homes need only the damaged or overloaded circuits replaced, while others are better served by a full rewire. Insurers and lenders often ask for replacement, so we document what we find and give you options.

Knob-and-tube relies on open air around the conductors to shed heat. Washington's rules (WAC 296-46B-394) allow loose or rolled insulation around existing knob-and-tube only when specific conditions are met, including written certification by a licensed electrical contractor and proper conductor protection — and foam insulation is not permitted. Have the wiring evaluated before you insulate an attic or wall cavity.

Not automatically. Seattle's electrical code still includes Article 394 covering concealed knob-and-tube, so its presence alone is not a violation. Replacement becomes necessary when the wiring is deteriorated, improperly modified, unsafe in context, or in the way of planned work. Energized abandoned knob-and-tube must be removed or properly terminated.

Only partly. A general home inspection covers what is visible and accessible — the panel, attic, basement and around fixtures — but most wiring is hidden behind finished walls. A focused electrician's evaluation gives you a much clearer picture of the service, panel and visible circuits, which is why homeowners and buyers across King and Snohomish County book one before insulating, remodeling or closing on an older home.

It depends on the size of the home and how much original wiring remains. Targeted circuit replacements can be finished in a day or two, while a full rewire with a panel upgrade takes longer. You get a written scope and timeline with your estimate.