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What is Knob And Tube Wiring?

Knob and Tube wiring (Or sometimes called K&T) is an early method of electrical wiring used in North America from roughly 1880 to the 1940s. Its called K&T because of the ceramic knobs that fasten it and by the ceramic tubes that protect the wires as it passes through the wood framing. Knob and Tube consisted of insulated copper conductors that ran within wall or ceiling cavities. It would pass through joist and stud drilled holes and guided by porcelain insulated tubes. Knob and Tube was the first type of electrical wiring ever used. The wiring was protected by flexible cloth insulating sleeves called loom. The first insulation was an asphalt soaked cotton cloth before rubber became standard. Wire splices in these types of installations were entwined together for strength, then soldered and wrapped with rubber insulating tape and asphalt saturated cloth.

Knob and tube wiring was soon replaced because of its high cost of installation compared to power cables, which combined power conductors of a circuit in one run and later included grounding conductors. If you’re not sure if you have Knob and Tube in your older home check the attic and basement.

Knob & Tube WiringDoes it need replaced?

Understanding Knob and Tube wiring and its common issues will help you decide whether or not it needs to be replaced.

The differences between modern wiring and knob and tube is in modern wiring the black wire, white wire and ground wire are all wrapped in one cable. In Knob and Tube, the black and white wires are spaced inches apart and run separately. Modern wiring is insulated with plastic, knob and tube uses rubber insulation. The eventual breakdown of that insulation for knob and tube is often the reason it becomes unsafe needs to be replaced

It’s not necessary to replace Knob and Tube wiring just because it is older, but you should have it inspected annually. If you do want to upgrade to modern wiring, consider doing it in a phase of remodel. It will cost you less than doing a full on upgrade.

Knob and Tube Issues:

Poor Connections: These connections were not made professionally and can become worn or exposed.

Age: Just the fact that Knob and Tube is so old, damage and wear is common.

Brittle: The rubber insulation and wires can become brittle if exposed too long to high heat.

Insurance: Some insurance companies will not insure homes with Knob and Tube wiring, no matter the condition.

Whether you need a complete upgrade or just an inspection, it’s good to have an electrician that understands Knob and Tube wiring and your specific house wiring needs.

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