Knob and Tube Rewire
Professional inspect, remove and rewire your home.
Arrow Insulation is a local professional insulation company. We understand that money and time are very valuable to you and for this reason we are certified to work directly with the local utility companies of Seattle, Tacoma, Bellingham and other surrounding communities of Western Washington. Insulation rebates from these utility companies can save you a lot of money.
Examples of Knob and Tube Wiring
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What is Knob and Tube Wiring?
Knob-and-tube wiring (sometimes abbreviated K&T) is an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s. It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted together for good mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape (asphalt saturated cloth), or made inside metal junction boxes.
Knob and tube wiring was eventually displaced from interior wiring systems because of the high cost of installation compared with use of power cables, which combined both power conductors of a circuit in one run (and which later included grounding conductors).
At present, new knob and tube installations are permitted in the US only in a few very specific situations listed in the National Electrical Code, such as certain industrial and agricultural environments.
Safety Hazard of Knob and Tube Wiring
- The porcelain knobs suspend the wire in open air to dissipate heat.
- The wiring was usually installed along the center of joists and studs away from potential nail punctures.
- Additional protection is provided by porcelain tubes where it passes through wood.
- The hot and neutral wires are always separated by at least 3 inches except near a connection to a box or fixture. At these places, an additional protective woven sleeve, or was used from the last knob.
- Splices were joined by wrapping one wire around another and then soldering the joint. Knobs were then placed within 6 inches of the splices to prevent stress on the connection.
- Wires were usually never loose or placed on top of joists where they could be easily damaged.