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  • Knob & Tube Wiring

  • Knob and tube wiring (sometimes abbreviated K&T) was 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.

    Should You Buy A Home With Knob & Tube Wiring?

    Many home buyers ask if they can buy a home with knob and tube wiring or if they should get it replaced. It’s important for home buyers to understand that knob and tube wiring itself is not unsafe. In fact, the necessary drilling, soldering, wrapping, and splicing during the original installation required great deal of skill, since the wiring was meant to last. However, home buyers may have a problem getting insurance for a home with knob and tube wiring.

    Issues with Knob and Tube Wiring

    When you are buying a home with knob and tube wiring, there are a few issues to be aware of.  For instance, insulation cannot touch the wires, as the heat from the wires cannot dissipate. Knob and tube wiring also does not provide a third wire for grounding. Even if two-slot outlets are replaced with three prong outlets (for devices that require them, such as kitchen appliances) there is still no third wire which protects against electric shock. One of the most common issues with knob and tube wiring is with incorrect modifications. Because it is easily accessible, some homeowners make their own repairs and do not splice the wire correctly or they make inadequate, unsafe modifications. Electric Unlimited can make changes or updates to knob and tube wiring.

    Knob and tube wiring is no longer used in homes because it doesn’t carry the same capacity for electricity that modern homes require. Modern households tend to use much higher loads of electricity than the wiring was originally designed for (usually 60 amps). Homeowners should not install higher amp fuses to match the increase in electricity use as this will cause the wires to overheat.