What is Knob and tube wiring?
Knob and tube wiring was the standard way in which homes were electrically wired from about 1880 to the 1940s; many homes in older, established areas in Ottawa still have knob and tube wiring. It consists of single insulated copper wiring that runs within wall or ceiling cavities. This wiring passes through joist and stud drill-holes via protective porcelain insulating tubes, and is supported by nailed-down porcelain knob insulators. Where wiring enters a wiring device, such as a lamp or switch, or where it is pulled into a wall, it is protected by a cloth insulating sleeving called “loom”.
Disadvantages of Knob and Tube Wiring
- Because the wire is old, its insulation may be damaged or brittle
- It is not a grounded system, making it potentially more dangerous than modern wiring methods
- It has two-prong outlets (versus three prong), restricting the use of small kitchen appliances and other household devices such as computer surge bars
Most existing residential knob and tube installations have fewer circuits than required for today’s electrical demands. While knob and tube installations were adequate for the electrical loads at the time of installation, modern households use a range and intensity of electrical equipment unforeseen at the time. Home buyers often find that existing Knob and Tube systems lack the capacity for today’s levels of power use.
As existing Knob and Tube wiring gets ever older, insurance companies are beginning to deny coverage due to increased risk. Several companies will not write new homeowners’ policies unless all Knob and Tube wiring is replaced and inspected.
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