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Knob and Tube Wiring

This type of wiring has not been used since the 1950s. Some older homes here in Peterborough may still have knob and tube wiring, although a lot of it has been replaced.

It is called knob and tube wiring because of its distinctive appearance of two separate wires connected to ceramic knobs and tubes (insulators) used to support the wires. The Tubes would often go through a joist, for example, supporting the wires through the structure.

ELECTRICAL: knob and tube wiring
Here you can see distinctive knob and tube wiring found in Peterborough, Ontario


Your inspector should report the presence of any visible knob and tube wiring. While undamaged knob and tube wiring is still considered to be very safe, over time, the insulation or sheathing surrounding the wires can become brittle and crack, exposing the wires. Furthermore, repairs and partial upgrades done to knob and tube wiring may create loose connection and pose safety hazards. Original spliced connections did not have to be in junction boxes, as they were soldered and cloth taped. Any modern knob and tube connections must be in a junction box.

Common problems with knob and tube wiring are therefore sheathing and insulation failures as well as amateurish modifications and extensions of the circuits.

Your home insurance company may deny insurance to homes that still have knb and tube wiring, or they may request that it be replaced within a certain time frame. If you are considering the purchase of a home with knob and tube wiring, you should speak to your insurance provider before hand. Replacing knob and tube wiring can be at a considerable expense.