Knob-and-Tube Wiring
Definition and meaning of Knob-and-Tube Wiring in real estate.
Knob-and-tube wiring is an early method of electrical wiring used in buildings from the late nineteenth century to the mid-twentieth century.
In more detail
Unlike modern three-wire cables, knob-and-tube systems use two separate wires (hot and neutral) that run parallel to each other. It lacks a grounding wire, which increases the risk of shock and damage to sensitive electronics. Additionally, the rubberized cloth insulation degrades over time, especially when exposed to heat or pests.
Because this wiring requires open air to dissipate heat, covering it with modern attic insulation is a fire hazard. Many home insurance companies refuse to write policies for homes with active knob-and-tube wiring, requiring a full upgrade to modern copper wiring.
Key facts
| Category | Property Types & Construction |
|---|---|
| Watch out for | Lack of grounding, insulation breakdown, and insurance denial |
| Typical timing | Found in homes built before 1950 |
| Required by | Most home insurance providers to be replaced before coverage is approved |
A home buyer orders an inspection on a Victorian home built in 1910 and discovers active knob-and-tube wiring in the attic. To secure home insurance, the buyer must renegotiate the sale to cover the cost of rewiring the house.
Frequently asked questions
Is knob-and-tube wiring illegal?
No, active systems are not illegal, but they do not meet modern building codes for new construction and are widely considered safety hazards due to the lack of grounding.
Can I cover knob-and-tube wiring with insulation?
No, wrapping or burying these wires in thermal insulation prevents heat dissipation, which can cause the wires to overheat and ignite surrounding materials.