What is Knob-and-Tube Wiring?

Knob-and-tube wiring is an early electrical system used in homes from the late 1800s to about the 1940s. It gets its name from the ceramic “knobs” that hold wires in place and “tubes” that protect wires as they pass through wooden framing.

This system uses single, insulated copper wires run separately through open air, rather than bundled together like modern cables. At the time, it was considered safe and effective because the spacing of wires allowed heat to dissipate easily.

However, knob-and-tube wiring has several drawbacks by today’s standards. It typically lacks a ground wire, which is an important safety feature in modern electrical systems. The insulation around the wires can also become brittle and deteriorate over time, increasing the risk of electrical fires. Additionally, it wasn’t designed to handle the electrical demands of modern appliances, which can lead to overloaded circuits.

While knob-and-tube wiring isn’t automatically unsafe if it’s in good condition, many insurance companies and home inspectors flag it as a concern.

As a result, homeowners often choose to replace or upgrade it to modern wiring for safety, capacity, and compliance with current electrical codes.