Knob-and-Tube Wiring: What Owners of Older Homes Should Know

Owners of older homes in Lexington, Concord, Winchester or Arlington have a real chance of some original knob-and-tube (K&T) wiring still hiding in the walls, attic or basement. Here is what that means and when to do something about it.

Knob-and-tube was the standard method of wiring homes from roughly the 1880s through the 1940s. It uses ceramic knobs and tubes to run individual wires through the framing. It was well-built for its time, but it was never designed for modern electrical loads, it has no ground wire, and its insulation becomes brittle with age.

The practical problems today are threefold. Safety comes first: old, damaged, or buried K&T can be a fire risk, especially where it has been covered by insulation or spliced into carelessly over the decades. Capacity is next, since it cannot safely support the demands of a modern kitchen, EV charger, or heat pump. Insurance is the third, as many carriers now refuse to write or renew policies on homes with active knob-and-tube, or charge more for them.

A whole house does not always have to be rewired at once. In many older homes, the active, accessible, and highest-risk runs can be prioritized first, then the rest worked through in stages. What matters is a clear picture of what is live, what is abandoned, and what needs to go.

Rewiring an occupied older home is as much about craft as it is about wiring. For anyone buying, selling, or insuring an older home who needs to know where things stand, a knob-and-tube assessment from a licensed electrician lays out the options.