The Forgotten Knob and Tube Wiring That Could Burn Down Your House

What is Knob and Tube Wiring?

Knob and tube wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall cavities, passing through joists and studs.

The system gets its name from the porcelain knobs used to hold the wiring away from frame members, and the porcelain tubes used to contain wires where they passed through joists and studs.

Key Features of Knob and Tube Wiring

Why Knob and Tube Wiring is a Fire Hazard

While knob and tube wiring was an important evolution in electrical safety when first introduced, it poses several fire risks by modern standards:

Deterioration Over Time

Lack of Grounding

Overloading Circuits

Exposure to Combustibles

Signs You May Still Have Knob and Tube Wiring

Many older homes may still contain knob and tube wiring hidden behind walls and ceilings. Here are some signs that your home may need inspection:

If your home was built before 1950 and exhibits any of these issues, it is wise to have a qualified electrician inspect for knob and tube wiring.

Dangers and Risks of Old Wiring

Knob and tube wiring poses not just fire risk but other dangers:

Upgrading Old Wiring

If your home does contain old knob and tube wiring, some upgrade options include:

I strongly recommend fully upgrading old wiring for maximum safety. Though expensive, it can prevent catastrophic house fires.


Knob and tube wiring was an important evolution in home electrification, but now poses serious fire and shock hazards due to deterioration over 80-100 years of use. If your older home exhibits any signs of old wiring, have it professionally inspected and upgraded. The investment is worthwhile to protect your home and family.