The Decline of Knob and Tube Wiring

The Decline of Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube wiring was an early standardized method of electrical wiring used in buildings in Canada and the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported on nailed-down porcelain knob insulators.

This old type of wiring has since been replaced in new construction with newer and safer wiring methods, such as non-metallic sheathed cable ("Romex") and metal clad cables ("BX"). However, there are still many old homes that contain original, outdated knob and tube wiring.

Why Knob and Tube Wiring is Problematic

While knob and tube wiring was considered safe when it was first introduced, it does not meet today's electrical standards and can pose several risks, such as:

The Decline of Knob and Tube Wiring

Knob and tube wiring systems started to decline in popularity in the 1930s and 40s as safer electrical wiring methods were developed and adopted, such as armored cable (BX) and non-metallic sheathed cable (Romex).

The National Electrical Code (NEC) was developed in 1897 and started prohibiting unsafe wiring practices. The code has been updated over the decades to completely phase out knob and tube wiring:

So over the past 70+ years, knob and tube wiring has been completely phased out through evolving safety standards and building codes. While previously commonplace, it is now considered a dangerous relic of the past.

Dangers of Outdated Knob and Tube Wiring

While knob and tube wiring has declined drastically, I still encounter it regularly in old homes I am inspecting or upgrading. As an electrician, I emphasize to clients that it poses substantial safety hazards and should be completely removed. Some of the dangers I highlight include:

I always recommend my customers completely replace old knob and tube wiring for health, safety, and liability reasons. The risks are simply too great to keep using this obsolete, dangerous wiring in a home.


Knob and tube wiring represented an important early standardized method that helped bring electricity into many homes. However, evolving safety codes and standards have now completely prohibited its use due to substantial fire and shock risks. As an electrician, I see these dangers regularly and advise customers to fully replace knob and tube wiring with modern, safer wiring methods. While previously common, knob and tube wiring has declined into obscurity and is now considered a dangerous relic of the past.