I live in an old house built in the 1920s. When I first moved in, I was unaware of the antiquated electrical system hidden inside the walls. Upon inspection, I discovered that the wiring was an obsolete 'knob and tube' system, which can pose serious fire and shock hazards in vintage homes. This prompted me to research this perilous method of wiring which still exists in millions of older dwellings across North America.

What is Knob and Tube Wiring?

Knob and tube (K&T) is an early standardized method of electrical wiring used in buildings from about 1880 to the 1940s. It consists of insulated copper conductors passing through ceramic knobs mounted on wooden framing and interconnected by porcelain tubes.

Some key features of knob and tube wiring:

This old-fashioned wiring system was phased out in favor of safer and more efficient systems using electrical cables and conduits. However, K&T wiring still exists in many old homes constructed prior to 1950.

Why Knob and Tube Wiring is Dangerous

There are several factors that make knob and tube wiring potentially unsafe:

For these reasons, insurance providers often will not cover houses with knob and tube wiring or require upgrades prior to issuing policies.

Where Does Knob and Tube Wiring Linger Today?

I was surprised to discover how common knob and tube wiring still is. Here are some facts about where it persists today:

Unless properly updated, any older home should be presumed to contain some obsolete and possibly compromised K&T circuits.

Is Knob and Tube Wiring Ever Acceptable to Leave In Place?

Some homeowners may be tempted to just leave vintage knob and tube wiring alone. However, there are very few cases where K&T can be safely maintained:

Otherwise, a full replacement of old knob and tube wiring is the only prudent option in most homes. Leaving damaged, overloaded, or concealed K&T in place indefinitely is asking for trouble down the line.

Signs Your Home May Still Have Hidden Knob and Tube Wiring:

If in doubt, consult with a qualified electrician to identify if your vintage home still harbors any knob and tube wiring. Stay vigilant for any indications of old wiring as a fire prevention measure.

Options for Replacing Knob and Tube Wiring:

  1. Full rewire - The most thorough option is to completely remove old wiring and install brand new modern wiring throughout the home. This allows incorporating safety features like grounding and GFCI outlets.

  2. Targeted upgrades - For budget reasons, some homeowners opt to only replace K&T wiring in the most hazardous or highest load locations. Prioritize kitchens, bathrooms, and laundry first.

  3. Wiring insulation - Special plastic sleeves can be installed over K&T wires as an interim protective measure. But this does not alleviate all risks.

  4. Circuit breakers - Upgrading outdated fuse boxes to modern circuit breaker panels can add capacity and safety to old wiring.

No matter the approach, it is wise for homeowners to be proactive about addressing vintage electrical systems. Replacing antiquated knob and tube wiring removes accrued dangers that come with improperly maintained older homes.


Knob and tube wiring has not disappeared entirely. In fact, it still lurks unseen in millions of North American homes over 70 years old. While convenient and innovative in its heyday, K&T wiring now poses unacceptable fire and shock risks due to deterioration and lack of grounding. Homeowners should be vigilant for signs of old wiring and work to upgrade or replace any existing knob and tube circuits. Although costly, a full rewiring is the safest long-term solution for vintage dwellings still relying on this obsolete and hazardous electrical system. With vigilance and proactive upgrades, the lingering dangers of old knob and tube wiring can be eliminated.