Knob and tube wiring was the standard method of electrical wiring used in buildings in North America from about 1880 to the 1940s. This old system is now often forgotten, but understanding its history and how it works is crucial - it could even save your life.

In this article, I will provide a comprehensive overview of knob and tube wiring, including:

Knowing about knob and tube can prevent fires and electrocution. While upgrading it is ideal, even just understanding knob and tube can help you use it more safely.

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring was the early standardized method used for electrical wiring in buildings in the United States from about 1880 to the 1940s. This wiring system consists of insulated copper conductors passing through lumber framing drill holes via protective porcelain insulating tubes or knobs.

K&T wiring has:

This system allowed electrical wires to be safely and neatly installed while being separate from framing.

When Was Knob and Tube Wiring Used?

Knob and tube wiring was first introduced in the 1880s as a safer standardized method than previous electrical wiring systems.

By the early 1900s, knob and tube wiring had been adopted into the National Electrical Code (NEC) standards and became the most common wiring method used in American buildings.

Millions of American homes, buildings, and industrial facilities built between 1880-1930 contain knob and tube wiring. Use of the wiring continued in some rural and industrial applications into the 1950s.

So while knob and tube wiring might seem antiquated, it powered America through the electrification boom of the early 20th century.

Why Was Knob and Tube Wiring So Common?

There are several key reasons knob and tube wiring became the dominant wiring method for decades:

For these reasons, knob and tube wiring became the standard electrical wiring method for decades. Millions of buildings throughout North America relied on it.

How Does Knob and Tube Wiring Work?

The knob and tube wiring system consists of:

Wires pass via knobs and tubes drilled through lumber framing. Wires are kept separate from each other and framing using the porcelain insulators. splice connections together along the path of the wires to connect the full system.

This creates an early electrical wiring system that delivers electricity while insulating wires separately for safety.

The Pros and Cons of Knob and Tube Wiring



Safety Concerns and Risks of Knob and Tube Wiring

While knob and tube wiring was safe when installed to code at the time, there are serious safety risks to be aware of with aging systems:

Safety with aging electrical systems is crucial. Damaged or overloaded knob and tube wiring can be deadly. Understanding the risks is the first step to staying safe.

Options for Replacing or Upgrading Knob and Tube Wiring

If your home or building has knob and tube wiring, some upgrade options include:

Reasons You May Still Have Knob and Tube Wiring

There are a few common reasons knob and tube wiring still exists in buildings today:

Unless wiring has been specifically replaced, assume residences from the 1930s or earlier contain some original knob and tube circuits. Knowing your home's history helps assess risk.

Signs That You Have Knob and Tube Wiring

Some clear signs your home likely has knob and tube wiring include:

Being aware of these signs of old wiring can prompt you to further investigate or take safety precautions.

Precautions to Take if You Have Knob and Tube Wiring

If you suspect or confirm your home contains old knob and tube wiring, some important safety precautions include:

With vigilance and proper precautions, knob and tube wiring can be used more safely until a full upgrade is feasible. But use extreme care, as safety issues can develop over time.

The Future of Knob and Tube Wiring

Knob and tube wiring still exists in an estimated 4-8 million U.S. homes, mostly out of sight and out of mind. But safety risks loom large with deterioration over time.

Most insurance companies and housing authorities now recommend fully replacing knob and tube wiring due to substantial fire and electrocution hazards as wiring ages. However, expensive costs lead many to delay upgrades.

As long as knob and tube remains, periodic inspections, maintenance and careful use are vital for preventing tragedy. Homeowners should have upgrade plans in place.

Full removal of all aging knob and tube wiring is the ideal future solution, though realistically a long way off. In the meantime, homeowners must become informed of the risks these old systems pose to keep their families safe.


Knob and tube wiring provided electricity to millions of North American buildings for decades, but still lingers as a modern safety threat we cannot ignore.

While upgrades are ideal, a combination of education, vigilant precautions, careful use, and eventual replacement of old wiring offers the best path forward. Understanding the forgotten history of knob and tube just might save your life.