Introduction to Knob-and-Tube Wiring

The knob-and-tube (K&T) wiring method was commonly used in North American homes and buildings from about 1880 to the 1940s. This early form of electrical wiring consisted of insulated copper conductors passing through ceramic knobs and tubes, which supported and separated the wires.

K&T wiring provided a safer, more reliable, and longer-lasting form of electrical wiring compared to previous methods. It was a vital transitional technology that helped enable the widespread adoption of electricity in homes and businesses. However, as electrical demands grew, K&T wiring became insufficient and has largely been forgotten.

The Dangers of Early Electrical Wiring Methods

In the late 19th century, electricity began entering buildings, but there were no safety standards. Some of the early wiring methods were downright dangerous:

These crude exposed wiring methods led to fires, shock hazards, and reliability issues. A safer, concealed wiring method was desperately needed.

How Knob-and-Tube Wiring Solved These Problems

The knob-and-tube wiring method neatly solved many of the problems with early electrical wiring:

This made knob-and-tube an efficient and reliable concealed wiring method that was a major improvement over previous methods. It minimized fire and shock risks and lasted much longer.

Why Knob-and-Tube Wiring Went Largely Unnoticed

Despite solving major safety and reliability problems, knob-and-tube wiring was mostly invisible once installed:

So although knob-and-tube wiring was essential for the introduction of electricity in buildings, homeowners may have barely noticed it. The lack of visibility allowed the important wiring method to be largely overlooked.

The Eventual Decline of Knob-and-Tube Wiring

By the 1930s and 40s, knob-and-tube wiring began to be phased out in favor of a new form of wiring - nonmetallic sheathed cable (NM, or Romex). Reasons for the decline include:

So although K&T served us well for many decades, it became outdated. But we shouldn't forget that it helped build the foundation for modern building wiring.


While largely forgotten today, knob-and-tube wiring was an important milestone in the introduction of electricity. It provided a concealed wiring method that minimized many of the fire and shock risks of early electrical systems. K&T wiring enabled homes and businesses to adopt electricity in a safe, reliable way - even if it went mostly unnoticed. We can appreciate that this transitional method helped pave the way for modern electrical wiring.