Introduction
Knob and tube wiring, also known as K&T wiring, was an early standardized method of electrical wiring used in North America from about 1880 to the 1930s. Despite its important role in bringing electricity to homes across the country, knob and tube wiring has largely faded from public memory. As I delved into the history of home electrification, I discovered the fascinating story of how knob and tube wiring powered the first electrified houses.
The Advent of Home Electricity
In the late 1800s, electricity was just beginning to enter American homes. The first houses were wired for electricity as early as 1878, though it remained uncommon until the turn of the century. Early electrical systems were hazardous, using exposed wires and splices that could start fires. Thomas Edison's Pearl Street Station, the first central power plant, began operating in New York City in 1882, providing 110 volts of direct current to 59 customers. But an electrical wiring standard was needed to safely bring electricity into the home.
The Development of Knob and Tube Wiring
Around 1880, the ancestors of knob and tube wiring were developed to meet the need for a standardized and safe electrical system. Wires were run through knobs - ceramic tubes attached to surfaces to hold the wires in place. This kept the wiring off wood framing to prevent fire hazards. The wires also passed through tubes when penetrating joists and studs.
Harvey Hubbell patented a variant in 1890 used twisted wiring and improved the installation process. His knob and tube system became the first widespread and commercial wiring method. By around 1905, some version of knob and tube wiring could be found in most electrified urban and suburban homes.
How Knob and Tube Wiring Worked
Knob and tube wiring consisted of insulated copper conductors passing through porcelain knobs fastened to surfaces, and through porcelain tubes where wires penetrated through walls and ceilings.
- The knobs held the wires in place and prevented contact with wood framing.
- The tubes routed wires through cavities, protecting wires from abrasion.
- Wires were separated by about one inch to prevent overheating.
- Only one conductor could pass through a tube, maintaining separation.
Since wires were open to the air rather than bundled together, knob and tube was Seen as a fireproof method despite its combustible insulation.
Wiring the First Electric Houses
I wanted to get a first-hand account of what it was like to wire homes for electricity using the early knob and tube method. I spoke with Herbert Guggenheim, a retired electrician who learned the knob and tube trade from his father in the 1920s.
"It was tricky getting those porcelain knobs perfectly spaced and keeping the tubes aligned when we fed the wiring through. We had to fish the wires through finished walls and ceilings, which took patience. But it was rewarding finally throwing that switch and lighting up a room for the first time."
Though tedious, knob and tube wiring allowed electricians to safely retrofit existing homes for electricity. By 1930, about half of urban homes in the US and Canada had electricity thanks to knob and tube.
The Later Years and Eventual Obsolescence
In the 1920s, a new rubber and cloth-insulated wiring method called BX became popular. Bundled BX wiring was cheaper and faster to install than knob and tube. The National Electrical Code prohibited new knob and tube installs in 1927. However, existing systems could remain until deemed unsafe.
By the 1950s, knob and tube wiring was finally obsolete. Very few homes today still have original knob and tube systems, which are forbidden by building codes. Though out of sight and out of mind, knob and tube played a vital part in bringing the convenience of electricity into 20th century homes.
Conclusion
Digging into the early history of home electrification gave me a new appreciation for knob and tube wiring. While hidden away in walls and quickly fading from memory, knob and tube systems powered the first electrically lit houses. The safety and standardization of knob and tube wiring paved the way for the reliable and convenient electrical systems we enjoy today. This largely overlooked chapter of electrical history deserves more recognition for the key role it played in lighting up our homes.