The Forgotten Knob and Tube Electrical Wiring Method of the 1920s

Introduction

As I research the history of residential electrical wiring, one method stands out as truly forgotten - knob and tube wiring. First coming into use in the late 19th century, knob and tube wiring was the dominant way homes were wired for electricity in North America from about 1880 to the 1930s. However, as wiring methods evolved and safety concerns arose, knob and tube was gradually phased out. Today, most homeowners have likely never heard of knob and tube, yet millions of homes still contain remnants of this antiquated wiring. In this article, I aim to uncover the origins, rise, and eventual decline of knob and tube wiring. By learning about this forgotten method, we can better appreciate how far residential electrical systems have advanced over the past century.

What Exactly is Knob and Tube Wiring?

To understand the knob and tube method, we must visualize how it worked. Rather than wiring being contained in metal conduits as we see today, knob and tube wires were run individually along the framing of a house. Insulated wires were mounted to porcelain knobs that attached to surfaces. Where wires crossed, they were separated by porcelain tubes. This allowed an air gap between wires to serve as insulation.

While knob and tube used only two wires compared to today's three wire (hot, neutral, ground) systems, it provided an effective early method of delivering electricity within homes. With air as the insulator instead of modern rubber or plastic, knob and tube was considered a fire-resistant and durable wiring technique for the time. The name comes from the nobs and tubes used as insulators, but this method also used various other fittings like junction boxes and ceiling rosettes.

When and Why Did Knob and Tube Wiring Emerge?

Knob and tube wiring came into prominence in North America in the late 1880s and 1890s. This was the very beginning of residential electrification, as power generation became widespread in urban areas.

Thomas Edison's firms helped drive the adoption of knob and tube, heavily promoting and installing this wiring technique in newly electrified homes, apartments, and businesses. It was well-suited to retrofitting existing buildings since wires could be fished through walls and ceilings without major demolition. The open air design was seen as reducing fire risk compared to early alternatives like running wires through wood molding.

For several decades, knob and tube served as an effective and widely accepted method of residential wiring. It was commonplace in American and Canadian homes of the early 20th century. The electrical capacity was limited by today's standards, but enabled lighting, appliances, and other amenities that made for modern living at that time.

The Heyday and Eventual Decline of Knob and Tube Wiring

By the 1920s, knob and tube wiring was firmly entrenched as the wiring method of choice for North American homes, used in an estimated 70-90% of residences. Even as the electrical needs of households grew more complex, knob and tube remained popular through this decade.

However, alternatives emerged by the 1930s like armored cable (BX) and non-metallic sheathed cable (NM, or Romex). New wiring codes also started prohibiting or restricting knob and tube installations. Concerns arose over inadequate wire size given increasing electric use, lack of grounding, and fire risks as systems aged.

By the 1950s, knob and tube was officially discontinued in the National Electrical Code. Most residential wiring projects now opted for more modern methods. However, the inexpensive and durable nature of knob and tube meant that many existing installations remained for decades. Even today, it is not uncommon for houses built before 1950 to still contain some intact knob and tube circuits.

Dangers and Downsides Lead to Eventual Phase-Out

While knob and tube wiring served homes well for many years, it does have concerning drawbacks by modern standards. These issues ultimately led to the demise of this wiring technique:

• Fire hazard - The insulation on wires can deteriorate over time, exposing live conductors. Air gaps and ventilation were supposed to reduce fire risks, but failures still occurred.

• Lack of grounding - With only two wires, knob and tube lacks a ground path. This makes it more prone to electrical issues and shock risks.

• Inadequate capacity - These systems were designed for simpler electrical loads. As more appliances came into use, capacity became insufficient.

• Inaccessible wiring - Running through walls, knob and tube is difficult to inspect and replace. This increased maintenance problems as homes aged.

• Safety and code compliance - By mid-century, knob and tube fell far short of evolving safety and electrical codes. Liability and insurance concerns accelerated its replacement.

While knob and tube was innovative for its time, technologies advanced well beyond its capabilities and safety by the mid-1900s. Wiring methods that contained wires made far more sense for supporting surging electrical demands. Though the fire risks were sometimes overstated, the writing was on the wall for knob and tube.

Gradual Replacement Persists in Many Older Homes

Given the massive scale of knob and tube wiring for decades, total replacement was gradual and remains incomplete. It is estimated that millions of North American homes still have some legacy knob and tube wiring even today.

As I discover these relics still hidden within walls, I'm compelled to properly update my own home's electrical system. However, full removal can be expensive if it requires extensive drywall demolition and re-wiring. Many homeowners undertake partial upgrades over time, focusing first on high priority areas like kitchens and bathrooms.

Persisting knob and tube wiring serves as reminder of the primitive nature of early electrical systems. For continued safety, it merits replacement. But it also represents an intriguing engineering innovation of the late 1800s. Knob and tube wiring powered society into the electrical age, even if its limitations became unacceptable. It remains an obscure wiring technique frozen in time, reminiscent of a forgotten era.