The Forgotten Knob-and-Tube Wiring of the 1920s

Introduction

As I walk through old houses built in the 1920s, I often come across an antiquated electrical system known as knob-and-tube wiring. This primitive wiring method was common in homes of that era but has since been mostly forgotten. In this article, I aim to provide a comprehensive overview of knob-and-tube wiring - what it is, why it was used, its advantages and disadvantages, and why it eventually became obsolete. There is a rich history behind this old wiring method that many have forgotten over time. Join me as I unravel the details of the knob-and-tube wiring of the 1920s.

What is Knob-and-Tube Wiring?

Knob-and-tube wiring, also known as knob-and-tube or K&T wiring, refers to an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consisted of insulated copper conductors passing through lumber framing drill holes via ceramic knobs and being supported along their length by porcelain tube insulators.

The knob served as an air spacer to prevent contact between the wire and the lumber. The tubes kept the wires separated from one another. This method provided protection against incidental contact with the structural components but was eventually rendered obsolete by nonmetallic sheathed electrical cables such as NM cables.

Why Was Knob-and-Tube Wiring Used?

In the early 20th century, knob-and-tube wiring became the standard for wiring buildings and homes. It offered several key advantages over previous wiring methods:

• Safety - The porcelain knobs and tubes provided excellent electrical insulation to prevent fires and shocks. This was safer than simply running wires through walls and ceilings.

• Adaptability - The wires could be snaked between wall studs and ceiling joists, allowing wiring to be added easily without major construction work.

• Ventilation - Air could circulate around the wires in the open spaces, keeping them cool and reducing fire risk.

• Affordability - Knob-and-tube wiring was relatively affordable compared to other options at the time. The rubber and porcelain materials were cheap and widely available.

For these reasons, knob-and-tube wiring was the standard wiring method for new construction in the 1920s and earlier. It was better than previous methods and a pragmatic choice before newer insulated cables were introduced.

What Did Knob-and-Tube Wiring Look Like?

Knob-and-tube wiring had a distinctive appearance:

• Wires - Single solid or stranded copper conductors with cloth or rubber insulation. Red for hot wires, black for neutral, bare for ground.

• Knobs - Glazed porcelain knobs spaced along wires where they passed through framing. Held wires in place.

• Tubes - Porcelain tubes with grooves for wires to pass through. Separated wire runs.

• Framing - Wires passed through holes drilled in floor joists, wall studs, roof rafters. Let wires pass through open framing cavities.

• Splicing - Wires spliced and joined together with electrical tape or rubber splicing compound. Created connections and branches.

• Fixtures - Wires connected to ceramic light sockets, switches, and outlets mounted on wooden boards or directly to framing.

This produced an installation with wires passing visibly through framing, following the structure of the building. It did not use concealed cables like modern wiring.

Advantages of Knob-and-Tube Wiring

Knob-and-tube wiring held some key advantages over previous electrical systems:

• Less fire risk - Open air spacing reduced chance of overheating compared to early insulated cables.

• Easier installations - Wires could be fished through finished walls and ceilings. Did not require as much demolition.

• Adaptable layouts - Wiring could be changed by simply adding new wire runs. Easy to upgrade and expand.

• Durable materials - Ceramic knobs and tubes were very sturdy and heat resistant.

• Bare ground wires - Ground wires were left bare for better grounding contacts.

For its time, knob-and-tube was a major improvement in safety and practicality compared to previous wiring methods. It was better suited for wiring old homes than its predecessors.

Disadvantages of Knob-and-Tube Wiring

However, knob-and-tube wiring did have some disadvantages that led to its eventual decline:

• Insulation degradation - The rubber/cloth insulation dried out over time, becoming brittle and dangerous.

• Lack of grounding - No ground wires, increasing shock risk. Only hot and neutral.

• Unsafe splicing - Splicing was crude compared to modern standards. More failure prone.

• imited capacity - Small wire gauges limited electric loads. Could not support large appliances.

• Difficult upgrades - Fishing new wires into packed walls was hard. Major renovations required.

• Fire spread - Open wiring let fires easily spread to surrounding structure. Modern cables are more fireproof.

The lack of modern conductor insulation and adequate grounding ultimately made knob-and-tube unacceptable by modern electrical standards. It simply could not provide the safety and capacity needed for modern homes and businesses.

The Decline of Knob-and-Tube Wiring

By the 1930s and 1940s, knob-and-tube wiring standards were beginning to fade in favor of a new type of wiring - nonmetallic sheathed cables. These early NM cables had insulated wire bundles and an overall sheath for physical protection and fire resistance.

NM cables offered major advantages over knob-and-tube:

• Fully insulated wires throughout
• Built-in grounding conductor
• Higher wire gauges for more capacity
• Flexible installation without open wiring
• Less fire spreading ability

Homes wired with NM cable also had easier wiring upgrades by simply running new cables through walls and ceilings. By 1950, the National Electrical Code prohibited knob-and-tube in new construction. And over time, most existing knob-and-tube was phased out or abandoned.

Very few homes still have working original knob-and-tube wiring today. It is considered obsolete and dangerous by modern standards. Any still in use requires careful inspection and upgrading. The era of knob-and-tube electrification ended as homes transitioned to safer and more capable NM cables.

Rare Remnants in Old Houses

While no longer used, knob-and-tube wiring can still occasionally be found in older homes that have not been rewired. Some identifiable signs include:

• Ceramic knobs - Glazed porcelain knobs in unfinished basements, crawlspaces, and attics.

• Tubes along rafters - Porcelain wiring tubes visible along roof rafters in attic spaces.

• Two-wire cables - Only two insulated wires, no grounding conductor. Red and black colored.

• Open splices - Early rubber tape and compound splices showing in junction boxes.

• Close wiring - Wires closely spaced through holes in framing without modern cables.

When encountered, old knob-and-tube wiring is usually dead or disconnected. It poses a safety hazard due to deterioration and lack of grounding. While a curiosity of old electrical systems, it should be completely removed and replaced with modern wiring.

Conclusion

The knob-and-tube wiring of the early 20th century powered the electrification of many American homes. But what was once a practical and innovative wiring method is now an obsolete relic. While it has largely faded from use, knob-and-tube reminds us of the early days of residential electricity. We can still find it hidden in old homes as a testament to the ever-advancing march of technology in even mundane things like house wiring. Knob-and-tube served its purpose for a time, but better wiring was inevitable as electricity demand increased. Even the forgotten wires in our walls have a story to tell.