Introduction
In the early days of electrical wiring, before the widespread use of rubber and plastic insulators, an unusual material was commonly used as insulation around wires: horsehair. For decades, the fine hairs from horses' manes and tails played a crucial role in allowing electricity to be used safely in buildings.
Though it may seem odd today, using horsehair as wiring insulation made sense in the late 1800s and early 1900s for several key reasons. As I'll explore in depth in this article, horsehair had a unique combination of properties that made it well-suited to help prevent dangerous electric shocks and building fires.
Understanding the history of horsehair's use in electrical systems provides interesting insights into the pioneering days of electrical engineering. So let's take a in-depth look at how and why horsehair wiring was invented, its properties and production, the transition to other insulation materials, and horsehair's legacy on wiring today.
The Need for Insulation in Early Electrical Systems
The invention of commercially viable electric lights and power systems in the late 1800s created a pressing need for wiring insulation materials. Thomas Edison’s first electric power stations began operating in 1882, with the first widespread electrical wiring appearing in buildings in the 1890s.
Early electrical systems used copper wiring to conduct electricity, and copper was prone to starting fires and shocking people if not insulated properly. When copper wires from a 100-volt system touched each other or the metal casing of a light fixture, the resulting short circuit could produce sparks hot enough to ignite nearby objects. The entire outside of wires also needed insulation to prevent electric shocks. Fires and fatal shocks due to early electrical systems were alarmingly common.
It was clear that effective insulation was critical for safety. But what materials could provide sufficient insulation while still being affordable and practical to manufacture? Options like rubber and plastics were still new and expensive. The challenge led to experimentation with many surprising and innovative materials, including horsehair.
How Horsehair’s Use as Insulation Began
Horsehair had been used for decades prior for stuffing mattresses and upholstery, so it was a readily available material in the late 1800s. As engineers tested options for wiring insulation, they discovered that tightly wrapped and varnished horsehair formed an effective barrier to contain electrical current within the copper conductors.
One of the key innovators in using horsehair for insulation was Granville Woods. He patented a horsehair insulation system in 1884. Woods' system involved twisting two strands of horsehair together, then winding this material spirally around a copper wire. This was then varnished to hold everything in place.
Another early pioneer of horsehair wiring, Thomas Edison, noted horsehair's unique advantages:
“Horsehair possesses greater tensile strength, is more resistant to moisture, is less likely to become brittle, and makes a lighter insulation than cotton and silk.”
Horsehair quickly became a common insulation material used by Edison Electric and other early electrical companies. For the next few decades, it served as an important temporary solution while other options were explored.
Why Horsehair Worked as an Insulator
Horsehair had a unique mix of properties that made it well suited as an electrical insulator in several ways:
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Non-conductive - Horsehair is composed of keratin rather than metal, so it does not conduct electricity. This prevented shorts.
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Heat-resistant - Horsehair can withstand high temperatures, so it did not burn or melt easily when wires heated up. This helped reduce fire risk.
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Moisture-resistant - Horsehair does not absorb much moisture. This maintained its insulating strength even in damp conditions.
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Durable - Horsehair is tough and abrasion-resistant. It did not wear out quickly when used in wiring systems.
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Cheap and abundant - Horsehair was easy to obtain as a waste product from horse husbandry and horsehair mattress production. This kept costs low compared to other options.
Thanks to these useful properties, companies were able to use horsehair to help insulate wires throughout buildings relatively safely and affordably. However, horsehair was far from an ideal solution.
Challenges and Drawbacks of Horsehair Wiring
While horsehair was well suited in some ways, it also had disadvantages that led to issues and accidents:
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Flammable - While resistant to moderate heat, horsehair can burn in a sufficiently intense fire. This contributed to some electrical fires.
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Brittle over time - Horsehair becomes brittle as it ages and is subjected to vibration. This led to cracks in the insulation over years of use.
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Rodent issues - Rats and mice liked chewing on horsehair. Rodent damage could gradually destroy insulation on wires.
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Labor-intensive - Wrapping horsehair on wires throughout a building was extremely time consuming and labor intensive.
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Inconsistent quality - There were variations in insulation quality depending on technique used. Poor wrapping lead to failures.
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Hard to repair - Damaged horsehair insulation was difficult to access and rewrap within walls.
These issues with horsehair wiring led to many fires and accidents even when done properly. As a result, electrical engineers kept seeking better solutions.
The Transition to Rubber, Plastics, and Other Insulation
In the late 1800s and early 1900s, chemists began developing early synthetic materials like Bakelite plastic and vulcanized rubber. These offered new options for insulating wires.
The benefits over horsehair included being fireproof, consistent in quality, and simpler to apply by extruding insulation directly over wires. As rubber and plastics improved in quality and dropped in price in the 1920s, they quickly displaced horsehair wiring.
Other modern insulation materials like PVC, fiberglass, nylon, and polyethylene were also invented and used for wiring starting in the 1930s and 1940s. Each new material made horsehair increasingly obsolete.
That said, horsehair wiring remained legal and in use in some homes into the 1950s in the United States and beyond. It took decades for modern wiring to fully replace horsehair across all existing buildings.
Legacy and Remnants of Horsehair Wiring Today
While no longer used today, horsehair wiring still has lasting impacts. In many older homes built before 1950, you may still find original horsehair-insulated wires behind walls and under floors.
This outdated wiring can be a safety hazard due to deterioration and insufficient insulation by modern standards. Proper precautions should be taken and upgrades considered when encountering old horsehair wiring in a building.
Horsehair wiring also left a legacy in electrical terminology. Even today, the overall diameter of a wired conductor and insulation is measured in "circular mils". This term originates from the area of a circle with a 1 mil (1/1000 inch) diameter. The large circular mil area of insulation needed for horsehair wiring led to its use as a unit of measurement.
So while horsehair itself is no longer used, its history remains tightly intertwined with the early days of bringing electricity into buildings. Horsehair wiring was an imperfect but important step along the way toward the insulated wires universally used today.
Conclusion
For a period of around 50 years, horsehair served a vital role as an electrical insulator during the pioneering era of electrical wiring systems. While it had flaws, its unique advantages of low cost, non-conductivity, heat resistance, and moisture resistance made it the best solution available at the time.
As materials science advanced, horsehair was phased out and replaced by far superior insulators like rubber and plastics. But the next time you see circular mils mentioned or encounter old wiring, remember that it was horsehair that first enabled homes and businesses to be lit and powered electrically safely and economically. The horsehair wiring era remains an important chapter in the ongoing story of harnessing electricity for human benefit.