The Forgotten History of Knob and Tube Wiring That Could Save Your Life

Introduction

Knob and tube wiring was the standard method of electrical wiring used in buildings in North America from about 1880 to the 1940s. This old system is now often forgotten, but understanding its history and how it works is crucial - it could even save your life.

In this article, I will provide a comprehensive overview of knob and tube wiring, including:

• What is knob and tube wiring?
• When was it used?
• Why was it so common?
• How does it work?
• The pros and cons of knob and tube wiring
• Safety concerns and risks
• Options for replacement and upgrades
• Reasons you may still have knob and tube wiring
• Signs that you have knob and tube wiring
• Precautions to take if you have knob and tube wiring
• The future of knob and tube wiring

Knowing about knob and tube can prevent fires and electrocution. While upgrading it is ideal, even just understanding knob and tube can help you use it more safely.

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring was the early standardized method used for electrical wiring in buildings in the United States from about 1880 to the 1940s. This wiring system consists of insulated copper conductors passing through lumber framing drill holes via protective porcelain insulating tubes or knobs.

K&T wiring has:

• Wires coated in rubber insulation
• Wires passing through porcelain knobs attached to framing
• Wires running through porcelain tubes through open spaces
• No ground wire
• Wires spliced together and wrapped with cloth tape

This system allowed electrical wires to be safely and neatly installed while being separate from framing.

When Was Knob and Tube Wiring Used?

Knob and tube wiring was first introduced in the 1880s as a safer standardized method than previous electrical wiring systems.

By the early 1900s, knob and tube wiring had been adopted into the National Electrical Code (NEC) standards and became the most common wiring method used in American buildings.

Millions of American homes, buildings, and industrial facilities built between 1880-1930 contain knob and tube wiring. Use of the wiring continued in some rural and industrial applications into the 1950s.

So while knob and tube wiring might seem antiquated, it powered America through the electrification boom of the early 20th century.

Why Was Knob and Tube Wiring So Common?

There are several key reasons knob and tube wiring became the dominant wiring method for decades:

• Safety - Knob and tube separated wires from flammable materials like wood framing and had insulation to prevent contact. This was safer than previous methods.

• Simplicity - The wiring method was relatively simple and inexpensive compared to other early wiring systems.

• Adaptability - The wiring could be easily installed in both new construction and retrofitted into existing buildings. This allowed buildings and homes to upgrade to electricity.

• Durability - Properly installed knob and tube wiring has proven to be extremely durable, with some systems lasting over 100 years.

• Standards - Its inclusion in the NEC gave knob and tube credibility and standardized its use across the country.

For these reasons, knob and tube wiring became the standard electrical wiring method for decades. Millions of buildings throughout North America relied on it.

How Does Knob and Tube Wiring Work?

The knob and tube wiring system consists of:

• Wires - Insulated copper wires coated in a rubber and cloth insulation. These conduct electricity through the system.

• Porcelain knobs - Nailed or screwed to framing, these hold the wires in place and insulate them from touching wood.

• Porcelain tubes - Hollow tubes that protect wires through open spaces like wall cavities and attics.

• Cloth tape - Used to splice wires together, sealing connections with insulating tape.

• No ground wire - Knob and tube systems typically do not include a ground wire.

Wires pass via knobs and tubes drilled through lumber framing. Wires are kept separate from each other and framing using the porcelain insulators. splice connections together along the path of the wires to connect the full system.

This creates an early electrical wiring system that delivers electricity while insulating wires separately for safety.

The Pros and Cons of Knob and Tube Wiring

Pros

• Durable and long-lasting if properly installed.
• Allows easy retrofitting of electricity into existing buildings.
• Keeps wires separated and insulated.
• Provides reliable electricity when properly maintained.

Cons

• Outdated system without modern safety features.
• No ground wire increases risk of electrocution and fire.
• Materials become brittle over time.
• Modifications are challenging and can be unsafe.
• Difficult to inspect wiring conditions.
• Fire and insurance risk with aging systems.
• Incompatible with modern electrical loads and needs.

Safety Concerns and Risks of Knob and Tube Wiring

While knob and tube wiring was safe when installed to code at the time, there are serious safety risks to be aware of with aging systems:

• Fire hazard - Outdated wiring is a major fire risk, especially as insulation breaks down over time. This can cause shorts, arcing, and fires.

• Electrocution risk - Lack of grounding combined with damaged insulation can lead to deadly electric shocks.

• Overloading circuits - Old systems aren't designed to handle the electricity needs of modern appliances and devices. This can lead to fires.

• Exposed wires - Knob and tube wiring can become exposed due to insulation damage, presenting a major shock hazard.

• Insurance issues - Many insurers will not cover homes with knob and tube wiring due to the substantial risks.

Safety with aging electrical systems is crucial. Damaged or overloaded knob and tube wiring can be deadly. Understanding the risks is the first step to staying safe.

Options for Replacing or Upgrading Knob and Tube Wiring

If your home or building has knob and tube wiring, some upgrade options include:

• Full rewire - Replacing all knob and tube wiring with modern wiring and a circuit breaker panel. This removes all risks but is costly.

• Targeted replacement - Strategically rewiring high-risk and high-use areas first, leaving remainders. More affordable but still has some old wiring.

• Pigtailing - Attaching modern wiring to properly functioning K&T circuits to power modern devices. Low cost but doesn't remove old wiring.

• Circuit breakers - Upgrading outdated fuse boxes to modern circuit breakers. Improves safety but keeps old wiring.

• GFCI outlets - Installing outlets with ground-fault protection on old wiring provides some safety where needed most.

• Electrical assessment - Have a licensed electrician inspect your K&T wiring and make custom recommendations for improving safety.

Reasons You May Still Have Knob and Tube Wiring

There are a few common reasons knob and tube wiring still exists in buildings today:

• Very old home or building - Any structure built before 1950 likely contains knob and tube wiring to some extent. Older commercial buildings commonly have it.

• Lack of renovations or upgrades - Homes that have not been rewired or had electrical work done in 40+ years often still have old systems intact.

• Rural buildings - Remote rural homes were some of the last to transition fully to modern wiring, sometimes into the 1970s or beyond.

• Concealed wiring - Walls, crawl spaces and attics may still hide old knob and tube wiring even in upgraded homes. It can easily go unnoticed.

Unless wiring has been specifically replaced, assume residences from the 1930s or earlier contain some original knob and tube circuits. Knowing your home's history helps assess risk.

Signs That You Have Knob and Tube Wiring

Some clear signs your home likely has knob and tube wiring include:

• Two-prong ungrounded outlets - A lack of three-prong grounded outlets indicates no ground wiring.

• Wiring through ceilings and walls - Visible ceramic knobs or tubes along framing.

• An in-use fuse box - Presence of a fuse box instead of circuit breakers.

• Wiring wrapped in cloth - Cloth-wrapped wire splices are a telltale knob and tube sign.

• Commercial armored cable (BX) - BX wiring alongside knob and tube may indicate some old wiring remains.

• Home age pre-1950 - Homes built before 1950 typically contain knob and tube unless wiring has been replaced.

Being aware of these signs of old wiring can prompt you to further investigate or take safety precautions.

Precautions to Take if You Have Knob and Tube Wiring

If you suspect or confirm your home contains old knob and tube wiring, some important safety precautions include:

• Have the system assessed by an electrician to identify any risks or needed repairs.

• Use bulbs and appliances below recommended wattages to avoid overloading circuits.

• Do not run high-wattage appliances like space heaters on old wiring.

• Avoid using extension cords or power strips off old circuits.

• Only have necessary upgrade work done by licensed electricians, not DIY.

• Never run modern grounded wiring off old ungrounded circuits.

• Check for hot spots or damage to wires and wiring insulation regularly.

• Confirm your homeowners insurance policy covers liability risks associated with old electrical systems.

With vigilance and proper precautions, knob and tube wiring can be used more safely until a full upgrade is feasible. But use extreme care, as safety issues can develop over time.

The Future of Knob and Tube Wiring

Knob and tube wiring still exists in an estimated 4-8 million U.S. homes, mostly out of sight and out of mind. But safety risks loom large with deterioration over time.

Most insurance companies and housing authorities now recommend fully replacing knob and tube wiring due to substantial fire and electrocution hazards as wiring ages. However, expensive costs lead many to delay upgrades.

As long as knob and tube remains, periodic inspections, maintenance and careful use are vital for preventing tragedy. Homeowners should have upgrade plans in place.

Full removal of all aging knob and tube wiring is the ideal future solution, though realistically a long way off. In the meantime, homeowners must become informed of the risks these old systems pose to keep their families safe.

Conclusion

Knob and tube wiring provided electricity to millions of North American buildings for decades, but still lingers as a modern safety threat we cannot ignore.

While upgrades are ideal, a combination of education, vigilant precautions, careful use, and eventual replacement of old wiring offers the best path forward. Understanding the forgotten history of knob and tube just might save your life.