The Forgotten History of Knob and Tube Wiring

Introduction

Knob and tube wiring was the first electrical wiring system used for lighting and appliances in homes and businesses. It was invented in the 1880s and was commonly installed until the 1930s when it began to be phased out. However, there are still many homes today, especially older ones, that contain original, hidden knob and tube wiring behind walls and ceilings. This old wiring system has largely been forgotten over time, but it's important to understand its history and how it works for both historical appreciation and safety reasons.

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring consists of insulated copper conductors run through open air spaces between walls and ceilings. The wires are supported by ceramic knobs attached to framing members and separated from each other by ceramic tubes.

Here's a quick overview of how knob and tube wiring works:

• Wires - Insulated copper wires, rubber or cloth wrapped. Typically 14 or 12 gauge.

• Knobs - Ceramic spacers that hold wires apart from framing. 1-2 inches long.

• Tubes - Hollow ceramic cylinders that keep wires separate from each other.

• Open air - Wires run through open spaces in walls, floors, attics. Not inside conduit.

• Cloth insulation - Early rubber insulations were eventually replaced by woven cotton or cloth insulation.

• Splices - Wires spliced and joined together with porcelain knobs.

This gave the wiring its name and allowed it to be run freely through open spaces in a home's framing.

When and Why Knob and Tube Wiring Was Used

Knob and tube wiring was prevalent from about 1880 to the late 1930s. It was considered a major improvement over previous methods of using exposed wiring secured by cleats or staples.

Here are some key reasons why knob and tube wiring became the standard electrical method for decades:

• Safety - Raised wires off surfaces and reduced fire risks from arc faults.

• Expandability - Easy to add to and splice. Could wire a little at a time.

• Affordability - Less copper wiring needed compared to modern systems.

• Efficiency - Open air spaces allowed heat dissipation and avoided insulation breakdown.

For nearly 50 years, knob and tube wiring was a cost-effective and safer way to bring electricity into homes compared to previous methods. Millions of homes in North America were wired this way.

How Knob and Tube Wiring Works and Is Installed

The installation of knob and tube wiring requires some specific techniques. Here is an overview of how K&T wiring is installed:

• Wires are run through holes drilled in floor and ceiling joists, keeping them separated from each other.

• Ceramic knobs are nailed to the joists every few feet to support the wires.

• Tubes keep wire runs spaced apart for isolation.

• Wires are also supported along rafters in attic spaces.

• Where wiring changes direction, junction boxes are mounted to framing members.

• Splices are connected by hand-twisting wires together and securing them under a ceramic knob.

• Early knob and tube did not use junction boxes very often. Wires were spliced in open cavities.

• By the 1920s, junction boxes became more common with knob and tube installs.

While simple in concept, installing knob and tube wiring correctly required an understanding of framing spaces and manual skills to keep wires cleanly separated.

Benefits of Knob and Tube Wiring

Knob and tube wiring had several advantages that made it the predominant electrical wiring method for decades:

Safety

• Air spaces and insulation reduced fire risks.
• Higher risk of damage from nails and other hazards compared to modern wiring.

Expandability

• Easy to tap into existing wires and add new branches.
• Allows wiring sections of home slowly over time.

Efficiency

• Open air circulation keeps wires cool.
• Less copper required compared to modern wiring systems.

Affordability

• Less wiring materials needed overall.
• Lower labor costs than wiring into conduits.

Knob and tube served homes well for many years and allowed electrification to spread in a safer, cost-effective manner.

The Decline of Knob and Tube Wiring

By the 1930s, knob and tube wiring was being phased out in favor of a new electrical wiring method - nonmetallic sheathed cable, or Romex wiring.

Here are some key reasons knob and tube wiring declined in popularity:

• Increasing demand for electricity due to more lights, appliances. Knob and tube was less adequate for higher loads.

• Safety concerns around open splices, worn insulation on older wires.

• Lack of grounding in knob and tube put homes at risk of electrical shorts and shocks.

• Permeation of water and moisture over time degrades knob and tube wires.

• Difficult to change or remove knob and tube wiring in retrofits or remodeling.

• Not up to modern code standards - by 1940s, knob and tube could not meet electrical code requirements in many areas.

• Romex offered key advantages like integrated grounding wire and enclosing wires in protective sheathing.

While knob and tube wiring revolutionized home electrification in the early 20th century, newer wiring methods eventually displaced it for safety and performance reasons.

Dangers and Risks of Old Knob and Tube Wiring

While historically commonplace, knob and tube wiring poses some well-known dangers that should not be overlooked today:

• Fire hazard - degraded insulation and brittle wires increase risk of sparks and electrical fire.

• Shocks and electrocution - lack of grounded connection can lead to electric shocks.

• Overloading - not designed for today's high wattage appliances and electronics.

• Exposed splices - unsafe junctions hidden in walls without junction boxes.

• Insurance issues - many companies won't insure a home with knob and tube.

• Resale problems - K&T wiring can deter buyers and lower value of a home.

• Code violations - K&T wiring does not meet any modern electrical code standards.

While once safely powering millions of early 20th century homes, knob and tube wiring now poses substantial risks that should not be ignored.

Replacing and Upgrading Knob and Tube Wiring

Homes with original knob and tube wiring often need full replacement and removal for safety. Here is an overview of K&T replacement:

• Full rewire - the only way to truly eliminate all risks of old K&T wiring.

• Romex wiring - standard replacement wiring method paired with modern junction boxes.

• Circuit breakers - upgrading electrical panels provides modern overcurrent protection.

• Copper wiring - new wires avoid the brittleness and deterioration of very old cables.

• Grounding - essential safety upgrade missing from knob and tube systems.

• Electrical load review - a certified electrician should ensure the new system can handle all electrical needs and avoid overloading.

• Permitting and inspections - work should be done to local code standards and checked by the authority having jurisdiction.

Properly replacing old knob and tube wiring requires hiring a licensed, professional electrician to ensure safety and compliance with all modern electrical codes. Property owners should not attempt DIY upgrades to K&T systems.

Preserving Knob and Tube Wiring in Historical Homes

For historic homes and buildings, steps can often be taken to safely preserve or work around knob and tube wiring and avoid a full rewire:

• Insulation - carefully installing new insulation around K&T reduces fire risks.

• Load management - use lower wattage bulbs, minimize high drain appliances.

• Junction boxes - encase any exposed splices in new electrical boxes.

• GFCI outlets - add ground fault protection to reduce shock hazards.

• Limited upgrades - selectively rewire some circuits but leave others.

• Electrical assessment - have a qualified electrician evaluate the full scope of needs and risks.

For qualified historic homes, it is often possible to selectively upgrade K&T wiring while keeping original systems intact where possible, all while maintaining safety.

The Forgotten Wiring Method that Powered Early America

While mostly phased out of buildings today, knob and tube wiring powered the electrification and modernization of America in the early 20th century. Millions of homes and businesses were wired using thedistinctive knobs and tubes that gave the system its name. While K&T wiring became obsolete over time, it remains an important part of the history of electrical work and is still found in many older properties. Understanding the origins, risks, and preservation needs for knob and tube wiring ensures that even this forgotten wiring method gets the appreciation and proper handling it deserves.