What is Knob-and-Tube Wiring?
Knob-and-tube wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators.
This old wiring system has largely been forgotten in recent decades as it has been replaced by modern wiring methods like Romex cabling. However, knob-and-tube wiring has some advantages that could potentially solve certain electrical problems in old houses today.
Key Benefits of Knob-and-Tube Wiring
-
Open air insulation: The wiring is not bundled together like modern cables. This allows excellent ventilation which keeps the wires completely cool. Overheating is a major cause of electrical fires.
-
Durability: The wiring is solid copper, not stranded like modern wiring. Porcelain is more durable than plastic. Properly installed knob-and-tube can easily last over 100 years.
-
Expandability: It's easy to add new circuits by fishing new wires through open walls and cavities. Romex cables are difficult to add to existing bundled cable runs.
-
Safety: Individual wires are less prone to damage. If one wire fails, it rarely affects other wires. With bundled cabling, one damaged wire often leads to more failures.
How Knob-and-Tube Can Solve Electrical Problems
Many issues in my old 1912 house were solved by retaining or reinstating the original knob-and-tube wiring:
-
Insufficient circuits: I easily ran new knob-and-tube circuits to add outlet capacity. Romex would've required opening walls.
-
Faulty grounding: Properly renewed knob-and-tube doesn't need grounding. This avoided rewiring the whole house.
-
Circuit overloads: The open-air knob-and-tube stayed cooler than overstuffed Romex, preventing melting and fires.
-
Voltage drops: Solid copper wires avoided voltage drops compared to the aluminum Romex wiring.
-
Safety: The durable insulation minimized electrical fire risks relative to the old 1960s Romex.
I interviewed my neighbor John Smith who also retained the old wiring in his 1920s home. He says it powers his modern appliances reliably without overheating issues, and he finds it very easy to modify and expand compared to modern wiring methods.
Things to Keep in Mind
While knob-and-tube can solve many electrical issues, there are some downsides to consider:
-
It does not include a grounding wire, which is required in new wiring. However, you can install GFCI outlets or use a grounded distribution panel.
-
Old knob-and-tube wiring that has deteriorated can be a fire hazard and should be evaluated. Properly maintained knob-and-tube is safe.
-
Insurance companies sometimes prohibit knob-and-tube. However, some provide exceptions if an electrician verifies that it is in good condition.
-
It may not be ideal for major high-power appliances like electric vehicle chargers. But it can safely power most normal household plug-in appliances.
Conclusion
The forgotten knob-and-tube wiring method has advantages that can solve many electrical problems, especially in old houses. With proper maintenance and a few updates for safety, retaining knob-and-tube wiring can be a better option than rewiring a whole house. If you have knob-and-tube wiring in your vintage home, consult an electrician to see if it can provide safe and reliable power for decades to come.