Does your old home hide a hidden menace?
Electric has played a major role in the American way of life for over a hundred years. In many antique homes you can still find the remnants of early electrical systems, especially the vintage knob-and-tube system common around 1900.
While K&T was incredibly resilient, the insulating components of any surviving system are well past their service life. They pose a huge fire risk. This article will teach you about knob and tube wiring, and why you should consider replacing it with a modern, grounded system.
What is Knob and Tube Wiring?
Knob-and-tube (K&T) is an antique style of wiring, first used in the 1880s. The “knobs” of the K&T system were ceramic posts, nailed into the frame of a house. These posts held the wire several inches away from any surface, to reduce the risk of fire.
The “tubes” of a K&T system were small ceramic pipes used to carry wire through floor joists. Where wire had to run through a plaster wall, a sheathe of enameled cloth, often asbestos fiber, would protect the cables from abrasion.
Knob and Tube wiring had quite a few oddities and variations. The hot and neutral wires were run separately, and electricians often had them take different paths through a house, so servicing the system without the original diagram can be almost impossible.
Most knob and tube systems were also installed before the use of junction boxes was widespread, so any new circuits added after installation were usually made by peeling back the insulation from another circuit and soldering jumper wires to power a new outlet or light fixture.
By the 1940s most residential electricians had transitioned to early versions of armored cables and non-metallic sheathed cables. However, rural farmers and older electricians are known to have used the K&T system well after the Second World War—in upstate New York, installations have been documented as late as 1975.
Is knob-and-tube wiring dangerous?
Yes! Even properly maintained, knob and tube wiring is much more dangerous than a similar system wired in the modern way. The insulation on an original K&T system in New Jersey is sixty to one hundred years old.
Even if it hasn’t cracked, the enameled cloth common on older wires is inherently flammable, while old natural rubber can rot away, leaving bare wires exposed-a major fire hazard.
The system also lacks a ground wire and relies on wire tension for safety, so if any of the ceramic knobs break or the wire sags, live wires will be drooping across wood or other flammable surfaces.
Decades of Modification
Most K&T systems have also been dangerously modified by shade-tree electricians and DIY homeowners. Common “improvements” includes splicing lamp cord into the old wires, replacing whole sections with extension cords, and wrapping frayed cables in electrical tape.
Worse still are old homes that were retrofitted with modern insulation. K&T systems were designed for notably higher amperage than the same gauge of wire would carry in modern electrical work.
This is because the wire is exposed to air on all sides, and though it will heat up considerably at maximum capacity, the system is effectively aircooled, while ceramic insulators further dissipate waste heat.
When fiberglass insulation is stuffed around K&T wires, it prevents the wires from breathing freely like intended and increases the chance of an electrical fire. DIY home owners often make this mistake in attics and basements when trying to upgrade their antique house.
Not Enough Power
No electrician in the 1920s could have predicted the power requirements of a modern 2019 family home. In an average single family house, K&T systems were often rigged with four 10amp or 15amp circuits in the days when the greatest power draw might have been an electric tea kettle.
Many antique houses were designed for 60 to 100 amps to the whole house, less than half of a modern home.
There have been dangerous DIY fixes over the years, like installing larger fuses in the 1950s or swapping out fuses boxes for even larger circuit breakers. These fixes are a recipe for a house fire by loading century old wires far beyond what they were meant to carry.
If you want an antique home but a modern lifestyle, the only safe solution is to have an electrician retrofit your home with modern wiring. Stopgap fixes by untrained DIY homeowners are unsafe and potentially illegal.
Having knob and tube wiring can cause problems when trying to find insurance on a newly purchased house.
Because of the inherent risks of the system, and the ease with which a homeowner can dangerously modify things, many home insurance policies consider K&T a no-write condition. Others will charge much higher rates. If you want to take out a mortgage on an antique home, removing K&T might be a demand of the insurance company.
Call An Electrician
If your home is still wired for K&T wiring, Prime Electrical Services can help. With over 20 years of experience in residential electrical work, we can remove dangerous old K&T wiring and replace it with a modern system that meets the highest standards of safety and professional installation.