Knob-and-tube wiring, the antique technology that strikes terror in the hearts of home buyers, is not a fire hazard! In theory. Technically. Much.
So says this report, which examined the rate at which the early 1900s wiring starts house fires. After studying a bunch of fires and fire-trap houses, these investigators concluded:
“Properly installed and unaltered K&T wiring is not an inherent fire hazard.”
But what the heck is knob and tube wiring, you ask?
It’s the aboriginal electrical wire, standard equipment from the 1880s to the 1940s. It carried electricity into your house in copper wire wrapped in cloth insulation. As they snaked through the walls, the hot wires were kept clear of the flammable wood with ceramic insulators, some shaped like knobs, some shaped like tubes.
Although K&T has been rendered obsolete by wire that’s wrapped in a metal or plastic jacket, remnants of the “legacy wiring” remain alive and well in many older houses. And contrary popular perception, it’s not particularly hazardous! I’m pleased to have found this study, in part because my Dad always contended that K&T was actually safer than the new stuff. But because he was prone to skepticism in the face of most technological “advances,” including computers, vacuum cleaners, and the clothes iron, I wasn’t entirely sure I should trust him on this point. Apparently, I can.
So, yay! K&T is a much maligned and innocent technology!
Now, there are just a few
minor GIANT caveats:
1: In an overhead light fixture, the heat of the bulb can slowly cook the cotton insulation off the copper wires. I stumbled upon this situation in my 1918 bungalow, and the black char marks on the ceiling plaster were legit scary.
2: Adding insulation over K&T can allow the warm wires to heat up and set things on fire. An awful lot of old houses have had insulation blown blindly into their walls and attics over the years.
3: Those pure and original K&T circuits have been tampered with over the years, pushing them WELL past their design specifications.
Now, how do you know if someone has twiddled around with your original K&T?
Oh, we just know they have: When these houses were built, electrical fixtures were limited to an overhead light in each room, and a couple of outlets for the Victrola and one of those crazy new toasters.
But since then, a tidal wave of electrical inventions has washed through the marketplace, and into the house. When the electric razor appeared in the 1930s, your Grandpa had to have one. He spliced a new wire into the old K&T circuit in the basement, and poked it up into the bathroom wall to power a new outlet. Electric refrigerator? Splice in another branch! Vacuum cleaner? New outlet! Washing machine? Electric iron, fan, coffee percolator, radio, television, microwave, clothes dryer, cook-stove?
So many splices!
Each with the risk of untwisting, or touching something flammable, or lacking sufficient insulating tape!
Each brighter light bulb and bigger fridge pulling more hot current through the humble wire wrapped in cotton!
So it’s mixed news, really: K&T is not inherently a fire hazard. But exherently, it really might be. It probably is. I’m glad mine is all gone. Sorry, Dad.