Edwardian home electrical wiring was scary stuff

Originally published at: https://boingboing.net/2020/11/09/edwardian-home-electrical-wiring-was-scary-stuff.html


In 120 years (probably less) they’ll be making a documentary like this about today’s social media platforms.


My house was built sometime between 1900 and 1937, depending on which documents you believe. In some places the electrical wires are secured inside the walls with ceramic insulators. This makes me think they weren’t too confident about the paper or whatever insulation the wires were wrapped in, so the insulators were an extra way of preventing wire from contacting wood other other building materials. I’ve heard this was standard, but still seems terrifying to me. It looks like the way electric fences are set up to contain livestock, with wires secured to posts by ceramic or plastic insulators.


This is why quite a few of these have since burned down…


This is called “knob and tube” wiring, and it was the standard before Romex. It’s actually quite safe if properly maintained. The wiring is secured around corners with ceramic “knobs”, and runs through joists are done through ceramic “tubes”. The reason is for expansion as the wiring heats up. Suspending it off the walls and in the tubes allows the wiring to expand and contract without chafing the insulation.

Modern Romex doesn’t expand as much because we use heavier gauges for the same current, and of course the insulation is a lot more durable, so we can just staple it to the studs. It still gets warm, but not as much. Romex was a big cost savings, mainly. It’s much easier (thus cheaper) to install.

Interestingly, the push is now to move to aluminum wiring, because the price of copper is through the roof. However aluminum expands a great deal more than copper under the same heat, so it has some special rules for installation that have to be followed. Improperly installed aluminum wiring has been the cause of a lot of electrical fires in modern houses. We’re kinda back to the problems that knob-and-tube solved.


our circa 1911 home has one section that’s all knob and tube. when we bought the house, we tried to get an electrician to come in to update all the wiring, but we couldn’t get anyone to do it. they all said basically the same thing: the knob & tube works, and it’s safe, so why mess with it? it kinda freaks us out, though, so we don’t plug anything in more than lamps and a stereo in those rooms.


Someone can make a documentary now about how we used to [gasp!] leave our homes and talk to other people. Not that we didn’t have the technology to do otherwise, we just thought that stuff was for weirdos and losers. Now we meet strangers almost exclusively online because we want to avoid the skeezy weirdos hanging around in meatspace.

And speaking of documentaries about the before times, every TV show I watch is like a shocking documentary of life before covid. I can’t watch TV anymore without being shocked at how irresponsible and reckless people are being.


My house, built in 1944, still has some knob-and-tube wiring in places that are hard to reach, although I’ve replaced most of it. As you say, it’s okay if left alone. The problem is the deterioration of the insulation over time. I went to replace a halogen ceiling fixture in the kitchen a few years ago, and found that the heat of the fixture had cooked the insulation to the point that I could crumble it with my fingers. That led to a major rewiring job in the attic to replace a couple of circuits that went all over the house.

The main problem with knob-and-tube now is that many insurance companies won’t insure a house that has it.

I’m surprised to hear that. After some bad experiences in the 1970s contractors in Ontario, and probably all of Canada, dropped the use of aluminum completely, although the big box stores still stock switches and outlets suitable for aluminum.


We’ve been running into this situation with my father in law’s house: no one will insure it because all of the wiring is knob and tube. Spouse and I had the opportunity to buy the home off of him (for a good price), but we would have had to sink a bunch of money into it to replace both the wiring and the plumbing system and decided that we just didn’t want the hassle right now.


Yah, nobody likes Al wiring, but the cost of copper has suddenly made a lot of people more okay with it.


I have a house of similar age and replaced all the knob and tube wiring myself with metal-clad cable when I bought it. There were no functional issues with the old wiring and honestly I kind of regret stripping away that part of the house’s history, but there were two reasons I did it:
I wanted to be able to walk through the attic space without fear of death if I tripped and landed in such a way that I’d be touching both wires


The unshielded wires that were a foot or two apart from each other put off a significant amount of EMF interference compared to modern wiring, especially the metal-clad type that I was using.

That said, knob and tube does hold up better in many circumstances to wiring that’s just a little bit newer by virtue of the fact that the wires are physically distant from each other. Some of the early insulation on stuff that pre-dates Romex (or, for all I know, Romex as well if you were to age it 100 years) can eventually fail and then you’ve got two wires contacting each other.


There are up to code wirings that use knobs and are up to code. There are some giveaways: there are three conductor and the treated cotton isn’t the main insulation but inside there is a plastic insulated wire.
Is some case in old house has sense to use this.


This is partly what motivated me to upgrade my grandparents’ old house from fuses to circuit breakers. The other part was the scary maintenance of handling melted fuses or dealing with old ones that were broken or stuck. :grimacing:


Maybe this is covered in the video, but my grampa, who was a carpenter, once told me that (way) back in the day people believed electricity might run out on the floor, like water. There were sockets with flaps that stayed closed until the user screwed in an adapter with slots to plug in to.


There’s a Thurber story about that (excerpt here), complete with an illustration:


Funnily enough only today a knob and tube insulator tube turned up in an archaeological finds identification group I follow. First time I’d heard of it and here we’re talking about it again!


Probably my favorite Three Stooges gag ever was in the episode where they were plumbers and mistook electrical conduits for water pipes. They removed the wires from the conduits and connected them to the water supply. Later when the homeowner flipped on a light switch the bulb filled up with water and burst, and water shot out of a television showing a broadcast of the Niagara Falls. Cartoon physics at its best!


I would have got it right away, but then I might turn up there any time. :grin:

The knobs I removed from my house were fastened with an unusual type of screw. Robertson drive, of course, this being Canada, but the threaded part of the screw is tapered over its whole length, probably to make driving easier in the days before power drivers.

The original wire nuts are glazed porcelain rather than plastic, with the threads molded into the ceramic.


Aside from the “if properly maintained” carve-out(hardly unique to knob and tube; but never something one likes to see, especially in comments about the safety of environments that don’t have well-regulated maintenance specialists); what makes me nervous about knob and tube is how many present day install procedures(for things like data cabling) are performed on the assumption that the interior of the wall is full of nuisance dust and fiberglass but otherwise benign; and as long as you don’t breach too many fire barriers it’s probably OK.

Wouldn’t matter so much if running fiber; but wouldn’t want data-copper nuzzling up to power if it can be avoided.

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I’m not sure if that was the real reason for the flaps.

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