Anyone knows what these are called?

Wes Bucey

I agree. Ceramic insulators for residential wiring. (No longer conform to building code in most jurisdictions. Now, most residential wiring is to be enclosed in metal conduit, not just armored BX cabling.)

:topic:this kind of wiring was one of the direct sources of fires in residences and apartment buildings in the early 20th century (1900 - 1940) because the insulation on the wires would be gnawed by rodents (rats and mice) to get material for nest building, exposing bare wiring which could either short and spark or heat up from heavy current loads and set fire to nearby flammable material.

Patricia Ravanello

Quite Involved in Discussions
Re: Anyone knows what these are called

The cylindrical thingmajigs?
Hello Richard,
I believe it was actually called "knob and tube wiring"....Here's what Wikipedia has to say about it...

Knob and tube wiring (sometimes abbreviated K&T) was an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s.[1][2] It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted together for good mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape (asphalt saturated cloth), or made inside metal junction boxes.
Knob and tube wiring was eventually displaced from interior wiring systems because of the high cost of installation compared with use of power cables, which combined both power conductors of a circuit in one run (and which later included grounding conductors).

At present, new knob and tube installations are permitted in the US only in a few very specific situations listed in the National Electrical Code, such as certain industrial and agricultural environments.

Happy Easter!
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Patricia got it right...knob and tube.

Watch out if you have to disturb a run before you take that run out of service, for the primary wire insulation to be embrittled and to crack off the wire. That especially occurred for circuits that were regularly loaded to almost the overcurrent trip point and therefore ran warm or hot.

Another problem was that sometimes the old copper was much harder/more brittle than modern stuff, and would break at an insulator when disturbed.

If you have to leave some of this stuff in service, my view is that it's a good idea to down-rate it, fuzing branch circuits at 10 amps.


Looking for Reality
I've worked a bit for Habitat for Humanity in the Philadelphia area.

Yep, that's knob and tube. (only the knobs showing in the pics...the tubes are used for going through rafters and joists). There is a lot of it in older buildings that have not been renovated.

If you look at replacing it (highly recommended), it tends to be most convenient to run your new Romex or BX cable first, connect it to the outlets and fixtures one at a time, and only then remove the old wiring. That way if you get interrupted during the job, you still have the unsafe power rather than no power.

So what will people think of today's building codes 50 years from now?

I hear "You run an explosive gas into your residence in a pipe, then light the end of it on fire intentionally?!?"

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