I liked the recent article on wall insulation but one caution:
If you have a house that is old enough to need insulation in the walls, there’s a chance you may have or had knob and tube wiring. The electrical code prohibits insulating cavities where this wiring may travel.
In many home this wiring was removed and replaced with romex. But some electricians who got lazy just replaced the visible knob and tube. Whatever was fished in the walls or ceilings remained.
If you know or suspect that knob and tube was in your house, check first before insulating.
Replies
Good Advice enthalpy.
Bad experience, I take it? A friend of mine said that knob and tube was the safest wiring. I've always heard the opposite. Anyone have a clue as to why he said that? He's a Master Electrician, by the way.
Undisturbed, it's pretty safe, since the wires are in free air where they can't easily overheat, and where the hot and neutral (actually, no one bothered keeping straight which was which) can't easily contact each other. Plus the wire was usually #12 or heavier, with soldered connections.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
speaking as one who has brushed a forearm across both wires a couple of times, I can think of them as safe
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Electricians liked that wiring because there's such a safe distance between the conductors. Unfortunately, the splices were nothing more than two wires finger-twisted together with some tape around it and not in an electrical box. Now splices have to be soldered.
Believe it or not, the code (NEC Art 394) still recognizes k&t wiring and even allows it to be extended in existing installations. But you can't use it in new construction or retrofits. Insurance companies hate it and very often won't insure a house with it.
I don't like it because it's one conductor with no jacket over its insulation. At least with romex (NM) or metal clad (MC), you have two layers of protection. I also don't like it because it's a two-wire, ungrounded system.
I was working in my brother's attic once and got bit when I touched the foil face on the insulation and a sanitary vent. A piece of k&t had lost its insulation (dried out in the attic heat) and was touching the foil. The staples conducted the voltage from section to section of insulation and the whole roof was "hot".