Dan wrote:

You almost certainly wouldn't find knob & tube wiring in a 1961 house.
There is nothing inherently wrong with it, but it did require real
workmanship to install properly and due to the insulation used had a
low temperature rating. To meet code it must be installed in free air
movement. When covered with thermal insulation, it no longer meets
the temperature rating required. In extreme cases, the heat could
build up and cause a fire in the wire insulation or surroundig
materials. In fact, knob & tube could still be installed in certain
cases and meet code.

As I posted, it was used in the Midwest almost exclusively until
right around 1965. As for conductor insulation, later installs
all used TW or better, so decaying rubber was no longer a problem.

We have millions of homes out here with original work dating
back to the 20's which is still in good/serviceable shape.
I'm not defending K&T, just saying it was widely used and
(left undisturbed) was very reliable.

Jim