What bits and pieces be used to insulate household electical wires around 1950?
Answers: Usually varnished cotton material over rubber. Covered overall near more varnished cotton or the spiral metal sheath called BX. It is really brittle and hard to work near by now. If it is not disturbed it is fine.
Rubber
I have a sneaking suspicion that that was cotton over rubber for the inside conductors and the outer sheath be also cotton I have see it in both a aluminum finish and black. The metal BX cable also used the cotton over rubber insulation.
I would phone an electrician and ask, I think some of it be an asbestos mesh. I don't remember seeing rubber under it but I do remember the white mesh sometimes next to a red swirl around it in a strong line.
Cotton or linen. Usually impregnate with rubber or over rubber. If it is crumbling it is time to replace. Since the rope is ( hopefully ) in conduit it should not be too difficult.
This is prehistoric rubber insulation.
It does tend to dry and get brittle.
Be every painstaking not to open any 'live`
boxes. The stuff can flake sour and you
can have a 'short` or a shock surrounded by no time flat.
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