House built in 1917. Partly rewired to current standards. Two questions about the rest of the wiring. (1) some Knob and Tube, must I replace? (2) some of the wiring is labeled (General Cable 12/2 with ground), the outer core looks like it is woven with a green color. How old is this cable? Is it safe?
Thanks.
Replies
Depends on the condition
I know that sounds, smarmy when I say it, but:
If the insulation is still flexible and intact, it is still good. The older woven insulations will become brittle over time, and some of the cloth/shellace onces will actually start to break off. They can also be eaten by crickets.
The old K&T should generally
The old K&T should generally be replaced as the opportunity presents itself (even though it may be perfectly sound and safe), since some insurance companies frown on it and some inspectors will downgrade a house because of it.
There are several generations of the cable with the woven cover. Yours isn't the oldest since it has a ground, so it's probably at least "post-war". The size of the uninsulated ground conductor is one indicator of age -- early cables had very lightweight ground wires, though I could only guess at the points where things changed. (I'm thinking that the fabric-covered cable was replaced with plastic-covered stuff about 1960.)
One thing to look at with the cables is the rubber-coated wire inside. In some cases the inside insulation is very brittle and crumbling, making it probably more of a hazard than the K&T. (This is especially a problem inside light fixtures where the heat does a number on the wiring.)
My track home in SoCal built in 1960 has all fabric covered wire. The green had the ground, the silver was just 2 conductor.
Oh, and the jackets has asbestos in them too.