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.
Listeners write in about ventilation and radon control and ask questions about tightening basement garages, ventilation solutions, and safer paint stripper.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
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.