On 29 Jun, 11:46, " wrote:
On Jun 28, 2:09 pm, (Geoffrey S. Mendelson) wrote:

No, he IS saying it is in use. Some of it has been replaced, but not
all of it.

Exactly that. The precise term is "Knob and Tube", The insulation is
a mixture of silk, rubber and asphaltic tar that remains quite stable
under most conditions, although it becomes brittle at temperature
extremes (hot and cold). One would think from the ingredients that the
insulation would burn from a sideways glance... not so at all.

I worked my way through college as an old-house electrician and ran
across scads of the stuff. Some of the original lighting circuits (but
nothing else) in our house are still operating from K&T wiring
installed in 1906. The house was built in 1890, originally piped with
gas for lighting.

http://images.google.com/images?hl=e...e+wiring&gbv=2

Will show you it in-situ.

If you keep in mind that the conductors are typically separated by
some distance, and where they penetrate boxes, walls and turn
corners, there is either a ceramic insulator (knob) or ceramic/
additional woven silk/asphalt/rubber (tube), as long as the copper
itself is not raised to ignition-point temperatures it is quite safe.

With reference to the NEC, it may be maintained but not installed-as-
new.

And an unbelievable amount of flea-market wind-chimes are made from
old ceramic tubes....

Peter Wieck
Wyncote, PA

Seems the US developed a long lasting wiring system long before we
did. It wasnt until ashathene and pvc cables in the 60s that we
finally got cables of types that would truly last long term. So old
wiring here is almost invariably highly risky, in a very bad way and
only very occasionally encountered at all.

The main old types here are
- cotton/rubber, and its normal for the insulation to have perished
and fallen off in places, and not just at the ends.
- lead sheathed rubber insulated from 1930s, the ends of which get
into a state.


NT