Connections to concealed knob-and-tube wiring. In cases where the
existing wiring is concealed knob-and-tube, the NEC does allow it to
be extended from an existing application. But that is seldom practical
because the hardware is no longer readily available, and the existing
knobs salvaged from old jobs have internal spacings for old Type R
conductor insulation that will not work on today’s thinner insulated
conductors. Concealed knob-and-tube, as a wiring method, has no
equipment grounding conductor carried with it. Over the generations,
NEC provisions have changed to the point that it is almost impossible
legally to wire anything without grounding it. For example, until the
1984 NEC, what is now 314.4 only required the grounding of metal boxes
used with concealed knob-and-tube wiring if in contact with metal lath
or metallic surfaces. Now all metal boxes must be grounded without
exception.
Meanwhile, grounding has been getting more difficult to arrange to
remote extensions of concealed knob-and-tube outlets. Until the 1993
NEC, you could go to a local bonded water pipe to pick up an equipment
grounding connection, and then extend from there with modern wiring
methods. Now 250.130(C), which governs this work, requires that the
equipment grounding connection be made on the equipment grounding
terminal bar of the supply panelboard, or directly to the grounding
electrode system or grounding electrode conductor. You will not be
inspecting grounding connections associated with concealed knob-and-
tube wiring in a steel-frame building. Rather you will see this in old
wood-frame buildings, probably residential. In such occupancies, even
if the water supply lateral is metallic, the water piping system
ceases to be considered as an electrode beyond 5 feet from the point
of entry. This usually means fishing into the basement. If the
contractor can fish a ground wire down to this point, he or she can
fish a modern circuit up in the reverse direction and avoid the entire
problem.
It is true that some geographical areas have more extensive use of
slab-on-grade construction, and here interior water piping is
sometimes permitted to qualify as electrodes because the pipes extend
to grade for the minimum threshold distance of 10 feet, and thereby
allow interior connections. But in almost every case, extensions of
concealed knob-and-tube wiring do not do well upon close inspection.
In addition to the grounding issue, beginning with the 1987 NEC this
wiring method cannot be used in wall or ceiling cavities that have
“loose, filled, or foamed-in-place insulating material that envelops
the conductors.” This effectively means that such cavities cannot be
insulated, because the only method of compliance involves opening all
the walls to install board insulation products, and no contractor is
going to keep this wiring method with the walls open. This rule is
particularly controversial because, to the extent enforced in existing
construction, it is a powerful economic disincentive for owners to
retrofit thermal insulation.3
bud I copied and pasted because obviously you are too lazy to click on
links, while you spout dis information it just adds to readers
confusion.
this is just a few of the references. who wants a obsolete system that
shouldnt be insulated?
few homebuyers will be interested in buying such a home.
rewiring isnt that expensive, when you consider how it increases your
homes value.
besides if a homebuyer cant get homeowners insurance its a no
sale...... for nearly every buyer out there.
so the seller must rewire, at that point the rewire must meet all
current safety codes...............
bud you want a 100 more? or a 1000?
just to discredit you i nwill be happy to keep on posting.
