On 9/11/2009 10:00 AM zxcvbob spake thus:

David Nebenzahl wrote:

But there's one thing about the old wiring that's puzzling to me.
Usually K&T runs are done with pairs of wires (Hot & neutral) running
alongside each other, and in most cases that's followed he a run up
into a wall will have a pair of wires going up into the subfloor.

But there are a couple of places where a *single wire* is routed up out
of the basement into the house above. In these cases, the wires are all
hots. No corresponding single neutral wire anywhere nearby. Presumably
the neutral side of the circuit is tied to the neutral of another pair
of wires.

This, of course, makes it difficult to map these circuits, since I can
only assume that the neutral connection is made to the neutral wire
corresponding to the hot wire. That's my operating assumption, anyhow:
my plan is to simply replace these single-wire runs with Romex, using
only the black wire. (Hmm, wonder if they make 12-1 Romex w/o ground?
Probably not.)

Anyone ever seen this situation in an older house?

The only singe-wire runs you *should* have are ground wires added later
to an existing ungrounded circuit. I would recommend leaving any sound
K&T wiring going to the bedrooms and such alone. Original wiring that
was done right and not messed with. The mess that you're talking about,
I'd replace it all with new NM cable; abandon in place the stuff that's
hidden in the walls and tear out what's exposed in the basement. DO NOT
do that black-wire-only thing you are talking about.

But I have to if I want to get rid of the K&T runs as the homeowner
wants me to. Since I'll be replacing it with NM cable (which is what I
proposed--*NOT* just running a single black wire, like the person before
me who ran a single white wire several feet for a neutral
conductor)--it'll be as safe or safer than what was there before.

Last time I checked (which was in 1995) K&T was an acceptable wiring
method in the electrical code, but not for new work. You could still
make repairs to old K&T and the NEC gave some details about it.

Maybe you could just cut those single wires and see what goes dead? :-)
(Probably switched lights or split outlets.)

I already did that, and I thought I posted that here. When I cut the
single wire, all the lights in the front of the house--living room and
front porch--went out. No outlets, just lights. So I know what's on that
circuit. I just don't know exactly where neutral wire for that circuit
comes out. But since it'll all be replaced by NM anyhow, doesn't really
matter. I was hoping someone could comment authoritatively on that
anomaly (the single-wire feeds), but I guess not.


--
Found--the gene that causes belief in genetic determinism