From: "David Jones"


"Speedy Jim" wrote in message ...
David Jones wrote:

guys, I was going to replace a dimmer switch when I ran across an
unusual
wiring method in the single-gang receptacle box. The dimmer controls a
chandelier in the dining room, it's the only switch for the fixture.

Two runs of NM cable enter the box just like a typical switch. The two
leads
on the old Lutron dimmer are connected to the white and black on the
first
cable. Black on the second cable is connected to the *white* on the
first
cable but the white on second cable is capped off with a wire nut. When
I
saw this mess I put the plate back on until I can understand it. The
wiring
makes no sense to me unless the switch is placed at the end of the run
and
the white on the first cable is being used as a hot, in which case it
should've been marked with some black tape. But then why is the black
from
the second cable wired to the same nut (nut connects the black from
second
cable, white from first cable, and the lead from dimmer) and why is the
white capped off? I can see several scenariors to explain this, none
pleasant.

The house is 35 years old and the whole subdivision supposedly had
aluminum
wiring originally. All the wiring I've run across is copper so it's
likely
that someone, sometime replaced all or most of the wiring...and who
knows
how qualified that party was.

I'm thinking that I should (1) disconnect the black on the second cable
(the
one with the disconnected white) and see if the dimmer and ceiling
fixture
operate, then (2) determine if there is current in the black wire of the
second cable, then go from there.

Any thoughts on this wiring setup? Thanks!

I think you're right on target that this was done when the Alum.
wiring was replaced. They probably had a nightmare job trying to
pull new NM cable thru all the wall/ceiling spaces.

In the case of this box, they needed a Hot and didn't have it so they
pulled a cable and only used one conductor.

Can you DO that??
Wellllllll......it's a very fine point.
There's nothing inherently wrong with only using one conductor,
but Code does require that currents cancel each other where
a conductor exits thru a hole in a metal box. (There was concern
about the box overheating due to induced eddy currents.)
The currents DO cancel if both conductors run thru the same hole
and carry opposite flow (the usual case).

DO boxes overheat in cases like this? Not likely.

That's a long-winded way of saying that, IMHO, put it all back together
and don't worry about it.

Jim

Thank you Jim.

I am always impressed with your knowledge and responses and general
gentlemanly ways. You are a real asset to the many who come here with
questions!

Just wondering, *is* there a 3-way switch in the vicinity of this mess? In some
older homes, it was not uncommon to use 2-wire cable to grab just a hot from a
local outlet, to feed the begining of a 3-way set. Then, 2-wire cable is again
used to bring the 2 travellers to the 2nd 3-way switch, another 2-wire cable is
used to bring the switched hot only from the 2nd switch to the light fixture,
and another 2-wire ran from the fixture to any local outlet for neutral.