On 11/25/2013 1:42 PM, Rick wrote:

"Rick" wrote in message
...

"TomR" wrote in message
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I am trying to solve a 3-way switch circuit issue in an old house.
The wiring in the house is old, and it is either knob and tube wiring
or whatever came after that and before "Romex" etc. There are no
ground wires visible anywhere in either circuit, and everything is so
dusty and dirty that I can't tell what is a white wire and what is a
black wire etc.

And, to be more precise, there are actually two different 3-way
switch circuits that I am trying to get resolved at the same time.

Downstairs, near the front door entrance, the are two 3-way switches
-- one of the 3-way switches controls the downstairs living room
ceiling light. The other 3-way switch controls the hallway light that
is outside of the upstairs bedrooms.

At the top of the stairs, there are two 3-way switches -- one of
those 3-way switches controls the downstairs living room ceiling
light, and the other 3-way switch controls the hallway light that is
outside of the upstairs bedrooms.

I can tell which 3-way switch (upstairs and downstairs) is for the
living room ceiling light, and which one (upstairs and downstairs) is
for the hallway light.

To make things a little more complicated, the whole setup was
intentionally temporarily wired incorrectly a few years back because
I couldn't figure out how to get things working correctly and I
needed a way to at least be able to turn the living room light and
the hallway light on and off -- even though the 3-way switch function
was disabled in the process. In other words, I temporarily have it
that only one switch controls each light. It's a long story why I did
that, but that is not important now.

Now, here's the story on the wiring: Coming into each of the 3-way
switch boxes upstairs, and each of the 3-way switch boxes downstairs,
are 3 exactly wires. There are no other wires in each switch box --
no neutrals wired together etc. -- just 3 wires in each box and no
other wires leaving the boxes etc.

I found the following link to various 3-way switch wiring options:
http://www.easy-do-it-yourself-home-...g-diagram.html
.



Based on what I have (just 3 wires in each box) I am assuming that
the two circuits are wired as shown in Option #8 on that link. The
power source appears to go to each light, and from each light, the
switch wires run to each of the switches. I concluded that because I
don't see any other wiring options where there are ONLY 3 wires in
each switch box.



And, now for the problem: I need to put new 3-way switches in, both
in the upstairs boxes and in the downstairs boxes. The downstairs
boxes have push button 3-way switches that are broken, so they need
to be replaced. I need to figure out how to rewire the system, using
the existing wires, and connecting those wires to the four new 3-way
switches that I bought.



I am thinking that, with the power on, but the switches removed, I
can figure out which wire is the hot "source" wire that goes to one
of the switches for each circuit. I can connect that hot wire to the
hot common for each of those two switches, and connect the other two
wires in each of those boxes to the "traveler" screws on those switches.



But, then, when I go to the other switch at the other end of each
circuit, how can I tell which wire in each of those boxes goes to the
hot "common" screw? Once I know that, I can connect that hot common
wire to the black "common" screw and just connect the other two wires
to the traveler screws. But, how do I know which of the 3 wires goes
to the hot "common" screw?



Given the age of the house and wiring method, keep in mind there may
be a possibility it's a "California 3 way"

A variation, with both hots on same leg



H--------o o--------H
o--------light----------o
N--------o o--------N

A "Carter" circuit. Has long been not code compliant (the screw shell of
the lamp has to connect to the neutral). I think it was once allowed
back in the K&T days. And someone might mistakenly use it. If you wire
it in any of the wrong ways it will blow a fuse.