3-way switches -- old house wiring

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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-improvements.com/3-way-switch-wiring-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?
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assuming everything was wired correctly originally. You need a no contact voltage tester like this: http://www.specialized.net/Specialized/VC200-SPCtelco-AC-Non-Contact-Voltage-DetectorTester-501000VAC-7281.aspx
Take one set of 3 ways and disconnect all of the wires. Turn the power on and test all of the wires. Only 1 of the 6 should be hot. When you find it, turn the power back off and mark that wire with black tape.
Wire this location with a 3-way using the wire with black tape as the common. The order of the other two don't matter.
Turn the power back on and go to the 3 wires at the other switch. Only 1 of those 3 will be hot. Get a helper to flip the other switch. The original hot wire will go dead another wire will become hot. Turn the power back off. The wire that is never hot at that switch location will be the common. Mark it with black tape and wire the other 3 way.
That should work.
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wrote:

Thanks Metspitzer. Great explanation, and I think that will do the trick. I have a no contact voltage tester, and I was already doing a little testing with it on Friday afternoon; but I decided that I should do some more searching and research first and then get back to it this coming week and do it the right way. It never occurred to me that the wire on the second 3-way switch that never gets hot (when doing what you said) would be the one that is the common. But, that makes sense, and I think it will work.
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wrote:

Let us know.
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wrote:

I will do that.
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I would suggest by process of elimination. Using the pic at Option 8.
After you identify the incoming Hot, get first switch installed, then the "red" or "white" at the 2nd switch will become hot, depending on position of first switch. The black at the 2nd switch will stay cold regardless of pos. of 1st switch.
Of course you want all the "loose" wires clear and not touching anything.
Do not assume that the first incoming Hot is in the downstairs boxes !!
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Makes sense. Thanks.
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probably best to safely abandon the current wiring and replace it with all new..
messing with knob and tube isnt really a good idea.......
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unmolested K&T is marginally ok. but tapping into it, modifying it, can add new hazards. a good friend had a small home fire where a solder joint deto riated and overheated, fortunately he cauht it just in time. it was smolder ing he could of lost the entire house. his dad had soldered that joint over 30 years ago....
which is why i said just replace the entire thing..... all the 3 way light switches etc, that the OP said he had intentionally miss wired
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I'm confused, so all I can say is write things down, to make a diagram of what wires you know about, at least the swtiches and an inch of wire whereever there's a wire, indicating what color every wire is (the real color too, in case any wire has been painted.) .
And make a chart of what they should do. LIke Switch 1, turn on lights A and B.
Then start enlarging the chart and the wiring diagram to show what wires you would need to make it do what the chart says you want it to do.
When you're not sure which switch is for which, see which actual switch and wires is closer to which item on the chart. Also, normally when both switches are near the bottom of the stairs, the switch for the living room will be closer to the living room than the switch for the stairs will be.
When I bought my house, the front hall was miswired so one switch only worked if the other switch was in the right position.
And of the switches by the stairs. the one closer to the basement stairs controlled the landing near the second floor. The switches worked but they were in the wrong place.
The electrician lived in the n'hood. A house might have been part of his payment for doing the wiring. You coudl tell his house because it had more lights than the rest of us, and he had a vent from the range hood above his sliding glass door. (For the rest of us, the air went through a filter and right back into the kitchen)
Anyhow, I saw him at a party 10 or 15 years after he'd wired our houses, and I told him about the two mistakes. I thought he'd think it was funny after all these years -- I thought it was funny when I had to fix them --, but I was totally wrong. He was annoyed, didn't believe me iirc, and I was sorry I said anything.
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I marked what should be going on. 1 (common) will be hot all the time. a and b will be the travelers and 2 (common) will go to the light. (BTW the color code on the ledger is wrong.) White is a traveler, not common.

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Metspitzer wrote:

Thanks. You're right. Where it says "White Wire (Common)", it should say something like "White Wire, coded black (Traveler). And, it looks like they coded the white wire black where needed to distinguish it from being a typical neutral wire.
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On 11/25/2013 04:16 PM, TomR wrote:

That's correct; electricians don't always do that but any time a white is used as a non-neutral conductor it should be relabeled with a ring of colored tape (any color other than white, grey, or green that is. "normal" colors for residential 120V wiring would be black or red.) This isn't a suggestion but a code requirement.
nate
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wrote:

I "paint" white wires that are repurposed as hots, with a red Sharpie. I keep one in my "electrical" toolbox. I don't know if it's kosher but it works.
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Given the age of the house and wiring method, keep in mind there may be a possibility it's a "California 3 way"
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A variation, with both hots on same leg
H--------o o--------H o--------light----------o
N--------o o--------N
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wrote:

I know there is always that possibility, but since I worked in mostly hospitals I have never encountered one. If he finds a hot at each switch with everything disconnected, that should tell us.
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Metspitzer wrote:

I'll check for that, just in case that's what I have. If I do, I'll probably post back because I don't think I'll know what to do in that case.
And, I have to admit that I was a little disappointed when I found out that a "California 3 way" didn't have anything to do with girls in bikinis.
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On 11/25/2013 1:42 PM, Rick wrote:

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.
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On 11/24/2013 03:25 PM, TomR wrote:

Easy way to troubleshoot:
get yourself a test light, voltmeter, or NCVD with adjustable sensitivity, and turn the sensitivity on the NCVD down so that you can "read" individual conductors. If using a test light or voltmeter plug an extension cord into an outlet that's not on the same circuit as the lights so you have a neutral available to test for voltage (I'm assuming that you don't have a ground to use for reference, since you said there were no obvious ground wires.)
Then, turn off the circuit for the lights, pull both 3-ways out of their boxes, and disconnect all wires from the switches, and leave them hanging out of the boxes and not touching anything/each other.
Turn the power back on. Check for voltage at all wires. There should only be one wire out of all six with power on it. That's your live feed, and should be connected to the common terminal at that switch. The other two are obviously the travelers. Turn the power back off and reinstall that one switch.
Turn the power back on. Go to the second switch location. There should again be only one wire with power on it. That is one of your travelers. Flip the first switch. Now there should be a different wire with power on it. That's your other traveler. The wire that was never hot throughout the procedure should be the wire that is directly connected to the light. If you want to verify this, carefully touch it to the traveler that's hot. The light should come on. That wire that goes directly to the light connects to the common terminal of the second switch. Turn the power off, make connections to the 2nd switch, turn power back on, test, drink beer, pat self on back.
I've been in your exact situation before, and I feel your pain :) Heat shrink and colored electrical tape is your friend when dealing with old dirty cloth covered wiring.
Hope this helps
nate
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