Confusing 3 way switch wiring

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Old 04-11-11, 09:01 PM
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Confusing 3 way switch wiring

I have a problem with replacing two three way switches. I figured, oh, simple, just replace and rewire the same, but the problem is that I lost track of the wiring and of course the wiring is old fabric wrapped and not really color coded.

There is one switch upstairs, and one downstairs. The upstairs electrical box has three BX cables going into it, all old wiring. One three wire, and two two wire. I think one two wire goes into the next room to power outlets (hot and neutral, unswitched). One two wire is the feed (I think from the floor below), and the three wire has one lead tied to the hot, one tied to neutral, and one white to fixtures in ceiling I want to turn on/off with threeway.

Downstairs has one three wire BX cable. One hot, one neutral, and one black to the fixtures in the ceiling. I'm not sure if the hot is coming from the switch box upstairs, but I think it is.

The problem is I have two hots, and my two feeds to the lights are from different locations and no traveller between! I don't know how this ever worked, but it did. I'm guessing they did something wonky with the neutrals, but every thing I've tried blows the breaker.

With the breaker on, I confirmed both hots are indeed hot. Testing the neutrals give continuity to ground (in this case, ground is the box as this is BX). The white wires in the fixtures definitely go to the box upstairs, and the black to the box downstairs (tested for continuity).

What's odd is the fixture wiring is relatively modern wiring, while the switch boxes are all old fabric insulated wiring. I don't know where they tie in unless someone did it behind the wall (wouldn't be surprised).

So anyone have an idea how to wire this up to two three way switches? Any advice would be greatly appreciated!
 
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Old 04-12-11, 08:20 AM
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Measurements can be misleading if any wires are still hooked up. Tag all the wires with a ID and record all of the wire connections. Remember the wire to the dark screw is the common and wires to the brass screws are the travelers. Location of screw on switch is meaningless.

Also we need to know the cables and connections at the light.
 
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Old 04-12-11, 11:51 AM
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Thanks for the response ray.

I did that for two of the three boxes (the two being the fixture and one switch). The third box presents a real problem - the wires are connected in the old style of wire wrapping to a stripped section, so there's no way I can test individual connections in that one without tearing out the box and redoing the wiring, but I was of course able to test the three pigtails by removing the switch.

With the others I was able to disconnect the wires and test each one individually, so I'm sure that the connections are hot/neutral/etc as stated.

At the light there are two wires, one black, one white. The black runs to one switch, the white to the other. That's the bizarre part. Two hots, two neutrals, and what should be travellers don't go to the right spot.
 
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Old 04-12-11, 07:09 PM
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If there is an unfinished attic above? If so you need to look for a Jbox where the light or switches are. Of course if there is one it might be some where else.

At the light there are two wires, one black, one white.
If there is no other wires and no cable is this from K&T?

Can you post pictures? http://www.doityourself.com/forum/el...your-post.html
 
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Old 04-12-11, 10:47 PM
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I am almost embarasssed to say I think I know what you are dealing with because I have seen it at my Mother-in-Law's house. Of course, you have a few other wrinkles that you'll probably work out yourself, but I will try to tell you what I think I remember of the strange wiring at "Grandma's" house.

It is wired in a big loop using only two-wire cables. There are two cables going to the light but only one wire in each of those cables is used. At each of the three-way switches hot and neutral are taken to the terminals which would normally be the travelers. The common goes to the light.

If both of the switches are in such a position that each sends 'hot' to the light, the light is off. Same if both are sending neutral. But if one is sending 'hot' and one is sending neutral, the light comes on. It doesn't matter which is which.

Crazy, huh?

Bob Hoyer, Bremerton WA
 
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Old 04-13-11, 07:08 AM
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I suspect Bompa is correct. That type of 3-way was common in the K&T days. It is dangerous and should not be reconnected. Your only safe option is to abandon and rewire correctly.

Bompa wrote:
It is wired in a big loop using only two-wire cables. There are two cables going to the light but only one wire in each of those cables is used. At each of the three-way switches hot and neutral are taken to the terminals which would normally be the travelers. The common goes to the light.
So if you have a 2-conductor cable to the travelers (brass screws) of each three way switch and both cables show hot between black and white when they are not connected to the switch that is the type of 3-way you have. You will need to run new cable.

OP wrote:
The problem is I have two hots, and my two feeds to the lights are from different locations and no traveller between!
 
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Old 04-13-11, 10:19 AM
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I chatted with a friend who is an electrician (unfortunately not in my neighborhood), and he said it's probably a switched neutral setup (common in the old days, and not to code today). Unfortunately rewiring isn't really an option (you tell my mom that her freshly painted walls and ceiling need to be torn open so new BX cable can be run!) I'd bet all the three ways in the house are not properly wired.

He also said one of the original switches could have been a single pole switch, with three posts, and not really a three pole switch.

Several options to check when I can get over there. I'll post once I have it back in working order.
 
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Old 04-13-11, 03:01 PM
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Is this New York City. If it is your wiring options may be more limited but if it is a single family residence in the suburbs you may be able to use NM-b (Romex). If there is an unfinished attic above you shouldn't have to destroy walls to run cable.
 
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Old 04-15-11, 04:02 PM
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It is a finished attic, and it's NYC, so BX it is.

It was indeed a switched neutral, and when I wired the switches up for that, it worked fine... Thanks everyone for your help!
 
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Old 04-15-11, 04:14 PM
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Originally Posted by alphawolf View Post
It is a finished attic, and it's NYC, so BX it is.

It was indeed a switched neutral, and when I wired the switches up for that, it worked fine... Thanks everyone for your help!
You just created a major safety hazard and code violation. You need to disconnect it immediately and leave it disconnected till it can be connected correctly. In it's present configuration it is possible for someone to get a severe, even deadly shock when changing a light bulb. In certain switch positions the bulb can be off but the threaded shell of the lamp hot. That means if someone changing the bulb comes in contact with ground and bulb base they will be shocked maybe killed.
 
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