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-   -   Weird 3-way switch behavior (http://www.houserepairtalk.com/f9/weird-3-way-switch-behavior-14182/)

bugvito 06-13-2012 11:56 AM

Weird 3-way switch behavior
 
Hi all,
This seems like a popular issue, but I have yet to find a solution. I have 2 switches, the first on the upper level, and a second on a bottom level (split home entrance light) here's the "truth table" with 1 2 3 being the 3 connections (not including the tested ground). All measurements have been made compared to ground (casing).

positions upper connectors lower connectors
upper lower light upper1 upper2 upper3 lower1 lower2 lower3
up down off 2.46V 123V 2.46V 2.46V 123V 123V
down down on 123V 123V 123V 123V 123V 123V
down up on 123V 123V 123V 123V 123V 123V
up up on 85V! 123V 123V 86V 123V 123V

I understand that a broken or shorted wire can mess up the behavior but the 85V scares me a bit. And of course the single off position makes this 3 way light unusable.

We got this house a year ago and have no idea if any contractor have made dramatic changes to the wiring prior to us buying the house. The issue has been like that since we got the house, but not using the feature much, it had slipped my mind. Any ideas would be welcomed!

Thanks

Blue Jay 06-13-2012 05:15 PM

Had trouble following your description, a 3 way circuit works as follows: Hot (120V) comes into 1st switch it then sends 120V out on one of the 2 travelers to the 2nd switch that then sends 120V to the light and then from the light to neutral. So at the 1st switch you would have 120V in and on 1 of the travelers only going to the second switch.

JoeD 06-13-2012 06:07 PM

If you disconnect all the wires from the switch and measure to ground what are the readings? How old is this house? Some older homes had very strange three way wiring.

nealtw 06-13-2012 06:09 PM

Unless he is working on a 240 volt system.

bugvito 06-14-2012 07:25 AM

haha yes, I intentionally omitted mentioning which of the positions were supposed to be travelers or neutral, sorry if this was confusing.

Disconnecting the wires must be the smartest yet simplest idea! I'll get to it right away!

And no 240V, it's all 120V. In the upper switch box, a second switch is present which is working as a 3-way switch for a corridor. I looked at the wiring, and it appears to be the exact same setup, with the same travelers connected at the exact same spot, with the only difference that this one works fine. So I'm starting to think that it could be an exposed/shorted wire.

Blue Jay 06-14-2012 01:44 PM

Quote:

Originally Posted by bugvito (Post 73850)
haha yes, I intentionally omitted mentioning which of the positions were supposed to be travelers or neutral, sorry if this was confusing.

Disconnecting the wires must be the smartest yet simplest idea! I'll get to it right away!

And no 240V, it's all 120V. In the upper switch box, a second switch is present which is working as a 3-way switch for a corridor. I looked at the wiring, and it appears to be the exact same setup, with the same travelers connected at the exact same spot, with the only difference that this one works fine. So I'm starting to think that it could be an exposed/shorted wire.

Or a bad switch.

bugvito 06-15-2012 06:48 AM

Well I did the unthinkable and called in an electrician. He did think of a bad switch right away as well, even though the switches felt like they were operating ok (not loose or weird noise). Not the problem.

He's down to think that the black and white wires between the two boxes are somehow touching, possibly a nail/screw. The problem is that this house has drywalled ceilings in the basement (walkout basement). I intend to replace this old cracked stucko ceiling with tiles, just not right away. So I have no access the the wires at the moment, and changing the wire by only pulling the old one and using it as a fish wont work as the wires seem to be stapled around the house.

Here's the key test though, switch off the breaker, disconnect all wires from the switches, and figure out which cable runs from one switch to the other. In my case the black and white offers very little resistance (ohmmeter) between them even though they should not be touching anywhere. So there you go, at least one of the possible problems.

For safety the upper level switch has been "dudded" and disconnected, and the bottom has been setup as a typical single switch. In the next year I should be able to change the ceiling, expose and replace the wire.

Thanks for the possible solutions guys!

viper 08-29-2012 10:48 PM

Could be a loose neutral somewhere and if the light bulb is still in essentially hot and neutral are connected through the light. what I would do is disconnect all wires in both boxes and light fixture(mark how they were hooked up) and then check for continuity on everything, if no continuity, reconnect with new wire nuts. Be sure to turn off breaker too( little disclaimer : -) )

Gib 08-30-2012 09:36 AM

Typically I find that somewhere along the line someone has replaced a switch and mixed up some wires. There are quite a few combinations for 3-way circuits, including whether they are fed (powered) at the light, at the switch, in conjunction with adjacent switches, or have multiple lights at several locations. If you would like to figure it out, the basic homeowners electrical guides provide some good diagrams for common examples. Calling an electrician who does troubleshooting is also a good idea.

The 85 volts you registered can be a problem or might be nothing. It could be due to something back feeding through a resistance point (like through another light bulb) or it could be inductive current (when 2 wires run side by side and only one is energized, the other wire will typically register some voltage).
No solution, just my 2 cents.
Gib


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