Three-Way Switch

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gadfly56

gadfly56

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Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
So, just headed down to the basement "office" and went to turn off the 3-way at the top of the stairs that controls the hall light. Flipped the switch, the light stayed on. Put it back, the light stayed on. Carefully put the switch in the center position, light went off. Went to the other switch (up position) with the light off and flipped that one a couple of times. No change, light stayed off, no momentary flicker whatsoever. Put that switch in the opposite position (down position), went to the offender, and now it works properly. Any hypotheses out there?
 
Barring any change in the wiring, one of the 3-ways is bad. Most of the time it's the switch that gets used more often. However, since I don't want a return trip in a short while, and given the switches are the same age, I usually change both switches.
 
The center-off means the switch is break-before-make, but is otherwise meaningless.

Either one switch is bad or mis-wired. Did it work and something has changed?
 
It sounds like one of the switches was making a connection from its common terminal to both of the travelers at the same time. In that case the light would be on when the other 3-way switch was in either of its positions. Given that the 3-way at the top of the stairs broke a connection when it was at a centered position, I'm thinking that this other 3-way is the one at fault. Maybe it has a weak spring that allowed it to stay in a position where both contacts were closed, or there is other damage that caused this to happen.
I agree with Little Bill that both switches should be changed, particularly since the problem appears to be intermittent which makes it harder to identify which switch is bad.
 
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LarryFine said:
The center-off means the switch is break-before-make, but is otherwise meaningless.

Either one switch is bad or mis-wired. Did it work and something has changed?
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It has previously been working. I don't recall having this issue before. Maybe this evening I'll see if I can reproduce the results. I'm not hearing any crackling or something that might indicate "bad things" are happening.
 
gadfly56 said:
It has previously been working. I don't recall having this issue before. Maybe this evening I'll see if I can reproduce the results. I'm not hearing any crackling or something that might indicate "bad things" are happening.
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If you're capable of replacing the switches, I wouldn't spend any time with trying to reproduce anything. It's obvious, since you said it had been working, that one of the switches is bad. To keep from guessing which one, just replace both. Either you or hire an electrician.
 
We run across that on my 3 ways also. If you rush by and hit the switch it can actually land in the center. Even though that is not a position for the switch it happens. Switch needs replacing-- I would just change both switches as they are the same age.
 
Dennis Alwon said:
We run across that on my 3 ways also. If you rush by and hit the switch it can actually land in the center. Even though that is not a position for the switch it happens. Switch needs replacing-- I would just change both switches as they are the same age.
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Sounds like this is the consensus. I will take my cue from more experienced hands.
 
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