4-way Troubleshooting Q and Brain Teaser

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jstjohnz

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I just installed a light controlled from 3 switches, normal configuration, a 3-way at each end and a 4-way in the center.

Of the 8 possible up/down combinations of the 3 switches, ie, up/up/up, up/dn/dn, etc, all but one combination works properly. The one switch combination that fails has the light off when it should be on.

Rather than troubleshooting with a voltmeter, I decided to use pencil and paper to try to determine what type of fault could make the light operate this way.

Now there are a lot of ways to mis-wire this circuit, in addition to the possibility of a faulty switch, but by my calculation, there is *only* 1 possible problem that can produce these symptoms.

So what do you guys say?

-jim-
 
jstjohnz said:
Now there are a lot of ways to mis-wire this circuit, in addition to the possibility of a faulty switch, but by my calculation, there is *only* 1 possible problem that can produce these symptoms.
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Defective 4-way switch.
 
LarryFine said:
Defective 4-way switch.
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I would agree if the symptom was 2 configurations of switches causing the light to be off when it should be on. With 2 3-ways and 1 4-way, there would be 2 on and 2 off combonations with the 4-way up and again in the down position. So a defective 4-way should have 2 on configurations not working instead of 1.

Edit: After thinking about this some more, my statement was premature, and I believe, wrong.
 
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I would start by hard wiring the 4way and test the 3way switches.

2 minutes.

If it still has a problem, hard wire a 3way, then the other if necesary.

Another 2 minutes.


Sometimes it's best not to think.
 
JohnConnolly said:
I would start by hard wiring the 4way and test the 3way switches.

2 minutes.

If it still has a problem, hard wire a 3way, then the other if necesary.

Another 2 minutes.

Sometimes it's best not to think.
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Don't get me wrong, I'm not saying that the pencil and paper approach is the quickest or best solution. I was not at the site when I heard about the problem, so I decided to sketch it out to see if I could figure out where the problem was *just* based on the symptoms.

And, unless my thinking is off base, with the symptoms I have it's possible to figure out *exactly* what the problem is.

I'm holding off on giving my answer to get a few more opinions......

-jim-
 
Sometimes it's best not to think.
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Amen. :)

6928757_6a221a8929_m.jpg
 
wrestless said:
Traveler is on common terminal and switch leg for light on traveler terminal
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However, there would still be two switch-position conditions with the 4-way and other 3-way.
 
wrestless said:
Traveler is on common terminal and switch leg for light on traveler terminal
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Several folks have said that a 3-way switch is mis-wired (interchanged switch leg and traveller). If that was so, then when the mis-wired switch was in the position that left the switch leg floating, the light would always be off.

Since there are 4 combinations of the other 2 switches, for all 4 of those combinations the light would be off instead of 2 off and 2 on, so there would be 2 faulty switch combinations, not 1.

-jim-
 
jstjohnz said:
Several folks have said that a 3-way switch is mis-wired (interchanged switch leg and traveller). If that was so, then when the mis-wired switch was in the position that left the switch leg floating, the light would always be off.

Since there are 4 combinations of the other 2 switches, for all 4 of those combinations the light would be off instead of 2 off and 2 on, so there would be 2 faulty switch combinations, not 1.

-jim-
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Still sounds to me like a traveller is not on the properly identified terminal. Maybe the identification of the pairs on the 4-way is being mis-interpreted.? :) Just a thought...
 
A 4-way switch is basically a reversing switch, and for each traveler terminal of one pair, one or the other traveler terminal of the other pair is always connected . . . nornally, that is.

However, the two 3-ways could still each be in either of two positions, so there would be two conditions where the light would be off, not one.

If you start with the light on, and then flip both 3-ways, the light should still be on . . . normally. But you do change which traveler path you're using.

If only one 4-way terminal doesn't make contact with only one other 4-way terminal (let's call them the "in" pair and the "out" pair) in only one position, only one of the two above-mentioned 3-way switch positions will work.

If one of the 3-ways was defective or mis-wired, the two remaining switches would still provide two conditions where the light would or would not work.

That's why I suggested the 4-way was defective, and not a mis-wiring somewhere.
 
I hereby amend my answer: it's possible that the 4-way is mis-wired. The two dark terminals should connect to the travelers from one 3-way, and the two light terminals should connect to the travelers of the other 3-way.

It's easy to think that you should connect a 3-conductor's black to a 4-way's dark terminal and its red to a light terminal, and the other 3-conductor's black and red to the 4-way's other dark and light terminals, respectively.

If someone connects one light and one dark to one 3-way, and the other light and dark to the other 3-way, the light will switch and work normally with the 4-way in one position, and never come on with it in the other position.

A test without disconnecting anything: with the switches in the no-light positions, the hot-fed 3-way will test with both traveler terminals as hot, because the mis-wired 4-way will feed the power back to it on the other traveler.
 
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LarryFine said:
I hereby amend my answer: it's possible that the 4-way is mis-wired. The two dark terminals should connect to the travelers from one 3-way, and the two light terminals should connect to the travelers of the other 3-way.

It's easy to think that you should connect a 3-conductor's black to a 4-way's dark terminal and its red to a light terminal, and the other 3-conductor's black and red to the 4-way's other dark and light terminals, respectively.

If someone connects one light and one dark to one 3-way, and the other light and dark to the other 3-way, the light will switch and work normally with the 4-way in one position, and never come on with it in the other position.

A test without disconnecting anything: with the switches in the no-light positions, the hot-fed 3-way will test with both traveler terminals as hot, because the mis-wired 4-way will feed the power back to it on the other traveler.
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Larry I think your first answer (bad 4-way) is correct. If the 4-way is mis-wired then it will operate as you describe, one position of the 4-way will *never* light the light, because it is just tying the 2 incoming travellers together and also tying the 2 outgoing travellers together. As you say this would show up as both travellers at the 'hot' 3-way showing voltage.

*But* the light would never come on with the 4-way in that position. There are 4 combinations of the other 2 switches, all of those combinations will have the light off, instead of 2 off and 2 on, so there will still be 2 non-working switch combinations instead of just 1.

The only scenario I can see that causes just 1 faulty switch combination is a faulty internal jumper in the 4-way switch. In one position it would work normally, in the other position one traveller would work while the other would not.

-jim-
 
jstjohnz said:
The only scenario I can see that causes just 1 faulty switch combination is a faulty internal jumper in the 4-way switch. In one position it would work normally, in the other position one traveller would work while the other would not.

-jim-
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Agreed, that's why I amended my earlier post.
 
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