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Weird Three-Way Switches. Help!

Posted by thebigad (My Page) on
Mon, May 20, 13 at 13:05

We have two three-way switches (we think) at either end of our hallway. One of the switches is a dimmer switch. The other is not.
The switch at the entrance to the hallway, the dimmable one, will turn on the light. Then, we go to the end of the hall, and turn off the light with the other switch. If we go back to the entrance and flip the dimmable switch, it won't turn on the light again. Moreover, if after doing that step, we go back to the end of the hall and flip the other switch, it won't turn on the light again.
The only way we can control the light is to either turn it on or off from the entrance dimmable switch, or if we turn it off at the other end, then we have to turn it back on from that end.

Some additional details from opening up the switches:

The entry dimmer three-way switch: The black wire is hot. The red wire appears to have been inserted in the "common" hole.

The other non-dimmer is also a three way switch. But on this end, the white wire is hot. And the black wire was in the "common" hole.

So, I thought this was simple, and put flipped the red/black wires, so that the red wire would be in the "common" hole, like in the dimmer three-way switch. When I did that, however, nothing worked at all. So, I returned everything the way it was, and the lights work as before, but not properly as a three-way should.
What's going on? How can we fix it?

Follow-Up Postings:

RE: Weird Three-Way Switches. Help!

Are you sure this is a three way dimmer?

Usually with three way switches the common goes to the light on one end and the power feed on the other. The two travellers go to the two throws of the switch.

RE: Weird Three-Way Switches. Help!

There may be a fourway in between, (electrically). De-construct it at the switch boxes and the fixture and make sure you can account for each conductor and its source and destination.

RE: Weird Three-Way Switches. Help!

Not sure of the fourway - wouldn't that mean there is another switch involved? Sorry, I'm not good at wiring.

When you say de-construct it at the switch boxes - do you mean unscrewing the light switches and evaluating the wires behind? I tried that before, but may need to do so again.

ronnatalie brought up a good point - I need to make sure there are two travelers. I thought it was a three way simply because both light switches control the same hallway light.

The other option I was thinking of, and maybe you all can help, is there a way to just replace the current two switches with a motion sensor version? That way, I can always leave it on and if somebody walks by, the lights will come on.


RE: Weird Three-Way Switches. Help!

The 4way suggestion involves another switch. The way you described wires in holes may mean the switches were "backstabbed" and these connections can fail more often than wires that are curled around the screws and held in place by tightening the screw.

This failure could have happened in the unknown 4way(s). If you can establish that all of the wires begin and/or end in the two switch boxes or at the fixture then there is no other switch, but, if there seems to be wires that appear from nowhere or disappear to parts unknown, then you may have a buried splice or one or more 4way switches.

The black wire that is hot at the dimmer is also hot at its other end unless it's broken, the same holds true for the white at the other switch. One of the common terminals should always be hot, that's the one that comes from the panel either directly or from another accessible splice. The other common should only be hot when power is sent to the light. The two screws that are the same color on the non-dimming switch should alternate between hot/not as either switch is thrown.

RE: Weird Three-Way Switches. Help!

First one assumes that this setup worked properly at some previous time. But that is not specifically stated. Did this problem start after someone changed something about the installation-- like installing a dimmer? If so, restore it to the previous setup. One failed traveler (connection) might cause some of the symptoms described.

This post was edited by bus_driver on Thu, May 23, 13 at 9:00

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