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Old 02-04-2009, 02:44 PM   #1
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Light switch help


I have two 3way light switches. One at the top of the stairs and one at the bottom. I can't get them to work properly. I've tried switching the wires, now what?

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Old 02-04-2009, 04:20 PM   #2
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Light switch help


Do you know the principle of wiring a 3 way switch? One common is the power feed and the other common goes to the light. The other two wires are travelers and can be on either terminal.
What did you do?
Before you played around with the wires, did the light work?
Did you put in a functioning light bulb before opening the boxes?
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Old 02-04-2009, 05:06 PM   #3
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The upstairs switch worked but not if the downstairs one was used to shut the light off. There are only 3 wires for each switch. White, Black and Red. I replaced both switches with new ones, but when I powered up the light didn't work. I moved the wires around on the switch upstairs and now the light works, but its the same as it was before.
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Old 02-04-2009, 08:12 PM   #4
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Light switch help


This might help. Remember that the C terminal on one of the switches goes to the incoming AC and on the other switch the C goes to the light.

http://www.electrical-online.com/ext...3wayswitch.htm

and here is one with Animation
http://www.electricalknowledge.com/f...e&TOPIC_ID=305
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Old 02-04-2009, 08:37 PM   #5
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With a good bulb in the controlled socket and power to the setup, pick a switch and measure the voltage from the common terminal to either of the other terminals. It should read zero or at least 60vac. You may be able to do this without removing the switches from the boxes.
Now flip the switch and confirm that the reading changes to the other value.
Now repeat with the other terminal on this same switch.

Then do the same test with the other switch.

Make up a chart of your results; it can be decoded to point out the problem, either with the switches or the wiring.

Usually the common terminal has a different color.
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Old 02-04-2009, 10:33 PM   #6
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Light switch help


Quote:
I've tried switching the wires, now what?
Keep trying. Eventually you will get it right

You only need to do one thing.

Identify the common wire in each box and install it on the common terminal of the switch. The other wires don't matter.

There are many wiring methods so with NO information, we have to guess which method is used.

Things to look for without a voltage tester.

In one of the boxes, are there more than one black wire with a short pigtail coming off them? If so, that's your common. You can guess at the other end and get it right in three trys or less.

If there are only 3 wires in each box, try it with black as common on both.

With a voltage tester, remove the switches and find the one hot wire in the six choices. It could be at either end. Put this on the common terminal and go to the other end. Try each wire on the common terminal. You will have a 1 in 3 shot and it will be faster than trying to explaing further testing to determine the common on that end.
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Old 02-04-2009, 10:34 PM   #7
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Light switch help


I have a similar problem with a 3 way switch in my place. It appears that both switches seem to have a white, black and red connected to each switch? The voltage readings are weird too. Either nothing on any terminal, or voltage on both??? Not sure where to even start on this one?
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Old 02-04-2009, 10:44 PM   #8
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Light switch help


Start by reading this ^
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Old 02-04-2009, 10:47 PM   #9
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Light switch help


You have a wire that should be on the common terminal (dark colored) that is incorrectly landed on a traveler screw most likely. If these are the only wires in each 3 ways box then power is at the fixture. Go back in this thread to 220/221's description on how to find the common constant hot at one switch box or the other.
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Old 02-04-2009, 11:29 PM   #10
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Light switch help


Quote:
Originally Posted by Yoyizit View Post
With a good bulb in the controlled socket and power to the setup, pick a switch and measure the voltage from the common terminal to either of the other terminals. It should read zero or at least 60vac. You may be able to do this without removing the switches from the boxes.
Now flip the switch and confirm that the reading changes to the other value.
Now repeat with the other terminal on this same switch.

Then do the same test with the other switch.

Make up a chart of your results; it can be decoded to point out the problem, either with the switches or the wiring.

Usually the common terminal has a different color.
Just curious, where do you come up with "zero or at least 60vac"

I guess what I'm saying is how do you get a measurement of 60vac?
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Old 02-05-2009, 02:08 AM   #11
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Quote:
Originally Posted by spankymn34 View Post
There are only 3 wires for each switch. White, Black and Red...................
My guess is that the travelers are the Red and Wht

That means the Common terminal on both switches is BLACK

Switching the Red and Black will not affect the switch functioning, only the Up/Down orientation, i.e. if you want SI & S2 rockers downwhen the lamp is OFF, then switch Red & Black.
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Old 02-05-2009, 12:21 PM   #12
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Quote:
Originally Posted by Steelhead View Post
Just curious, where do you come up with "zero or at least 60vac"

I guess what I'm saying is how do you get a measurement of 60vac?
It's capacitively coupled voltages on the travelers. Depending on how much your meter loads down the circuit you're measuring, the voltage will vary. It's also different if there is a grounded wire in the cable along with the travelers. Figure 100 pF per foot of Romex.

With 3 wires each and two positions for each switch and two switches there are many, many wrong ways to hook this up and even more ways to get weird readings.

For a properly working setup, no power applied, disconnecting one common wire from one switch,
you should have continuity (less than 1/2 Ω) from one switch common to the other, 2 times out of 4 possible switch positions.

For a properly working setup with power applied and a good lamp in the controlled socket, disconnecting one common wire from one switch,
you should see 120v from one common wire to the other.
If you now put a 100w bulb across your voltmeter leads, you should see a drop of at least 18v (from 120v).

Last edited by Yoyizit; 02-05-2009 at 01:54 PM.
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Old 02-07-2009, 10:12 AM   #13
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. . .you should see a drop of at least 18v (from 120v).

should read
. . .if you see a drop of 0v (so you still read 120v) or of 120v (so now you read 0v), there is a problem.


Last edited by Yoyizit; 02-07-2009 at 10:17 AM.
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