Three Way Light Switch Stays Lit


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Old 02-14-23, 04:16 AM
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Three Way Light Switch Stays Lit

I am the original owner of a 24 year old condo. The three way switch in my mud room suddenly will not turn off in the fully down position. It will shut off it I leave the switch in the middle. This will work on both of them. I have replaced both switches, double-checked that the wiring is correct (I replaced the switches a wire at a time - in other words as I removed a wire from one, I connected it in its corresponding place on the new switch.) Is there any thing else I should be considering other than the very unlikely issue of a new switch that is defective?



 
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Old 02-14-23, 04:48 AM
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We can't tell looking at one switch but you could have it wired correctly. There are several different ways to wire a 3 way switch. Below is a diagram of one possibility of how yours might be wired.

Where are your ground conductors?

The back stab connectors you are using do work and are approved. But, it is more reliable to bend a loop into the end of the wire and attach to the screws on the side of the switch.

 
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Old 02-14-23, 05:24 AM
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Did you replace both switches and it still does not work?

If you flip one switch and the light stays on, it is possible the problem could be in the other switch.

Check for too much insulation stripped from the end of a wire and bare copper touching other screws or metal parts.

Caution. Words like below or corner or left or diagonally or middle or opposite are completely unreliable to use to describe "corresponding place" on the new switch..
 
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Old 02-14-23, 06:41 AM
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Pilot Dane:

On mine, the black (not the common) and red wires are reversed on both switches, compared to your diagram.

When I replaced both switches, I replaced them one wire at a time (cut-connect, cut-connect and cut-connect). Based on past history with the builder, I can't rule out that they were mis-wired. But, they did work for over twenty years before this happened.

The ground wires are NOT connected to the switches! They are crimped together with a copper sleeve.

I will bend the wire around the contact in the future.

Allanj:

Both are new switches. I don't see that any of the wires are hitting another metal part.
 
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Old 02-14-23, 06:45 AM
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I also note that the single toggle switch near the three way switch has one wire leading to the common bundle.
 
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Old 02-14-23, 06:58 AM
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Not sure I understand the problem. Are you saying the new switches operate the same as original switches? Do you have an AC voltmeter?
 
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Old 02-14-23, 07:36 AM
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beelzebob:

The problem is that the light stays on all them time unless I put either one of the switches in "mid position" and break the circuit. This just came out of the blue after working for 20 years. I have replaced both switches, being careful to make sure the wires corresponded to what they were originally. And the problem persists.

Yes, I have a voltmeter.
 
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Old 02-14-23, 08:33 AM
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You can't move wires based on position on three way switches. Not all switches are the same. You have to identify the common connection and make sure the same wire gets to the new common connection. The common connection is usually the black screw and marked common on the back of the switch.

In your diagrams your switches have two black wires and a red. One black should be coming from the same cable as the red. Those two wires are the traveller wires. The other black is the common.
 
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Old 02-14-23, 09:33 AM
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I had noted the position of "common" on all four switches used. All of the black common wires lead to the cable with only white, black and ground cables, and they lead to the position marked common on the switches.

The black and red wires are coming from the same cable and they connect on the horizontal connections.

Would it matter the travelers wires are reversed on both (in other words the black and red wires are on the same position on the switches, which are the same) ? Is the lack of a ground wire connection an issue?
 
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Old 02-14-23, 12:15 PM
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The black and red wires are coming from the same cable and they connect on the horizontal connections.
There is no such thing as horizontal or horizontal side.
Those red and black wires from the same bundle are the travelers and go on the two brass screws. There is no polarity to the travelers. The remaining black wire is the common wire and goes on the dark/black screw.
 
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Old 02-14-23, 01:10 PM
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A 3 way switch has a form C contact arrangement. The 3 contacts are referred to as common, traveler 1 and traveler 2. Designations 1 and 2 are for references only. In one switch position (not mid travel) traveler 1 has continuity with the common contact and traveler 2 has no continuity with the common contact. Flip the switch (not mid travel) and traveler 2 has continuity with the common contact and traveler 1 has no continuity with the common contact. However continuity does not reflect the wires connected to the switches so AC voltage measurements are a better trouble shooting method. With the light on you should measure 120 vac between neutral and common, neutral and traveler1or2 and 0 vac between neutral and the other traveler. Measure at both switches. If you get these readings, either switch should turn off the light. If you donít have these readings, there is a wiring error.
 
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Old 02-15-23, 01:12 AM
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When you replaced the switches you said you matched up wire for wire from old to new switch. However, not all 3 way switches have the "common" screw in the same position and you can't assume that.

On a 3 way switch setup you have two 3 way switches. On one 3 way you take the incoming hot and connect to the "common" screw and on the other you connect to the "common" screw the load going to the light/s, in between you have the two travelers connecting to the switches. Many people interchange the meaning of the word common which ends up confusing them (some call a neutral common, you referred to a bundle as common etc). In this sense the word common is referring to an actual screw on the 3 ways switches. The 3 way switches will have of the 3 screws (forget ground screw for now) one odd colored screw, usually dark/black where the other two screws are the same color, usually brass/silver. Or the switch may have a designation on the back of the switch "C" or "Common" next to the "common" screw. Again, just matching wire to wire from old switch to new does not necessarily mean it will work the same as the "common" screw may not be in the same location on the new switch as it was on the old switch..
 
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Old 02-15-23, 07:45 AM
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Per the diagram and using my voltmeter, all wires are powered in every situation (both switches down, up, and both combinations of one up and one down.Per the diagram above (as indicated in the pictures), both traveler cables are connected to the 2 sets of gold colored screws). I used a method I saw on youtube to identify (reconfirm) the hot wires with the voltmeter They are connected to the black screws.



I can't figure out on these ends where the wiring mistake is made.

Could it be one of the new switches is bad? How can I test the switches?
 
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Old 02-15-23, 09:37 AM
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Even with a wiring mistake the light should turn off.
Take all the wires off the switches and measure for voltage on them to neutral. Only one wire should have voltage on it.
It is actin like the travellers are shorted to each other.
 
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Old 02-15-23, 11:37 AM
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Only one wire is hot. The others don't register. I had identified it as a common wire before. I've checked the wires in the boxes and I can't see any bare wires touching each other. If the travelers are shorted to each other, could one reason be this switch, which is new, bad? If so, is there a way to test the switch other than putting it in other three way?


I intentionally wired a mistake (swapped common and a traveler) and one switch would turn the light off. But not the other.
 
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Old 02-15-23, 02:41 PM
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I would test the switch with an ohmmeter. Measuring common to one traveller should toggle with the switch flip. The other traveller should work opposite.
 
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Old 02-15-23, 03:31 PM
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I am having a hard time visualizing this. I tried with the wire connected to the terminals on both switches and got all zeros. That didn't make sense.

If I disconnect a traveler and the common from the switch, and connect it through the voltmeter, that makes a circuit no matter what switch position is toggled. That doesn't make sense.

Now wait a minute: should instead of connecting the voltmeter between a traveler and common, shouldn't I position it between the traveler terminal(s) and neutral? That would test the output through the switch.
 

Last edited by semocssom; 02-15-23 at 03:55 PM.
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Old 02-15-23, 04:12 PM
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Post 11 provided steps to check the switch for continuity. Remove all wires to the switch before checking.
 
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Old 02-15-23, 04:12 PM
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Yes.... traveler terminals and neutral.
Don't use the ohms section with any attached wiring to the switch.

In the single box..... the switch is wired correctly.
That C wire - black - goes to the light.

The hot should be on the common at the two gang box.
 
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Old 02-15-23, 05:35 PM
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Ok. I removed the switches and tested them with the Ohms section of the voltmeter. All 4 positions worked properly. So in my mind, the switches are good.

I doubt if I did the continuity test in step 11 right. I am sure that left the switches in, but in #18, it says the switch should be removed. I assume that means the other switch is to remain in. I am having a hard time visualizing #11 and how removing the switch allows me to determine continuity, since in my mind, the ability to test continuity is lost with the removal of the switch. I am confused about this. Sorry.

Now, if I do what I propose in #17, I identify which switch position is hot (and ID its wire color) and that the other isn't active, I then have the info to test the other switch. First I test both traveling incoming wires to make sure that power is coming through. If those are good, I should install them on the switches in the same screw position as the first switch (right?).

Hot wire is the one leading into the gang box. It comes from the bottom, while the travelers are shown in the pic on the right.
 
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Old 02-16-23, 04:58 AM
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Try this.

Turn off the power.

Label and unhook both traveler wires from both switches.

Set your multimeter to ohms or resistance or continuity.

Measure between the two traveler ends at one of the switch locations.

Do you get near zero ohms/resistance or full continuity?

Loosen the cable clamp and/or wiggle the wire ends inside the switch box. Does the meter reading change or fluctuate?

Maybe a staple holding the cable to a stud in the wall (or cable clamp at a box) was too tight and finally broke through the cable sheath and insulation and bridged the two travelers creating in one sense a short.

Problems with wiring are almost always at one end or the other of a wire or cable but if we got the discussion this far without a solution perhaps it is time to consider the possibility of a wire or cable failure between its ends, maybe inside the wall.


No easy fix.\
 
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Old 02-16-23, 06:51 AM
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My multimeter is old, so it doesn't have continuity. So I tested ohms: 15 on each switch. I giggled the wiring on there was no major change. One switch doesn't have a cable clamp and the other is hard plastic that keeps the cables tight.

I think this corresponds to another test I did. I tested the output of the switch with the hot wire. With the switch in one position, there was no voltage on one of the travelers. With the switch in the opposite position, all the travelers had power, including both at the other switchbox.

And I think I just confirmed it. I had a cable lying around, I connected it to the traveler terminals and the ground. It worked as it should have.

This sounds like it is inside the wall. Makes sense, another time bomb from my mediocre builder going off.

For a temporary non-fix, any issue if I cap the red traveler on both sides and wire together the black traveler and use a single pole switch, which I will ground?

 
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Old 02-16-23, 03:53 PM
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Odd that an installed cable fails after 20 years. Was there any recent construction in the walls where this cable runs between the two switches?
 
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Old 02-16-23, 05:45 PM
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Open the fixture and inspect the wires. It is possible the travellers pass through the fixture box. It is also possible someone put a nail through the cable hanging a picture. Any new pictures or TVs on the wall?
 
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Old 02-17-23, 04:39 AM
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It's the mud room, so no nails or changes to that space have been made. Other than cleaning the light cover or replacing a bulb, I've not done anything to the fixture. If I recall right, the wire across the top is likely exposed to void spaces in the roof outside the insulation, thus there would be a considerable amount of temperature change there. In order to access it from the top, I would have to cut a whole in the drywall in the garage crawl space (not problem), but then cut through plywood from the unexposed roof to access the space where I would expect the wire to go.

I will check the light fixture. Not out anything!
 
 

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