3 way switch-I think I did something wrong-One switch always has to be "On".

[vyacheslav]

Greetings,

I have a 1st floor small bedroom/office which has two doorways (from front hall and a from a smaller hall to the kitchen). There is a 3 way switch by each doorway that controls an overhead light. It worked fine before with no problems, but the switches were very old and were the bulky, fat three way switch type.

I replaced them with modern, standard off/on toggle three way switches and I think I must have done something wrong. One of the switches always has to be in the "on" position for anything to work. If Switch A is in the off position, Switch B does nothing. If Switch B is in the off position, Switch A does nothing. If Switch A is in the on position, I can turn the light on and off from Switch B (I can also turn on and off from Switch A if I leave Switch B on). If Switch B is in the on position, I can turn the light on and off from Switch A (I can also turn it on and off from Switch B if I leave Switch A on). If Switch A and Switch B are both in the on position, the light is on and can turn it off from either switch. I can also turn it back on from that same switch (because the other switch is in the on position). One of the switches has to be in the on position at all times. If one of them is in the off position, the light doesn't work.

I took pictures with my phone of the way it was wired originally, and I repeated that wiring precisely. It is a side wired switch with the screws and hooks like standard. With the switch in the upright position, there is a single black screw on the top right (that's the main power source), there is nothing on the top left. On the bottom there are two gold/brass screws on either side. I don't think it matters which "Carrier" line goes on which side on the bottom, but I kept it the same as it was before.

Anyone know what I did wrong? Do I have to break off some sort of tab on the switch like you do with outlets sometimes?

Thanks,

V

 

[Snoonyb]

Are the conductors colored, and it does have an affect, how the carriers are connected.

 

[vyacheslav]

Thanks for the reply. On Switch A, the power line is Black (top by itself) and the conductors are Red and Black. I hooked them back up the same way they were in the picture I took before I disassembled the old one (red on the left, black on the right underneath the power line). On Switch B, the power line is Black (on top by itself) and the connectors are Red (Left) and White (Right, underneath the power line). Again, this is how it was assembled prior.

 

[Snoonyb]

Thanks, now, how many conductors are in each box?
Are these both single gang boxes?
Are there any other devices in the 2 boxes?

 

[vyacheslav]

There is only one switch in each box, single gang. No other devices other than the single switch per box. Three wires coming into each box. Switch A Power (Black-older wiring from the 50's), Red and black conductors (newer wiring). Switch B Power (Black, newer wiring) Red and white conductors (newer wiring).

Here's something else to consider: I don't think this would have any effect, but I'll ask just to be sure:

There are no grounding wires coming into either gang box. The wall/gang boxes are metal. I took a small length of grounding wire from a roll of new Romex and I attached one end to the switch like you normally would where the grounding wire goes, and I attached the other end to the side of the metal gang box with a short, self-drilling sheet metal screw into one of the existing holes that was already in the box. I don't think this would have any effect other than the switches are properly grounded now but the folks here would know better than I.

I guess I can also assume the switches aren't faulty? They are brand new and I assume that one or both wouldn't work at all if they were somehow faulty?

Thanks for the help!

V

 

[Snoonyb]

Interesting.
Short of taking the fixture loose and starting there, are there any known grounds in the room?

 

[Snoonyb]

I'd suggest we continue in the daylite.

 

[afjes_2016]

I hooked them back up the same way they were in the picture I took before I disassembled the old on

All 3 way switches have a "common" screw/connection. They are indicated on the switch as either an odd colored screw (compared to the other two) usually being black or dark colored OR you will see "common" indicated on the back of the switch behind the common screw.

Forget about the ground screws for now on any of the two switches as you read on.

On one switch common screw you need to connect the incoming power and the other common screw you need to connect the wire going to the load which is the light.

Take a look at the new switches and identify the positions of the "common screw" on each switch. Now look at the old switches and identify the "common screw" on each of those two switches. Not all manufacturers put the screw in the same place which is why they identify them using a odd colored screw or on the back of the switch imprint "common".

Looking at the old switches after you identify the common screw on each switch look at the pictures you took before you disconnected the wires. See if you can now figure out which wire in each box was connected to the "common screw" of each of the old switches. Let's just work with the common screw wires for now. Try and match the wire that was on the common screw of the old switch and place that wire on the common screw of the new switch. Once you do that then the other two wires which are the "travelers" can be placed on either of the other two screws; does not matter which one goes on any of the other two screws.

You have made the mistake that many DIYers gave made in the past. You were correct in taking pictures but you did not mark which wire came off of the common screw of the old switch which was your mistake - no biggie though.

Again, in short; one common screw has the incoming power on one switch and the other switch has the outgoing load to the light; the two travelers can go on either of the two remaining screws.

Once you have those wires secured on the switches then you can worry about connecting the ground wires to the switches.
If your new switches have a brass colored piece of metal like in the picture below in the red circle you do not have to run the ground wire to the ground screw on the new switch (you can if you want to though). These are considered a self-grounding receptacle/outlet or it can be on a switch. BUT, in order to use this type of switch or receptacle/outlet you must be using a metal box and the box must be grounded properly.

 

[Steve123]

You positive both are 3 way (single pole double throw) switches ?

 

[bud16415]

You are getting good help here.



All I will add is hopefully you still have the old switches and the photos you took. Go back to the old switch and compare what wire in your photos went to what screw on the old switch and then look at the old switch for identification of that screw.



I think you get my point and what @afjes_2016 has explained as how the screws in the new switch may be located different and you are looking for the one that is the common.

 

[PJB12]

That's a great explanation Afjes.

I wish I had your gift for words on any of the many times I've been asked by people how to wire three & four ways.
Attached below is a sketch I made for someone long ago. Maybe it will help the original poster even more.


Enjoy Today!

Paul

PS:
Post #5 mentioned using a sheet metal screw for grounding.

NFPA-70 250.8 doesn't allow sheet metal screws to serve for the equipment grounding conductor. It's a common error people make. (Another misconception is that people think the screw has to be green & hex head. It doesn't.)

In the back of your box, unless it is really old, there is a hole with"GR" stamped next to it. It is tapped #10-32 in the United States & it's to allow the grounding screw to engage two threads, as required by code.

Plan B: Use a Grounding Clip. No screw needed. (Photo Attached) Just shove the wire under it and push it on the edge of the box.

When Afjes mentioned the automatic grounding device, it's not allowed to serve as the grounding means if the device mounts to the cover of the box unless the device is mounted with two machine screws and nuts. If not, you'll still need to use a jumper to the box.

 

[Snoonyb]

He's already identified the black screw on the new switches as the common screw.

And I, in practice, have found this to not be the case; "Once you do that then the other two wires which are the "travelers" can be placed on either of the other two screws; does not matter which one goes on any of the other two screws."

Also of note, the conductors are not the same in both boxes.

 

[vyacheslav]

You positive both are 3 way (single pole double throw) switches ?

Yes. Single pole switches only have two screws/terminals for hookups. These have three.

 

[Eddie_T]

A neon tester or VOM could tell the story in 10 minutes or less.

 

[Snoonyb]

If you have a VOM, and a known ground, disconnect both switches and measure from each conductor to ground. The conductor that reads 120V is the power so connect that to the black screw. Then measure the remaining conductors for continuity, these 2 will be the travelers. I connect one end of one to the screw below the black primary screw and at the other side on the 2nd switch, connect the other traveler to the other side of the primary switch and to the screw below the black screw on the 2nd switch. connect the remaining conductor to the black screw of the second switch, switch is the switch leg.

A neon tester will only tell you that voltage is present.

 

[Eddie_T]

A neon tester will only tell you that voltage is present.

I would have him make a truth table w/o disconnecting anything. The table would show voltage presence or absence for all terminals and switch positions.

 

[Snoonyb]

And with 3 showing the presence of voltage, which, of the 3, is the primary and which, of the 3, is the switch leg?

 

[Eddie_T]

And with 3 showing the presence of voltage, which, of the 3, is the primary and which, of the 3, is the switch leg?

I'm sorry, did I miss something, did one switch indicate voltage on all three terminals?

 

[Snoonyb]

My apologies, there are two, yes 2 switches, so instead of 3 reading the presents of voltage, it would be 4, reading the presents of voltage, so, which of the 4, reading the presents of voltage, would be the primary, and which, reading the presents of voltage, be the switch leg, and in which combination of switch positions?

 

[Eddie_T]

With the truth table one could compare (even redraw) with the top sketch in post #11 above.