3 way dimmer switch funny behavior/functioning as two isolated single poles

Question

I replaced a Lutron 3 way dimmer (wiring guide here) installed by another, with a Leviton dimmer whose style and color I liked better. The far switch was just your basic toggle. Note that it was working before as a 3 way with a 'digital' dimmer of maybe 4 or 5 levels of brightness.

I used the onlne instructions of this product to determine what wires were the travellers and which was common and of course the ground. Each device, the old and new, have four wires. I wired it up as I thought it should go and when I flipped the circuit breaker, the lights went back on.

However, the problem is it's functioning like two individual single poles- call them A and B. What I mean is that you can turn the light on and off with each one individually but they won't turn off the light when the other is controlling it. It doesn't yield control and that goes both ways I think.

I really don't understand what could be happening here unless it's within the product itself. I assume the common wire is right or the light wouldn't work at all. If that's true, the traveler should be switching out unless the product is short circuiting them.

One more interesting thing is that actually there is a split second where it goes dark when I'd expect it to, but turns back on a split second later, only when I try turn off the light with A (dinner) that I turned on with B (toggle). This makes me wonder different things.

Is there something I don't know is there anything I did wrong? I'm curious to know what could be going on with this. I picked up another product, a similar 3 way dimmer by Lutron and will try tomorrow to see if just changing the device fixes it, and using the initial brand.

I don't have a picture of the old dimmer but this is the new one.

I also noticed other wires in the back of the box. Out of curiosity what would those do? I thought I shouldn't need to touch them at all and I don't want to play around with electricity.

Also I heard something about a companion switches. What are they and do I need one?

UPDATE: I'm embarrassed by the truth but I wanted to ask the question when it was fresh in my mind. Taking the other switch apart, I find it's only a single pole, with two wires and a ground. I guess it never worked as a 3 way- only a pseudo three way, and the other old dimmer switch was a weird design in my mind. That changes my question to how hard would it be to set the other box up as three way and what would it run me for an average electrician? Thanks

Answer 1

I've since rewired things, but it sounds like what was happening with one switch in my home before I did some rewiring. I didn't really understand what was going on either at first, but I had an electrician come in and tell me that this switch used the Carter system which was designed to save wire by only running a single wire to each switch.

Carter system wiring is no longer code compliant and can be dangerous and was never designed to support dimming. Ideally you should rewire the whole thing. This question is related.

In my case, I solved the problem by installing a Lutron Caséta smart dimmer at one location and removed the switch at the other location, replacing it with a remote (companion switch). You can purchase them both as a package on Amazon.