Need Help with Confusing Circuit - standard wiring diagram caused cable arc

[superdeleted]

So I was upgrading two different 3 way circuits with Caseta Dimmers and Pico remotes on the other end but I can't tell 100% what I did to cause it and I followed the Lutron wiring diagram exactly but when flipping the circuit back on yesterday I had an outlet (dead end 3 way I think it is called) majorly arc and toast up the box for a second before the breaker flipped back. All the connections were tight so one of those cables was in the wrong spot but even though I have what I think it is I would rather someone more knowledgeable confirm before I proceed further. So, I am hoping someone will be able to help here.

I'll do my best to try and list what I have without making it super confusing.

So it turns out both 3-way groups are on the same electrical circuit. One pair of switches controls the light over the laundry area (Light A) and the other pair of switches controls the light over the stairs (Light B). I have 3 boxes. A single gang at base of stairs (Box A), a 2 gang at top of stairs (Box B), and another 2 gang by the laundry folding doors (Box C). The boxes have the following:

Box A: Single Gang, 3 Way Toggle Switch, one 3 wire cable, Red and Black wires on the brass screws and the White wire marked Black on the black screw or the different colored screw.
Box B: Double Gang, Two 3 Way Toggle Switches (Switch A and B), Two 2 wire cables and Two 3 wire cables.

1. one of the 3 wire cables is going out of the box down, the other three all leave going up out of the box.
2. The white wire marked black from Box A is in the 3 Wire cable leaving down out of the box (which would make sense as it would be going to the 1st floor base of stairs. it is nutted with the other blacks in a big bundle. The Red and Black wire go to Switch A. Then the Black from one of the 2 wire cables is also on Switch A which I assume is the cable going to Light B
3. Light B has only one cable going to it that must be one of the two 2 wire but I haven't been able to verify as of yet.
4. the whites (not counting the black marked one) are all joined in a bundle
5. The second 2 wire has the Black going to the Bundle and the White going to the bundle
6. Switch B has the Red and Black from the second 3 wire and then a black jumper to the Black bundle.

Box C: Double Gang, One On/Off Switch and One 3 Way Toggle Switch. Now as I am writing this, I realize I left my notes at home so I will have to update the post in a few hours but what I recall is 5 cables. The 3-way switch turns on one light and the standard switch turns on a group of 3. I did take some pictures but I don’t think they are that good but I will attach them. When I get back home, I’ll update with more details on this box.
Back to the problem. Now after removing all the switches and I replaced the 3-Way at Box C and the 3-Way at Box B (that connects to the wire Going to Box A) with full Caseta Dimmers, then I have Pico remotes at Box A and Box B.
Since I used a Pico at Box A it had me group the wires together. That with whatever I did in Box B made that go up in smoke, Additionally I found what appeared to be the start of it doing the same in Box B. One cable had started to melt through the connector but didn’t get very far.

I have many options here and just want to have the smart capability for the two 3-Way lights. I don’t care about whatever combination is needed. I have other Lutron switches or can stick with the mechanical on one end if needed. Just need it safe.

So Any guidance or help I would greatly appreciate.

[Brandon W.]

Hello superdeleted,

We are glad to hear that you and your property are ok after the arcing event that may have occurred. It sounds as if this may be a dead-end 3-way where the electrician ran one 14/3 cable to the other location. Would you be able to update the thread with some photos or any diagrams you may have drawn out so we could get a better understanding? Also, what is the model number of the Caseta control that will be wired in here?

Finally, it may be a bit easier to reach out to us over the phone at 1(888)588-7661. We have a great service that allows you to share your back camera with our team and we can take a look together.

[superdeleted]

Thank you for reminding me I had this thread still open. Since I didn't get any responses I had to just act like it was all new wiring and started over. Going one cable at a time I was able to diagram / map it all out. Then once I had all the cabling figured out I reinstalled all 5 devices, again one at a time doing the only non 3 way switch first then proceeding and completing a full 3 way setup for the laundry room light and the other 3 way setup for the stairs. This worked and I now have automations in place utilizing the locations which was the goal to brgin with.

Thanks for your reply, and I thought I had uploaded photos already but turns out they didn't get finalized or sent.

You are correct on the dead end, but your directions when using a pico remote as the companion in the 3 way should have not caused that. What I found, and I can't explain why I did it, was that up in Box B a jumper was placed accidentally connecting line to load which turned that bundle of 3 wires capped behind the Pico device hot and arc/pop/fry everything behind the pico. Going back through it redoing all the switches gave me the opportunity to understand it better and get it all cleaned up and functioning. Works great now, love the Lutron Caseta system and if it wasn't out of my price range at times my whole home would have them!