Joed, I am working on remodeling my kitchen. I have common coming into the bottom of the 3 gang box at one doorway, which will eventually control a ceiliing fan (only from that location) a ceiling light (controled from two locations) and also some recessed lights( again controlled from two locations. So there will be two circuits that can be controlled at the two doorways coming into our kitchen. SO..I have a 3 gang box into which the common comes and a two gang box on the other side of the room. I have not yet installed the recessed lights, and at this stage am trying to simply get our existing ceiling light to work with the new wiring. At the the 3 gang box I have common (black) with 3 pigtails. One is taped off for the eventual ceiling fan. The other two I connected to the BLACK screw on the 2 3-way switches. On switches, the black screw and a brass screw are on one side and a brass screw on the other. ON both of the switches I connected common to the black screw, the black wire from the 12-3 to the brass screw on the same side as the black screw and the red wire to the sole brass screw on the other side. I connected the three white wires from the 2 12-3 lines and the single 12-2 line (ceiling fan) to the white wire from the common feed. And then I have this ugly series of pigtails which I need to re-do, that connects the ground from the common wire to the grounds from the 12-3s and 12-2 and also the ground lugs on the switches. Although I pulled all the wire, I did not connect anything else except a single 3 way switch at the other side of the room (in the 2 gang box). At that box I wired red to the single screw, black to the black screw and white to the other screw on the same side as the black, and I wrapped the white wire with black tape. In the middle at the ceiling fixture I wired white from the common (3 gang box) to white of the fixture. Black from the other side (the two gang box) to the black from the fixture and I connected the black/white wire from the 2 gang to the black from the 3 gang. This circuit works fine, able to turn on and off from the either side of the room. What I noticed though is that when I flip the second 3 way switch in the 3 gang box which is currently only connected to the pigtailed common, and a black and red from a 12-3 that is taped off and not connected to anything, my breaker pops. I forgot to mention that this 2nd 12-3 is also connected to the pigtailed whites and the rats nest of grounds all connected. Thanks for the help Tom

Do you know where it goes? Is it possible that this used to be a three way switch but the other switch was removed at some point? If the second black wire has power when the switch is "off" (I'm assuming you mean 'down' since a 3-way switch isn't on/off ... it's up/down), but nothing turned on when you flicked it "off", then I'd say it's safe to just cap that black wire and push it to the back of the box. It isn't being used for anything anymore.

On 3-way switches, you have two travelers and a common power line. If you look at the switch, you will see a bronze colored screw. It is important to figure which is the common as it will be the same on both switches. Usually the common is a single black wire,that is it enters the box by itself. The two travelers come into the box together and it makes no difference how they are connected to the two other screws. Pay no attention to the color of the wires. The only critical wire is the common and it must be on the bronze screw on both switches

Let me add this is off a garage subpanel that has 2- 20A breakers tied together so I assume its sharing a neural. The extra black wire in box 1 controls one of three lights (single pole, one of the red travelers are capped). Is it possible to cap one of the travelers in box 2 (3way switch, 3 wires in box) and installing a single pole there? Is there a hazard keeping it as it is now. ?? ie: One box with single pole controling all 3 lights. Second box with 3 way only controling 2 of the lights when power is on at switch one.... no power to switch when switch one is off. Again about the hazard, is this a fire/shock hazard or one of those things that it works or it doesnt?