Why does my 3 way switch have so many wires?

I have a very confusing set up on my dining room switch, which should be a 3-way switch as there are only 2 switches in the whole room that control the light, but it kind of looks like a 4 way switch but even still, there are way too many wires back there. There are 4 cables coming in from behind the wall, top left(TL), top right (TR), bottom left (BL) and bottom right (BR). TL and TR both have black, red, white and copper wires, BL and BR have black, white and copper wires only (no red). The TL, BL and BR white wires are all tied together. The TL black and red, and TR white wires are all tied together (not attached to the switch).



The TR red wire is attached to the TL hole in the switch (this switch doesn't have screws but little square holes in the back of the switch that you put the wires into and they lock into place). The TR black wire is attached to the TR hole in the switch. The BR black wire is attached to the BR hole in the switch. The BL black wire is also attached to an actual screw that is on the TR side of the switch. All 4 copper wires are tied together, with one of them (can't tell which one) attached to a screw on the top left of the switch. So there are 3 black, 1 red and 1 copper wire attached to the switch.



Please help me identify why there are so many wires and what kind of switch this is! My goal is to change this switch to a dimmer switch but don't know what to do with all these wires and how to connect them since there are 3 black wires not just 2.



Thanks so much!Why does my 3 way switch have so many wires?It sounds like you have 1 cable to the lamp, 1 cable to the panel, and 1 cable to the second switch, and 1 cable that goes to power up other rooms or receptacle(s) elsewhere (ie: a socket for a plug, 1' from the floor).



1) All bare copper wires should be pigtailed together. By code, in Ontario, Canada, the bare copper wire from the fuse / breaker panel should be screwed to the box first, then pigtailed to the others. This should identify which cable comes from your fuse panel - chances are, it has only white, black and bare wires - probably one of your bottom cables.



2) When the breaker is off, do other sockets or lamps go out? If so, remove bulbs or unplug for the next step. We want to identify which cable goes to your ceiling fixture, using 1 known good incandescent bulb in it, and every other possible lamp, or appliance on that branch disconnected and or unplugged. Using an ohm meter, measure between the black and white wires of each of the 2 conductor cables. If it measures infinity, probably goes the panel. If it measures 240 ohms, you've got a 60 watt bulb attached to the other end of the cable. (60 watts divided by 120 volts = 1/2 amp, and 120 volts divided by 1/2 amp = 240 ohms.)



3) to identify which 3 conductor cable goes to the other switch, go look at the other switch. there should be 3 screws, one bright brass common), 2 darker brass. Look at the colour going to the common or middle screw (typically white). go back to the first switch, and put the meter between that colour wire from a 3 conductor cable, and one of the other colours. flip the remote switch. If you can turn the beeping meter on and off with the remote switch, you've found the other end of the cable.



4) ideally, what you'd find is:

a) all ground wires joined together.

b) white from panel goes to white to lamp.

c) black from panel goes to middle of 3 screws on switch 1.

d) black and red from switch 1 goes to switch 2.

e) white goes from middle screw on switch 2 back to box holding switch 1, and has a piece of black tape on it. It goes to black wire of lamp.



5) ideally, what you want (assuming you're disconnecting switch 2 permanently) is

a) all ground wires connected

b) white from panel goes to white of lamp.

c) black from panel goes to 1 of 2 screws on dimmer.

d) black to lamp goes to 2nd of 2 screws on dimmer.

e) wires to second switch are wrapped in tape and or marrettes (as per local code) to prevent them from touching anything live in this box.





[EDIT1]



I suspect one of the bottom cables goes to the panel, and the other bottom cable goes to other receptacles.



Since the top left cable has white connected to two other whites, it probably goes to the lamp.



Was there a ceiling fan there once upon a time? That would explain the red wire in top left cable.



Sounds like the top right cable goes to the far switch. I anticipate that the white wire should have a black strip painted or taped onto it.



My recommendation (sight unseen, attempt at your own risk) is to



1) attach both bottom black wires to one side of your dimmer.



2) Attach both top left black and red wires to the other side of the dimmer.



3) Disconnect and tape / cap all top right wires individually.



4) Get an electrical inspector to verify your work before you turn the breaker on. Cost in Ontario is about $15.Why does my 3 way switch have so many wires?Call a qualified professional electrician to do the work. This sounds like a 3 way switch with the line and the load and the other switch all in the same box on the wall. I'm not sure you can install a dimmer in this situation, but it might be possible. A mistake made in this situation could cause a fire, or the whole thing does not work. Call a pro. Why does my 3 way switch have so many wires?Don't worry about the wires in the box ground and neutral most likely, but you can not install a dimmer on a three way if you want to be able to use both switches. It can be done with Insteon or other brand RF switches but that is a whole other process.

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