I would like to combine a couple of lights into one four way circuit. Is it possible?:

Here's how the current wiring exists.

12/2 is shown as --
12/3 is shown as ==

pwr -- sw1
sw1 == sw2
sw1 == sw3
sw3 -- light

 

A four-way switch is wired between the two three-way switches. Two wires (travelers) from the first three-way to the four-way and then two wires (travelers) continue from the four-way to the other three-way.

 

OK, thanks. So, to make my idea work, I'll need to run a 12/2 power source to the light, and disconnect the power source in the sw1 box, right? Then, I would have

sw1 == sw2
sw1 == sw3
sw3 -- light
pwr -- light

where sw1 would be my 4-way switch
sw2 would be my 3-way switch
sw3 would be the other 3-way switch

wiring would be:

sw1 red (to sw2) to black traveler
sw1 black (to sw2) to black traveler
sw1 red (to sw3) to silver traveler
sw1 black (to sw3) silver traveler
sw1 white wired together, and marked black.

sw2 white (marked black) to common
sw2 red to traveler
sw2 black to traveler

sw3 white wired together, and marked black.
sw3 black (to light) to common
sw3 black (to sw1) to traveler
sw3 red (to sw1) to traveler

light black (to pwr) and white (from sw3) together
light white (to pwr) and white (from fixture) together
light black (from sw3) and black (from fixture) together.

my head is spinning... i've never done a 4-way circuit, so if someone can check my problem, I would say thanks!

 

Look, the power source can come into any box and still be wired correctly. if walls and ceiling are open, i.e. you have absolute access, then the simplest thing to bring power into one of the 3-way switches.

You say you've never wired a 4-way switch system. So you have experience with a 3-way system? If that's so, think of it like this. Basically, in a 3-way system, power comes to one of the switches, goes to the second switch on the travelers, then goes to the light. Right? A 4-way system is just taking a 3-way system and putting a "stopover" in the middle of the travelers. You break the travelers with a 4-way switch. The 4-way must be between the 3-ways!

This is the easiest thing to do. 2-wire to the first 3-way switch. This is your feed in, constant power, the black conductor on the common terminal of the switch. Then take a 3-wire from this switch to the 4-way switch, using black and red as your travelers, and splice the whites together. From the 4-way switch run another 3-wire to the second 3-way switch, again using the black and red conductors as the travelers, and splicing the whites (neutrals) through. From the second 3-way switch run a 2-wire to the light, using the black as your switch leg (the hot on the fixture) coming from the common terminal on the switch, and the whites spliced and then to your neutral on the fixture.

This is the simplest method because there is no switched loop. What you suggested is to make a switched loop, which requires reidentification of wires. If you can run whatever you want anywhere you want, the loop and reidentification are not necessary.

Oh, and you can put any switch anywhere you want in the walls. The 4-way could be the one nearest the main entrance if need be. That doesn't matter, just keep the circuit consistent.

 

Rewiring down the walls will be difficult, so I want to use existing wiring.

And, becuase only one switchbox (sw1) has two 12/3 wires going to it, I need the 4-way switch to be there. This is also where the power source is. I can't connect power source to 4-way switch because there is no common. So, if I run power to light fixture (easy because of open attic) then everything else doesn't need any attention other than install 3-way switches at the ends of the 12/3 wires (which are in sw2 and sw3).

I think my heads on straight now. Thanks for your help.

 

Ok, then just make sure that when use the white as a hot you reidentify it with a piece of electrical tape that isn't white, yellow or green. Also, make sure that when you have to use the white as hot, you don't use the white as a hot leg. Make it a traveler.

A bit of advice, try drawing the circuit out on paper if you have to.