Steve, you ol' devil. You could have just called me, y'know. (You should anyway; we need to get together.) I know; you just wanted to see me wear out my fingertips (all two of them!)
Okay, here goes:
Remember from lesson #1 that each 3-way switch has three wires attached, the common on each switch's darker terminal, and the two travelers.
One of the commons is fed always hot, and the other common feeds the switched power to the load. Remember the load? The fixture or whatever.
By simply testing for hot from each common to ground or neutral, you can determine which one is hot all the time, and which one is only hot when the fixture is on.
Also, you can usually tell that the always-hot common is fed from a connection with another wire or two, and the load's common is almost always a single wire.
It's a good idea to check all of the wires before disconnecting any, because the switch helps hold the wires for convenient testing. Make a mental (or better) note of each wire.
If the travelers at each 3-way are not the same two colors (red and white are often used differently at each end when the both come from the fixture box.) You can't assume.
It's a good idea to make note of each traveler at both ends by testing for hot at one end, and then at the other end. Both ends of each traveler will be either hot or not hot at the same time.
Sometimes, two two-conductor cables are used; one for hot'n'neutral, and the other as the travelers. I often do this if the hot'n'neutral need to go to several switch boxes.
Other times, three-conductor is used, and the white may be a traveler on one and the hot-feed on the other. This is done when the hot'n'neutral go to the ceiling box, and both 3-ways branch from there.
Occasionally, I'll use two-conductor to one switch, and three-conductor to the other; one of them may be remotely located, relatively speaking, and not need a neutral.
As far as how they work, which is a great help towards understanding X-10'ing them, it goes something like this:
In 3-way switches, aka single-pole, double-throw, the common is always switched to one traveler or the other; if both commons are switched to the same traveler, the light is on; if not, it's off. Simple!
What about 4-ways, you ask? A 4-way switch is inserted in the pair of travelers, and acts as a reversing switch. There are two dark terminals and two light ones. It's easy to mis-wire these.
The two dark terminals connect to one 3-way's travelers, and the lights to the other 3-way's travelers; it doesn't matter which. (Don't assume blacks to darks and reds to lights, etc.)
There can be any number of 4-ways between 3-ways, but there must always be a pair of 3-ways, one at each end of the string. Again, the principle is to either switch the two commons together or break 'em.
Now, what about X-10's? It really gets fun here. That will be lesson #3, if anyone is interested. Let me know. (Not you, Steve! LOL) I don't even know if Tester or anyone else even read the "primer". No feedback (*sniff*). Golly, Wally!
Larry
www.fineelectricco.com
