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What you need are two 2-way switches and one 4-way switch which goes in the middle.
A three way switch has one wire coming in (the common?) and two wires going out (the travelers). The switch connects the incoming common to one or the other travelers. I.e. up, it goes to wire A; down, it connects to wire B.
A four way switch is like an “X”. It has four connections: 2 in and 2 out. Call them A and B in and C and D out. In the up position A is connected to C and B is connected to D. In the down position, A is connected to D and B is connected to C.
Since it is getting late, I’ll have to leave it at that for now as I have to get up early (4 am) to go to work tomorrow morning, but I hope this helps you for the nonce. It probably is confusing but its really neat. Tomorrow I’ll try to work up a diagram for you.
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If you wire the 3-way/4-way switches as above, you will have problems. The wires from box to box are ok but the wiring is not. Remember these simple rules: The white wire from the power coming in always goes to the fixture. The incoming hot goes the common terminal of the first switch. The black wire going to the fixture attaches to the common terminal of the other 3-way switch. Connect the travelers (red and black in this case) to the other switch terminals and add as many 4-way switches between the 3-ways as you need (they connect to the traveler wires).
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In my county a homeowner can do his own wiring if he wants to and can usually save some money. My son is wiring his basement addition with my help.
He is a brand new cival engineer and has never wired anything so I am trying to show him how to do the wiring no problem, but he insists he has a light that must be controled from three different switches. I seldon run into this because I try not to. I think I can wire the thing by carefully following the diagrams I have looked at in several DIY books,but I worry because I dont understand what is actually happening in the switches. Can someone tell me how the current flows in the 3 way and 4way switches when they are up and when they are down ? If I better understood how they work I could probably wire the thing without a diagram. Thanks
*Arrowshooter,I am in the process of wiring my own home now with a little coaching from a real electrician friend. I also had some conceptual problems with three and four way switches. This is how my friend told me to proceed.The circut your son wants to run is really very simple. The key is to avoid trying to think too hard about it. It also helps for beginners to make all connections in a series of boxes ending at the light fixture. It takes more wire but it avoids the confusing bird's nest of wires you get when you try to run all switch wires (legs) to the box at the fixture.In addition to the light fixture and it's box, you will need two three way switches and, one four way switch, 3 boxes, and 12/2 WG and 12/3 W/G Romex type cable.Bring power to the first switch location/box (12/2 W/G). From this box run 12/3 W/G to the second and third boxes and 12/2 W/G to the light fixture.The white wire is your neutral. Connect all of the white wires from your power source to the light fixture.The bare copper wire is your ground. It should also be connected from your power source to the light fixture. If your switches have grounding terminals (green screws) then you should provide a jumper.All of the switches will have terminals marked "common." These terminals are also designated with a screw of a different color. Connect the red wires to the common terminals.Connect the black wires to the remaining terminals.Wire up the fixture, screw in a bulb, power up the circut and see what happens. Now to your question. In a two switch system there are two paths for the electricity to follow, red and black. Add a switch and the number of paths increases dramatically; black-black, black-red, red-black, and red-red. Add another switch and you get, well, you get the idea. Any path can be broken by any switch in the system. Any switch can restore power by connecting a new path. If the drawings on the switch packaging and in the books confuse you take some short lengths of wire and your switches and mock up a circuit like the one I described. If it works go full scale.
*A three way switch arrangement uses a hot wire into one switch, two travelers between the switches and a switched wire up to the light. A four way switch arrangement is wired similarly to the three way, putting any number of four way switches in the travelers between the two three way switches. All this sounds complex, but perhaps the drawing will help explain it.Maybe this will help. Extend the index and middle fingers of each hand and touch them together, index to index, middle to middle. Now turn one hand over and touch your fingers together again - index left to middle right and index right to middle left. That's what a four way switch does - it just flip flops the connections between the travelers.
*What you need are two 2-way switches and one 4-way switch which goes in the middle.A three way switch has one wire coming in (the common?) and two wires going out (the travelers). The switch connects the incoming common to one or the other travelers. I.e. up, it goes to wire A; down, it connects to wire B.A four way switch is like an "X". It has four connections: 2 in and 2 out. Call them A and B in and C and D out. In the up position A is connected to C and B is connected to D. In the down position, A is connected to D and B is connected to C.Since it is getting late, I'll have to leave it at that for now as I have to get up early (4 am) to go to work tomorrow morning, but I hope this helps you for the nonce. It probably is confusing but its really neat. Tomorrow I'll try to work up a diagram for you.