A 4 way lighting circuit has made many electricians scratch there heads at some point in time. The magic of the circuit is the 4 way switch. It is a specially manufactured light switch that enables you to put together a lighting circuit that will control a light from 3 different rooms or locations.
The wiring diagram above shows a typical 4 way switch installation.
Here is a schematic of the 4 way switch circuit from the first illustration. Start at switch 1 and follow the black (power), power travels through switch 1 through the black wire (travelers) over to switch 2 (4 way switch) through the 4 way switch, across the red traveler wire over to switch 3 then stops because switch 3 breaks the path. The light is off!
Now we have flipped switch 1, lets follow the power again. Power travels through switch 1 across the red traveler wire to switch 2 then through the 4 way switch to the black wire and over to switch 3, switch 3 passes the power to the black wire going to the light. The light is on!
So far we have been controlling the light from switch 1, now lets go into a different room and use switch 3. The above illustration shows that we have flipped switch 3, you can see that we have broken the power path and the light is now off.
Now lets go into another room and flip switch 2, if you follow the power you can see that the light has come back on. The 4 way switch is feeding power from red wire to red wire now and completing the circuit.
Now lets flip switch 1 again and follow the power. The power stops at switch 3 so the light is again off.
So there you go, we have turned the light on and off from every room. The circuit is really not that complicated, it is only a 3 way switch circuit with a 4 way switch put in the middle breaking the travelers.
Just remember to pay attention to the terminals on the light switches, the 3 ways will always have a common, NO, and NC, the common gets the power and the load. The 4 way is always 2 travelers on one side and 2 traveler on the other.
