One 3 way circuit controls a light at the top of the stairs. All the 4 way switches are optional.
How To Wire A 4 Way Switch
Adding a 4 way switch to a 3 way circuit. You will need to cutbreak this and add the 4 way switch in between. Here are another couple of variations of 3 and 4 way switch circuits. If you only need two switches leave out both the 4 way switches. All you need to do is find the 4 wire that currently runs from one of your 3 way switches to the other. I have an older home with a stair way down to a hallway. Connect the returning travellers from the new switch box location red and white and connect them to the in or the out terminals on the new 4 way switch.
The second controls the light in the hall. In this application where two 3way switches already exist a 4way switch may be added by simply installing two 2 wire with ground cables of the same wire gauge as the circuit wiring from either of the 3way light switches to the location of the new 4way switch. Connect the black wire of the new 3 wire cable to the common screw of the 3 way switch that you will move to the new location. The 4 way switch will have 2 terminals marked in and 2 marked out. Is it possible to connect 2 separate 3 way circuits to make a single 4 way circuit. Hi phil great article helps me understand how 3 and 4 way circuits work.
Here is an example of a light in the middle of the run. You can also add as many 4 way switches as you like in place of any one shown in the circuits that follow.
Gallery of Adding A 4 Way Switch To A 3 Way Circuit
