When nothing is hooked up there is power in the 2 wire plus ground cable on the upstairs switch. A three conductor cable with a ground is then installed between the two 3 way switch boxes.
1872 Diagram For Wiring A Three Way Switch Wiring Library
How to wire two three way switches. Connect the wire marked common to the black or dark colored screw. I think that the most common method used to wire a set of 3 way switches is to bring the two wire line cable into one switch box and bring the two wire load cable into the other switch box. Power through the lights to three way switches has two wire cable and ground between the light boxes and three wire cable and ground at the switches. Take all three ends and hold them together then twist on the wire nut so they are all securely fastened together. The black screw is the common which we identified in the steps above as the switch leg or hot power source. You will see a black screw and two gold screws on the switch.
There is only the single 3 wire plus ground in the downstairs switch box and only two 2 wire plus ground cables at the fixture. White or neutral wire taped with black electricians tape is used as black power wire to make connections throughout. Feed a length of 14 3 type nm cable or 12 3 if youre connecting to 12 gauge wire between the two boxes. Take your three way switch. Use wire nuts to attach the two pairs of greenorange grounding wires together adding a 6 piece of copper grounding wire to each pair as well. When wiring a 3 way switch first screw the terminal screws of the new switch until they are difficult to turn.
Connect the wires to the new 3 way switches with ground screws using one of the two wiring diagrams fig. The two switches appear to be connected by a 3 wire plus ground cable. White black and red plus a bare ground wire. Connect the ground wire to the green screw. The 14 3 cable has three insulated conductors. Connect the two remaining traveler wires to the two brass or light colored screws.
Strip all three wires with wire strippers.
Gallery of How To Wire Two Three Way Switches
