First run a 2 wire cable from the wall power to the black screw on 1 of the switches. This story features diagrams that show how to wire 3 way switches.
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3 way switch with 2 wires. To wire a 3 way light switch youll need 2 3 way light switches 2 2 wire non metallic cables 1 3 wire non metallic cable and 2 6 inch grounding wires. The following is the simple schematic of a three wire 2 way switch wiring. The wiring is more complicated than a traditional single pole switch but well explain how to make the connections. Two way switches are single pole single throw spst with two connection wires and are wired with 122 or 142 cable between the switch and fixture. Once youre done youll be able to control a light from two switches. You can observe in the schematic that both the com terminals are connected together.
The two switches appear to be connected by a 3 wire plus ground cable. Wiring a 3 way light switch is certainly more. The l1 terminals of both the switches are connected to line or phase or live of the ac supply. A three way wall switch is single pole double throw spdt with three connection wires and is typically wired with 123 or 143 cable between the two switches. When nothing is hooked up there is power in the 2 wire plus ground cable on the upstairs switch. Try to keep the 2 wire traveler cable bundled close to the cable with the hot and neutral.
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. The red and black wires travelers of the 3 wire cable get connected to the common terminals on the three way switch. At the line switch box the black wire of the two wire line cable gets connected to the copper or black screw terminal on the three way switch. Description power at both ends switch leg at one with a 2 wire 142 or 122 used as travelers. Run the traveler 2 wire through the same holes as the receptacle feeder 2 wire instead of alone across the attic.