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How does a three-way switch work?
Thursday, June 13, 2019
Three-Way Switch Wiring Diagram
The pair of three-way switches that many homes have for lighting at the top and bottom of stairs, or opposite ends of a long hallway, use an ingenious configuration of a two wires between them in a loop that electricians refer to as “travelers.” Unlike a regular light switch with up-means-on and down-means-off, anytime you throw one of these switches it turns the circuit from on-to-off or off-to-on—and here’s a diagram of the four possible switch positions and how it does it.
Red indicates where the wire is energized, and it must complete the circuit back to the neutral to turn on the light. So either switch change can turn the current on or off individually.
Also, see our blog post Which rooms in a house require switched lights per code?
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