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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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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:
• Which house appliances need a dedicated electrical circuit?
• Can a short circuit cause a high electric bill?
• What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?
• Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?
• What causes copper wires to turn green or black in an electric panel?
• What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?
• Why is it unsafe to bond neutral and ground wiring at subpanels?
• Should I get a lightning rod system to protect my house?
• Why is a strain relief clamp necessary for the cord connection to some electric appliances?
• Does a wire nut connection need to be wrapped with electrical tape?
• What is the minimum clearance of overhead electric service drop wires above a house roof?
• What are the requirements for NM-cables entering an electric panel box?
• What is the color code for NM cable (Romex®) sheathing?
• Why is undersize electric wiring in a house dangerous?
• What causes flickering or blinking lights in a house?
• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?
• How can I find out the size of the electric service to a house?
• What could cause an extremely high electric bill?
• Can old electrical wiring go bad inside a wall?
• What is an open electrical splice?
• What are the most common electrical defects found in a home inspection?
• What is the life expectancy of electrical wiring in a house?
• What is an "open junction box"?
• How dangerous is old electrical wiring?
• I heard that aluminum wiring is bad. How do you check for aluminum wiring?
• What is "knob and tube" wiring?
Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.
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