Jan 14, 2012
Installing a 3 way light switch is not a complex process, but it does require a little understanding of what is going one with a 3 way light. First of all you need to understand that 3 way switches only can be used where you want a switch in 2 areas of the room. An example would be a kitchen with 2 entries. You would want a switch at each entry to turn on and off the lights. If you have more than 2 entries you have to use a 4 way switch.
Three way switches have 3 types of wires that feed to them. This is sold as 14/3WG Romex cable . It is available in several lengths from 10 feet to 500 feet. Always get more than you think you will need. You will also need 2- 3 way switches to do this installation.
- Black: This is the hot wire, the one that carries the load and will shock you
- White: This is a neutral wire or a traveler
- Red: This is a traveler wire
- Bare Copper: This is a ground wire to prevent shocks
Reminder: Always make sure the power is cut to light you are working on. It is a good idea to test the wires even after you think you have cut power. If in doubt you should turn off power to the whole house.
This diagram assumes you plan on or already have standard 14/2 wiring running to the first electrical box with power. You will need to run a 14/3 wire with ground from switch 1’s box to switch 2’s box, leave around 6″ of wire protruding from the wall, and strip off the sheathing to expose the wires. You will then need to pull standard 14/2 wire from box 2 to the light. Once all the wire is pulled you should tie all the white ( neutral wiring) off with wingnuts in each box. as well as the bare (ground) wire. You will also need to ground the switches with the green screw in the lower left side of the switch.
Wiring the 3 way switches are pretty straight forward. The first switch with power from the home breaker box should have the black wire from the breaker tied into the lower right side darker screw. This leaves only the 2 travelers to wire up at the top. It doesn’t matter which side you put them on as long as the other switch is a mirror image.
The second box will need the black wire going to the light screwed in with the dark screw in the lower right. Then the travelers will need to be screwed in. Lastly the light will need to be connected with wingnuts, grounded and mounted.
This is a nice video explaining how 3 ways work from an engineering point of view.
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