Three way switches are used to have two switches turn on light(s). This can be useful if you have two doorways into your backyard shed or any other place you need two switches. They can operate two switches because there is always power to both switches even if one of the switches is turned off.
A three way switch has 4 screw terminals:
The First Box: The First box has the power come into it with a 2 wire cable, and a 3 wire cable going out if it to the second box and switch.
The Second Box: The second box has the 3 wire cable coming in from the first box and a 2 wire cable going out to the light.
The Traveler Wire: The 3 wire cable that goes between boxes has a 3rd wire in it that is red. It is called the "Traveler". The 3 wire cable allows power to go to the second switch even when the first switch is turned off.
Attach the 2 wire cable FROM THE POWER SOURCE to the screw on the first switch:
Attach the 3 wire traveler cable GOING BETWEEN THE TWO BOXES to the traveler terminals on the first switch:(The "Traveler" screws are the same color)
Attach the White Wire:
Ground Wires
Push the wires into the box and screw the switch to the box.
Attach the 3 wire traveler cable coming FROM THE FIRST BOX: (The "Traveler" screws are the same color)
Attach the 2 wire cable going TO THE LIGHTS:
Attach the White Wire:
Ground Wires
Attach the light to the 2 wire cable. Black to Black, White to White, and Ground to Ground. Push the wires into the ceiling box on the ceiling or wall of the backyard shed and attach the light fixture to it.
Turn the breaker on in your shed electrical sub panel and test your 3 way light switches.
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