Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.
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VERY IMPORTANT! Before working on any electrical modifications of your home read the first article in this series: Electrical Safety.
A three way switch circuit is used for turning one or more lights on from two different places. For example, turning the light on from the top of the stairs and turning it off at the bottom of the stairs.
The trick with wiring switches is that you only wire the black or hot wire. You'll notice that in the diagram, the white or neutral wire goes through the switch boxes and connects to the light - it is not switched. In the 3 way the white wire is used as an extra switch wire and I said it is colored black. When ever an electrician uses a white wire as a hot wire, he/she will put black tape on it to distinguish it as a hot wire, rather than a neutral. Notice that the same wire is connected to the common terminal of each 3 wire switch.
Notice in the diagram: How to Wire a Three Way Switch Power to Light the black wire is used for switching purposes in combination with the red and white wires. The white wire connected to the three way switch is colored black to show it is not a neutral wire. The black wire shown connected to the three way switch is connected at the common terminal on the three way switch. This terminal usually has a red screw and the word COMMON stamped on the back.
The first drawing shows the wiring of a three way switch with the power source entering the light box.
This second drawing: How to Wire a Three Way Switch Power to Switch shows the wiring for a three way switch when the power source enters one of the three way switch boxes.
Dave(Ask Dave) (About Dave)
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