Over the weekend I had to reacquaint myself with how to wire three-way electrical switches. As it can be somewhat complicated (certainly more so than “normal” switches), I wanted to write it down for my future reference.
Three-way switches are when you have two switches controlling the same device (light fixture, outlets, etc). They differ from normal switches in that there are three wires, instead of two wires (not counting ground and neutral) – and the switches are wired together with traveler wires.
In a normal three way switches, you have two wiring boxes where the switches reside. One switch box has the hot line coming from the circuit breaker panel, the other has the load wire going to the fixture.
Typically the line wire will be black, the neutral wire will be white and the travelers will be red and black. Sometimes one of the travelers will be white, but marked with black tape.
First – let me start off with a warning: Electricity is no joke, and not something to take lightly. Before working on wiring switches be sure to turn off power to them. If you’re unsure if power is really off use a multimeter to test them. To be completely clear: Do not attempt to work on wiring until you have confirmed power is off to the box you’re working in!
Under normal circumstances, you would wire the line to the common screw on the three way switch. You would then wire the two travelers (one is usually red, the other is either black or white marked with black tape) to the other two screws. In the other wiring box you would wire the two travelers to the same screws as the previous box, and the load (wire going to the fixture) would be wired to the common screw (same as the line in the first switch).
When using Insteon switches to do home automation, however, it’s a little bit different as you don’t wire the switches together at all – instead doing virtual three-way configurations.
For Insteon switches – like a SwitchLinc – you would have a “secondary” switch and the “primary” switch. The primary switch controls the load to the light – and is located in the wiring box where the wiring goes out to the light fixture. The secondary switch is located in the wiring box where the line comes in from the circuit breaker box.
In these cases, you wire the black wire from the Switchlinc, and the black traveler wire, to the Line with a wiring nut. You then hook the white wire from the Switchlinc to the common wires with a wiring nut. The red traveler and the red wire from the SwitchLinc are each capped with a wiring nut (Separately, not together!) – they are not needed. Don’t forget to also hook up the ground wire to the ground wires in the box.
At the primary switch, you would hook the black wire from the Switchlinc to the black traveler with a wiring nut. The red wire from the Switchlinc is then wired to the Load wire to the fixture with a wiring nut, and finally the white wire is wired to the Neutral wires with a wiring nut. As in the other box – the red wire should be capped as it’s not needed and the ground wire should be hooked up to ground in the box.
The secondary switch will then need to be linked to the primary switch using Insteon such that when you toggle the secondary switch it sends an Insteon signal to the primary switch, which then turns on the light.
The instructions that come with the switches will detail how to link them together – it’s a very simple process.
Important disclaimer: I am not a licensed electrician, nor am I claiming to be one. Use the information provided at your own risk. I’m writing this mostly for me to reference later as I do some DIY projects on my own house. Also – be sure to follow any local electrical codes for your area when doing any sort of wiring.
Photo #1 from FamilyHandyman.com – more information on wiring three way switches can be found there.
Photo #2 from SmartHome.com – great resource on all things Insteon.