FAQ: Zwave Switches 101 for Noobie (What's an Add-on Switch for and Do You Have to Replace All the Switches in a 3-Way?)

Welcome! :sunglasses:

  1. yes, you usually have to replace all the switches in a three-way

If you have a three-way or four-way set up, you will have to replace all of the switches with switches specifically designed to work together. This is because network switches are not wired quite the same way as nonnetworked switches. A network switch has to always have power so that it can hear the next “on” command from the network even though the switch appears to be off.

With non-networked switches, a three-way is often wired in a sort of figure 8 loop so that one switch is completing the circuit and the other switch has been dropped out of the circuit. You can’t do that with the networked switches because of that need to always have power for the radio.

Consequently, you usually have to replace all the switches. And because different models use somewhat different methods to communicate between the switches, you have to replace all the switches with ones specifically designed to work together.

There is occasionally an exception to this rule. One model of the 2017 Zooz switches and some of the Lutron Caseta models can use an existing toggle switch as an auxiliary depending on the specific wiring in the house, but that’s unusual.

  1. What’s an add-on switch?

In a three-way set up with network switches, one switch will be the master. That’s the one that actually controls the load to the light fixture. The other switches will basically just act as remote controls for the master switch. They may be connected to the master switch through physical wires (usually called traveler wires) or they may communicate to it wirelessly. But all they’re doing is telling the master to turn the current on or off to the load.

Different manufacturers call the non-master switch by different names. “Auxiliary,” “add-on,” “dummy,” “slave,” “remote”-- it all means the same thing, a switch which does not directly control the current to the fixture but rather just sends a signal to the master switch.

  1. different brands have different features

For more about the different features that you might find in network switches, see the following thread (this is a clickable link)

In particular, note that some brands, such as Linear/GoControl, include a Z wave radio in their auxiliary switches. These still are not load control switches, but because the auxiliary can talk directly to the hub, it can be used in some situations without a master, such as when you want the dummy switch to control a smart lightbulb. Even so, these auxiliary switches cannot control the current to a light fixture. But they do show up on your things list.

Other brands, such as GE, do not include any radio in the auxiliary switch. Instead, it must be connected by a physical traveler wire to the master switch, and it must be on the same circuit. So these add-on switches are invisible to the SmartThings hub and can’t be used for any other purpose except to communicate with their matching master switch.