3 Way Swiches
Belkin and TP Link say no, and they're right, at least officially. But unofficially it is possible to make an IoT light switch work in a 3 way application.
- Use one IoT device and one 3 way switch. Change the 3 way wiring so that Black is line in, White is neutral, and the Red traveler is for the load. See below for details.
- Use two IoT devices. Wire as above, see below for details.
- Use an IoT device and an inexpensive or old android phone running WemoHome or AutomationManager as the other switch. See below.
NOTE! This is electricity and getting it wrong can be hazardous or fatal. So consult or hire a qualified electrician if you're not able to do this on your own, or you live someplace where you are legally required to do so. I'm not advising you do to these changes, nor can I be held in any way accountable if you do something wrong. Make changes at your own risk.
One IoT Switch
This is the least expensive route.
Inspect both switch boxes to determine the wiring type: 3 way switchwiring diagrams (power through switch or power through fixture).
A neutral line must be available in at least one of the switch boxes for the IoT installation to comply with code (older homes may not have this). See if you can route neutral from another location if neither box has neutral. Wiring to neutral to ground will work, but NOT that this is NOT allowed by most wiring codes. It won't work at all if the circuit is on a GFI breaker.
Be careful, white wires are not always neutral! Test before proceeding.
Wire as per the middle diagram below. Your switches will work a little differently than before, but will probably comply with local codes (it's best to always check with an electrician!).
- When either the light switch or IoT switch is ON the load (light fixture) will have power.
- With the physical switch OFF the load will follow the IoT switch.
So this means you can control the load from the IoT device either locally or using your phone, but you can force it on with the light switch when necessary.
A second possibility is to wire the IoT switch as an add on to and in parallel with the existing multi-way switches. You would install the IoT switch where you have access to the line, neutral, and load wires. Wire to the line/load as if it were a single way switch. If either the IoT switch is on or the mutli-way switches are feeding power to the load the load is active. It turns off only if both the switches and IoT switch is off.
Two IoT Switches
More expensive but easier. As above, inspect the switches to determine the circuit type, neutral, line in and load wires. Wire as per the last diagram below.
In this configuration the fixture will have power if EITHER of the IoT switches is on.
If you're using AutomationManager the new "SynchronizeDevices" action (and rule) is ideal to use here - if either IoT switch is changed, the other will be changed to match (so both on or both off).
Smart Phone Switch
This is an inexpensive route and is quite practical. A low end android phone (see: Running MPP Servers/Hubs) running your IoT vendor app is used in place of one of the original switches. This phone could be running WemoHome, AutomationManager/WemoManager, and could even be your WemoServer.
Again, determine the circuit type and which wires are load, line, and neutral. Re-wire as per one of the lower two diagrams. You WILL need neutral in this case.
Install an IoT switch in one of the boxes. As above, use the red wire for the load, white for neutral and black for line.
Remove the other switch, and convert the box to provide USB power out (or look for a nearby outlet for your USB charger). Configure the main screen with a toggle style widget to control the IoT switch.
Check with your local electrical code to confirm you can replace a physical switch with this "smart" phone style switch. Modern codes allow smart switches, low power switches, motion controlled switches, etc, so arguably this type of switch will comply.
Battery Powered Wifi Switch
Read more about this inexpensive option here: 3 Way Switches. Some assembly required.
3 Way Switch Wiring
The first step is to determine which of the diagrams (left or right) applies to the circuit you are changing. You can swap in two IoT switches for the two (or more) switches. If only one IoT switch is used it can be placed in either location if the other 3-way switch is re-wired as shown. If any switch is on the light will be on. Turning off the light requires all switches to be off.
Important! A ground connection is required on all devices where present.
Note these diagrams will work with any number of switches on the circuit.
3 Way Switch Wiring Options