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I am looking at having my dumb (3 and 4 gang) switches upgraded to smart switches. The biggest issue I foresee is that one of the switches is a 2-way switch.

My understanding is a 2-way switch is 2 switches that control the one light.

Do I need a special smart switch to be compatible with my current 3-way switch set up? Specifically, I'm asking from a wiring perspective.

The other issue could be that turning on both switches "smartly" will have no effect because of the way a 2-way switch is wired. Does anyone have experience/advice with this?

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  • \$\begingroup\$ I’m voting to close this question because questions about the usage of products, the selections of products to purchase, and home wiring are off topic. If you were building these smart switches yourself, very specific sub-parts could potentially be on-topic design questions. But what you have is a user problem; you'll need to find products which promise to meet your need. Most on the market likely will not, though using per-light smart switches and multiple remotes (and never touching the mains switches) might work. \$\endgroup\$
    – Chris Stratton
    Commented Sep 1, 2020 at 13:37
  • \$\begingroup\$ 2-way switches are just single pole double throw (SPDT) switches. What you want (as far as I can make out), is a "3-way" switch that controls one light with two SPDT switches, like described in this Wikipedia article. Sonoff has made a simple schematic for wiring this up with their Mini Smart Switches. \$\endgroup\$
    – StarCat
    Commented Sep 1, 2020 at 14:47
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    \$\begingroup\$ OP seems to be in the UK. A 2-way switch in the UK is the same as a 3-way switch in the US. \$\endgroup\$
    – Graham Nye
    Commented Sep 1, 2020 at 19:09

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The diagram below shows how a 2 way switch wiring works.

2 way Switch

Image source: Circuit Digest - 2-Way Light Switch

Let's name the first switch as switch1 and second as switch. If you look closely these two switches are SPDT switches (Single Pole Double Throw), how a SPDT switch works is - it has a main pole that can be connected to two different outputs.

In the above diagram the switch1 is connected to output 1 and switch2 is connected to output 1 then its an open circuit and the bulb will be in off state. Imagine if you toggle switch1, it now connects to output 2 which is connected to neutral, this closes the circuit, effectively turning the bulb on, now flipping the switch 2 connects the output 2 which opens the circuit and this now switches the bulb off.

This is the basic working model of a 2 way switch, for electronically controlling this we can use a SPDT relay.

relay

Image source: What Is a Relay?

This is what a relay's diagram looks like, and if you did notice, this is exactly what a 2 way switch looks like but with an addition of a coil which is used to control the output of the relay.

You can replace the 2 way switches in the above diagram with relays, and then control the relay using an output from a microcontroller.

With the basics cleared, I hope you yourself can figure out how a 3 way switching system works.

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  • \$\begingroup\$ Hi, sorry, I've edited my question. I meant 2-way switch. I know how they work, but smart switches usually AFAIK don't support 2-way switching. Is there a way around 2-way switching if the switch has a single throw? \$\endgroup\$
    – Coomie
    Commented Sep 1, 2020 at 7:27
  • \$\begingroup\$ There is another way of wiring the switches that should be shown because that is also a possibility that the OP may encounter. \$\endgroup\$
    – Andy aka
    Commented Sep 1, 2020 at 9:38

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