I'm looking for a set of Z-Wave (preferably Z-Wave Plus) components to use in order to merge two 2-way light switch circuits and allow control of both lights from all switch positions. I've looked at Fibaro FGD-212 modules but I don't think they'll meet my needs.

I'll give as much detail below as I can about my current setup and what I've investigated.

This is for UK home wiring, in case that matters.

My lounge and stairs leading from it have one ceiling light each and both have two switches (making 4 distinct switches in total, no correlation in placement).

I've also been investing (slowly) in Z-Wave equipment, and have started to design a replacement for the switches which would allow:

  • Both the stairs switches to have 2 physical switches each, one controlling the upstairs hallway and another controlling the lounge
  • One of the lounge switches to have 2 physical switches, with the controls the same as above
  • The other lounge switch to have a single physical switch which only controls the lounge light (not a problem if they are all double, though)

My initial hope was to use 3 * double switches and a single switch, wire them up and control it all with code, but that was before I learnt how 2-way circuits work.

Current setup

3-core (plus ground) 2-way light switch circuits for both the stairs/hallway and lounge:

current wiring diagram

Explored approach

I stumbled upon a guide to using Fibaro Dimmer 2 modules to achieve this, which would change the circuit to the following:

Circuit diagram with Fibaro Dimmer 2 modules

I can see how the wiring and module would work, but my issues with using the module are:

  • The modules (FGD-212) seem large to be wired behind the existing switch (20.3mm thick)
  • They only use a single, standard light switch, so doesn't solve my initial problem as far as I can tell
    • Can't use z-wave switches on top of the hidden modules. I'd rather use smart switches rather than hidden modules (for indicator lights, multi-function buttons, etc)
  • To use it with my CFL lights I'll need to buy another device with it, a Bypass 2 (FGB-002), which will increase the amount of stuff I have to fit behind my switch, or inside my light fixture.
  • It only advertises to control dimmable lights, not switching
    • Their 'switch' equivalent modules are not capable of 2-way circuits

I've considered changing the circuits so that only one of the switches in each physically control the light, but that isn't an option as I'd like to plan for a failure scenario which would leave one of the switches on each circuit useless.

Is there a combination of z-wave switches which will enable 2-way switches? It must be a common problem.


You've explicitly rejected the factory recommended way to configure the circuit, which is to have only one switch controlling the load, and using remote-only signalling switches for the others. And you're doing this on the supposition that someday one of the switches will fail; but you've only said that it would leave a switch "useless", without saying why you wouldn't replace the failed switch. I would advise you to reject this plan.

Having two points of electrical load control are going to leave you with a mess that will require extensive special configuration of the system, and goes against the design philosophy of automation installation, which is to have a single point of load control but as many decoupled user interfaces as you want.

For 3-way or n-way control, there are several choices. Some companies sell a 3-way kit including a hard-wired "load controlling switch", and a hard-wired "remote signalling switch". These are intended for easy direct replacement of existing 3-wire switch systems; wire the circuit using the documents that come with the switch. As a bonus, the remote switches are much cheaper than the full Z-wave switches, so the pair costs much less than two full Z-Wave switches.

Z-Wave automation gives you other options: use a regular Z-Wave switch as the load controller, and add Z-Wave remote switches (aka "single scene controllers") as needed. You can even purchase battery-operated wall-mount Z-Wave switches, if you don't want to run electric power wires to all the desired switch locations. One set of batteries will last several years.

If you decide to go the Fibaro route, consider installing the Fibaro module inside the light fixture's electrical box instead of the switch box. Most light fixture boxes have a bit of room to spare. That can preserve space in a crowded switch box.

Also, be careful with the dimmer switch purchase, especially with CFLs. Some dimmers are designed to work with CFLs and/or LED light bulbs, but many are designed only to work with incandescent bulbs. It may also be time to consider swapping out the CFLs for LEDs, but buy the right kind of "dimmable LEDs" - some are designed only for non-electronic dimmer switches! So be sure to pair the correct switch with the bulb technology you plan to use - the wrong dimmer will quickly destroy a CFL. The marketplace is quite a mess right now.

If all else fails you can use an "appliance switch" to control the CFLs, which uses a mechanical relay to operate the circuit. But they are not dimmable, they are not as cheap as dimmer switches, they may not respond to an "All lights on" broadcast signal, and they may not be available with a cheap external 3-way remote signalling switch.

( And if you're still wanting to set foot on the "let's make it complex because it might fail" path, then you owe it to yourself to run all the numbers. What is the MTTF and/or failure rate of the switches you're planning to buy? What losses will you incur from a failed switch? Will you have an inaccessible room? Is it controlling a single safety critical light, with no windows or alternative lighting possible in the area? How much will it cost to replace? What kind of Service Level Agreement are the users willing to tolerate? What kind of SLA can you afford?

Instead, if a switch fails, plan to replace it. If it's operating a light needed for safety, plan to replace it quickly. )

  • "You've explicitly rejected the factory recommended way to configure the circuit, which is to have only one switch controlling the load, and using remote-only signalling switches for the others." Not intentionally to make things difficult, it just seemed like it should be possible. I didn't know that was the recommendation. The only mention of 2-way switches I could find was about the Fibaro modules. I'd like to know more if you have a link? Is there a way to have the remote switches mains powered with the current wires, or will I have to use battery powered?
    – dsample
    Mar 22 '17 at 6:24
  • Another problem when looking at having a single load control as some remote switches is that I can't find a series of components that have both light switch modules with local load as well as modules with no local load, so I can have a single style of switch (preferably aesthetically pleasing). Any recommendations there would be great.
    – dsample
    Mar 22 '17 at 7:09
  • In the dimmer switch kits I got from GE/Jasco, there are two options for wiring: one is to provide Hot and Neutral to the switch, the other is for a switch that doesn't have a neutral lead. The switch powers the Z-wave by allowing a very small current to leak through the bulb even when it's off. This wiring may have worked with incandescent bulbs, but fails horribly on CFLs and LEDs. In either case, the "remote" 3-way switch draws its power from its wire to the main "load control" switch. Mar 23 '17 at 22:05
  • Here's one such "remote" switch from Jasco: byjasco.com/products/ge-z-wave-wall-add-switch . Their manuals byjasco.com/sites/default/files/product/manuals/… have some wiring diagrams; in them they call the data wire the "traveller". (These are much newer than my switches, and are similar but not quite the same.) They support up to 5 add-on switches per load control switch. Here's a battery operated switch: byjasco.com/products/ge-z-wave-wireless-keypad-controller Mar 23 '17 at 22:16
  • The UK has far fewer options in terms of styles. The best I can is a TKB switch: vesternet.com/z-wave-tkb-dual-paddle-wall-switch-gen5 which claims to have a "Auxiliary switch signal input" wire, but it doesn't document what this does. I can't find any 'accessory' switches for the UK that just need mains power (or even battery) with the same style as the 'load' switch.
    – dsample
    Mar 26 '17 at 12:40

In-line dimmers have to be dimmers rather than switches because they have no neutral return at the switch. This makes any multi-way arrangement nigh impossible.

The 'obvious' homebrew solution is a z-wave relay, and a unit to aggregate 'switch' requests into a control toggle. Probably requires an mcu or SBC to facilitate this, and this would extend to more than 2-way switching. Using a transmit only faceplace, Rx and Tx on your SBC, and Rx at some convenient point in the electrical circuit.

Without the Z-wave requirement, you could pair a dimmer switch with a wire free control. Wire free means there is no requirement to replicate the standard 4 wire, 2 way switch arrangement. All switches have an equal input on the lamp.

  • 1
    I'm only trying to do 2-way switching. Control of the opposite circuit from tyre third switch would be through a controller (there's no cabling to make an n-way circuit). Right now I'd be happy with a single control of each light as long as all four switches could be the same style, and preferably mains powered. Can a switch be used without actually triggering the relay behind, so I could power it and just use the signals for remote triggering?
    – dsample
    Mar 22 '17 at 13:49
  • @dsample Sorry, mis-understood the question (too much detail). Also, there is likely a trivially simple answer... Mar 22 '17 at 14:01

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