Smart dimmers under existing wall switches (UK hub, German home)



I have a couple of newbie questions. I have a few of wall switches that I want to keep and make smart. In one room I have 3 x 9 W LED bulbs connected to one wall switch (bistable). My understanding is that it is possible to control and dim the lights from my SmartThings and the wall switch itself independently, regardless of the actual state (correct me if I’m wroing). Will I need a bypass since my load is quite small?

Can’t seem to find these in the “works with SmartThings” list, do they work?

In another room I have two wall switches that control the same ceiling lamp. This means that either of the buttons will change the state of the lamp. Is there something similar which will work with that kind of setup?

Greatly appreciate the help.


@RobinWinbourne has done his entire house with Fibaro kit, he should be able to answer your questions. :sunglasses:

With regard to your second question, in the UK that is referred to as a “two-way setup” and it definitely should be doable, although it does depend on the details of your wiring. Again, Robin can probably say more. ( The same setup in the US would be referred to as a “three-way” in case you are reading other forum threads, just so you don’t get confused. The UK counts the number of switches, while the US counts the number of circuit branches.)

(Edward Niedziejko) #3

Yeah, 3way doesn’t really make any logical sense at all. There’s only 2 travellers, and only two switches. It’s not like a single switch is called a “2 way” switch, though it can be called a single throw switch. Technically a “3way” is just a paired set of double throw switches, so … 2 + 2 = 3?


In the US, it describes current flow. From Mike Holt’s electrical systems forum:

It is not a matter of how many positions the switch can have (i.e., up or down is only two positions). It is a matter of how many ways current can get to the switch, how many paths current can take on its way to the switch. Think of driving down a road, and coming to an intersection at which you have to take either the left fork or the right fork. That is commonly called a �3-way intersection.�

But, yes, in most other countries you just count the number of switches. :wink:

(Edward Niedziejko) #5

Yeah, that’d make sense if there was two way traffic (which I suppose there technically is because of alternating current flow) but from a block diagram perspective, it more closely resembles a fork and a merge.

If it was called a “3 wire switch” I’d be convinced. :wink:

(Robin) #6

Two way (U.K.) wiring for a Fibaro Dimmer 2:

Your load is under 50W so you’ll need a bypass wired across the load in the ceiling.

Not on the WWST list but still works very well with the following custom handler:

But be warned that ST is going through a paradigm shift right now, changing to new API’s, so there’s no guarantee this handler will work in the long term (year or so)… hopefully someone cleverer than me will port this handler over before D-day comes!

(Robin) #7

Oh… and if you want to control the dimming from the wall you’ll need to swap your existing switches for momentary (retractive / push-to-make) ones.


What a great community, thank you for the replies guys!

After taking a look inside, I realized it might be hard to fit the dimmer behind the switch because of all the cables. Also seems to be a bit different from the cables in the chart. I have 1 cable of each color coming from the bottom, and 2 of each color going up. Only the brown cables are connected to the switch.

But since it’s probably a good idea to exchange the switch to one with a dimmer, I might as well get one with Z-Wave/ZigBee. Any specific (European) switch you could recommend?

(Robin) #9

You can put micros in the ceiling as well :sunglasses:

(Edward Niedziejko) #10

Green/yellow is your ground wire. Blue is your “common” wire, and brown is your switched wire, most likely.

(Robin) #11

I’d say the blues are just bunches neutrals that are there for smart wiring.

The two browns connected to the switch are live and switched live.

Greens are Earth.

You’ll notice in my diagrams that the blue connected to the switch actually has a brown sleeve on the wire which is the modern way of showing switched live… older way just used two brown wires.

I thought this thread was for the U.K.? Your round back box is very very unusual for the U.K.???


Hi, once again thank you for your replies. It would definitely be more convenient to have it under the switch, than the ceiling, in our case. But I might look for a smart switch, since we won’t be able to dim the lights with the current one anyway.

As for your question, I can’t recall adding UK to my title, but if I did then I must have been referring to the SmartThings Hub being from the UK (not that it matters). But this particular installation is actually in Germany, and it’s an old house from the early 1900’s, but I’m sure the electric installation has been changed at least once since then. If wires are used differently in the UK and in Germany then perhaps I should look for information regarding what the different wires are used for.


Hi @Qliver, I think the confusion lies in the topic title “Smart dimmers under existing wall switches (UK)” …might be leading readers to think you’re in the UK. :slight_smile:

(Robin) #14

It would appear that @JDRoberts changed the topic title and added the UK reference… the OP never claimed to be in the UK (unless a post has been deleted somewhere?)


Yes, UK meaning UK frequency hub. The first post all had links to European Z wave devices. Sorry for any confusion. In the devices section we generally just divide between the two hub regions, US or UK, but I understand the wiring can be very different in different individual countries. :sunglasses:


I really can’t figure this out. Can I not use rotary dimmers together with the Fibaro dimmer? I guess the wall dimmer would always have dimming priority over the Fibaro? It would be nice to have one like this

because then it would also be possible to dim the lights from the wall. But like I said I don’t know if that’s even possible.

So far I’ve only been able to find one build-in wall dimmer with Zigbee/Z-Wave, also from Busch-Jaeger, but it was crazy expensive. Anyone got any tips?

(Robin) #17

You can dim a Fibaro module from the wall when using a momentary switch… push and hold phases brightness up and down… rotary switches are naff anyway.


Okay, so just a regular dumb momentary wall switch, doesn’t have to be anything special about it? Don’t understand why it’s so hard to find, the switches I find are either rotary or smart. Would be appreciated if you had a link to something for reference.

(Robin) #19

Surely you can go to an electrical store and ask them for a momentary switch… they exist everywhere, I’m just not sure if German terminology so wouldn’t know what to search for on Google.


To be fair they are really not that common over here, took me some time to find any whatsoever. First found some info on Vesternet, and I think what you meant is something like this:

Must say they are quite pricey.

Does anybody know if the wall dimmer also has to work with LED light sources? If it is a LED dimmer like the one in my link, do I still need the Fibaro bypass? Or can I use any dimmer as long as I have a bypass?