Three way switch and Sonoff ZBMINI-L

Am considering buying a few Sonoff ZBMINI-L no neutral smart switches

One application currently has a three way switch controlling one light.

From https://itead.cc/product/sonoff-zbmini-l-zigbee-smart-switch-no-neutral-wire-required/

【Two-way Control】By installing ZBMINI-L in one of your existing two- or multi-way control junction boxes to make the connected light smart.

Checked the manual and nothing is said about wiring for a three way circuit other than this diagram illustrating what looks to be a three way circuit but nothing is connected to the other circuit.

Will this work in a three way circuit?

The standard ZBMINI toggles the output relay every time the input switch changes state. If the switch circuit is wired as shown, flipping either of the 3-way switches will change the state of the switch circuit and will cause the relay to toggle.

I expect this version to act similarly.

The Sonoff switches should be here in a few days.

Both three way switches have a red traveler wire, a black hot wire, and a white neutral.

Just so I don’t desmoke something, check my plan :

Remove both 3 way switches and cap the red wire at both ends.

Connect the black wire to L in and the white wire to L out at both locations.

I have two momentary Decora switches that will be connected to S1 and S2.

Hopefully in a perfect world when either switch is pressed, the light will turn on if it is off and turn off if it is on.

In a three way setup, both red and black are known as travelers and either can be "hot" depending on switch position.

Why not just wire it like the diagram?

This could be bad...

Switch configurations can be all over the map. Can you sketch your existing wiring setup, including the light fixture(s)?

@dylan.c

I would wire it like the diagram but it doesn’t show both three way switches. I am more comfortable around 12 volts DC

Without ripping out the walls I am only guessing. I do know there is a black wire and a white wire at the light and both switches have a black, a white, and a red wire.

Should I power down the circuit and do a continuity test of each wire?

There are at least 2 ways to wire a circuit as you've described your wiring...


You'll need to confirm exactly how yours is wired before you can proceed safely.

It does show the switches, just not in a user-friendly format. See below. I've outlined each switch in a black box and labeled the "common" terminals with a C and the travelers with a Tr.

And if you've never worked with 120VAC, I'd recommend a trip to your local home center for a few items...

  1. A book on wiring for homeowners. The pictures I posted above are from books and magazines that I've found very helpful.
  2. A non-contact voltage tester. Because safety should always come first.
  3. A wire stripper.
  4. Some wire nuts...usually the yellow ones.
  5. a small amount of 14-3 wire for "pigtails" if needed, or 12-3...whatever matches the circuit you are working on.

Jumping right into a non-standard 3-way circuit as your first effort in home wiring might not be the best idea. Just sayin...

Your diagram makes it clear. Thank you

When we moved to our home in 1982 the basement was 4 concrete walls with a furnace and water heater in the middle. I must have bought 100 2x4s, lots of drywall, 200 feet of 14/3 with ground, loads of can lights, wall outlets, and switches. Had no qualms about any of that. My weakness is three way switches. Thankfully I don’t have any 4 way switches.

Don't feel bad about that part. Those pictures I shared above...I have them bookmarked. Every time I mess with a three way switch I need to match my circuit to one of the pictures before i feel confident enough to start pulling off wire nuts and loosening screws.

Looking at the diagram you edited, it appears there should be no power at either switch when everything is finished.

Bezos called and said my delivery is delayed and won’t be here until Monday.

There may still be 120 volts somewhere in the same box, but you are correct that neither switch is connected to the main voltage. There is likely some low voltage control power that the zbmini uses on the switch circuit, but I've never measured it.

Different circuit and simple but …

Have a bathroom exhaust fan that is controlled by a standard 2 wire toggle switch. Bought a Zooz ZAC99 dumb momentary switch and a a Sonoff ZBMINI-L.

I want the fan to come on when the switch is pressed and turn off when it is pressed again.

As it is, when the switch is pressed the fan comes on but turns off when the switch is released.

I thought the Sonoff latched?

I have tried the generic zigbee switch driver and the driver from Markus.

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A momentary switch might work with a quick tap (fast as you can), otherwise it will see both the close AND open of the momentary switch and will toggle the output for each of those events.

Try this

From this

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@mpoole32

That did it. Thanks!

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I’m going in. Here are 2 photos of one of the three way switches. Black white and red


Here are two photos of the other three way switch. Black white and red. Ignore the other black and white wires. Those connect to another Sonoff switch for the exhaust fan.


At the fixture there is a black and white wire.

Once both switches are out, I will power the circuit up and check voltages at the wires.

This is more me thinking out loud.

With all the wires disconnected at one switch the voltage tester shows voltage across the black and white wires and also the black and red wires.
At the other switch there is no voltage from the white to the black nor from the white to the red nor from the white to the red.

Now I’m stuck. Wire nuts on all the exposed wires and no light in the bathroom.
Really don’t want to fry one of these Sonoff switches.

Going to disconnect the light fixture and run continuity tests and build my own wiring diagram. But first off to take my wife out for early Mother’s Day. :smiling_face_with_three_hearts:

Update. Connected the black to the white at each switch and the light came on with no sparks.

As a retired auto mechanic I used complex schematics like this with hundreds of circuits

A ‘simple’ three way switch circuit baffles me.

I wouldn't normally expect to see

This is a good time to dig out the non-contact voltage tester. I would normally shut off the breaker, disconnect all the switch and fixture wires, wire-nut the ends and then turn the breaker back on. The non-contact tester will beep when you find the hot wire. Knowing where the power enters the circuit is a big help. If you don't have a non-contact tester, check voltage with each one compared to ground. Once you know where the hot is at, you can start to reconnect wires one box at a time and see how it travels through the circuit. There are a couple other items that might be helpful.

Do any of the white or red wires have black tape on them, or another sort of marking that would identify them as "hot?"

You should be able to see all 3 or 4 wires that are part of the same cable. Are there any wires that are wire-nutted together and do not land on a switch or fixture terminal? THese will typically be either a neutral or a hot which simply passes through the box on it's way to the next device.

And I'm not sure if you saw this, but wanted to point it out...


At some point this switch shorted out on the ground conductor. Always a good idea to push the ground conductors as far back as possible and "fold" the wires neatly behind any switches or receptacles to try and prevent this kind of thing.

And here are two more variations of 3-way circuits. Combined with the two I shared earlier, that's all that I am aware of.


Yours should fall into one of these 4 cases, but your wire colors may not match the "standard" colors shown here.

I noticed that also. We had the bathroom remodeled about 20 years ago. They moved the switches from the wall to the side of a cabinet. The circuit must have been live and the hot touched the ground. I replaced the box with a plastic quick box and am tidying up the mess.

The switch in the other location is the source.

Need to revisit your edited diagram and get both switch locations controlling the light.

I can connect the white and black at one location and control the light by opening and closing a switch connected to the other back and white wires. The red wire is not connected to anything and appears to be the traveler. I currently have a two way circuit.

The other Sonoff controls the bathroom fan. It is a simple two way circuit .

My wife hasn’t complained yet about the stuff hanging out

Need to take the quick box back out and enlarge the opening some more because the right side is pinched . The old metal box was a bit smaller.

I have an older home with 100 amp service and a fuse panel with 10 fuses and no neutrals.

My father had issues installing ceiling fixtures in my childhood home. It was built in 1890. There was a gas pipe at each fixture that he had to work around.

Edit - I realize there is bare copper showing.

Once this is working this will be corrected.

Hmmm
Is there still a plate cover at the original location?

The large vertical cabinet covered up the original box so I would have to remove it to access the box. I am assuming they just extended the wiring.