Center-Off, Single Pole, Double Throw Latching smart switch?

I have two attic fans, one in the roof and one on one gable end. Right now they are controlled via a set of switches located in a large closet on the second floor. From the switches I have a separate 12/3 cable running to each fan’s thermostat. These are the switches I am currently using: or

They are a center-off, single pole, double throw. Center is off of course, up gives power to the thermostat so the fan can go on and off automatically based on the temp up there, and down I have wired as a bypass so I can turn the fan on no matter what the temp is. Both switches are mounted in a two gang metal box, about 2-1/4" deep (just so you guys know how much room I have for things)

Is there a smart switch or a combination of switches I can use to replace those two? I’ve been searching and searching but can’t find anything. I’ve been looking at smart relays and all sorts of things but I really don’t have room to put anything like that in that box. I’m not even quite sure how the relay would work to be honest.

I basically want to keep the same functionality I have now with the set of SPDT switches but also add the ability to integrate these into my Smart Home setup via SmartThings.

Anyone have any ideas?

So you are looking for something which is trI – stable? That is, when you flip it to the position it stays in the up position until you manually move it to another position?

Those are really tricky with smart switches, I’m not sure you can do it with a single pole switch, You may have to use a dual relay and just treat the top position and the bottom position as two separate switches.

Since you are going to automate it, you could create a rule so that when the bottom switch is turned on the top switch gets turned off, But I’m not sure that fits your use case.

OK, I looked at them, and those are indeed tri-stable (Called “locking position” in one of the product descriptions and “maintained contact” in the other).

The tricky part is that there has to be some current even when the device appears to be off so that the radio in the switch can hear the next “on “command.” You don’t just cut it out of the circuit like you generally do with dumb switches.

Maybe @Navat604 Or one of the other electrical experts in the community will have an idea. Off the top of my head I can’t think of a smart switch that has this behavior. There are some that work with momentary contact switches in an on/off/on Configuration, but not maintained contact.

@anon36505037 Might also know, although I don’t know if he’s running to that particular configuration request.

Yup, I’m sure I can’t keep what I have since they are maintained contact. I just need whatever someone comes up with to have the same functionality and yet still fit in that box if at all possible.

I thought I came across a double z-wave switch at some point and thought I could somehow work with that but I’m not sure, plus those don’t seem to be made anymore anyway.

What is the amp rating that the fan will pull? Or the horsepower of the motor? For example, the 1000W GE z-wave switch can only handle 15A resistive, 8A incandecent, and a 1/2 HP motor. The switch you linked to is a 20A switch. I haven’t seen anything that can handle that kind if load. Not saying they’re not out there, but it’s going to be damn expensive if you do. What about controlling the thermostat connected to each fan? Can that be swapped out for a smart thermostat? Or just a smart switch? Because you know there’s not 20A going through the thermostat. That might be easier than swapping those switches.

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There was a double Z wave switch it one point, but as @ryan780 Mentioned, it didn’t handle 20 A. That’s a lot.

There is a smartenIT dual zigbee inwall micro ( although it’s pretty big) which could handle higher loads and was used for pool equipment and stuff like that. It used to be on the “works with smartthings“ official list, but it hasn’t been for about a year and the last person I saw a post about it said they had gotten a new one and couldn’t get it to work. So I don’t know what’s going on with that.

It’s just going to come down to the exact specs you need. And how much room you have in the switchbox.

The fan motors are not that heavy duty. They’re both about the same, and the specs on the one show it’s rated at 3.4A. There’s nothing about horsepower unfortunately. Any switch rated 10A and under will definitely be enough.

Providing you have room and the proper wiring config. You can use a GE smart switch and a vision single relay to control just one fan.
The vision relay has Common, NO (normally open), NC (normally closed). The relay is used for up thermostat and down manual bypass On.
The GE load connects to the common of the vision relay for cutting power to the common contact of the vision relay.
Won’t be cheap to do both but it’s doable.

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Ok, but only thing I just looked up the vision relay and it’s specifically stating to not use it with a motor. I’m assuming since when motors kick on they spike in amperage and might just fry the relay after a few uses.

If I do go the relay route, I’ll have to find something that can be used with a fan motor as well as figuring out how to get it all in that box. I might have to try to put in a much larger box.

1 HP is 746W. 1/2HP is only 373W, so a switch capable of 1/2hp won’t run one fan, let alone two (~3A maximum). Smart devices have separate load ratings by device type for a reason (incandescent /= led /= motors). Motors have an inrush current (for starting) that’s higher than the rated running current, which is why motor breakers and wiring are higher ratings than resistive loads.

My suggestion? Find a simple on/off smart switch rated for at least 1.5HP or 800W motor load, and use a smart thermostat and rules for switching between manual and automatic control.

Alternately, if you can’t find a smart switch with those requirements, a contactor is a better option than a relay for that load level.

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I might just do that in the end… It’s a shame I had ran that 12/3 wire all up through the attic for nothing, I won’t need that extra wire anymore. I like having a physical thermostat up there, but I guess I can make it completely Smart Home automated. I use Aeotec Multisensor 6’s all over the place now, I even have two in the attic (one on each end). I can just use those as my thermostats to turn the fans on and off automatically, and I can still turn them on manually from my phone if I want too.

There’s no reason to give up. If wattage is a problem and you have room in the attic. Why not control the fan with a 110VAC contactor? Same suggestion as above but instead of controlling the fan directly. You will just control the coil of a contactor. Something similar to this.

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Lol, I wasn’t really going to give up, but at least I have a backup plan. I’m going to have to look into contactors better to see how the wiring would work exactly. Does the line source go directly to the contactor first and not to the switch?

This is a sketch I had made myself a while back to make sure I had my wiring straight. This setup works the way I intended.

I also called Broan who makes the one fan, and Lomanco makes the motor in the other. This is about the most info I am going to get about these two fan motors. Aside from buying a fancy multimeter that supports “in-rush” readings, I’m never really going to know the true starting amperage.

Broan 353 Gable Mount 120-Volt Powered Attic Ventilator, 1020 CFM
??? HP
1030 RPMS
Startup Amperage - 5A (Best guess from a Broan tech, although not a guarantee)

Lomanco Power Vent Motor Replacement F0510B2944
1/10 HP
1100 RPMS
Startup Amperage - ???

A contactor is just like a switch that is remotely controlled. You’d still need to provide power to the switch and a switch leg to the contractor. Constant hot also needs to go to the contactor.

To maintain the control system you currently have you might need two smart switches.

You could just leave the manual A/off/B switch in place, and use a pair of micro controllers to turn on each leg (manual fan and thermostat) and then use a contactor to control the fans. The contactor would have to be in proximity to the switch box though, or you’d need another wire for it to all work.

To summarize: Nano switches connected to the A/off/B switches control the coil of the contactor, which connects to the fans. You’d have to run a new 3 wire direct from the Ventamatic to the nano switch though, to add thermostat/humidistat control.

For this to function correctly you’d have to add in a “if Nano1 is on, turn off Nano2” and vice versa rules in RM or WebCoRE. You might have to switch to a temporary switch instead of the A/off/B switch you’re using… With both being used as toggles. Click up once for Manual on, Click up again for manual off. Click down once for automatic on, down again for automatic off. Something like that.

Thank you for the diagram, I definitely need to study that and see how I can make it work for me. I might end up having to put in new, even bigger boxes at the current switch locations to fit anything else in there. I’m pretty sure a contactor won’t fit in there, but let me see. I have two of those center-off SPDT switches, one for each fan. So that would mean four nano switches and two contactors if I really one to keep everything separate. Hmmmm…

How about using a “power relay” (not a dry contact relay), and not a contactor? Something like this:

Their schematic leaves much to be desired, but it would seem that unlike a dry contact relay, energizing one of the poles will trigger the relay one way or the other. If I use something like this, I can keep it in a new box up in the attic between the thermostat and fan.

Have you looked at the qubino flush shutter module? Not sure it meets the amperage specs, but it does what you need it to do. That said, I’ve had bad experience with 2/5 failed modules and haven’t liked the support. Plus, ST won’t officially provide support as they’re not on the official list.