automatable open call for heat w/240v heater controlled by Nest

andrewco

So - I have a contact relay (RC840T) that is allowing a Nest to control a 240v garage heater and it's working fine.

The only additional thing I would like to do is be able to cut off the heat for my garage workshop if the garage door is open. I have a myq garage door sensor so I can detect when the door is open or closed.

I just need some way to break the call for heat (W wire?) from the nest with a device that can be controlled by something like IFTTT - wirelessly would be preferable.

Here's the current wiring:



Any ideas?

mattmia2

I'm not sure about only switching 1 leg of the 240v to a 240v load being allowed by code, I think t needs to be a double pole contactor to switch all ungrounded conductors, but the control for the door just needs to open w when the door is open, either a normally closed switch that the door holds open when it is open(like a microswitch with a long operating arm or even a magnetic switch) or you might be able to get an accessory for the operator that will produce an open contact when the door is open.

andrewco

Right - I'm not looking at switching the 240v but rather the 24v thermostat side. I'm already using a contactor relay for controlling the 240v heater with the Nest. I was thinking I could accomplish what I need to by breaking the call for heat (W) wire which would still allow 24v to be supplied to the smart thermostat. I just don't know what to use to do this.

Zman

If you can run a wire, you could use a magnetic switch with a relay and be done with it.
For wireless, unless you can find a wireless door alarm with contacts. You could do it with a zwave home automation system as well.

andrewco

@zman - there is a wire. It's the thermostat wire. I already have a signal from the myq door sensor that I can receive through IFTTT. I'm hoping to be able to break the connection of the W (call for heat) wire with a wireless IFTTT controllable switch...maybe something like this

I'd like to have it located with the heater if possible so that would mean powering it with 240v from the heater circuit.

Zman

Ideally you could find a switch with dry contacts that is compatible with your network, The link you posted probably needs 120 volts to work.

andrewco

Well...it would still need to be powered. The one I posted can run off of anything from 100-240v so it should be able to be powered by the 240v of the heater. I'm just not sure how to switch the 24v side (the W wire) of the circuit with that device.

mattmia2

you would want a dry contact device that is compatible with your system rather than a 120 v control device. you could also use that device to control a small relay with a 240vac coil, usually called a "fan relay" to switch w but that probably wouldn't be the simplest way to go.

Jamie Hall

Got to admit I'm a simple minded soul, so I'd probably put a magnetic reed switch, normally open, next to where the garage door runs, and the actuating magnet on the door, located wo that when the door was closed the switch was pulled closed by the magnet. Run the white wire from the thermostat to one pole of the switch, run a wire from the other pole to the white wire input on your gizmo, and call it a day. Or you could do it with a cam on the door and a microswitch. Either way, pocket change, 15 minutes of work and you're done.

pecmsg

Why do you want to complicate things? The more controls the more chance something breaks. When the door opens the heater shuts off but when it closes it turns back on? Your not going to save anything.

Zman

Jamie's plan is the easy way to do this. The one you are considering will run of 120 but will only break that same circuit.
Do you leave the door open for long periods of time? If not, I would leave it alone.
I have done similar setups with DDC system on commercial garages where the mechanics like to leave the door open for long periods. They close the door when they get cold because the heaters are off...

josephny

Why not a simple normally closed (NC) relay that, when power is applied to the relay by the ifttt circuit, it disconnects (breaks) the W circuit?

The relay would essentially be a second thermostat in series with the first.  That means both the Tstat and the relay would need to close the circuit in order for heat to be generated.  

EdTheHeaterMan

I'm with Jamie on this one. Simple switch that opens when the door is open and breaks the W wire.

To quote an Almost Famous Zman "If you can't explain it simply, you don't understand it well enough" Albert Einstein

KISS

Yours Truly,
Mr.Ed

mattmia2

I would put the switch in the open position and make it normally closed so when it gets misaligned the heat still works.

andrewco

Ok - I'll address some of the suggestions here:

1) Running another wire is definitely not preferred. The thermostat and the heater are WAAAAY away from the door.
2) There are instances that I open the door slightly to allow for exhaust and pets to move in an out and I have my door sensor set so that in those cases the door is still considered down
3) I already have a very reliable sensor that never, ever gets misaligned and provides a signal for the door being open or closed

I want to confirm - if I just break the call for heat wire (W) then the other two wires (C & Rh) should provide voltage to the thermostat to continue running but just cut off any heating circuit?

@zman - Wouldn't there be 24v running through the W wire when there is a call for heat and breaking that with a dry contact would require something that can handle that?

Zman

A relay has 2 parts. The coil which is doing the work and a switch that is opening and closing the circuit,. The model you are looking at has both parts cooked into one unit. It will only work with line voltage.

andrewco

"the model you are looking at" are you referring to the RC840T or the sonoff (connected unit)? I guess another way to skin this cat would be to replace the RC840T with a connected controller but I haven't found anything like that either.

Zman

I was referring to the wireless device you posted a link to. I have worked with Zwave, they have switches and relays that can do what you are suggesting. I do not know what parts will work with your smart network.

ratio

andrewco said:

I want to confirm - if I just break the call for heat wire (W) then the other two wires (C & Rh) should provide voltage to the thermostat to continue running but just cut off any heating circuit.

In a word, yes. Breaking the W wire after the stat will interrupt the heat call without effective the power to the Nest. It may interfere with its "learning" features, YMMV.

As for wireless, I've had great success with Honeywell wireless security receivers & door transmitters to control air curtains, the very function you're looking for. Around here, I get them from the local ADI storefront. I'd imagine they're available on the internets as well.

andrewco

@ratio Ok - thanks for confirming that! WRT air curtain - I'm not looking to control or detect the garage door position at all. All I want to do is have an automatable device (IFTTT or similar) that can be powered by 240v and open and close the W wire on request.

ratio

I see, I must've misread upthread. In any case, interrupting the W call will still stop the heat. There may be some delay before the heat stops completely (blowers, if any, come to mind), but it should eventually shut off.

andrewco

Sounds good. It's an electric heater so it stops pretty instantaneously - startup is delayed to wait for the fan for about 15s or so - but that timing is just noise in this setup. Now to find a device that does what I'm looking for.

I assume that when the heater is running there's actually 24v running through the W wire? Would this prevent me from using a dry contact to control this circuit?

Jamie Hall

No -- any switch (dry contact) will do. There's very little current involved, though there is some. What you must NOT do is place any other voltage source on that line. Just pure plain and simple open or close a switch. Be especially cautious about electronic (typically Triac) switches. They can and sometimes do introduce stray voltages. You will be much better off with a simple switch, as suggested, or with isolating whatever fancier arrangement from the W wire with an isolation relay which in its turn can be controlled by whatever.

andrewco

@Jamie Hall got it. Thanks for the clarification.

andrewco

I think I found what I'm looking for here. Powered by 240v, dry contacts (has other switchable terminations as well) and obviously controllable.

Zman

I think you've got it!

andrewco

I just want to make sure I understand this correctly. I can only feed it 10A @ 240v so if my heater (load) is running at 20A @ 240v then I need to step it down to only top out at 10A if I'm powering it from the same power source as the heater?

mattmia2

No. you would need to use it to control a relay with a 240vac coil and use that relay to break w (or use it to control a double pole contactor with a 240vac coil rated for the load of the heater)

mattmia2

Or only connect that device to power and leave the load unconnected and use the auxiliary contact to switch w.

andrewco

@mattmia2 I don't think so (but I could be wrong) I'm just referring to input power to actually power the unit. I'm using the dry contacts on it to break the w contact for heat.

Zman

andrewco said:

I just want to make sure I understand this correctly. I can only feed it 10A @ 240v so if my heater (load) is running at 20A @ 240v then I need to step it down to only top out at 10A if I'm powering it from the same power source as the heater?

Where does this fit in? Are you using it to power a relay with a 120 volt coil? In that case you could use it in parallel with the heater load.

andrewco

This is the device that will simply break the W wire (call for heat) circuit from the thermostat through its dry contacts. I'm locating it near the heater so my only power supply for it is 240v. My concern is that since it's power input is rated at 10A but the heater load is 20A I need to step down the rating just to supply power to this device.

ratio

The 'heat call' is the white wire that's landed on the Nest, right? That conductor carries a nominal 24 VAC at a handful of VAs. If that's where you're interrupting the heat call, the 240 V power to the heater itself doesn't come into play. I haven't looked at whatever you're using to control the output of the Nest, but if it has an aux contact like @mattmia2 suggested, you should use that. If it doesn't, use a relay with a 240 VAC rated coil connected to the output of your wireless control to switch the heat call.

andrewco

I need to power the actual unit that is actually breaking the w wire. The dry contact must be actuated from somewhere and that takes power. 

ratio

Ok, I looked at that wireless relay. It doesn't have an aux contact, it's straight 240 VAC. Use a relay with a 240 VAC coil & pilot duty contacts to switch the 24 VAC heat call. One of these should work admirably: https://www.functionaldevices.com/products/building-automation/details/RIBH1C. They offer wireless relays as well…

andrewco

Yes it does. The sonoff mini r2 has dry contacts labeled s1 and s2. It can also switch up to 240v @ 10A but I’m not using it for switching line voltage, but I still need to power the actual device so it can switch the dry contact and run the rest of the logic board. 

Jamie Hall

The device takes standard 110 VAC current. Plug it into a wall outlet or something handy. Use the dry contacts to make and break the white wire, which is on 24 VAC and carries practically no current at all. Let that white wire control, as it does now, the contactors in the heater.

Consider this: suppose you just wanted the Nest to control the device? You wouldn't have your widget on the white wire -- it would just be connected to the device, no? I assure you, if you tried to power the Nest with 120 or 240 volts -- at any amperage rating -- it would light up. Very briefly, and very spectacularly.

Your RC 840T does the heavy lifting on controlling the power to the heater -- not the white wire, the Nest, or your widget.

andrewco

Except....I don’t have that near the heater. I have the 240v heater load circuit and that’s it. And the thermostat wires coming from the nest that go to the contact relay to switch line voltage. 

andrewco

I post another redrawing soon to clarify. 

andrewco

It's not a pretty diagram but it should work (the diagram that is ;-)

Zman

The MiniR2 device you are looking at is just a lighting controller. It it just designed to break a line voltage circuit. Just like a light switch does.
If you wire a separate relay to the controller instead of the light, that relay can break your low voltage circuit.https://www.grainger.com/product/SIEMENS-Plug-In-Relay-56JX25