For my paranoia and absolute clarity, this goes inline with a 240v baseboard and allows smart HVAC type t-stat/Nest/EcoBee etc to work

Yes, it has built-in relay & 24volt transformer, so it allows low voltage (24v components) control of the line voltage (240v) loads... Which is the 240 v baseboard heat er(s). Fits in heater wiring compartment.

Can i use a single relay to control 2 baseboard heaters?

Yes, I have mine running 5, 4 1000 watt baseboards and 1 1250 watt forced air wall heater. you just run them all in parrallel after the relay. No problem as long as your total amps does not exceed22.

Is anyone running two of these off of one thermostat? I contacted Aube tech support and they said you can do it but they must be in phase?

Yes, think of this relay as a 2 pole switch. You apply lower voltage to the coil (24 v from t-stat), and that activates the 2 pole relay switch... which turns on anything downstreat... 1 heater, 2 heaters etc.

What are the options for installing this? I read the installtion manual, but I'd like to hear from some who have actually done it.

I had an existing baseboard heating system, with a round Honeywell thermostat, and an older relay module that works exactly the same way as the Aube. The older relay was sticking and no longer reliable, so I replaced it with the Aube, and, at the same time, I replaced the mechanical Honeywell thermostat with a Nest. Physically, the little Aube box goes on the side of an electrical junction box, fitting in one of the "knockouts." This is because no electrical code would allow the low-voltage circuitry of the Aube, or your low-voltage thermostat wires, to occupy the SAME junction box as your 240v heating wiring. So the tube sticks into the knockout of the junction box, and fastens on with the nut, and that's how the Aube's three high-voltage wires safely enter the junction box. Electrically, it's also pretty simple. You have two wires providing 240v power from your panel, a black hot wire and a white neutral. (These should be coming into the same junction box where you're attaching the Aube.) And, you have a black and a white wire heading off to your baseboard heater. You can just connect the white wire from the panel to the white wire for the heater, i.e. the heater's neutral wire is just connected all the time and not switched. If you also connected the black wire from the panel directly to the black wire of the heater, your heat would run, but it would be on 24/7/365, and you'd be living in the tropics, and maybe burn your house down. Obviously, you don't want that. You want the heat to switch on and off. The Aube is your switch, so it sits BETWEEN the panel's hot wire and the heater's hot wire. The Aube's BLACK wire connects to the black power wire from the panel, and the Aube's RED wire connects to the black wire leading to your baseboard heater. The Aube turns the red wire on and off, to turn your heat on and off. So that leaves the blue wire. The blue wire is ONLY there to power the little transformer inside the Aube that runs the relay and your thermostat. So, the blue wire connects to the white neutral power wire from your panel. Remember when you connected the white panel neutral to the white heater neutral? You can just also twist the Aube's blue wire together with those two white wires, and you're set. You might notice that the Aube's red and black wires are 12 gauge, because they switch the full current load of your heater. But the blue wire is only thinner 16 gauge, because it's only there to power the Aube's internal transformer. In all cases, use good heavy-duty wire nuts or other wire connectors that are rated for 240V 12 gauge wire. And, do I even need to tell you to turn OFF the circuit breaker that runs your heat FIRST? (If I HAVE to tell you that, you probably should get a professional to hook this up for you!) Now, you have your thermostat wires. If you have a simple two-wire mechanical thermostat like a round Honeywell mercury-bulb thermostat, it connects across the Aube's R and W screws. And probably your existing thermostat wires -- thin-conductor wires that look like telephone wiring -- will actually BE red and white. The R screw terminal is low-voltage 24v power, provided by the Aube's internal transformer. The W terminal is the signal wire to turn the Aube's relay (and your heat) on and off. The C is the common terminal often discussed in setting up smart thermostats like the Nest. Having that third "common" wire lets your thermostat draw 24v power for itself all the time, independently from turning your heat on and off via the white wire. My existing installation already HAD an unused third wire in the cable leading to the thermostat. It happened to be colored green, not the blue that is more standard now, but it worked just as well. The three thermostat wires, red, white, and green, went on the R, W, and C screws on the Aube, and, on the Rh, W, and C terminals of the Nest base plate on the other end. Voila!

Connector Type	Screw
Contact Type	Normally Open
Mounting Type	Panel Mount
Brand	AUBE TECHNOLOGIES
Operation Mode	Electric
Coil Voltage	24 Volts
Contact Current Rating	8 Amps
Maximum Switching Voltage	24 Volts
Number of Terminals	3
UPC	775264094620 811241030264
Manufacturer	Aube Technologies
Part Number	RC840T-240
Item Weight	12.8 ounces
Product Dimensions	1 x 1 x 2 inches
Item model number	RC840T-240
Is Discontinued By Manufacturer	No
Color	Black
Voltage	24 Volts
Item Package Quantity	1
Measurement System	Imperial
Included Components	Electromechanical heating relay with a 24V - 208/240V transformer
Batteries Included?	No
Batteries Required?	No

RC840T-240 On/Off Switching Electric Heating Relay with Built-in 24 V Transformer, Black

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