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One Nest, two loads, two circuits.
chrismaki
Member Posts: 5
My main living area has two separate baseboard heaters on two circuits. For years I’ve been running only one of them from a Honeywell R841C1169 which is an SPST 220VAC relay with a 24VAC coil. I ran the 24VAC side to W1 and RH of the Nest, this all worked fine for a long time except only one heater was connected. I finally got around to buying two Aube (now Honeywell) RC840’s and a White Rodgers 220 → 24VAC transformer. When I was trying to wire this new setup, I managed to burn out a terminal on the Nest baseplate, Nest is replacing this even though I fully admitted to it being my fault, great customer service. Right now I have both Aubes installed each inline on the load-side of either heater. I also tapped one of the circuits to provide 220VAC to the transformer. The 24VAC side of the transformer runs to my thermostat location, which right now I have temporarily installed an old (read: dumb) thermostat which is basically just a switch so when it engages, 24V from the transformer goes to the C and W connections of both relays, turning on both circuits/heaters. When my new Nest baseplate arrives, knowing that I only have two wires to my thermostat, how do I wire it? For the sake of simplicity, we can completely ignore the 220VAC side of the conversation, that’s all setup fine. I have the following connections that I need help mapping out:
* 24VAC Transformer:
* Blue/C →
* Yellow/24VAC →
* Aube1:
* C →
* W →
* Aube 2:
* C →
* W →
* Nest:
* W1 →
* RH →
I’m assuming any solution would have 24VAC running to the Nest at all times to keep it powered and online. I guess I don’t actually understand how with the old setup with the R841C1169 actually worked. I assume that when the Nest calls for heat, that it shorts the 24VAC leads and this feedback engages the relay, allowing 220VAC to flow to the heater.
Running a Common wire is not an option.
* 24VAC Transformer:
* Blue/C →
* Yellow/24VAC →
* Aube1:
* C →
* W →
* Aube 2:
* C →
* W →
* Nest:
* W1 →
* RH →
I’m assuming any solution would have 24VAC running to the Nest at all times to keep it powered and online. I guess I don’t actually understand how with the old setup with the R841C1169 actually worked. I assume that when the Nest calls for heat, that it shorts the 24VAC leads and this feedback engages the relay, allowing 220VAC to flow to the heater.
Running a Common wire is not an option.
0
Comments
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If I wire it like this, won't the Nest only get current for charging while the heat is activated?0 -
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I note that the OP states that running a common wire -- third wire -- is not an option. Well... the Nest, like all other wi-fi thermostats, is a power hog, and without a common wire it works somewhat erratically. Sorry about that...Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Ah, I hadn't noticed that. It's possible that a power-stealing thermostat like the Nest will work, wire as per the diagram above & hope for the best.0
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Thanks for the help guys, I've determined the best course of action is to put the 24VAC transformer at the thermostat and not at the relays so that I can run a common (C) wire and just push 24VAC back to the relays over the existing copper pair. Just need to find a way to hide it behind the wall because yes, the Nest will have to cycle the heat periodically (even in the Summer) just to stay charged, not ideal.0
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