NEST RELAY

EBEBRATT-Ed

Aube RC840T120 relay and transformer in a box.

This would be an easy fix for the NEST common wire problem.

I can't take credit for finding this. @Zman pointed out in another post they have a 240 volt model that can be used for controlling electric baseboard with a low voltage thermostat. It got me to thinking if they had a 120volt model and they do.

This will work for heating

And I guess it would work for cooling as well by just running Y from the Nest direct to the condensing unit

pecmsg

A fix for a known issue?

109A_5

Hello @EBEBRATT-Ed,
Oh boy, yes it will fix the NEST issue... permanently !!! Did you notice the contacts and the load is on the 120 VAC side ???? So in this case the relay is useless for buffering the NEST to other 24 VAC equipment.

And would 1.2 VA be enough to run the NEST and an additional relay ???

Aube RC840T120

Alan (California Radiant) Forbes

Aube RC840T120 = Taco SR501 = Caleffi ZSR101

109A_5

Alan (California Radiant) Forbes said:

Aube RC840T120 = Taco SR501 = Caleffi ZSR101

Look closely, with the Taco SR501 & Caleffi ZSR101 the relay contacts are NOT permanently bonded to the 120 VAC input power supply. The Aube RC840T120 it sure looks like one side of the contacts is permanently (internally) connected to the 120 VAC side of the transformer.

And the transformers may be more robust with Taco SR501 & Caleffi ZSR101. 12 VA for the Caleffi ZSR101, could not find a VA rating on the transformer in the Taco SR501.

The 1.2 VA transformer in the Aube RC840T120 is probably mostly just for the internal relay's coil, not for external loads.

EBEBRATT-Ed

OK scratch that idea. don't know what i was thinking.

Steamhead

This is what we use:

https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC%20Catalog&pid=R8239A1052/U&category=R8239&catpath=1.2.8.3.1&rank=1&v1=Sort.1.Product.Rank&asc=1

The switching is completely isolated from the transformer so no issues there. There's also a DPDT version if needed- this can be used as a circulator relay.

STEVEusaPA

Thanks to @Robert O'Brien, this is all I use, for oil

Alan (California Radiant) Forbes

@109A_5 I'm clueless about what you're explaining. Does internally bonded effect it's operation?

109A_5

Hello @Alan (California Radiant) Forbes,

Alan (California Radiant) Forbes said:

@109A_5 I'm clueless about what you're explaining. Does internally bonded effect it's operation?

Effect its operation ? No. I'm sure the Aube RC840T120 works fine for what ever situation it was designed to satisfy. Like an isolated external contact closure (R to W) energizing the relay which then supplies 120 VAC to a load (Red wire).

OP "NEST RELAY", In the case of a NEST power transformer and buffer relay it is not a good choice. Since one side of its normal open contacts are connected or bonded to the Black (or Hot) wire on the 120 VAC side of the transformer. How does that help buffer a NEST thermostat that is usually connected to 24 VAC equipment ? I think it is obvious (or should be) that something will let out the magic smoke. Why would you apply 120 VAC via a relay contact to a 24 VAC circuit ?



With the Taco SR501 & Caleffi ZSR101 you can connect any of the contacts of the relay to what ever you want, a 120 VAC circuit or a 24 VAC since the contacts are not permanently connected to either, the relay contacts connections can be easily changed by moving (or removing) a wire or a jumper.

Also the transformer in the Aube RC840T120 is quite small 1.2 VA. With only 1.2 VA, I believe the coil of the relay was the only intended load, not charging and/or operating a NEST. The Taco SR501 & Caleffi ZSR101have significantly larger transformers.

Alan (California Radiant) Forbes

With the Taco SR501 & Caleffi ZSR101 you can connect any of the contacts of the relay to what ever you want, a 120 VAC circuit or a 24 VAC since the contacts are not permanently connected to either

Now I get it. Thank you!