# Yet another Nest install issue



## thearchitect (Nov 22, 2010)

Hello friends!

So I finally caved and sold a pint of blood and bought a Nest Learning Thermostat! 

I installed it last Friday and it powered up no problem. I tested the heat and AC and everything seemed to be working fine...that is until Sunday @ 4:00am.

I woke up to a freezing house and the Nest had a message on it something like "Your wiring configuration has changed" and it appeared to have reset and kicked me back to the test menu. 

I went down to the basement and checked my Taco valve panel connected to my boiler and the T-Stat Call orange light that corresponds to that zone was flickering and not solid, like it normally is when activated. My guess is this is a t-stat power issue (lack of common wire).

My system is confugured as follows....(pic attached of how my Nest is wired)
- AC unit in attic has G-Y-Rc running to Nest
- Boiler in basement has W-Rh running to Nest

Any words of wisdom would be much appreicated!


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## beenthere (Oct 11, 2008)

Run a common from the air handler in the attic to the Nest.


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## thearchitect (Nov 22, 2010)

Thanks bennthere! So I ran the common wire to the air handler thermostat control panel in the attic. The same error came up on my Nest (N72 : No power to the Rh wire)

BUT the heat is working when activated. The only thing that is still a little funky is that when that zone is not activated the orange T-Stat call light on my Taco flickers and is not solid. Any thing to be concerned with there?

Thanks again for the help!


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## beenthere (Oct 11, 2008)

Its still stealing power from the zone panel. May or may not be okay. Don't work with those stats to know.


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## supers05 (May 23, 2015)

Restart the configuration wizard. It needs to be reset to use the common wire. 

Pictures of your new wiring will help. 

Cheers!


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## thearchitect (Nov 22, 2010)

Thanks supers05. When I powered the Nest back up after connecting the common wire, the display said "Your wiring configuration has changed" and it showed that it recognized the common. Are you saying that despite this, I should still reset the Nest?

Attached is the Nest wiring configuration that I have. (Not an actual pic, but it's my actual config). The Y-G-Rc-C are being fed from the AC unit in the attic and the W-Rh are being fed from the boiler in the basement.

Thanks again!


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## supers05 (May 23, 2015)

Yes, and an actual picture of the thermostat wiring in the air handler might help. 

Cheers!


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## thearchitect (Nov 22, 2010)

Ok, so I reset the Nest and the Rh wire is still greyed out and the T-Stat Call light on my Taco is still flickering when zone in inactive (and solid when active).

Again, it seems that everything is working normally, but I'm concerned about the filckering light on my Taco panel. 

I've attached pictures of my Unico panel for my AC (where the common is tied in) and the Taco panel for my boiler.

Thank you!


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## beenthere (Oct 11, 2008)

Its possible that Nest wants the common to come from the heating side. Might want to call their tech support and find out.


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## CaptTom (Dec 31, 2017)

I was just about to post a long-winded story that amounts to basically what beenthere just said.

But I have the same Taco ZVC valve as you, and I've updated the diagram from the manual with the location of the W, R and C terminals. Any of the ones marked "C" will work, you don't have to use any specific zone block.









And here's a snapshot I grabbed from another manual which may also be part of your problem.









I think this one was talking about jumpering the two "R" terminals. I was looking up how I could turn off the air conditioner in winter without killing my Honeywell WiFi thermostat, which only takes power from the Rc terminal.


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## thearchitect (Nov 22, 2010)

Thanks CaptTom! I called Nest Tech and they seem to think there may be an issue with the Rh wire not supplying enough power, which they said is why it's greyed out on the Nest wiring configuration. I thought installing the common wire would satisfy all of the power requirements for the Nest, but apparently that's not the case. Why wouldn't the Rh wire be generating enough power? The Taco seems more than capable enough of supplying 24 volts.

About to throw in the towel with this and go back to my mercury driven Honeywell :sad:


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## CaptTom (Dec 31, 2017)

Is there 24VAC between Rh and C? If so, that doesn't necessarily prove anything, although it's a good start. But if not, you have your answer.

Before tossing the Nest, I'd bring it to the zone valve control and wire it up directly there, just to rule out all the wiring in between.

I guess the Nest runs off the heat side, that's great. The Honeywell WiFi I have requires power to the air conditioner or it won't run at all. We need that about 2 weeks out of the year here! I'd have gone with the Nest but (1) I'm retired and don't have a schedule for it to learn, and (2) I need three thermostats, so you can do the math on what three Nest t-stats would have cost.


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## supers05 (May 23, 2015)

If you have a meter, check the voltage between rc and rh. (Vac setting) 

If it's roughly 48V, then turn off the power to the zone panel. Swap the black and white wires from the transformer. (so it'll be white(tx)-black(line) etc, instead of matched, blk-blk, etc.) Make sure that you don't join the 2 main line wires together. Turn the power back on once you have the wires safe again. 

If it's nearly 0, then we're looking something else. 

PS. Most thermostats take power between Rc and C. I thought nest was the same, but it's been a while since I've tested that. 

Cheers!


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## user_12345a (Nov 23, 2014)

Nest not detecting voltage when Rh and C are connected and have power?

There's no app for that, but there's a universal debugging kit they released which resolves most nest problems...


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## BayouRunner (Feb 5, 2016)

I think Super is on the right track. With thermostat wires disconnected measure from the common wire (low voltage side) of transformer to ground on both units. You should not get any voltage. If you do reverse those transformer leads. I think you are getting some type of backfeed.


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## CaptTom (Dec 31, 2017)

Thanks Supers05 and BayouRunner, I'm still learning this stuff.

It sounds like you're saying most t-stats are like my Honeywell, in that they power the brain off Rc and C. It sounded like the OP was saying the Nest used Rh. I don't have a Nest so I don't know.

You both imply that the transformer(s) might have their hot and neutral reversed. The manual where I saw the "Warning" text I posted also seems to imply that if the two transformers are connected properly to power and in phase, you can jumper Rh and Rc inside the t-stat, essentially tying the "hot" sides together.

Does this make sense? It goes against everything I've ever learned about keeping different circuits separate.


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## thearchitect (Nov 22, 2010)

Thanks BayouRunner! Just to be clear, are you referring to the transformer on the Taco unit?


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## BayouRunner (Feb 5, 2016)

In referring to both transformers. One in each unit. The nest is a funny stat and your having a different type of issue. I can’t guarantee that’s your problem but the way you are describing the light coming on could be a possibility. I’ve had some service calls from the nest stat that took some time to figure out. Best way I can say it is the nest likes it their way and no other way. A call to their tech support line is a good idea as well but I’ve never tried it. Don’t know how good the support is but I’ve not heard anything bad about it 


Sent from my iPhone using Tapatalk


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## supers05 (May 23, 2015)

CaptTom said:


> .... The manual where I saw the "Warning" text I posted also seems to imply that if the two transformers are connected properly to power and in phase, you can jumper Rh and Rc inside the t-stat, essentially tying the "hot" sides together..


No, you don't want to jumper them together. Most thermostats cannot tolerate 48v difference between terminals though. The "internal automatic jumper" likely can't handle it and is letting current through. In your wiring case it should be off. The nest should recognise that you have Rh and Rc connected. It won't work right until it does. 

Cheers!


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## CaptTom (Dec 31, 2017)

supers05 said:


> No, you don't want to jumper them together. Most thermostats cannot tolerate 48v difference between terminals though. The "internal automatic jumper" likely can't handle it and is letting current through. In your wiring case it should be off. The nest should recognise that you have Rh and Rc connected. It won't work right until it does.
> 
> Cheers!


Thanks, but I'm the one with the Honeywell, not the Nest. Mine works fine, but only because I'm currently only running heat. Rh and Rc are jumpered, the air conditioner breaker is off and the "Rc" terminal is not connected.

The blurb I posted was from a manual which talked about jumpering Rh and Rc with two "live" connections to two different transformers ONLY if there was less than a 12V difference between them. In other words, no chance of getting 48V to the t-stat. From a functionality standpoint, this would be ideal. From an electrical standpoint I'm still stuck on having two circuits cross-connected, even if it's through two transformers.

I'm only asking on the off chance I'm wrong, the manual is right, and it's perfectly OK to do. BTW the manual was from another smart t-stat, not the Nest or Honeywell, so don't blame them!


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## supers05 (May 23, 2015)

CaptTom said:


> Thanks, but I'm the one with the Honeywell, not the Nest. Mine works fine, but only because I'm currently only running heat. Rh and Rc are jumpered, the air conditioner breaker is off and the "Rc" terminal is not connected.
> 
> The blurb I posted was from a manual which talked about jumpering Rh and Rc with two "live" connections to two different transformers ONLY if there was less than a 12V difference between them. In other words, no chance of getting 48V to the t-stat. From a functionality standpoint, this would be ideal. From an electrical standpoint I'm still stuck on having two circuits cross-connected, even if it's through two transformers.
> 
> I'm only asking on the off chance I'm wrong, the manual is right, and it's perfectly OK to do. BTW the manual was from another smart t-stat, not the Nest or Honeywell, so don't blame them!


The manual is misleading and shouldn't have said that. 

Yes, it's possible to do, and will actually work for a time. It's very bad practice. You'd have 2 power separate power sources, on different breakers. The bigger problem would be if both commons were grounded. That would create the full circuit path needed to cause trouble when one of the 2 units of shut off. (Although it probably would be for long, either because the low voltage fuse blows or you'd melt down the transformer, however transformers work in both directions. You'd potentially have high voltage on the unit that you thought was shut off. There'd be enough current available to give you a zap and throw off readings. Nothing usable would run though.) 

I believe the manual was trying to say that you should only connect rh and rc when there is less then 24v between them. This should be checked. The jumper is used when one doesn't exist. 

Cheers!


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## CaptTom (Dec 31, 2017)

supers05 said:


> The manual is misleading and shouldn't have said that.
> ...
> I believe the manual was trying to say that you should only connect rh and rc when there is less then 24v between them. This should be checked. The jumper is used when one doesn't exist.


Your reading of that part of the manual makes more sense than what the way I was interpreting it. Thanks for setting me straight! It would have taken a LOT more evidence to convince me it would be OK to connect the two transformers.


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## thearchitect (Nov 22, 2010)

Hi CaptTom,

I took your advice and hooked the Nest directly up to my Taco panel and VIOLA!. Power to the Rh! So am I to assume there is an issue with the original wire run from the t-stat to the panel? It's the longest run in the house (3 level house - upstairs to basement) and my worry is that the wire may be tacked to the studs. Thoughts?

Thank you!


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## supers05 (May 23, 2015)

thearchitect said:


> Hi CaptTom,
> 
> I took your advice and hooked the Nest directly up to my Taco panel and VIOLA!. Power to the Rh! So am I to assume there is an issue with the original wire run from the t-stat to the panel? It's the longest run in the house (3 level house - upstairs to basement) and my worry is that the wire may be tacked to the studs. Thoughts?
> 
> Thank you!


The wire is likely tacked to the studs. 

Most wire breaks are near either end. I'd check the first. 

Try to run a new cable. If not, you have options, just not with nest. 

Cheers!


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## thearchitect (Nov 22, 2010)

My house was built in 1920, and the thermostat wire doesn't look as old, so I'm hopeful it was pulled during a reno is isn't tacked in to anything.

Thanks for all the helpful advice!


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## CaptTom (Dec 31, 2017)

thearchitect said:


> Hi CaptTom,
> 
> I took your advice and hooked the Nest directly up to my Taco panel and VIOLA!. Power to the Rh!
> 
> Thoughts?


How many conductors in the current cable? You only need 3 for the heat.

Fishing a new wire would be a bear. I just did that for three t-stats, two of which were on the 2nd floor. If I had to go 3 stories I'd probably have given up.


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## supers05 (May 23, 2015)

CaptTom said:


> How many conductors in the current cable? You only need 3 for the heat.
> 
> Fishing a new wire would be a bear. I just did that for three t-stats, two of which were on the 2nd floor. If I had to go 3 stories I'd probably have given up.


Heat only, requires only 2 conductors. 

Cheers!


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## CaptTom (Dec 31, 2017)

supers05 said:


> Heat only, requires only 2 conductors.


In the context of the OP's situation, for the Nest t-stat, you'd need three wires from the "heat" side to the zone control valve; Rh, W and C. This assumes the Nest gets it's internal power from Rh and C, as suggested elsewhere in this thread.

Then you'd need at least two wires (Rc and Y1) going to the air conditioner controller, possibly more if it's multi-stage (Y2) and/or requires t-stat control of the fan (G). But those wires are no doubt already in place if the old t-stat was working.


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## supers05 (May 23, 2015)

CaptTom said:


> In the context of the OP's situation, for the Nest t-stat, you'd need three wires from the "heat" side to the zone control valve; Rh, W and C. This assumes the Nest gets it's internal power from Rh and C, as suggested elsewhere in this thread.
> 
> Then you'd need at least two wires (Rc and Y1) going to the air conditioner controller, possibly more if it's multi-stage (Y2) and/or requires t-stat control of the fan (G). But those wires are no doubt already in place if the old t-stat was working.


It's being powered by the air handler, Rc and C. It can get power from Rh and W, but IIRC, not Rh and C when using Rc on a separate transformer. 

With that said, I always run extra wires when I can. You never know when you'll need them. 

Cheers!


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## thearchitect (Nov 22, 2010)

And the saga continues...

So I pulled a new 18-3 wire to my Taco panel at my boilier. I kept the common wired to the Unico panel (W-Rh to Taco/Y-G-Rc-C to Unico) in the attic and powered everything up and.....WAH WAH WAAAAAAH. Same 'ol story...no power to the Rh wire. Even though when I wired it directly to the Taco (just Rh and W) the power on the Rh showed up just fine. So it seems there wasn't an issue with the 18-2 wire that was previously there. I suppose my next experiment will be to try using the common terminal at the Taco panel instead of the Unico? This might be Rocky's final round...


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## supers05 (May 23, 2015)

thearchitect said:


> And the saga continues...
> 
> So I pulled a new 18-3 wire to my Taco panel at my boilier. I kept the common wired to the Unico panel (W-Rh to Taco/Y-G-Rc-C to Unico) in the attic and powered everything up and.....WAH WAH WAAAAAAH. Same 'ol story...no power to the Rh wire. Even though when I wired it directly to the Taco (just Rh and W) the power on the Rh showed up just fine. So it seems there wasn't an issue with the 18-2 wire that was previously there. I suppose my next experiment will be to try using the common terminal at the Taco panel instead of the Unico? This might be Rocky's final round...


Swap the rh and w terminals at the nest 

Cheers!


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## thearchitect (Nov 22, 2010)

Supers05...I have yet to rule this out. Need to get a low voltage meter and check the voltage between the Rc and Rh wires. I'll keep you posted with the results. Thank you!


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## CaptTom (Dec 31, 2017)

The voltage between Rc and Rh is going to depend on how each transformer is connected, and whether or not they're in phase. Nothing in the thermostat is going to depend on any particular voltage between them. As long as they're not jumpered together (and they shouldn't be, if you have both) you don't really care.

The thermostat is going to power its internal electronics off the "C" and one of the "R" terminals. Whether it's Rc or Rh, I can't tell from the Nest documentation. Someone suggested Rh, but on my (different brand) thermostat it's Rc. That is where you should be measuring 24VAC.


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## thearchitect (Nov 22, 2010)

ok thanks CaptTom. Got my multimeter, but I've never used one to measure thermostat wires. Can you please describe which leads (Black and Red) connect to the appropriate thermostat wires? Thank you!


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## supers05 (May 23, 2015)

CaptTom said:


> The voltage between Rc and Rh is going to depend on how each transformer is connected, and whether or not they're in phase. Nothing in the thermostat is going to depend on any particular voltage between them. As long as they're not jumpered together (and they shouldn't be, if you have both) you don't really care...


The nest uses an internal "jumper". It's actually a special "switch".

Anyways, yes it can matter, especially if the nest is using C as a reference when connected. 

The nest is being powered at the moment, so that verifies that it's using Rc and C.

Cheers!


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## supers05 (May 23, 2015)

thearchitect said:


> ok thanks CaptTom. Got my multimeter, but I've never used one to measure thermostat wires. Can you please describe which leads (Black and Red) connect to the appropriate thermostat wires? Thank you!


Set your meter to Vac. Put your leads on Rh and Rc and record the result. 

Repeat with Rh and C.
Repeat with W and C.

For this, it doesn't matter which lead is which. Polarity doesn't matter. 

Cheers!


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## thearchitect (Nov 22, 2010)

Thanks supers05. Below are my results...

between Rh and Rc = 0 VAC
Rh and C = 27 VAC
W and C = 27 VAC

Here's what Nest tech support had to say about my current situation...

"Since they are 2 different systems, this is causing the issue. To solve this, you would have to contact a technician so that they can relay both system to one control panel and then set it up to connect to the Nest Thermostat."


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## supers05 (May 23, 2015)

thearchitect said:


> Thanks supers05. Below are my results...
> 
> between Rh and Rc = 0 VAC
> Rh and C = 27 VAC
> ...


That is with the nest disconnected from the base right? 

Cheers!


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## thearchitect (Nov 22, 2010)

Yes, with the Nest disconnected from the base.


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## supers05 (May 23, 2015)

thearchitect said:


> Yes, with the Nest disconnected from the base.


The heating side is ungrounded. We need to ground the common side at the valve. 

Cheers!


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## thearchitect (Nov 22, 2010)

I did notice that supers05 and thought that was unusual! Do you think the solution to all this nest-mess is just that??? I see the green ground screws on the side of my taco, but am not sure where the wire would go inside the panel. Also, does this mean the common wire should be wired to the taco and not the unico? THANKS!


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## thearchitect (Nov 22, 2010)

From a user in an HVAC forum...

"add a RIBUC1 to the Taco zone box - yellow - orange to R W of your zone - white/yellow and white/blue of rib to r w that used to be there from stat . Cap spare rib wires . Now at Nest twist together Blue (C) from AC with red (old heat Rh ) and add a 3rd blue color wire splice with tiny wirenut - tuck behind nest base - connect blue wire to C -nest base . Then, old white W back to W - nest base , reconnect Y, G , Rc . Try heat and AC . If Heat does not turn on , try Rc to Rh wire switch , if AC or heat does not then base is no good , order new base from nest. keep wire configuration as told - powered from the AC trans only . Go to settings - equipment - pro setup - turn all yellow lights green by selecting your new configuring , and all will be fine ."

Thoughts?


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## supers05 (May 23, 2015)

thearchitect said:


> I did notice that supers05 and thought that was unusual! Do you think the solution to all this nest-mess is just that??? I see the green ground screws on the side of my taco, but am not sure where the wire would go inside the panel. Also, does this mean the common wire should be wired to the taco and not the unico? THANKS!


Post some clear pictures of the wiring in the taco. 

No, the common should stay where it is. 

Cheers!


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## supers05 (May 23, 2015)

thearchitect said:


> From a user in an HVAC forum...
> 
> "add a RIBUC1 to the Taco zone box - yellow - orange to R W of your zone - white/yellow and white/blue of rib to r w that used to be there from stat . Cap spare rib wires . Now at Nest twist together Blue (C) from AC with red (old heat Rh ) and add a 3rd blue color wire splice with tiny wirenut - tuck behind nest base - connect blue wire to C -nest base . Then, old white W back to W - nest base , reconnect Y, G , Rc . Try heat and AC . If Heat does not turn on , try Rc to Rh wire switch , if AC or heat does not then base is no good , order new base from nest. keep wire configuration as told - powered from the AC trans only . Go to settings - equipment - pro setup - turn all yellow lights green by selecting your new configuring , and all will be fine ."
> 
> Thoughts?


It's out of context. It sounds like they are using a relay board. I think it's unnecessary for your setup. 

Cheers!


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## thearchitect (Nov 22, 2010)

Sorry....here is the first post regarding installing a relay to the zone panel...

"Add a relay at the heat zone panel and power it from the Nest AC side of the wiring . Must use one power source - at Nest use the AC -blue splice behind it , wire to common nest base and red of heat wire - , white goes to w - nest base - then powers the relay at heater."

I'll try toget a better photo of my Taco panel.

Thanks!


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## thearchitect (Nov 22, 2010)

Here is a high res pic of my Taco panel at my boiler. 

I was digging around on the internet and stumbled across this post. Sounds like a similar issue and similar solution. The wiring is a little diffrerent than described in my previous post, but end goal is the same.

https://wegotserved.com/2015/12/18/review-nest-learning-thermostat-3rd-generation/2/


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## supers05 (May 23, 2015)

Yes, IIRC, those panels aren't grounded. They are floating. Cut a small piece of thermostat wire and connect it to "C" of any of the thermostat connections and the ground screw on the box. (Hopefully that AC cable is grounded at the other end.) 

Cheers!


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## thearchitect (Nov 22, 2010)

ok thanks supers05! In one of your previous posts you said _"The bigger problem would be if both commons were grounded. That would create the full circuit path needed to cause trouble when one of the 2 units of shut off."_ Does this just pertain to a situation when the Rc and Rh are jumpered?


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## supers05 (May 23, 2015)

thearchitect said:


> ok thanks supers05! In one of your previous posts you said _"The bigger problem would be if both commons were grounded. That would create the full circuit path needed to cause trouble when one of the 2 units of shut off."_ Does this just pertain to a situation when the Rc and Rh are jumpered?


Only applies if they are jumped. 

Sent from my SM-G900T using Tapatalk


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## thearchitect (Nov 22, 2010)

Hello! Just a follow up to say that my Nest issues have been resolved!

I grounded the Taco panel, but that still had no effect on the issue of the Rh power error that I was getting at the Nest.

So I went with the relay solution and installed a RIBU1C on my Taco and I'm happy to say it worked! Heat and AC zones are functioning properly and the Nest seems content with it's insatiable need for power!

Thank you all very much for the guidance and wisdom!


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## CaptTom (Dec 31, 2017)

thearchitect said:


> Hello! Just a follow up to say that my Nest issues have been resolved!


Thanks for closing the loop on this!

Any chance of posting a wiring diagram for future viewers? I'd like to see it too.


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## supers05 (May 23, 2015)

With a bit more patience and troubleshooting, it should have worked without the relay. However, the relay doesn't hurt, just adds a bit more complexity to someone seeing it for the first time. (ie. some tech that gets called when you're away for whatever reason.) 

That relay model is fairly reliable from the reports that I've seen. You should be good for a long while.

Cheers!


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## thearchitect (Nov 22, 2010)

Here's the wiring diagram of how I hooked up the relay to my Taco panel. I apologize for the crude format. I'm not learned in the ways of technical wiring diagrams. Hopefully this makes sense! I'm happy to clarify anything.


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## CaptTom (Dec 31, 2017)

Very nice! Thanks!

I'm assuming Rh and Rc are jumpered in the Nest.

I was thinking of doing something similar, but backwards, in that the air conditioner switch would be powered by the relay. I'd lose the "fan only" (G) capability, but I never used that anyway. That would allow me to turn off the A/C circuit breaker for the 9 months out of the year we don't use it.


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## supers05 (May 23, 2015)

CaptTom said:


> I'm assuming Rh and Rc are jumpered in the Nest.
> .


Yes. 


Cheers!


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## thearchitect (Nov 22, 2010)

No jumper between Rh and Rc. Can’t really explain why. My understanding is the Nest wants to think it’s getting power from one source. In my case the AC Handler. I just followed the instructions from the poster about the relay and everything seems to be working as expected. Good luck!


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## CaptTom (Dec 31, 2017)

Hmm. Now that you mention it, I recall reading somewhere that the Nest will try to figure out where the power's coming from on it's own, and has a relay which automatically jumpers Rh & Rc if needed. Those things are just too darn smart!


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