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Connecting Nest Thermostat to Taco SR506 6-zone switching relay

VThomeowner85
Community Member

I have a home with an oil furnace and six zone Taco SR506 switching relay. When we purchased the house, 4 zones were in use with traditional, non-digital Honeywell thermostats. They each have two wires (red and white) leading to them. About a year ago I replaced one thermostats with a Nest Learning Thermostat -- I did not need a C wire, and it receives enough power from the R wire to remain charged.

Recently I purchased 3 Nest Thermostats (not the Learning Thermostats), but did not realize they require a C wire -- a support tech told me because they don't have a rechargeable battery, they need constant, steady power. It's too complicated to run new C wires in our house, and I was told a Google Power Connection at the furnace could rectify the issue. Two questions: (1) Do I need a separate Nest Power Connector for each zone/thermostat? (2) This Taco box does NOT have a C connection for each zone, however on the lower left there are two ports, one labeled COM and the other 24 VAC -- can I use those as the C ports for 2 of the Nest Power Connectors? Would I need a 24 VAC transformer for the 3rd Nest Power Connector? Photos attached of the setup. Thank you for the help!

IMG_0872.jpgIMG_0871.jpgIMG_0873.jpg

11 REPLIES 11

Houptee
Silver Product Expert
Silver Product Expert

Looks like a spare green wire is not being used in each cable wrapped around the cable, that can be your C wires to each Nest.

Connect all greens together then into the COMMON screw on the Taco.

Other issue you will have is the Nest Learning uses the Nest app and the Nest uses Google Home app!

Might be easier to get one more Nest so all can be on one app.

I think you can migrate nest to the home app but never tried to do that .


Houptee -- NJ Master HVAC Licensed Contractor

VThomeowner85
Community Member

Thank you for the quick response, Houptee! While I see the unused green wires, they don't appear to run to each thermostat -- I only see a white and green wire at each thermostat location (see photo). Are the green wires typically spliced into the red to send additional power, or are they supposed to run separately? IMG_0868.jpg

Houptee
Silver Product Expert
Silver Product Expert

Each cable looks like it has 3 wires inside red white and green, they might have snipped it off at the thermostat end but if you have slack in the wall cut back the brown covering to expose the green wire inside.


Houptee -- NJ Master HVAC Licensed Contractor

Houptee
Silver Product Expert
Silver Product Expert

Unless they only ran the 3 conductor cables to some point and spliced onto a old 2 wire cable to some of the t-stats?


Houptee -- NJ Master HVAC Licensed Contractor

VThomeowner85
Community Member

This is so helpful. I'll look tomorrow morning to see if there is a green wire further back in the wall. I will report what I find.

If there IS a common wire at the t-stat in the wall, those green C wires could all be fed into the single COM screw?

Houptee
Silver Product Expert
Silver Product Expert

Yes you can wire nut them all together and use one wire into the COM screw hole since all will not fit into that tiny hole. The C wire is basically like Negative on a battery and Red is Positive.


Houptee -- NJ Master HVAC Licensed Contractor

Unfortunately the green wire does not run to the t-stats -- they must have spliced to the old 2-wire cables.

Given that, would I need to install Nest Power Connectors to use these Nest Thermostats? And if so, my questions would be (1) do I need a separate power connector for each t-stat and (2) where would the C wire from the Power Connector run? Would I need a 24 VAC transformer or would the COM/24VAC port on the box suffice?

Houptee
Silver Product Expert
Silver Product Expert

Ideal way to do it is run new thermostat cables to each with 5 conductors but only use 3 red white blue.

If not possible then you would need a power adapter for each Nest.

Or you could buy plug in wall chargers on Amazon and plug into a outlet near each Nest and snake the wire up the wall from the base trim so its hidden.

The way to hook those up is the cord is marked - - - (common) would go to C and the solid wire you put in the Nest R with the existing Red wire.

Here is a video about how to do it

https://www.youtube.com/watch?v=yi5kfn3bmEk&t=871s&ab_channel=OneHourSmartHome

Here is a transformer

www.amazon.com/LIANSUM-Thermostat-Transformer-Compatible-Honeywell/dp/B08TWDT4J2


Houptee -- NJ Master HVAC Licensed Contractor

Jhonleanmel
Community Specialist
Community Specialist

Hey folks,

We appreciate your help here, @Houptee.
@VThomeowner85, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

Hey there,

Checking back in should you still have some questions here. Let us know by replying to this thread. 

Best, 
Mel

Hi everyone,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,
Mel