2 zones one common wire

[Danwinters1]

I have an older boiler that feeds one thermostat for my zone 1 and a switch relay that feeds my second thermostat, zone 2.  The zone 1 connection is early 90s and  has no common lead, but my zone 2 switch relay is a taco sr501-4 with a common (c) lead.  Right now I have both thermostats with two wires for heat (red and white).  What I was thinking about doing was using two nest power connectors, and have the c lead for the power connectors going to the taco switch relay common.  Then using the two sets of red and white to power the two nest learning thermostats.  Can I run my two nest learning thermostats off the common lead on the switch relay using two nest power connectors ?  Will it have enough power for both nest thermostats, or will that cause an error? 

zone 1 also has my AC connected too, zone 2 in my basement is heat only if that makes a difference?  

[zoeuvre]

Hi Danwinters1, 

Thanks for posting. You can use a normal wire from a switch to give power to two Nest Learning Thermostats. The Nest Power Connectors can give power to thermostats. This is done by joining the C lead from the switch relay to each Nest Power Connector's C terminal. The red and white cords from each thermostat can then be joined to the R (power) and W (heat) points on the Nest Power Connectors. 

Powering the Nest thermostats with the normal lead from the switch relay should give enough power for them to work well. But remember, the exact matching and power needs can change based on the type of Nest thermostat you have. It's best to check Nest's information or call their help for clear directions on how to wire things up and understand power needs for your particular plan. Also, because you said your AC is in zone 1 too, it's important to make sure the wires and setup work with both heating and cool air systems.
 

Let us know if that helps.

Best,

Zoe