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Can additional 24V Transformer power multiple C-Wires for multiple zones for Taco ZVC404-EXP?

I'm adding an additional 24V HVAC transformer to power C-wire for the zones for my Taco ZVC404-EXP. Can I use a single 24V transformer for all the zones or do I need an additional transformer for each of the 6 zones? I'm using this setup http://www.taco-hvac.com/tmp/ExternalxfrmerZVC-4Powerrobbingthermostat.pdf that Taco recommends for "Power Robbing Thermostat".


I have two old Taco ZVC404-EXP (to power 6 zones). Unfortunately the old Tacos do not have a single COM port nor additional C ports on each of the zones.

I have referenced https://forum.heatinghelp.com/discussion/172451/ecobee3-taco-zvc404exp-c-wire and faced the same issue, I cannot connect use the neutral on the left (J4) as the common/COM/C. Heater will start when connecting R<->C.

Based on this thread: https://www.reddit.com/r/ecobee/comments/92i5xj/ecobee4_and_taco_sr503_zvc406/
"I have a ZVC406. When I contacted Taco they instructed me to purchase another external 24V HVAC transformer and provided me with a specific "Power Robbing Thermostat" wiring schematic PDF. They, perhaps conservatively, cautioned the transformers would not be able to provide enough power for the board, zone valve controllers, and multiple ecobees.



  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    It's not a matter of how many zones, it's a matter of how many VA the transformer can put out. Just get one transformer -- and make sure it's big enough.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England