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Installation of a c wire

mograteful Member Posts: 2
I am using a taco SR 501 switching relay for my three zone propane, gas furnace. I have the basic thermostats now just use a red and white wire. I want to add a setback thermostat that requires a c wire. The switching relay has a 24 V AC common. My thermostats are not directly connected to the TT terminals. How can I use the c wire or do I need to connect a separate 24v transformer between my c wire and my red wire going to the thermostat 


  • Zman
    Zman Member Posts: 7,542
    Do you have zone valves or zone pumps?
    With zone pumps the SR-503-4 would be appropriate.
    With zone valves the ZVC-403-4 Would be best.
    I don’t understand how you intend to use a single zone pump relay to run 3 zones. The transformer is not sized for that.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mograteful
    mograteful Member Posts: 2
    I agree with you 100%. The system in my mind was putting incorrectly but then again I’m not an expert. I bought a 24 V transformer. I solved the problem with that. I just thought that I could use the one that was on the Taco, thank you 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,499
    @mograteful, we need to get back to basics. What is the thermostat that you want to replace connected to? Since you have 3 zones I assume you have three thermostats. each of those thermostats has a wire connected to the W terminal on the thermostat. The other end of that wire is connected to __________?

    I feel like Gene Rayburn with that last question.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Joe Mattiello
    Joe Mattiello Member Posts: 703
    you can use the com terminal located on SR control. there are a couple Rev existing, so I cannot be specific, however, you can reach out to Taco tech support at 401-942-8000 for support. have the complete model number available when you call.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions