looking for assurance on what I think is the right setup to add a c wire to a current 2 wire zone setup. See pic of transformer junction box.

Currently I have 3 zones using one transformer and 3 taco zones. All stats use 2 wires, Rh and w.

Looking at my transformer setup it looks like they took all the stat wires from the different apartments, zones, bundled them up and connected all the Rh wires pigtailed together to one of the leads on the transformer. ( see pics. Note I didn't remove junction cover yet )

I'm assuming they then pigtailed all the W wires from the stats along with all the wires from taco zone terminal 1 together and pigtailed together to the other transformer lead. Then took taco zone terminals 2/3 pigtailed out of the junction box (I saw the 2 wire cable go to relay box) to relay then boiler on the t terminals.

My doubt is if I introduce a new stat wire for c, where do I connect the c wire. Should that go on the bundle of wires that connect the stat W and zone valve terminal 1?? Or is there a better way.

Also the transformer terminalit doesn't seem to be marked with + or - so am assuming you can just connect the R/W to any terminal as long as it's consistent.[![enter image description here nhi][1]][2]

Thanks very much for the forum and everyone that's been helping.


[2]: https://i.stack.imgur.com/M7vrA.jpg![enter image description here](https://i.stack.imgur.com/bU3DV.jpg)

1 Answer 1


One of those transformer terminals is "R" the other is "C"

If the red wire joins to the thermostat "R" wires then the beige wire is "C"

Thermostat wires should not be inside that junction box with the mains wiring, get a new box for the thermostat wires.

  • After looking at pictures I posted I can now see one of the terminals on the thermostat is positive which has the beige wire. I'm assuming that inside that box that beige is going to R. Not sure why they didn't keep colors consistent. I'll note your suggestion on thise separate boxes. Put its same to assume I have the right concept where the new c wire connects, do the same p look Ave the bundle connected to the c terminal on the transformer in this case the red wire. Thank you for taking time to respond.
    – Da P.A
    Nov 25, 2020 at 13:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.