Swapping out an ST series zone control to model NCM-3z zone control

[Davi S.]

In a similar situation to other threads here, I fell into the trap of purchasing Nest thermostats only to find out my zone control board (ST-2E) was not compatible. I ordered an NCM-300 upgrade board and had planned to perform the upgrade following the appropriate technical bulletin. However, I got up to labeling my wires before noticing that the board I was sent was a NCM-3z instead of the 300 model (which appears to have been discontinued and replaced by the 3z). I've searched for a similar technical bulletin for wiring up the 3z board, and have found the manual, which contains detailed diagrams for various heating/cooling configurations but no direct relationship to the ST series boards. Therefore, in order to mitigate risk of damage to my system I wanted to run my rewiring plan by you guys before going forward with the upgrade. Please see the attached images.

Specific questions:
1. Do I need a new Common for System? NCM-3z manual shows one but the ST-2E did not have one connected.
2. Is my motor/damper configuration correct? Anything else look off/out of place?
3. I do not plan to use the orange and blue wires that are currently connected to the board at Zone 1, but will add a new Common to Zone 1 & 2 if required by the thermostats (The blue wire at Zone 2 was added in such an attempt as I tried to troubleshoot why the new Nest thermostats were not working).
4. Anything else (unknown unknowns) that I should watch out for?

I will likely have a followup question regarding optimal installation location of the temperature sensor once i can get pictures of my duct work.

thanks in advance,
Davi

[Barsenault]

I also ordered a NCM-300, but received a NCM-3Z controller. I do not see a response to your post, but after reviewing the following documents, I am aligned with your conclusions and wiring diagram. Did this work for you? Can someone from EWC confirm before I perform this swap on my system?

Models EWC-ST-2E & EWC-ST-3E (090375a0115.pdf)
Model NCM300 Zone Control System (090375a0226.pdf)
Swapping out an ST series zone control to model NCM300 zone control (090512A0369_C.pdf)
NCM-3z Zone Control System (90375a0269.pdf)

Thanks,
Barry

[Ariaa]

Specific questions:
1. Do I need a new Common for System? NCM-3z manual shows one but the ST-2E did not have one connected.
2. Is my motor/damper configuration correct? Anything else look off/out of place?
3. I do not plan to use the orange and blue wires that are currently connected to the board at Zone 1, but will add a new Common to Zone 1 & 2 if required by the thermostats (driving gamesThe blue wire at Zone 2 was added in such an attempt as I tried to troubleshoot why the new Nest thermostats were not working).
4. Anything else (unknown unknowns) that I should watch out for?

1. Yes, you need to connect a dedicated 24V Common (C) wire from your transformer to the NCM-3z board. Smart thermostats like Nest require a continuous C-wire power supply, whereas older boards like the ST-2E did not strictly require it.

[WyattMcCoy]

I would treat the NCM 3z as a fresh install rather than trying to copy the ST 2E wiring terminal for terminal. The functions are similar, but the way power and commons are handled is not necessarily identical.

If the NCM 3z manual shows a System Common, I would wire it exactly as the manual specifies rather than assuming the old ST 2E arrangement carries over. Same with the thermostats. If the Nest units need a proper C connection, I would provide one instead of trying to make the old wiring arrangement work around it.

Your damper wiring may well be correct, but I would verify the actuator type and terminal functions before moving anything. Some dampers are powered open, some powered closed, and some use three wires, so matching the labels alone can get you into trouble if the old and new boards describe them differently.

The other thing I would do is take clear photos and label every conductor before disconnecting the ST 2E. Then move one circuit at a time and test heat, cooling and each zone separately before calling it finished.

Since the NCM 3z is not the exact board covered by the bulletin you originally found, I think following the current NCM 3z manual is safer than trying to adapt the old NCM 300 instructions.

[lyraellington12]

I agree with Wyatt’s approach here. Since the NCM-3z isn’t exactly the same board as the older NCM-300, I’d be more comfortable treating it as a fresh install and following the current 3z manual rather than assuming the old terminal-to-terminal wiring will carry over.slope game The damper actuator type is definitely something I’d double-check before powering anything up.