EWC ST Control, thermostat question

[nlagaros]

Why is it that the C terminal cannot be used? If the thermostat supports running off of 24v, shouldn't I be able to use the C terminal. I have done this with some Venstar thermostats and they work fine in Zone 1. Zone 2 is another issue alltogether - thinking now that hooking up C in Zone 1 is causing some sort of issue?

[Eric K.]

With the ST control panel, the R terminals for the thermostats do not provide a constant 24vac. When ever the master thermostat is switched between heat and cool, the R terminal will loss power momentarily and when switched off will lose power all together.

The R1 terminal on Zone 1 is constant, so it is acceptable to use the common on zone 1.

If you wish to use a common on Zone 2, you should wire the R from the thermostat to the R1 on Zone 1 input.
DO NOT jumper the R on the Zone 2 input terminal to the Zone 1 terminal.

[nlagaros]

With the ST control panel, the R terminals for the thermostats do not provide a constant 24vac. When ever the master thermostat is switched between heat and cool, the R terminal will loss power momentarily and when switched off will lose power all together.

The R1 terminal on Zone 1 is constant, so it is acceptable to use the common on zone 1.

If you wish to use a common on Zone 2, you should wire the R from the thermostat to the R1 on Zone 1 input.
DO NOT jumper the R on the Zone 2 input terminal to the Zone 1 terminal.

Thanks. This makes complete sense based on voltage readings I was getting. Turns out I'm going to be swapping zone controllers to the NCM300 so I can use the Venstar in multiple zones.