NCM300 upgrade

[jbis]

Just like this thread viewtopic.php?f=4&t=404 I am installing Nest thermostats and need to upgrade to the NCM300 from the ST-3. I have a question on the wiring. My zone 1 thermostat has both a blue and brown wire hooked up to separate B and O connections. (zone 2 & 3 are simple 3 wire (red, white, yellow) connections) The ST-3 also has these O and B connections coming into it, however, going out to the furnace, they are not even connected to the board OR the furnace. So, is the zone panel doing something with these connections or can I take the blue wire and feed the thermostats a C wire?

[jbis]

Here's the furnace shot

[Erik W.]

You do not need to hook the O or the B anymore. Your old panel required it because it was a master slave but the NCM-300 is not and only requires an O or a B if you have a heat pump, you can use one of those wires as your common wire .

Erik

[jbis]

Excellent! Thank you!