NCM-300 with Ecobee 3

[IgorjekG]

Dear all,
I am trying to install an Ecobee 3 at home. I am from Europe, so forced air systems are rather foreign to me.

When I opened my thermostat upstairs, I discovered that there was not C-Wire (see attached), so I thought OK, just go to page 40 of the manual and install a power extender kit. When I arrived downstairs in the utility room and opened the AC unit, there was only one cable connected to the main board, which made me wonder, as I have to thermostats. I then remembered my home inspector saying something about single AC unit with two zones and discovered an EWC unit with NCM-300 board (see attached).

Am I right in my assumption that I am supposed to wire the Power Extender Kit to the NCM-300 board rather than to the AC unit itself?
Thank you for your patience.

P.S. It appears that the cables running between the board and the individual thermostats include in fact 5 conductors - would it not be easier to utilize the 5th conductor (blue in pictures below) and wire it to the C-terminal?

[Steven W.]

Good Morning;
Yes it would be easier to use your spare (Blue) wire for the C-terminal.