I'm trying to understand where the common wire would be from my system's wiring diagram. The thermostat itself only has the R and W connected.

Is my understanding correct that it would be the wire leading to 'earth' from the transformer in the below diagram?

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Any help or info is much appreciated.


Your system has no "C" wire brought out to the connector. This is not uncommon as many systems don't. If you need a "C" wire, you'll want to connect it here:

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