Hi @Jsmith1977,
Thank you for posting in the community. I understand you'd like to know if the Nest Learning Thermostat (2nd gen) requires a common or C wire to operate. I'm here to provide you the correct information.
While Nest Thermostats are designed to use very little power, and in many cases they can use your system’s heating and cooling wires to get enough consistent power, depending on the scenario you may need to connect a common wire (C wire) or power accessory, like the Nest Power Connector, to make your system compatible, since having a common wire depends only on the system you have.
The Google Home app will often tell you during setup if you need to connect a C wire. I recommend you check the compatibility between your system and the thermostat first by visiting the Compatibility Checker. Some systems, including heating-only, cooling-only, zone-controlled, and heat pump systems, require a C wire or a compatible power accessory, like the Nest Power Connector. The app will tell you if you need this.
You can learn more by visiting the article Learn about the common or C wire.
Let me know if you have any further questions.
Regards,
Anders
