Alternative for systems that need C wire for operating a Nest thermostat Works with the Nest Thermostat, Nest Thermostat E, and Nest Learning Thermostat Works with only 24VAC systems and is not compatible with millivolt and high-voltage systems Easy to install design with simple instruction attaches to the furnace, air handler, or zone controller, without the need for new wiring, drilling, or electrician's assistance IP51 design offers resistance against dust and water to keep the connector protected