Once you’ve completed the wiring of the Thermostat and Equipment Interface, you can apply power to the Equipment Interface and restore power to the heating and air conditioning equipment.
There are two methods of powering the Thermostat. You can power it directly from a 24VAC source capable of at least 3VA.
The second method requires the optional 120V to 12Vdc power adaptor. Plug the power supply into a standard electrical outlet and plug the barrel connector into the Equipment Interface.