Product Description: Compatible with a 2-wire and 3-wire thermostat, this all-in-one relay includes a built-in 24V transformer, replacement for any brand relay. Compatible with 24V thermostats with 3-wire connections (R, W, C) or 2-wire connections (R, W). Immediate relay activation provides improved temperature control and comfort. Easy to Install, merely mounted it on the side of the existing junction box and attached the wires from the new thermostat. Specifications: Transformer Ratings: 24 VAC/ 1.2VA/ Class 2 Ambient Operating Temperature: -4? to 140? (-20? to 60?) Ambient Storage: -40? to 175? (-40? to 80?) Humidity Limits: 0 to 95% non-condensing Terminal Wire Size: 12 AWG