The 24VAC power adapter will provide power to the LS-60(i) and LS-90(i) from any standard electrical outlet. This can be used if you do not have an existing C-Wire coming up from your furnace to your thermostat. This transformer converts 110VAC to 24VAC for use with LS-60(i) and LS-90(i) thermostats. Simply connect one end to the "Rh" terminal and the other end to the "C" terminal. You can connect either wire to either terminal (there is no polarity).