Connect the transformer. Attach the two black wires from the transformer to the 120 VAC power supply wires. One supply wire will be the black voltage wire, attached to the fuse or circuit breaker. The other power supply wire will be white--this is the electrical systems neutral or common.
C wire The C wire, or “common wire” enables the continuous flow of 24 VAC power to the thermostat. Technically speaking, power flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a common wire to complete the circuit.
Copper and aluminium are the two conductors used in transformer windings. In distribution and small power transformers, aluminium–aluminium windings have been successful. For large power transformers, a copper–copper design is more common.
Calculate an example as follows. A 120-volt motor has a load amperage of 5 amps. Multiply 120 volts times 5 amps this equals 600VA now lets multiply the 125 percent start factor. Take 600 times 1.25 this equals 720VA and most transformers are sized by a factor of 25VA or 50VA.
1:153:37Wiring 480/240V to 240/120V on Epoxy Resin - YouTubeYouTube
Input Connections - The input side of a transformer is called the primary side because the main electrical power to be changed is connected at this point. Output Connections - The output side or secondary side of the transformer is where the electrical power is sent to the load.