Explanation of how we derive 120/240 V and 120/208 V from various Transformer Secondaries.

Additional video of interest: "120/240 V In-Phase or Out-of-Phase"    • 120/240 V  In-Phase or Out-of-Phase  

PLEASE NOTE: The arrows above the left schematic show that this is one winding that has simply been tapped in the center. The waveforms below it in the lower left can give the wrong impression that the "halves" of the winding are out-of-phase with each other. This is because I'm using the neutral as a reference and as I mention in the video, from the perspective of the neutral you look "up-arrow" to one end and "down-arrow" to the other end of the winding. BUT, from either end (i.e: black wire to red wire, or vice-versa) you will be looking "up-arrow" or "down-arrow" for the entire length of the winding (i.e: in-phase).
You can dig through the comments for further discussion on this. I have made a video addressing the phase relationship within 120/240 V systems, and I hope to create other videos focusing on current flow in each of the scenarios that will further our understanding of these transformer configurations.
Thank you,
Dave