What does the dot mean on a single phase transformer wiring schematic?
Typically, a single phase transformer wiring schematic has a dot on both the primary and secondary windings.
The placement of these dots next to the ends of the primary and secondary windings informs us that the instantaneous voltage polarity seen across the primary winding will be the same across the secondary winding. In other words, the phase shift from primary to secondary will be zero degrees, which is important for some types of circuits. If the wiring to the dots is reversed on one side, the primary and secondary will be 180 degrees out of phase.