Final answer:
The 'Y' on a transformer nameplate indicates a star or Y-connection, one of the two primary configurations for connecting transformer windings, with the other being a Delta connection.
Step-by-step explanation:
The 'Y' on a nameplate of a transformer is an indication to connect the transformer windings in a star configuration or Y-connection. This is one of the two common methods used for connecting the windings of a three-phase transformer, the other being the Delta (Δ) connection. In a Y-connection, one end of each winding is connected to form a common point known as the neutral or star point, while the other ends are connected to the power lines. This type of connection typically allows for both multiple voltages and the use of a neutral.