One of the more popular electrical services that is supplied to medium-size commercial buildings is the Wye or Star configuration. The name comes from the transformer’s secondary winding configuration, which looks like a ‘Y’ or three-sided star (Figure 1). This dual voltage, three-phase electrical service usually delivers four wires to the building.
There are actually three 120-V windings in the secondary of the step-down transformer that are 120 degrees apart. They consist of three hot wires and a neutral or ground. The secondary winding of the Wye is center-tapped and grounded. This makes the center tap perfectly symmetrical to all three phases of its power.