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