Which type of connection is required for a 120/208-volt, 3-ph, 4-wire secondary transformer system?

In a 120/208-volt, 3-phase, 4-wire secondary transformer system, a Wye (or Star) connection is required to provide the necessary voltage levels and neutral point. The Wye configuration enables the phase voltage to be 120 volts (line-to-neutral) while producing line voltages of 208 volts (line-to-line). This connection is particularly useful in distribution systems where a neutral conductor is needed for single-phase loads and ensures balanced load distribution among the three phases.

In Wye configurations, the three phases are connected to a central neutral point, which allows for the safe and efficient distribution of electrical power. This setup supports both three-phase and single-phase loads, making it versatile for various applications.

In contrast, a Delta connection would not provide a neutral point, which could be essential for many systems that require standard single-phase 120-volt circuits alongside the three-phase power. Series and parallel connections do not apply to this context in the way required for transformer connections in three-phase systems. They are more relevant to other types of electrical configurations rather than for transforming voltages in a three-phase system.