When the power is generated, it is usually done so by a 3 phase generator that is separated by 120 degrees of rotation. All 3 phases inside the generator are bo

When the power is generated, it is usually done so by a 3 phase generator that is separated by 120 degrees of rotation. All 3 phases inside the generator are bonded together on one end. The other end are the 3 current carrying conductors leaving the generator. The bonding of the phases on each side of the conductors is what creates the closed circuit. https://en.wikipedia.org/wiki/Three-phase_electric_power https://en.wikipedia.org/wiki/Three-phase_electric_power