This connection considerably generates interference with the communication lines hence with this connection configuration, telephone lines cannot be run in parallel. Due to these disadvantages, the star-star connection was rarely used and not employed in practice.

If the neutral connection is not provided or an unbalanced load is connected, then the phase voltages tend to become severely unbalanced. Thus, the star-star connection was not satisfactory for the unbalanced loading in the absence of the neutral connection.

The low voltage side of a 3-phase distribution transformer was star-connected. This star point forms the neutral of the LV system and would be solidly connected to Earth at all times. For the single-phase transformers, one terminal would be designated as the neutral point and would again be solidly connected to Earth.

Generally, a star connection is used where you need a neutral and two separate voltages, like our distribution system. Delta connection is generally preferred where the neutral conductor is not needed like for transmission of high-voltage power.

The voltage in star wiring is √3 higher than in the delta wiring, i.e. a motor specified as the 40S has a nominal voltage of 400 V in star wiring or 400 V or √3 = 230 V in delta wiring, a motor specified as 70S has been a nominal voltage of approx. 690 V in star wiring and 690 V or √3 = 400 V delta wiring.