1. Failure of a primary-side phase. Here the star point can reach a higher potential in an uncontrolled manner. This can lead to the destruction of the consumers and the transformer.
2. Network form: Centre tap grounded. This is a typical network in North America. For example, there are voltages of 3x 480 V or 2x 240 V to the grounded center tap grounded.
3. Network form: Corner grounded delta. This is also a typical network form in North America and Asia. Here, 3-core cables are mostly used, whereby the green/yellow wire is used simultaneously for the outer conductor. This should not be confused with the cables used in European countries for single-phase networks!
4. In many applications the neutral conductor of the transformer is grounded. This is sometimes required in different standards and regulations. This earth connection would then have a direct contact to the “center tap grounded” or “corner grounded” point and thus a short circuit to the outer conductor!
5. Consumers on the output side, such as line filters, primary switching regulators, frequency inverters (DC-links) are usually equipped with Y capacitors. These cause the same error as described in point 4.