Voltage is produced across the transformer winding. ONLY one side of each of the windings is connected to the similar side of the other two windings. This junction of the common side of all three windings is called the neutral. The other sides of the three windings are the individual phases (A, B, & C). Usually the neutral is connected to the local ground.
If the non neutral side of the winding (phase A, B, or C) is connected to the same point as the neutral side(ground), THEN you have a ground fault. Depending on the total resistance of all the wires and connections and available power, you will probably have some fireworks until the overcurrent protection opens up the circuit.
Does that explain it?
