If voltage readings are taken on a 3 phase, 4 wire, 240 volt, delta connected service and two phases show 230 volts phase-to-ground while the third shows 50 volts, what is the probable cause?

• A. A partial ground or ground fault
• B. Load too great
• C. Incorrect transformer settings
• D. Incorrect wire size

Answer: (A)

In a 3-phase, 4-wire delta setup, the neutral is created from a center-tapped winding, and phase-to-ground voltages can shift if there’s any leakage to earth. When two phases read about the full system voltage to ground and the third reads a much lower value, it points to a leakage path to ground on that third phase. A high-impedance ground fault pulls the neutral reference toward that leg, so the faulted phase drops toward ground (about 50 V), while the other two phases stay near the expected line-to-ground voltage (around 230 V). This pattern is the telltale sign of a partial ground or ground fault on that leg. Other issues like overload, transformer setting errors, or wrong conductor size wouldn’t produce this specific unbalance to ground.