Which test result would most strongly indicate that the transformer's neutral is not bonded within the transformer?

Which test result would most strongly indicate that the transformer's neutral is not bonded within the transformer?

• A. Phase voltages to neutral are within normal range
• B. Neutral to Ground shows significant voltage
• C. Phase-to-phase voltages are balanced
• D. Phase voltages to ground show 0 V

Answer: (B)

The test logic hinges on how a transformer neutral is tied to ground. When the neutral is properly bonded to ground, they sit at essentially the same potential, so you expect the neutral-to-ground reading to be very close to zero. If the neutral is not bonded, or the bond is open, the neutral can float relative to ground and develop a noticeable voltage due to loads, leakage, and capacitances in the system. That neutral-to-ground voltage is the clearest sign that there isn’t a solid neutral-to-ground bond inside the transformer, because it directly reflects the presence or absence of a low-impedance bond. Phase voltages to neutral being within normal range doesn’t by itself prove a bond exists, since the neutral could still float to a nominal value under certain load conditions. Phase-to-phase voltages being balanced tells you about how evenly the loads are across phases, not about neutral bonding. Phase voltages to ground showing zero volts would be expected in a properly grounded system but doesn’t directly confirm the status of the neutral bond inside the transformer.

The test logic hinges on how a transformer neutral is tied to ground. When the neutral is properly bonded to ground, they sit at essentially the same potential, so you expect the neutral-to-ground reading to be very close to zero. If the neutral is not bonded, or the bond is open, the neutral can float relative to ground and develop a noticeable voltage due to loads, leakage, and capacitances in the system. That neutral-to-ground voltage is the clearest sign that there isn’t a solid neutral-to-ground bond inside the transformer, because it directly reflects the presence or absence of a low-impedance bond.

Phase voltages to neutral being within normal range doesn’t by itself prove a bond exists, since the neutral could still float to a nominal value under certain load conditions. Phase-to-phase voltages being balanced tells you about how evenly the loads are across phases, not about neutral bonding. Phase voltages to ground showing zero volts would be expected in a properly grounded system but doesn’t directly confirm the status of the neutral bond inside the transformer.