The secondary side of a 480/277 volt to 208/120 volt transformer feeds a panelboard. The readings show varying phase-to-ground voltages and phase-to-neutral voltages around 120 V, with Neutral to Ground at 54 volts. Is the transformer operating normally? If not, what is a possible reason why?

• A. Everything is normal
• B. Neutral wasn't bonded in the transformer
• C. Phase A and neutral were swapped
• D. Transformer reverse wired (208 on high side, 480 on low side)

Answer: (B)

Neutral reference to earth is the reference point that keeps all voltages predictable on a wye secondary. In a 208/120 V secondary, the neutral conductor should be bonded to earth at a single point so the neutral sits at earth potential. When the neutral isn’t bonded, it can float and pick up voltage from capacitive coupling and loads, so you’ll often see the neutral-to-ground reading some nonzero value while phase-to-neutral voltages stay near 120 V. That nonzero neutral-to-ground value (54 V) signals that the system isn’t referencing earth as intended, which means the transformer isn’t operating with the proper neutral-ground bond.

So the issue isn’t the phase voltages themselves—they’re around the expected 120 V—but the lack of a solid neutral-to-earth bond. Bonding the neutral to ground at a single point, typically at the service equipment or transformer output, will reference the neutral to earth and bring neutral-to-ground voltage back to near zero.

Other scenarios would produce different patterns. Swapping a phase with neutral would show inconsistent phase-to-neutral readings, and reversing high/low sides would alter the expected relationships in a way not indicated by the observed measurements.