What is the phase-to-ground voltage in a 480V transformer?

What is the phase-to-ground voltage in a 480V transformer?

• A. 277 volts
• B. 480 volts
• C. 240 volts
• D. 120 volts

Answer: (A)

In a 480 V transformer that is wired in a wye (star) arrangement with a grounded neutral, the voltage from each phase to ground equals the phase-to-neutral voltage. The relationship between line-to-line and line-to-neutral is V_LL = sqrt(3) × V_LN. So V_LN = 480 / sqrt(3) ≈ 277 V. Therefore each phase to ground is about 277 V. This 480Y/277 V setup is common for providing 277 V to lighting and other equipment. If the transformer were delta-connected with no neutral, there wouldn’t be a defined phase-to-ground voltage in the same way.

In a 480 V transformer that is wired in a wye (star) arrangement with a grounded neutral, the voltage from each phase to ground equals the phase-to-neutral voltage. The relationship between line-to-line and line-to-neutral is V_LL = sqrt(3) × V_LN. So V_LN = 480 / sqrt(3) ≈ 277 V. Therefore each phase to ground is about 277 V. This 480Y/277 V setup is common for providing 277 V to lighting and other equipment. If the transformer were delta-connected with no neutral, there wouldn’t be a defined phase-to-ground voltage in the same way.