In a 208VAC, three-phase power source, what is the nominal voltage level from any phase to ground?

In a 208VAC, three-phase power source, what is the nominal voltage level from any phase to ground?

• A. 0 VAC
• B. 104 VAC
• C. 120 VAC
• D. 208 VAC

Answer: (C)

In a 208 V three-phase system that is wired as a wye with a grounded neutral, the voltage from any phase to ground is the phase-to-neutral voltage. The three-phase line-to-line voltage is related to line-to-neutral by V_LL = √3 × V_LN. So V_LN = V_LL / √3 = 208 / 1.732 ≈ 120 V. That’s why the nominal voltage from a phase to ground is about 120 VAC. The other numbers don’t apply here: 0 VAC would only occur if that phase were effectively tied to ground by a fault; 104 VAC isn’t a standard value for this configuration; and 208 VAC is the line-to-line voltage, not phase-to-ground.

In a 208 V three-phase system that is wired as a wye with a grounded neutral, the voltage from any phase to ground is the phase-to-neutral voltage. The three-phase line-to-line voltage is related to line-to-neutral by V_LL = √3 × V_LN. So V_LN = V_LL / √3 = 208 / 1.732 ≈ 120 V. That’s why the nominal voltage from a phase to ground is about 120 VAC. The other numbers don’t apply here: 0 VAC would only occur if that phase were effectively tied to ground by a fault; 104 VAC isn’t a standard value for this configuration; and 208 VAC is the line-to-line voltage, not phase-to-ground.