In a 120/208 V three-phase system, what is the voltage between phase A and neutral?

In a 120/208 V three-phase system, what is the voltage between phase A and neutral?

• A. 120
• B. 208
• C. 277
• D. 0

Answer: (A)

In a 120/208 V three-phase system wired in a wye, the voltage from any phase to neutral is 120 V. This comes from the relationship between line-to-line voltage and phase (line-to-neutral) voltage: V_LL = √3 × V_phase. With a line-to-line voltage of 208 V, the phase-to-neutral voltage is 208 / √3 ≈ 120 V. So the voltage between phase A and neutral is 120 V. The 208 V figure is the voltage between two phases, not from a phase to neutral. 277 V would belong to a different system (277/480 V), and 0 V would only occur if the phase were tied directly to neutral.

In a 120/208 V three-phase system wired in a wye, the voltage from any phase to neutral is 120 V. This comes from the relationship between line-to-line voltage and phase (line-to-neutral) voltage: V_LL = √3 × V_phase. With a line-to-line voltage of 208 V, the phase-to-neutral voltage is 208 / √3 ≈ 120 V. So the voltage between phase A and neutral is 120 V. The 208 V figure is the voltage between two phases, not from a phase to neutral. 277 V would belong to a different system (277/480 V), and 0 V would only occur if the phase were tied directly to neutral.