In a 480Y/277 three-phase system, what is the voltage between phase A and phase B?

In a 480Y/277 three-phase system, what is the voltage between phase A and phase B?

• A. 277
• B. 480
• C. 0
• D. 120

Answer: (C)

In a 480Y/277 system, the 277 V is the line-to-neutral voltage, while the voltage between two different phases is the line-to-line voltage. For a wye system, V_LL = sqrt(3) × V_LN, so 277 V × sqrt(3) ≈ 480 V. Therefore the voltage between phase A and phase B is about 480 V. The 277 V option would be the voltage from a phase to neutral, and 0 V would only occur if you measured the same conductor, which isn’t the case for two different phases.

In a 480Y/277 system, the 277 V is the line-to-neutral voltage, while the voltage between two different phases is the line-to-line voltage. For a wye system, V_LL = sqrt(3) × V_LN, so 277 V × sqrt(3) ≈ 480 V. Therefore the voltage between phase A and phase B is about 480 V. The 277 V option would be the voltage from a phase to neutral, and 0 V would only occur if you measured the same conductor, which isn’t the case for two different phases.