What voltage should a meter indicate when placing the leads on phase A and ground of a 480/277, 3-phase, 4-wire system?

What voltage should a meter indicate when placing the leads on phase A and ground of a 480/277, 3-phase, 4-wire system?

• A. 277
• B. 480
• C. 0
• D. 240

Answer: (A)

In a 480Y/277V three-phase four-wire system, the voltage from any phase to neutral (which is bonded to ground at the service) is 277 V. This follows the relationship V_LL = sqrt(3) × V_LN, so the phase-to-neutral (or phase-to-ground) voltage is V_LN = 480 / sqrt(3) ≈ 277 V. Since you're measuring between phase A and ground, the meter should read about 277 volts. The 480 V reading would be for a phase-to-phase measurement, not phase-to-ground; 0 V or 240 V don’t apply to this configuration.

In a 480Y/277V three-phase four-wire system, the voltage from any phase to neutral (which is bonded to ground at the service) is 277 V. This follows the relationship V_LL = sqrt(3) × V_LN, so the phase-to-neutral (or phase-to-ground) voltage is V_LN = 480 / sqrt(3) ≈ 277 V. Since you're measuring between phase A and ground, the meter should read about 277 volts. The 480 V reading would be for a phase-to-phase measurement, not phase-to-ground; 0 V or 240 V don’t apply to this configuration.