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

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

• A. 240
• B. 480
• C. 0
• D. 277

Answer: (D)

In a 3-phase 4-wire system that uses a wye (star) connection, the voltage from any phase to neutral is the phase voltage, which equals the line-to-line voltage divided by the square root of 3. For a 480/277 V system, the line-to-line voltage is 480 V, so the line-to-neutral voltage is 480 ÷ √3 ≈ 277 V. Therefore, measuring between phase A and neutral should read about 277 V (nominal). The 480 V reading would be the voltage between two phases, not phase to neutral; 0 V would only occur if there were no potential difference between the points being measured; and 240 V corresponds to different systems, not this one.

In a 3-phase 4-wire system that uses a wye (star) connection, the voltage from any phase to neutral is the phase voltage, which equals the line-to-line voltage divided by the square root of 3. For a 480/277 V system, the line-to-line voltage is 480 V, so the line-to-neutral voltage is 480 ÷ √3 ≈ 277 V. Therefore, measuring between phase A and neutral should read about 277 V (nominal). The 480 V reading would be the voltage between two phases, not phase to neutral; 0 V would only occur if there were no potential difference between the points being measured; and 240 V corresponds to different systems, not this one.