Which system commonly provides 277 V as the phase-to-neutral voltage?

Which system commonly provides 277 V as the phase-to-neutral voltage?

• A. 120/240 V
• B. 277/480 V
• C. 120/208 V
• D. 480 V delta

Answer: (B)

In a three‑phase system, the phase‑to‑neutral (line‑to‑neutral) voltage is the voltage from any one phase to the neutral point. In a wye (star) connection, the line‑to‑line voltage is √3 times the line‑to‑neutral voltage. So, if the line‑to‑line is 480 V, the line‑to‑neutral is 480 / √3 ≈ 277 V. That’s why a 480Y/277 V system provides about 277 V phase‑to‑neutral. This setup is commonly used for lighting and certain 277 V equipment. The other options don’t give 277 V to neutral: 120/240 V and 120/208 V systems provide 120 V to neutral (or 120 V/208 V line-to-line), and a 480 V delta configuration doesn’t have a standard neutral voltage of 277 V.

In a three‑phase system, the phase‑to‑neutral (line‑to‑neutral) voltage is the voltage from any one phase to the neutral point. In a wye (star) connection, the line‑to‑line voltage is √3 times the line‑to‑neutral voltage. So, if the line‑to‑line is 480 V, the line‑to‑neutral is 480 / √3 ≈ 277 V. That’s why a 480Y/277 V system provides about 277 V phase‑to‑neutral.

This setup is commonly used for lighting and certain 277 V equipment. The other options don’t give 277 V to neutral: 120/240 V and 120/208 V systems provide 120 V to neutral (or 120 V/208 V line-to-line), and a 480 V delta configuration doesn’t have a standard neutral voltage of 277 V.