In a 120/208 V, 3-phase, 4-wire system, what is the voltage from phase A to neutral?

In a 120/208 V, 3-phase, 4-wire system, what is the voltage from phase A to neutral?

• A. 120
• B. 208
• C. 277
• D. 240

Answer: (A)

In a 120/208 V, 3-phase, 4-wire system the neutral is the common point of a wye-connected transformer, so each phase-to-neutral voltage is the phase (or "line-to-neutral") voltage. The line-to-line voltage is higher and relates to the phase voltage by VLL = √3 × VPH. Here the line-to-line is 208 V, so the phase-to-neutral voltage is 208 ÷ √3 ≈ 120 V. That means the voltage from phase A to neutral is 120 V. Other numbers won’t fit this setup: 208 V is the voltage between two phases, not phase-to-neutral; 277 V is typical for a 480Y/277 V system; 240 V is not the phase-to-neutral voltage for this 120/208 configuration.

In a 120/208 V, 3-phase, 4-wire system the neutral is the common point of a wye-connected transformer, so each phase-to-neutral voltage is the phase (or "line-to-neutral") voltage. The line-to-line voltage is higher and relates to the phase voltage by VLL = √3 × VPH. Here the line-to-line is 208 V, so the phase-to-neutral voltage is 208 ÷ √3 ≈ 120 V. That means the voltage from phase A to neutral is 120 V.

Other numbers won’t fit this setup: 208 V is the voltage between two phases, not phase-to-neutral; 277 V is typical for a 480Y/277 V system; 240 V is not the phase-to-neutral voltage for this 120/208 configuration.