In a triple phase system, metering from one phase to another, how many volts should there be?

In a triple phase system, metering from one phase to another, how many volts should there be?

• A. 110 volts
• B. 208 volts
• C. 220 volts
• D. 240 volts

Answer: (C)

In a three-phase system, measuring from one phase to another gives the line-to-line voltage. For a wye-connected setup, the line-to-line voltage equals the phase-to-neutral voltage multiplied by the square root of three. If the phase voltage is 127 volts (a common configuration), the line-to-line voltage is 127 × 1.732 ≈ 220 volts, so you’d read about 220 volts between any two phases. If you were in a 120/208V system, you'd expect about 208 volts between phases; in a 120/240V system, about 240 volts. A measurement of 110 volts would not be between two phases in these typical configurations, but rather between a phase and neutral.

In a three-phase system, measuring from one phase to another gives the line-to-line voltage. For a wye-connected setup, the line-to-line voltage equals the phase-to-neutral voltage multiplied by the square root of three. If the phase voltage is 127 volts (a common configuration), the line-to-line voltage is 127 × 1.732 ≈ 220 volts, so you’d read about 220 volts between any two phases.

If you were in a 120/208V system, you'd expect about 208 volts between phases; in a 120/240V system, about 240 volts. A measurement of 110 volts would not be between two phases in these typical configurations, but rather between a phase and neutral.