In three-phase circuits, which voltage is typically used in voltage drop calculations?

• A. Line-to-neutral voltage
• B. Line-to-line voltage
• C. Peak voltage
• D. Average voltage

Answer: (B)

In a three-phase system, voltage drop is determined by the voltage difference between the two conductors that form the path of the load, which is the line-to-line voltage. This is the actual voltage that a load connected between two lines experiences, and it’s the quantity that drives power and sets the drop along a feeder. In a balanced Y system, line-to-line voltage is related to line-to-neutral voltage by a factor of sqrt(3), linking the phase voltages to the overall bus voltage. Since impedance and currents are evaluated using RMS values, the drop calculation uses the RMS line-to-line voltage rather than peak or average values. If a load were connected from a line to neutral, you’d use the line-to-neutral voltage, but for typical three-phase drops between lines, line-to-line is the standard reference.