Phase-to-phase voltage, also known as line voltage, is an important concept in the study of electric power distribution. These quantities are generally calculated in a three-phase power system, which is the most commonly used electric power system in motors and large-scale electric power distribution. Calculating the line voltage ensures that the system is producing voltages within the acceptable range and will not overheat or fail. Calculating the phase-to-phase voltage is a fairly straightforward process if you have an adequate knowledge of circuits.
Label the voltages within your multiphase system. Three-phase systems are the most common multiphase systems, and have well known properties.
Determine the voltage between any single conductor and ground, called the phase voltage. If not already known, you may have to measure the voltage with a voltmeter. As an example, assume the measured voltage is 10 volts (V).
Multiply the phase voltage by 1.7321. The resulting number is the phase-to-phase voltage (or line voltage). In our example, multiplying 10 V by 1.7321 gives 17.321 V, which is the phase-to-phase voltage.
Take all necessary precautions when working with electrical power sources.