Three-phase systems are prevalent in many power distribution systems. This is because 3-phase systems have built in efficiencies for high power transmission systems. The word 3-phase means the system has three separate lines, spaced 120 degrees apart, where each line carries the identical voltage. This identical voltage is the line to ground voltage.
Find the kilovolt-amperes or "KVA" rating associated with the three-phase power distribution system. This is a standard rating associated with power distribution systems. Refer to system specification and/or circuit diagram. As an example, assume it's 20 KVA
Find the current rating, or "A", in units of amperes or amps. Refer to system specifications and/or circuit diagram. As an example, assume it's 30 amps.
Calculate the line to ground voltage using the formula: V (line to ground) = (KVA x 1000)/(I x 1.73). Continuing with the example:
V (line to ground) = (20 x 1000)/(30 x 1.73) = 20000/51.9 = 385.4 volts.