Electric energy leaves the distribution substation and is distributed to different areas by distribution lines. Distribution lines on the high voltage side of the distribution transformer are called primary distribution lines or primaries. Those on the low-voltage side of the distribution transformer are called secondary distribution lines or secondaries.
Primary lines have voltages ranging from 2,300 to 39,000 volts. Common primary line voltages are 2,300, 4,160, 12,470, 13,800, 25,000 and 34,500 volts depending on which distribution voltages a utility uses. Common secondary line voltages are 120, 208, 240, 277 and 480 volts.