Low-Voltage Cables
"Transmission and Distribution Electrical Engineering" breaks down transmission and distribution cables into five separate categories. The most basic category is "low voltage." This includes cables used for telephone wires, as well as fire-retarded and resistant cables. These cables have the lowest maximum voltage of the four groups, ranging from 50 to 1,000 volts.
Medium-Voltage Cables
Medium-voltage cables --- which have a maximum capacity ranging from three to 7.2 kilovolts --- are the next class of transmission and distribution lines. These cables are typically used for solid dielectric and MI/MIND purposes.
High-Voltage Cables
The third class of transmission and distribution cables is high voltage. These power lines can carry a maximum voltage capacity of 10 to 150 kilovolts. While these cables can be used for the same purposes as low- and medium-voltage cables, their higher threshold makes them less cost-efficient than lower-grade wires. The main purposes of high-voltage wires include oil-filled cables, as well as gas-pressure or gas-insulated ducts.
Very High-Voltage Cables
Like medium- and high-voltage cables, very high-voltage lines are used for solid dielectric, oil-filled and gas-insulated ducts, but in situations where a higher maximum voltage is required. These cables have a maximum capacity of 150 to 300 kilovolts. Because of their very high-voltage capacity, these are typically transmission lines and not distribution lines.
