Underground cable terminations for a 230 kV system. The connections to the overhead lines use outdoor-type potheads.

Copper-conductor underground transmission cables for 69 kV to 345 kV installations are generally referred to as High-Voltage Underground Transmission Cables. For installations above 345 kV (usually up to 735 kV) they are known as Extra-High-Voltage Underground Transmission Cables.

The most frequent installations for these cables are between generating and distribution systems, such as for example, between substations, for the main transmission of electrical power. The underground transmission system supplies electricity to the underground distribution network, which feeds industrial plants, office buildings, street lighting, residences, and so forth. Distribution and installation cables are covered in detail in Copper Medium-Voltage Power Cables and Copper Wire and Cable in Buildings.