Copper power distribution cables in a multi-storey building. Specially designed, interlocked steel armoured cables are available for the vertical risers.

Power cables for 5 kV to 46 kV installations are generally referred to as Medium-Voltage Power Cables. The first power cable of significant size was Vincent de Ferranti's famous 10,000-volt concentric cable, installed in London, England, in 1890. The development of electrical cables continued, and by the turn of the century 25 kV cables had been installed in Montreal and Chicago.

Copper Underground Electrical Transmission Systems, deals with the transmission of high-voltage power between the electrical generating stations and distribution systems, and for example, between substations. Medium-voltage cables are used for the distribution systems which spread from the substations to the consumers of the electrical power.

Beyond the medium-voltage systems, a final phase is necessary to place the power in the hands of the consumer. This involves such items as service entrance cables, the internal building wire circuits to the individual equipment, lights, appliances, and communication systems. They are covered in Copper Wire and Cable in Buildings.

A substation for a large manufacturing plant. Transmission lines bring power to the transformers which reduce it to medium voltages for distribution to the consumer.