Conductors used from 2.4 kV up to 35 kV must be designed with much greater care than those used at lower voltages. Electrical stresses in the insulating material are the primary concern. For example, it would be disastrous for anyone to use conductors with 600-Volt insulation in a circuit subject to these voltage levels. 
Splicing and terminating must also be performed according to exacting standards.
Cable for medium and high-voltage systems must specify both the voltage and the nature of the system, whether ungrounded, impedance grounded, or solidly grounded. The cable manufacturer's recommendations for cable selection should be carefully followed.
These medium-voltage cables are quite costly, so particular care should be exercised to specify them with sufficient size that they do not become damaged by overheating. Operating temperature, total system short circuit current, and the length of time to clear a fault should all be conservatively specified.
Most of the wiring methods discussed under low-voltage systems can be used for medium-voltage systems with some minor changes. Uninsulated wire can be used outside of buildings, but the spacing between conductors and the spacing from buildings and other objects must be increased.
