It depends more on regulations than in good practices. Get yourself a copy of NEC and of the standard IEE 141 (Electric Power Distribution for Industrial Facilities) or IEC 60364 (Electrical Building Installations)
Googling around you should be able to get some course notes on electrical installations. Cable sizing is one of the main subjects.
Don't worry. Cable sizing would be less than 100 pages to read. 150 at most.