The selection of the primary distribution system voltage is primarily a matter of economics: the combination of purchased power costs, required transformers and maintenance, and the cost of served equipment.
Primary voltages have nominal ratings for both system and equipment ratings similar to low voltage. MEDIUM SYSTEM AND EQUIPMENT VOLTAGES Table in Appendix page 241, lists medium system and equipment voltages derived from ANSI standards and manufacturers' listings.
2.4 kV Versus 4.16 kV
4.16 kV To 13.8 kV
