This standard is intended to set forth characteristics relating to performance, limited electrical and mechanical interchangeability, and safety of the equipment described, and to assist in the proper selection of such equipment.1.2 This standard describes certain electrical and mechanical characteristics and takes into consideration certain safety features of 60-Hz, two-winding, three phase, sealed dry-type transformers rated 501 kVA and larger, generally used for step-down purposes.Specific rating combinations are described in the range from 750 to 5000 kVA inclusive, with high-voltage 2400 to 34 500 volts inclusive and low-voltage 208Y/120 to 4160 volts inclusive.1.3 This standard does not apply to other types of transformers, such as specialty, ventilated dry-type, pad-mounted dry type, liquid immersed, instrument, regulating, furnace, mine, and rectifier transformers.1.4 When this document is used on a mandatory basis, the word shall indicates mandatory requirements, and the words