This standard is intended to set forth characteristics relating t o performance, limited electrical and mechanical interchangeability, and safety of the equip- ment described, and to assist in the proper selection of such equipment.

This standard describes certain electrical and me- chanical 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 t o 34 500 volts inclusive and low-voltage 208Y/120 t o 4160 volts inclusive.

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.

When this document is used on a mandatory basis, the word “shall” indicates mandatory requirements, and the words “should” and “may” refer to matters that are recommended and permissive, respectively, but not mandatory.

NOTE: The. Foreword of this standard describes the circum- stances under which the document may be used on a manda- tory basis.

Part I of this standard describes basic electrical and mechanical requirements. Part II describes other requirements or alternatives which may be specified for some applications.