Electrical, mechanical, and safety requirements of ventilated, non-ventilated, and sealed dry-type distribution and power transformers or auto transformers (single and polyphase, with a voltage of 601 V or higher in the highest voltage winding) are described.

This revision will include the addition of reference to NEMA Std ST-20 definitions and terminology. Major change in partial discharge requirements, change in testing requirements of tables 3A and 3B, additional information on flame retardation seismic cautions and minimum temperature for cast resin transformers.

This revision will fill a void that now exists in reference with similar items in NEMA standards. Improved partial discharge requirements, update testing guidelines, add suggestions on minimum temperature for cast resin transformers and make the entire standard easier to read and understand with the addition of definition and terminology.