New IEEE Standard - Superseded. This IEEE Standards product is part of the C57 family on Power Distribution and Regulating Transformers. The performance, electrical and mechanical interchangeability as well as the safety of the equipment are covered. The proper selection of such equipment is established as a basis for use in this standard. Certain electrical, dimensional, and mechanical characteristics are described, and certain safety features of three-phase, 60 Hz, low-voltage 600 V and below network protectors are taken into consideration. They are used for automatically connecting and disconnecting a network transformer from a secondary spot or grid network.