This standard is intended for use as a basis for establishing the performance, interchangeability, and safety of the equipment covered and to assist in the proper selection of such equipment. This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of three-phase, 60 Hz, liquid-immersed, secondary network transformers with a three-position grounding switch, subway and vault types, rated 2500 kVA and smaller; primary 34 400 V and below; secondary 216Y/125 V and 480Y/277 V. A subway-type network transformer is one that is suitable for frequent or continuous submerged operation. A vault-type network transformer is one that is suitable for occasional submerged operation. Revision Standard - Superseded. This standard is intended for use as a basis for establishing the performance,interchangeability, and safety of the equipment covered and to assist in the proper selection of such equipment.