NEMA ST 20:2014

This standards publication applies to single-phase and polyphase dry-type transformers (including autotransformers and non-current-limiting reactors) for supplying energy to power, heating, and lighting circuits and designed to be installed and used in accordance with the National Electrical Code®. It applies to transformers with and/or without accessories having ratings of 1.2 kV class, 0.25 kVA through 4000 kVA. Transformers not covered by this standard may be covered by NEMA TR 1. This standards publication applies to transformers, commonly known as general-purpose transformers for commercial, institutional and industrial use in nonhazardous locations both indoors and outdoors. The publication includes ratings and information on the application, design, construction, installation, operation, inspection, and maintenance as an aid in obtaining a high level of safe performance. These standards, except for those for ratings, may be applicable to transformers having other than standard ratings. These standards, as well as applicable local codes and regulations should be consulted to secure the safe installation, operation, and maintenance of dry-type transformers. Also included are unit substation transformers and transformers in distribution centers. This publication does not apply to the following types of specialty transformers: control, industrial control, Class 2, signaling, oil- or gas-burner ignition, luminous tube, cold cathode lighting, incandescent, mercury lamp, and instrument transformers.