The National Electrical Manufacturers Association (NEMA) published
ST 20-2014 Dry Type Transformers for
The reinstated and revised edition of NEMA ST 20 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 also covers transformers with or without accessories having ratings of 1.2 kV class, 0.25 kVA through 4000 kVA.
NEMA ST 20 is one of the few standards in the marketplace that specifically addresses sound levels for this particular type of transformer. The U.S. Army Corps of Engineers still references it in their criteria documents. Changes in the latest version include a single average sound level table, more alignment with IEEE (Institute of Electrical and Electronics Engineers), and a new appendix providing a brief introduction to U.S. efficiency regulations.
ST 20-2014 may be downloaded at no cost or purchased in hardcopy for $71 on the NEMA
NEMA is the association of electrical equipment and medical imaging manufacturers, founded in 1926 and headquartered in Rosslyn, Virginia. Nearly 400 members strong, its companies manufacture a diverse set of products including power transmission and distribution equipment, lighting systems, factory automation and control systems, and medical imaging and radiation therapy systems. Total U.S. shipments for electroindustry products exceed $100 billion annually.
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