NEMA has published NEMA ST 20-2014 Dry Type Transformers for General Applications, which applies to single-phase and polyphase dry-type transformers for supplying power, heating, and lighting circuits, and designed to be installed and used in accordance with National Electrical Code®. Standard also covers transformers with or without accessories having ratings of 1.2 kV class, 0.25–4,000 kVA. NEMA ST 20 specifically addresses sound levels for these types of transformers.
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