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What is NEMA ST 20?

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. The current specification was updated in 2014.

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