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IEEE C57.12.38-2014
IEEE Standard for Pad-Mounted-Type, Self-Cooled, Single-Phase Distribution Transformers 250 kVA and Smaller: High Voltage, 34 500 GrdY/19 920 V and Below, Low Voltage, 480/240 V and Below
Certain electrical, dimensional, and mechanical characteristics are covered in this standard, and certain safety features of single-phase, 60-Hz, mineral-oil-immersed, self-cooled, pad-mounted, compartmental-type distribution transformers are taken into consideration. These transformers are rated 250 kVA and smaller with high voltages of 34 500 GrdY/19 920 V and below and with low voltages of 480/240 V and below. These transformers are generally used for step-down purposes from an underground primary cable supply. The connector, bushing, and terminal arrangements for radial or loop feed systems are covered in this standard. The electrical and mechanical requirements of any accessory devices that may be supplied with the transformer are not covered in this standard.
Institute of Electrical and Electronics Engineers [ieee]