According to IEEE C57.

The correct answer isA, manufacturer. IEEE C57.12.00 requires that each transformer be provided with adurable metal nameplateattached by themanufacturer. This requirement exists because the nameplate is a permanent identification and rating record for the transformer. It contains critical information such as manufacturer identity, serial number, kVA rating, voltage ratings, frequency, impedance, cooling class, temperature rise, and other essential design and operating data. Since this information originates from the transformer design and production records, responsibility for affixing the plate belongs to the manufacturer, not to the owner, purchaser, or inspector.

From an API source inspection perspective, the nameplate is an important verification point during final inspection. The source inspector checks that the plate is present, permanently attached, legible, and consistent with the approved data sheet, purchase order, drawings, and test records. A missing, incorrect, or improperly marked nameplate can create traceability problems and may result in nonconformance. Therefore, the correct party responsible for affixing the durable metal nameplate is themanufacturer, makingAthe verified answer.