Unrated transformers fall under 8504312000, the dedicated line for transformers at or below 1 KVA that carry no rated capacity marking. Importers should document the absence of a rating on the commercial invoice and technical specs. If a transformer is capable of being rated but simply lacks a nameplate, CBP may request engineering data to confirm it does not exceed 1 KVA; having that documentation ready at entry avoids delays.

Transformers (8504.31) transfer electrical energy between two or more circuits through electromagnetic induction, typically with a defined turns ratio and separate primary and secondary windings. Inductors and chokes (8504.50) are single-winding devices used primarily for energy storage, filtering, or impedance control rather than voltage transformation. When a component performs both functions, classification follows the principal function, and a binding ruling from CBP may be warranted for borderline designs.