An autotransformer uses a single winding with a common electrical connection between primary and secondary circuits, while an isolation transformer uses separate, magnetically coupled windings with no direct electrical connection. This design difference can place them under distinct HTS subheadings within the broader transformer heading, affecting applicable duty rates and any trade-remedy exposure. Manufacturer datasheets confirming winding configuration are the key supporting document.

The HTS schedule subdivides transformers by kVA rating at several breakpoints, and the applicable subheading — and therefore the duty rate and any AD/CVD order scope — can shift significantly depending on rated capacity. Importers should obtain the transformer's nameplate kVA rating from the manufacturer and map it to the precise HTS subheading before filing entry, rather than relying on a general category classification.