HS Codes and Customs Classification for Magnetic Components

Why the HS Code Decides Your Landed Cost

Two shipments of the same transformer can clear customs at different duty rates because the classification depends on function and construction, not on the product name your supplier uses. Getting the HS code right is therefore a pricing decision, not a paperwork formality: a misclassification can mean duty paid twice (once at import, once as a correction with penalty), or an origin claim that collapses at audit.

This guide covers the classifications that actually apply to magnetic components, the documents that support them, and the questions to settle with your customs broker before the first shipment.

The Codes That Apply

Common classifications for magnetic components (verify against your national tariff schedule)
Product	Heading	Subheading usually applied	Notes
Static converter (power supply, inverter, charger)	8504.40	8504.40.xx	Function defines the heading, not the presence of a transformer
Liquid dielectric transformer	8504.21 / 8504.22	by power rating	Rare in electronics supply chains
Dry-type transformer, ≤ 650 kVA	8504.31 / 8504.32	by rating	Covers most low-frequency transformer products sold as goods
Dry-type transformer, > 650 kVA	8504.33 / 8504.34	by rating	Distribution and traction class
Inductor / choke (ballast, reactor)	8504.50	—	Inductors presented separately from their equipment
Parts of transformers and inductors	8504.90	—	Ferrite cores, bobbins, assembled windings sold as parts

A ferrite core shipped on its own is generally a part under 8504.90, while the same core potted into a choke is a finished inductor under 8504.50. That distinction is the single most common classification dispute in this product family.

Documents That Make the Classification Defensible

A commercial invoice that describes the goods by function, with the material and rating, not with a marketing name.
A packing list matching the invoice line by line, including net and gross weight per line.
A bill of materials or technical datasheet supporting the classification argument.
Certificate of origin, with the criterion used under the applicable trade agreement stated explicitly.
For EU shipments: an EORI number on the importer side, and a statement of the product’s customs value basis.
For the US: an HTSUS code with the 10-digit statistical suffix, plus the manufacturer’s identification for Section 301 or 232 applicability.

Duty, Origin and the China Question

Most-favoured-nation duty on 8504.31 and 8504.50 lines is low in many markets, but additional duties may apply depending on origin and the trade measures in force at the time of entry. The origin question is not the country of the seller; it is where the goods were last substantially transformed. A transformer wound and assembled in China from Japanese cores is Chinese-origin for most purposes; a core made in China and potted in Vietnam may or may not change origin depending on the transformation criteria in the relevant agreement.

Because rates and measures change frequently, treat any specific rate in an article as illustrative and confirm with your broker at booking. What does not change is the need for a written origin analysis with supporting cost data, kept on file.

Valuation Points Buyers Get Wrong

Customs value is normally the transaction value plus the adjustments that law requires: tooling paid by the buyer, assists such as free-issue cores or wire, royalties as a condition of sale, and the cost of packing. A customer who supplies free cores to a Chinese winder and does not declare that assist has an undervaluation exposure that only surfaces at audit. Declare tooling as an assist at the time it is paid, and keep the amortization schedule with the entry file.

A Practical Checklist Before the First Shipment

Get a written classification opinion from your broker for each new part family, with the reasoning recorded.
Standardize the invoice description template across suppliers so line items are comparable.
Confirm whether cores, bobbins, and wound parts ship separately at any point — their codes differ.
Document origin with cost build-up, not with a supplier letter alone.
Record any assist (tooling, free-issue material) in the entry file.
Review the classification annually, and whenever the construction changes.