Sourcing circuit-breaker trip units from China

Zero duty on qualifying trip-unit parts

Heading 8538 covers parts suitable solely or principally for the apparatus of headings 8535, 8536 or 8537. This guide concerns separate circuit-breaker trip units and their assemblies. Complete circuit breakers have different classifications. For the wider parts heading, see circuit-breaker operating mechanisms.

Read from the UK Trade Tariff on 1 October 2026, the supplied facts record 0% duty for goods from China across heading 8538. The electronic-assembly and other-parts lines used here have no listed anti-dumping or countervailing measures, suspensions or import controls. Zero customs duty does not remove import VAT; see UK import duty and VAT.

The table groups trip-unit variants under shared candidate codes. Electronic assemblies may fit 8538 90 91 89; other qualifying parts may fit 8538 90 99 99. These are not automatic classifications for every device called a trip unit. Confirm the commodity code using the function, construction, circuit diagram and intended breaker.

Specify the breaker interface and trip behaviour

Name the breaker manufacturer, frame, model and compatible trip-unit version. Specify thermal-magnetic or electronic operation, current sensing, auxiliary supply, mounting points, connectors and mechanical release interface. Agree the overload, short-circuit and earth-fault functions required, their adjustment ranges, time-current curves and acceptance tolerances. For electronic units, record firmware and settings, test connections and any communications functions.

Agree a test procedure with the breaker maker or a suitable laboratory. It should distinguish tests of the trip unit from tests proving that the complete breaker opens. Ask for calibration records tied to the supplied unit and test equipment, with results at the agreed settings and operating conditions. Arrange testing and certification around the exact unit and breaker combination.

For Great Britain, products imported for further manufacture are not considered placed on the market at that stage. A separately sold component can instead constitute a finished product and may require individual conformity assessment and marking. Establish the supply status before ordering. Where the Electrical Equipment (Safety) Regulations apply, check technical documentation, the declaration of conformity, CE or UKCA marking and importer identification.

For electronic versions, assess whether the electromagnetic compatibility rules apply; their scope covers equipment liable to generate electromagnetic disturbance, subject to exceptions. Hazardous-substance guidance distinguishes business-to-business components from finished equipment: an in-scope final assembly must comply, including its components. Request material evidence for the circuit board, solder, connectors and housing.

Worked duty example

Illustrative example, not a quote: 400 electronic trip-unit assemblies for breaker production, illustrative only under 8538 90 91 89, invoiced at £12,000 free on board, with £600 of freight and insurance to the UK. The customs value is £12,600. Duty at 0% is £0. Import VAT at 20% is charged on the customs value plus duty, £12,600, so it is £2,520. With no duty, the only import tax is the VAT, which a VAT-registered importer can usually reclaim. The import duty and VAT guide explains each step.

Inspection checklist

Identity: match the model, sensor rating, firmware where fitted, adjustment labels and batch identification to the approved sample and order.

Fit: trial-fit samples to the specified breaker; check mounting, connector keying, sensor connections and release engagement without forcing parts.

Trip performance: use the agreed injection procedure to compare pickup and operating times with the specified curves, then confirm breaker opening in the agreed assembly test.

Arrival condition: during quality inspection, check for cracked housings, bent pins, loose adjustments, corrosion and packing damage; match calibration records to the received units.

What goes wrong

A unit can fit the mounting space yet have the wrong sensor relationship, connector wiring or release travel. Incorrect settings or firmware can produce nuisance trips or fail to release the breaker when expected. Approve the exact combination and retain its drawings, settings and test results before accepting substitutes.

A display powering up or a test button operating does not establish the specified time-current behaviour. Calibration paperwork for another model also leaves the supplied batch unverified. Compare bulk samples with the approved configuration and investigate any mismatch before installation.

Cambridge China Bridge sources these products for UK businesses, checking the factory and the documents before shipment. See factory verification. For components and parts, see sourcing for manufacturers.