Does Moving Production to a Different Factory Require Retesting?

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Answer first, because this question usually arrives with a shipment date attached: moving production to a different factory does not, by itself, invalidate a test report. What decides whether you need to test again is whether the product built at the new site is still the same product that was tested - same circuit, same critical components, same enclosure, same firmware, same antenna and cable arrangement. The factory address is not a test parameter. The construction is.

That said, the address is rarely the only thing that moves. In most transfers we review, three or four other things move with it, and those are what turn a paperwork exercise into a retest.

What a test report actually records

A test report is a record of measurements made on a specific sample, built a specific way, assessed against a specific edition of a standard, on specific dates. It documents the sample's construction in words and photographs, lists the critical components, records the operating modes selected as worst case, and states the results. It does not certify a factory, a production line, or a quality system, and it carries no legal expiry date.

This is why the same report can survive a factory move and fail to survive a component substitution. The report is evidence about a design as built. Move the building, keep the build, and the evidence still describes the product. Change the build, and the evidence describes something that is no longer being made.

The distinction between a report and the legal documents built on top of it matters here, and it is worth restating: a report is third-party evidence, a Declaration of Conformity is your own legal statement, and a certificate is a document issued by a body for a named holder. Only the third one tends to have an address printed on it - the differences are set out in test report vs certificate.

Split the question into three

"Do I need to retest?" is usually three questions wearing one coat. Answer them separately and the project scope writes itself.

1. Is the product still the same? Compare the new build against the tested construction: schematic, PCB layout, BOM and critical component list, firmware version, antenna type and position, cable routing, enclosure material and coating, and the external adapter. Any difference here is a technical question.
2. Do the documents still name the right parties? The Declaration of Conformity, the label, the technical file, and any certificate issued to a named holder. A factory move can leave the product identical and the paperwork wrong.
3. Does the scheme, or the buyer, require a site-specific approval? Some certification schemes register the factory itself. Some retailers and platform compliance teams treat a production site change as a change notification regardless of what the law requires.

Most arguments about retesting are question 2 or 3 being answered with a test. That is an expensive way to fix a document.

What travels with the product, and what stays with the factory

Travels with the product (tested construction)	Stays with the factory (process)
Circuit design, PCB layout, stack-up	Solder paste, reflow profile, operator training
Critical component list: transformer, X/Y capacitors, fuse, varistor, optocoupler, switching devices, cells	Incoming inspection rules, supplier approval process
Firmware version, RF output settings, operating modes	Programming fixture and calibration routine
Antenna type, position, cable length and routing	Assembly sequence, torque values, cable dressing discipline
Enclosure material, coating, shielding, vents	Mould condition, gate location, colour batch
External adapter model and rating	Which adapter the line actually packs

Everything in the left column can trigger a retest. Everything in the right column is a process control question - important for consistency, but not something a type test measures.

What actually changes in a factory move

In practice, the left column changes more often than the right one stays the same. These are the five shifts we see most.

Critical components get re-sourced. The new factory has its own approved vendor list, and a transformer, X2 capacitor, varistor or fuse that is "equivalent" on paper can differ in leakage current, creepage distance, surge withstand, or conducted emissions. A power supply that passed with one transformer frequently fails conducted emissions at 150 kHz to 500 kHz with the next one, without any change to the circuit. This is the same mechanism as any other component change after certification, and it is judged the same way: by whether the part is critical for the clauses that were tested.

The PCB fabrication changes. Identical Gerber files, different laminate supplier, copper weight or surface finish. Usually harmless, occasionally not - especially for RF boards, where dielectric constant and soldermask thickness shift matching and radiated behaviour slightly.

Tooling is new. A new injection mould means different gate locations, different shrinkage, sometimes a different flame-retardant grade because the previous resin is not available locally. An enclosure that used to have conductive coating on the inside and now does not is an EMC change, not a cosmetic one.

Assembly and cable dressing change. Hand-soldered shields, grounding screw torque, and the way a ribbon cable is folded inside the case. Cable routing is one of the most common causes of a radiated emissions shift in otherwise identical products, because the cable is part of the antenna whether or not the designer intended it to be.

Firmware and calibration drift. A new programming fixture, a different build, a region setting applied on the line. Output power, duty cycle and the set of enabled radio modes have to stay inside what was tested. A product that ships with an extra band enabled is not the product in the report.

There is a sixth, less technical one: the adapter. If the new factory sources its own power adapter because the old one was supplied by the previous plant, the tested configuration has changed, even though nothing about the product itself did.

By scheme: does the factory appear on the document?

Route	Is the factory named?	What a site change normally requires
EU CE, self-declaration (EMC, LVD, RoHS)	No. The DoC names the manufacturer or authorised representative.	Update the technical file and manufacturing description; retest only if the construction changed.
EU RED with an EU-type examination certificate	The certificate is issued to a named manufacturer.	A different legal manufacturer means a new application - an EU-type examination certificate is not transferable by reprinting it.
FCC SDoC	No. The responsible party signs the statement.	Keep the test records and the compliance statement current; no site-specific filing exists.
FCC ID (certification)	No. The grant names the grantee, not the plant.	No new FCC ID for a site change alone. A different grantee, trade name or model identity falls under the change-in-identification rules.
UKCA	No, same logic as CE for GB.	Update the UK declaration and technical file; retest only on construction change.
CB Scheme certificate	Yes - applicant, manufacturer and factory are all listed.	A change of factory name or address is normally handled as an amendment to the existing certificate. A genuinely different plant is assessed on whether product and critical components are unchanged.
CCC, BIS and similar national licences	Yes. The licence is tied to the manufacturing premises.	A new site needs its own application and factory inspection. The old certificate does not follow the product.

The pattern is simple: schemes that regulate the product's design do not care where it is built. Schemes that license a production site do. If your product holds both kinds of document, a factory move splits your file in two - one half needs a memo, the other half needs a new application.

The documents to update even when no retest is needed

This is the part that gets skipped, and it is the part a market surveillance authority or a buyer's compliance team will actually look at.

• Technical file / technical documentation. Update the manufacturing description and the drawings that reference the production process. The file has to describe the product as it is actually made, not as it was made two years ago.
• Declaration of Conformity. If the manufacturer's name or address changed, the declaration changes. The list of standards normally does not.
• Label and packaging. Manufacturer address, importer details where required, country of origin, and the model designation. A label that still shows the old plant address is a labelling non-conformity even when the product is fine.
• Buyer file. Most retail and platform compliance teams want a change notification, a first article inspection report, and the new site's quality certificate. None of that is a certification document, but shipping without it causes more delays than testing does.

Four transfers we have seen

Same design, new assembly plant, same component vendors. The brand owner moved final assembly to a second plant in the same province, kept the PCB supplier and all critical parts, and changed nothing in firmware. Comparison of BOM, Gerber files, firmware version strings and enclosure photos showed no delta. No retest. The work was a technical file update, a new label revision, and a change notification to two buyers.

A transformer that was not equivalent. A power adapter moved to a new factory that substituted the transformer for a lower-cost unit with the same rated output. Safety spacing passed, but conducted emissions failed in the lower band. The fix was a small input filter change plus a partial retest of the emissions clauses - not a full re-certification, because the failure was confined to one measurement.

An RF product with a new enclosure coating. A wireless device changed plants and the new tooling dropped the internal conductive coating to save a process step. Radiated spurious emissions moved enough to matter. Nothing on the BOM flagged it, because the coating was part of the moulding process, not a line item.

A certificate held by the factory. The brand owner had been relying on a certificate issued to the previous factory, the arrangement described in using a supplier's report for your own brand. When production moved, the certificate did not move with it, and the buyer found out during a supplier audit. The product was unchanged, the test data was still valid, but the certificate had to be reissued to the new holder - which meant a new application, not a memo.

When I tell clients not to test

Retesting is not a default good. There are cases where the right advice is to spend the money on something else.

• Nothing in the tested construction changed. If the BOM, layout, firmware, antenna and enclosure are identical, a new test would reproduce the old results at your expense. Fix the document instead, and keep the delta declaration on file.
• The new line is not stable yet. Testing the first few hand-built units off a new line proves very little, and a failure at that stage is often a process problem rather than a design problem. Run first article inspection and a small pilot batch first; test a sample that represents what you will actually ship.
• The only delta is a component the standard treats as non-critical. A documented delta assessment, signed by the laboratory, is cheaper and just as defensible as a full retest - provided the component really is outside the critical list for that standard.
• The deadline cannot fit a full programme. Then the honest answer is to ship against the existing report only if the construction genuinely is unchanged, and to agree a reduced scope in writing before the shipment leaves. Shipping first and testing later is the option that turns a compliance question into a recall question.

What to send for a transfer review

1. The existing report and certificate set, with the holder named on each document.
2. A BOM comparison between the old and new build, with changed lines highlighted.
3. The critical component list from the original report, and the corresponding parts at the new site.
4. PCB Gerber files or a layout comparison, plus stack-up if the fabrication source changed.
5. Firmware version and the list of enabled radio modes and output settings.
6. Photos of the new build inside and out, including cable routing and any shielding or coating.

With those six items, a transfer review is usually a short piece of work. Without them, the only safe answer anyone can give is "test everything again", which is not advice, it is a hedge.

The short answer

A factory move only invalidates a test report if the product built at the new site no longer matches the construction described in that report. The report documents a sample, its critical components, its firmware and its operating modes - not the address of the building. Under EU self-declaration routes (EMC, LVD, RoHS) and under FCC SDoC or an existing FCC ID, there is no site-specific approval to re-apply for, so the work is a technical file update and a label revision unless the construction changed. Under schemes that license the premises - CCC, BIS and similar national marks - the certificate belongs to the factory and a new site needs its own application and factory inspection. CB certificates sit in between: the factory is named, and a change of factory name or address is normally handled as an amendment rather than a new test. In every case, the practical trigger for retesting is not the move, it is what moved with it: a re-sourced transformer, a new mould without its conductive coating, a different cable route, or a firmware build that enables a mode nobody tested.

We run these reviews as a comparison rather than a test programme: the old construction against the new one, line by line, with a written statement of which test clauses are affected and which are not. Where the answer is "no retest", you get that in writing for your buyer. Where the answer is a partial retest, the scope is limited to the clauses the delta actually touches - conducted and radiated emissions for a supply change, safety spacing and abnormal operation for a transformer or enclosure change, output power and spurious emissions for an RF or antenna change. The same logic covers the other markets in the file: an FCC grant, a UKCA declaration and a CB certificate each get a separate line in the assessment, because a factory move does not affect them in the same way.

That written scope is usually the document that settles the discussion with a buyer or an auditor, and it is worth more than a fresh full report that answers questions nobody asked. All of it sits inside our testing and certification programme, which is built around comparing a product against its documented construction rather than re-testing it by default.