When does a conversion become a substantial modification and need new CE marking?
New CE marking is required if the conversion creates a new hazard or increases an existing risk so much that it can no longer be safely controlled by simply adding safeguards. If a simple protective measure is sufficient, there is no substantial modification.
How does the assessment run step by step?
Which conversions are typically uncritical?
- Replacing wear parts and assemblies with parts identical in construction and function.
- Repair that restores the original condition.
- Adding non-safety-related periphery, such as lighting, extraction or labelling.
- Moving the machine to a different location without design changes; here the operating company's workplace risk assessment applies.
- Software updates from the manufacturer that leave the intended use and the safety functions unchanged.
Which conversions typically amount to a substantial modification?
- Increase in performance: higher speed, greater forces, higher throughput.
- Extension of the intended use, for instance new materials or new operating modes.
- Automation of a process previously carried out manually.
- Replacing the control system in a retrofit where the safety logic is rebuilt in the process.
- Adding a robot or handling device to an existing machine.
- Linking with other machines into a functional unit.
Who becomes the manufacturer after the conversion?
Whoever carries out or commissions the substantial modification and then puts the modified machine into service. In practice that is usually the operating company, less often a contracted plant builder.
The original manufacturer is no longer responsible for the modified machine. Their declaration of conformity relates to the condition at placing on the market and does not cover your conversion.
In concrete terms this means: a full risk assessment of the modified machine, updated technical documentation, adapted instructions for use, a new EU declaration of conformity and new CE marking, issued under your name. You can rely on the original manufacturer's documents as far as the unchanged part is concerned, but you need access to them.
What changes with the Machinery Regulation from 2027?
Substantial modification was not a term of the directive text but the result of interpretation, shaped largely by the German Federal Ministry of Labour's interpretation paper.
Machinery Regulation (EU) 2023/1230 defines it in law for the first time in Art. 3(16). In substance the assessment logic remains essentially the same; what is new is that digital modifications are expressly included.
For practice this means: from 20 January 2027 the assessment standard is worded more bindingly and is therefore easier to check. Anyone who has documented conversions only internally so far should move the process onto a footing that can serve as evidence.
Sources and standards
- Machinery Regulation (EU) 2023/1230, Art. 3(16): definition of substantial modification
- German Federal Ministry of Labour interpretation paper on substantial modification of machinery
- German Ordinance on Industrial Safety and Health (BetrSichV), Section 3
- EN ISO 12100: risk assessment and risk reduction
Editions of standards and their harmonised status change continuously. Check standard numbers and editions against the current list in the Official Journal of the EU before applying them. This article is a technical classification and does not replace legal advice.
Frequently asked questions
Do I need new CE marking after a retrofit?
Only if the retrofit amounts to a substantial modification. Simply replacing defective components with equivalent ones does not. Replacing the control system with a rebuilt safety logic usually does.
Does the operating company become the manufacturer when converting a machine?
Yes, if it carries out or commissions a substantial modification and then puts the machine into service. It then takes on all manufacturer duties for the modified machine.
Does the German interpretation paper still apply after 2027?
The paper relates to the Machinery Directive. From 20 January 2027 the legal definition in Art. 3(16) of the Machinery Regulation is decisive. The paper's assessment logic remains technically useful but does not replace assessment against the text of the regulation.
Do I have to remove the old CE marking?
With a substantial modification a new machine comes into being, marked under your name. The old rating plate must not give the impression that the original manufacturer is responsible for the current condition. Mark clearly who is responsible for which version.
What about simply extending the installation by one station?
Check two questions separately: is the extension in itself a substantial modification? And does the connection create an assembly of machinery? Both can apply independently of each other.
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This article was produced with AI assistance and reviewed for technical accuracy before publication. Editorial responsibility within the meaning of Art. 50(4) of the AI Act (EU) 2024/1689 lies with Heinrich Knutas.
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