For Machine Integrators: What Counts as a ‘Substantial Modification’ Under the New EU Machinery Regulation

Under Regulation (EU) 2023/1230, a modification is substantial if it is a physical or digital change made after the machine was placed on the market or put into service, not foreseen or planned by the manufacturer, which creates a new hazard or increases an existing risk and therefore requires new guards or protective devices that mean modifying the existing safety control system, or extra measures for stability or mechanical strength. If your organisation carries it out, Article 18 treats you as the manufacturer of the affected machinery.

Before you quote: which regime are you working under?

This article covers EU law, relevant when a UK integrator upgrades a cell or line in a factory inside the EU. The UK has its own machinery regime, which is not in the Kopik base, so nothing here should be read as describing work on UK sites. The Regulation applies from 20 January 2027; until then the Machinery Directive 2006/42/EC governs, under which, as the European Commission puts it, the rules applied when machinery was modified ‘to such extent that it becomes de facto new machinery’. EU-OSHA describes the Regulation as clarifying ‘substantial modifications’ compared with the Directive.

The five-part test in Article 3(16)

All five elements must be present. Use them as a scoping questionnaire with the customer:

The ‘foreseen or planned’ element connects to the Regulation's definition of lifetime, which includes the ‘physical or digital modifications foreseen by the manufacturer’. A change the original manufacturer designed for and documented is part of the machine's planned life, not a substantial modification.

Becoming the manufacturer: scope and duties

Article 18 makes whoever carries out a substantial modification a manufacturer, subject to Article 10. In practice that means:

• Designing the modified machinery to the essential health and safety requirements in Annex III, starting from a risk assessment.
• Compiling the Annex IV, Part A technical documentation.
• Applying the relevant Article 25 procedure: internal production control for machinery not in Annex I, stricter routes for Annex I categories.
• Declaring conformity ‘on its sole responsibility’, drawing up the EU declaration of conformity and affixing the CE marking.
• Keeping the file and declaration for at least 10 years (Article 10(3)).

Article 18 also limits the scope on assemblies: where the modification affects the safety of only one machine within an assembly, the obligations attach to that affected machinery, ‘as demonstrated in the risk assessment’. On a palletising line with four robot stations, a change confined to station three can stay confined to station three, if your risk assessment shows the interactions with the other stations are unaffected.

Three retrofit examples, read against the text

These are illustrations of how the criteria apply, not official interpretations; the European Commission has not yet published a guide to Regulation 2023/1230.

• New collaborative station on a fenced line. Opening part of the fence and adding presence-sensing devices that feed the existing safety logic engages point (a). Likely substantial. If the new safety function uses self-evolving machine learning, it also falls under Annex I, Part A and needs a notified-body route under Article 25(2).
• Higher-reach robot on the original pedestal. If the larger moment loads require reinforcing the pedestal or new floor anchoring the original manufacturer did not plan for, point (b) is engaged. Likely substantial.
• Gripper swap within the documented range. If the original instructions list the new gripper type and payload as supported, the change was foreseen. Outside the definition, though your own risk assessment still applies.

Digital modifications are now visible

The new essential requirements make undocumented software changes hard to hide. Annex III, section 1.1.9 requires machinery to identify its safety-relevant software and to collect evidence of legitimate or illegitimate interventions in the software or its configuration. Section 1.2.1 requires a tracing log of safety software versions uploaded after placing on the market, kept for five years after each upload and available to authorities on reasoned request. It also requires that the limits of safety functions are set in the manufacturer's risk assessment and that changes to settings which could lead to hazardous situations are prevented.

Practical consequence: version-control every safety parameter change, and record why each one does or does not meet the Article 3(16) test. You can check the precise wording against the sources in the robot and cobot machinery safety base, for example by asking what turns a change to an already-placed machine into a substantial modification rather than routine maintenance.

If the change is substantial: the conformity route

Article 18 sends the person carrying out the substantial modification to the procedures of Article 25(2), (3) or (4), exactly as for a new machine. Which one depends on the category of the affected machinery:

• Not listed in Annex I: internal production control, module A (Article 25(4)). Most robot cells fall here, unless they are or contain a listed category.
• Annex I, Part B (for example presses for the cold working of metals with manual loading or unloading, injection or compression moulding machinery with manual loading or unloading, protective devices designed to detect the presence of persons, logic units ensuring safety functions): module A only if harmonised standards or common specifications covering all relevant requirements were applied; otherwise EU type-examination plus conformity to type, full quality assurance or unit verification (Article 25(3)).
• Annex I, Part A (machine-learning safety functions with self-evolving behaviour): EU type-examination plus conformity to type, full quality assurance or unit verification, with a notified body (Article 25(2)).

Where a notified body is involved, its identification number follows the CE marking (Article 24(3)). The technical file must then reflect the modified machine: updated risk assessment, the list of applicable essential requirements with the protective measures taken, drawings and circuit schemes, test reports and the updated instructions for use (Annex IV, Part A). Keep it, with the new declaration of conformity, for at least 10 years (Article 10(3)); where relevant, the source code or programming logic of safety software must be made available to national authorities on a reasoned request.

Common mistakes

• Judging by cost or size of the job rather than by the hazard and the required response.
• Ignoring software: the definition expressly includes digital means.
• Assuming the whole line becomes yours: Article 18 lets the risk assessment limit the scope to the affected machinery.
• Relying on the Directive-era ‘de facto new machinery’ reasoning: from 20 January 2027, the Regulation, including Articles 3(16) and 18, is the applicable text.