Is replacing a programmable logic controller a substantial modification?

Not automatically: the criterion is threefold — the modification was not foreseen by the manufacturer, it affects safety, and it requires new protective measures. A replacement with an identical component is not substantial; redesigning the safety logic can be. What is always required: a written, dated, and signed assessment, intervention by intervention.

What risk does someone take who retrofits and does nothing?

If they have in fact carried out a substantial modification, they are considered a manufacturer under the Regulation: technical documentation, essential requirements, EU declaration, marking, and the accompanying liability, particularly in the event of an accident. The lack of a documented assessment is itself the first failing.

Home / Guide

Article 3, point 16 · Article 18

The retrofit that makes you a manufacturer

Updated on 26 August 2026 · articles verified against the official text

This is the blind spot of Regulation (EU) 2023/1230, which integrators, maintenance departments, and purchasers of retrofitted second-hand machinery discover too late. The text sets out a definition (Art. 3, point 16) and a consequence (Art. 18): a substantial modification is treated as a new placing on the market, and the person who carries it out is deemed to be a manufacturer, assuming all associated obligations: technical documentation, essential requirements, EU declaration, and CE marking.

The three cumulative criteria

A modification is substantial when it satisfies three cumulative conditions: it is made by physical or digital means after placing on the market and was not foreseen by the manufacturer; it affects safety by creating a new hazard or increasing an existing risk; and it necessitates new protective measures (guards, devices, or safety logic). Three "yes" answers = you are the manufacturer of the modified machinery.

Type of intervention	Probable interpretation
Replacement of a component with an identical one (same function, same characteristics)	Non-substantial: this constitutes maintenance. It should nevertheless be documented.
Replacement of the automation system with redesign of the safety logic	Strong indication of a substantial modification: mandatory assessment, technical documentation probable.
Addition of a station or a robot, line extension	Almost always substantial for the added scope, and often for the reconfigured assembly as a whole.
Increase in throughput, load, or speed beyond what was originally foreseen	Substantial if new protective measures become necessary.

The tool

Ask the question in the order of the legal text.

Six questions, the three criteria addressed one by one, a reasoned conclusion, and an assessment record to print and sign, demonstrating that the question was evaluated and resolved. Everything is computed directly in your browser.

Open the decision tree →

The safeguard: a systematic, traceable record

The risk is not in carrying out a retrofit, but in doing so without leaving an audit trail. The protective discipline fits onto a single page per intervention: description of the modification, the three criteria assessed one by one, reasoned conclusion ("substantial: yes / no"), date, and signature of the technical manager. If the line is crossed, technical documentation is drawn up properly and the machine returns to service with its declaration. If it is not, the signed sheet serves as your evidence, legally opposable to third parties, that the question was examined and resolved.

One does not become a manufacturer by modifying a machine, but by modifying it without documenting it in writing.

What we do for retrofitters

The assessment sheet integrated into the work-order workflow: every intervention is processed through it, and the outcome is versioned in the machine passport;
When it is substantial: the complete technical documentation structured according to Annex IV, the tests conducted and signed off by your staff based on the protocols provided, the draft EU declaration;
The modification log for each machine, retained alongside its versions: the audit trail that every machinery fleet lacks.

Assess my exposure — rapid diagnostic

Sources

Regulation (EU) 2023/1230, Art. 3, point 16 (definition), and Art. 18 (obligations in case of substantial modification) — EUR-Lex. Verified on 26.08.2026.