Harmonised standard

A harmonised standard is a European standard (EN) developed by CEN/CENELEC under a Commission standardisation request whose reference the Commission has published in the Official Journal in support of a piece of EU law — for rail, the Interoperability Directive (EU) 2016/797. Publication triggers the presumption of conformity: applying the cited standard is presumed to satisfy the essential requirements the citation covers, which reverses the burden of proof in conformity assessment and is why suppliers care intensely about the OJ list. Three practical subtleties follow. First, the presumption attaches to the exact edition cited — EN 45545-2 is cited in its 2013+A1 edition, so building to the newer 2020 edition means demonstrating equivalence rather than presuming it. Second, an EN standard that is not cited is simply voluntary — excellent engineering practice, but carrying no legal presumption. Third, citations move: EN 50128 and EN 50657 were delisted when EN 50716 was cited in 2025. Each standard's page in this library shows its current OJ-cited editions.