What the standard governs
EN 50155 is the standard for electronic equipment installed on rolling stock. It does not describe a product: it describes the conditions in which that product must keep working, and how this has to be demonstrated.
Its scope is broad and specific at once. It governs power supply — the nominal battery voltage, the admitted excursion around it and the supply interruptions the equipment must ride through without rebooting, all declared by class. It governs the ambient temperature of the installation point, again by class: equipment in the cab and equipment under the car body do not see the same environment and do not carry the same class. It governs insulation, cooling, required documentation and the tests that close the loop: type tests first, then routine tests.
The practical point is this: the class is part of the compliance. Equipment complies with EN 50155 in a temperature class and in an interruption class, and those are what must be compared with the installation point — not the standard's number.
What the standard delegates to others
This is where specifications go wrong. Three families of requirements that everyone assumes are included actually live in separate standards, with separate tests and separate reports:
- Electromagnetic compatibility answers to
EN 50121-3-2, the part of the EN 50121 series dedicated to on-board apparatus. EN 50155 equipment without an EN 50121 report has not demonstrated that it can live alongside the rest of the train. - Fire behaviour answers to
EN 45545-2, which classifies materials and components by hazard level according to vehicle type and operation. It is a qualification on materials, not on electronics: enclosures, cables and plastics. - Shock and vibration answer to
EN 61373, which distinguishes categories depending on where the equipment is mounted — on the body, on the bogie or on the axle. These are wildly different mechanical environments, and the wrong category is a failure that shows up after months in service.
None of the three is optional when the specification calls for it, and none is implied by the first.
Four questions that settle it
Before putting a reference in a quotation, four questions do more than any datasheet:
- In which temperature class is compliance declared, and does it match the point where the equipment will be mounted?
- Which supply interruption class does it withstand, and can the downstream system tolerate a reboot if that class is not enough?
- Does the test report exist, or only the declaration? "Designed to" and "tested to" are different sentences, and they carry different weight in a tender.
- Are EMC and fire covered by their own reports, or is EN 50155 being assumed to include them?
How this reads in the catalogue
A technical catalogue can do one thing well: say which references declare which qualification, and keep the three standards separate instead of melting them into a single "railway" label. That is exactly what the table below shows — the figures are current, read from the catalogue as the page loads.
The gap between the three rows is not a catalogue defect: it is the market. EN 50155 is declared widely, on-board EMC and fire behaviour far less, because they require more expensive testing and get qualified when the project demands it. When all three appear in a specification the field of possible references narrows sharply — and that is the moment to talk to our engineering desk rather than to a filter.
