What Is EN 50155? A Quick Summary of the Rolling Stock Standard

EN 50155, often written EN50155, is the European standard for electronic equipment used on rolling stock: the computers, displays, controllers, power supplies and network devices fitted to trains, trams and metro vehicles. Its full title is Railway applications – Rolling stock – Electronic equipment, and it sets the operating conditions that equipment must survive on board, including temperature, humidity, supply voltage variation, power interruptions, shock and vibration, electromagnetic compatibility, insulation and fire behavior, along with the design, documentation and testing that show it does.

The standard does not issue a certificate in its own right. It classifies the conditions on a railway vehicle so that a train builder, an operator and an equipment supplier can describe them in the same terms, then sets out the type tests and routine tests that demonstrate equipment is fit for that environment. A railway computer described as EN 50155 compliant should come with a declaration and test evidence that name the classes it meets, and those classes are what you check against the vehicle.

This guide covers what EN 50155 requires, the temperature, interruption and change-over classes and what OT4, S2 or C1 actually mean, how the 2017 revision changed the standard, the related standards for EMC, shock and vibration and fire, and how computers and panel PCs are designed and specified for onboard use. Our news on the Sintrones VBOX-3631 covers a recent fanless computer designed for railway and road vehicles.

EN 50155 is a broad standard. Some of its clauses set environmental classes, some point to other standards for the detailed test method, and some cover design practice and documentation. The table brings the parts that matter for a computer or display together in one place.

Two things stand out. First, many of the hardest requirements are electrical rather than environmental: an onboard supply is noisy, it dips, it surges and it is interrupted, and EN 50155 is precise about how equipment must behave through all of that. Second, the classes are chosen per project. A computer in an air-conditioned equipment cabinet and one in an unheated driver’s cab on the same train can need different temperature classes.

Not in the way a product safety listing is. There is no EN 50155 mark and no single body that issues an EN 50155 certificate. A manufacturer declares that a product complies, supported by type test reports for each requirement, and train builders and operators often ask for the key tests to be carried out or witnessed by an accredited laboratory or a notified body. In practice, the test reports are the evidence.

That is why wording matters when you read a datasheet. “Designed to EN 50155” or “compliant with EN 50155” should be backed by a report that lists the classes tested. “Meets EN 50155 EMC”, on the other hand, usually means the equipment has passed the EN 50121-3-2 emission and immunity tests that EN 50155 calls on, not the full standard. Both are useful, but they are not the same thing, and we state which one applies to each product in our range.

For the operator, conformity is assessed as part of the vehicle. Under the Technical Specifications for Interoperability (TSIs) in Europe, and national rules in Great Britain, the train builder brings the equipment evidence together with the vehicle’s own tests. Equipment that already has clear EN 50155 evidence simply makes that work shorter.

EN 50155 has been revised several times since its first edition. The 2007 edition was in use for a decade and many older datasheets still quote its classes. The 2017 revision restructured the standard, and the current edition, EN 50155:2021, follows that structure. The IEC counterpart, IEC 60571, covers the same ground for markets outside Europe.

If a supplier quotes TX, the product was tested to the 2007 edition, where TX meant −40 to 85 °C. That is still useful information, but the test evidence may need reviewing against the current edition before it goes into a new vehicle project.

EN 50155 groups onboard temperatures into six operating temperature classes. Each sets the external ambient range the equipment must operate across, measured at the equipment rather than outside the train. Switch-on extended classes add a short period above the upper limit when equipment is powered up in a hot vehicle that has been standing in the sun.

The figures are the class limits as commonly published; confirm them against the edition named in your contract, because the test conditions, dwell times and switch-on rules are set out in the standard itself. Storage temperatures are specified separately and are usually wider than the operating range.

Temperature classes and real cabinets do not always line up. A computer rated to 70 °C in free air can run hotter inside a closed equipment cabinet with other electronics, so we size the thermal margin against the cabinet, not the class alone. Our industrial temperature range explainer sets out how commercial, industrial and extended ranges compare.

OT4 is the EN 50155 operating temperature class for equipment that must work from −40 to 70 °C. It combines the cold-start requirement of trains that stand overnight in northern winters with the heat of a closed cabinet in summer, which is why it has become the class most rail operators ask for and the one most onboard computers are designed to. An OT4 computer usually needs industrial-temperature memory and storage, a fanless thermal design and, for displays, a heater or a panel rated for cold start.

OT3 at −25 to 70 °C is often enough in milder climates and in heated vehicles. OT5 and OT6, to 85 °C, are normally reserved for equipment mounted outside the body shell, and few computers are offered in those classes.

Power is where onboard computers most often fail in service. Rolling stock runs its electronics from a battery-backed DC supply, typically at one of five nominal voltages, and that supply varies with battery charge, dips when large loads switch, surges, and is briefly lost when the vehicle changes supply source or passes through a neutral section. EN 50155 sets limits for each case.

Many manufacturers simplify the input stage with converters that cover a 4:1 range, such as 10 to 40 V, 18 to 72 V or 40 to 160 V, so one design spans several nominal voltages. A 110 V train, for example, can fall to 77 V and rise to about 137.5 V continuously, which a 40 to 160 V input covers with margin. The DFI RC300-CS series takes 77 to 137.5 V DC on its 110 V builds for exactly this reason.

Interruption classes decide how much stored energy the computer needs. S2 and S3 are usually met with hold-up capacitors in the power stage. Longer gaps, or a controlled shutdown when the train is switched off, need a supercapacitor or battery UPS. Our comparison of supercapacitor and battery UPS options covers the ride-through times each gives.

Take a CCTV recorder for a regional train with a 110 V DC battery supply, mounted in an equipment cabinet behind the driver’s cab. The operator asks for OT4, S2 and C1. Working through the power requirements in order gives a short list of what to ask the supplier for.

The fluctuation figures are simply 0.6 and 1.4 times the nominal 110 V. Where the recorder writes video continuously, we would also check the storage for power loss protection, because a supply drop mid-write is the most common cause of corrupted footage on board. The power loss protection explainer covers what to look for in an SSD.

EN 50155 calls on other standards for the detailed test methods, and a rolling stock project usually lists several of them together. Knowing which does what makes datasheets much easier to read.

Of these, three are almost always quoted on an onboard computer’s datasheet: EN 50121-3-2, IEC 61373 and EN 45545-2. The next three sections summarize each, and our FAQs go into the detail.

EN 50155 is the overall standard for onboard electronic equipment. EN 50121-3-2 is the part of the EN 50121 railway EMC series that sets emission limits and immunity tests for apparatus on rolling stock, and EN 50155 refers to it for EMC. A product can therefore meet EN 50121-3-2 without meeting the rest of EN 50155.

This is common, and it is not a weakness in itself. Many rugged computers built for vehicles are tested to EN 50121-3-2 so they can be used on trains, without carrying the full EN 50155 test program. Premio, for example, lists EMC to EN 50121-3-2 on the Premio ACO-6000-RPL fanless computer, alongside ignition management and MIL-STD-810H shock and vibration design. Whether that is enough depends on the vehicle specification: some operators accept EN 50121-3-2 plus separate shock, vibration and power testing, others require the full EN 50155 evidence.

EN 50155 calls on IEC 61373 (EN 61373 in Europe) for shock and vibration, so in practice the two travel together. IEC 61373 groups equipment by where it is mounted, because vibration on an axle is far more severe than on the body of the carriage.

Each category combines a long-life random vibration test, which simulates years of service in hours, with functional random vibration and shock tests. Almost all computers and displays sit in Category 1, which is why datasheets quote “IEC 61373 Category 1 Class B” or “Class A”. Inside the computer, locking M12 connectors, soldered memory or memory retention clips and SSDs rather than hard drives keep it working through the test and in service.

EN 45545-2 is the part of the EN 45545 railway fire protection series that sets the fire behavior of materials and components used on trains. It works on hazard levels, HL1 to HL3, chosen from the vehicle’s operating category and design category, so a sleeper train or a metro running in long tunnels sits at a higher level than a vehicle with easy evacuation. Each material is then tested against a requirement set, such as R22, R23, R24, R25 or R26, depending on what it is and where it is fitted.

For electronic equipment the requirement sets that cover small electrotechnical products and their housings apply, and manufacturers quote the set they designed to. Sintrones, for example, lists design to EN 45545-2 R25 requirements on the Sintrones IBOX-601-M12X Jetson railway computer. On a project, the train builder’s fire assessment decides which set applies; the equipment supplier provides the material test evidence.

A computer for rolling stock looks much like any rugged computer from the outside, but the design choices inside follow the standard closely. The table maps each requirement to the feature that answers it.

M12 connectors deserve their own mention. X-coded M12 Ethernet with PoE is now the standard way to connect onboard IP cameras, because it seals, locks and carries power and data on one cable. Our guide to M12 connectors covers the codings, and conformal coating explains the board protection the PC2 class refers to.

EN 50155 asks the manufacturer to state the useful life the equipment is designed for, expressed as a life class. The figure drives component choice, especially electrolytic capacitors, fans, batteries and flash storage, which wear out faster than the rest of a computer.

A life class is not the same as MTBF. MTBF describes the failure rate during the useful life, while the life class says how long that useful life is. Our guide to MTBF covers the difference. Trains run for 30 years or more, so even an L4 computer will be replaced at least once; long product availability and a clear last-time-buy plan matter as much as the class. How long computers last sets out what wears first.

Onboard systems have multiplied as operators digitize fleets. These are the applications we see most often, with the computer and the requirement that usually decides the specification.

Control room systems, depot equipment and trackside cabinets do not sit on the train and are not covered by EN 50155; trackside and signaling equipment is normally assessed against EN 50121-4 instead. Two of our case studies show onboard systems in practice: MXM GPU computing on board a digital train and an end of train device link with SuperCAP backup. For track inspection, see how rugged railway computers support track inspection.

The products below state EN 50155 classes or related railway standards in their manufacturers’ specifications. As your system integrator we configure each computer, image the operating system and application, and test it before it ships; displays are configured and tested. Railway approvals belong to the manufacturer and the vehicle project, so we supply the manufacturer’s test evidence for your file and confirm the classes for the exact build you order.

Where a project needs a class a model does not hold, such as OT6 or an EN 45545-2 hazard level beyond the published one, we say so at the quotation stage. Our rail industry page shows how we support onboard and trackside projects.