EN 50155:2017 is the European standard that defines the requirements for electronic equipment used on railway rolling stock. Any power converter, inverter, battery charger or electronic system installed on a train in Europe must comply with it. Yet it is in the way compliance is specified that most mistakes are made.

This article explains, in practical terms, how to use EN 50155 to specify the power electronics of a railway project correctly. It is not an academic summary of the standard: it is an operational guide based on what we have learned across hundreds of railway projects. For a general introduction to the standard, see What is EN 50155 for railway applications?

The most common mistake: “EN 50155 compliant”

Specifying that a unit must be “EN 50155 compliant” is like ordering a car “compliant with emissions regulations” without saying whether you need a city runabout or an off-roader. EN 50155 defines a framework of options, and each project must select the right ones. If your specification simply says “EN 50155”, the supplier will choose the options that are easiest (and cheapest) to meet, which may not be the ones your application needs.

Parameter 1: temperature class

EN 50155 defines six temperature classes that set the operating range of the equipment:

Choosing the temperature class is not trivial. Our ODS-3000 inverter was originally designed for OT2. When a rolling-stock manufacturer needed an OT4 variant for arctic service, we had to change the electrolytic capacitors (standard parts lose 80% of their capacitance at −40 °C), add a pre-conditioning circuit and run a full qualification campaign including 96-hour soaks at −40 °C.

Parameter 2: input voltage range

The standard defines nominal voltage ranges for the train’s DC buses:

The converter must operate correctly across the whole specified range, including the transient conditions defined in the standard. Always specify the full range, not just the nominal voltage.

Parameter 3: supply interruption class

EN 50155 defines how equipment must behave when the supply is briefly interrupted (for example, when crossing a neutral section or when the pantograph loses contact with the overhead line):

• S1: no ride-through. The unit shuts down and restarts when the supply returns.
• S2: 10 ms ride-through. Withstands short interruptions without restarting.
• S3: system-specific ride-through (defined by the operator).

For critical systems (protection, communications, signalling), S2 or S3 is usual. For comfort systems (passenger sockets, non-essential lighting), S1 may be acceptable.

Beyond EN 50155: the companion standards

EN 50155 is not the only applicable standard. All railway electronic equipment must also comply with:

• EN 50121-3-2: electromagnetic compatibility (EMC). The electromagnetic environment on a train is extremely harsh.
• EN 45545-2: fire protection. Materials must meet specific requirements for flammability, smoke emission and toxicity.
• EN 61373: shock and vibration. Vibration levels on rolling stock are significantly more severe than in industrial applications.

Make sure your specification covers all four standards. A unit that meets EN 50155 but not EN 45545-2 cannot be installed on a European train.

How to specify correctly: a practical summary

For your next project, include at least the following in the specification:

With these six parameters clearly defined, you will receive comparable quotations and avoid the surprises that appear when a specification is ambiguous. Need help specifying EN 50155 power electronics? Our technical team in Barcelona can advise you.