What EN 50155 actually covers
EN 50155 ("Railway applications — Rolling stock — Electronic equipment") is the umbrella standard covering electronic devices used on board passenger and freight rolling stock. It does not test sensors directly — it specifies the environment the sensor must survive. Compliance is by reference to the relevant sub-standards.
The four critical sections for current sensors
1. Operating temperature class (Section 4.3)
| Class | Internal-equipment temp | External-equipment temp |
|---|---|---|
| OT1 | -25 to +55°C | -25 to +70°C |
| OT2 | -40 to +55°C | -40 to +70°C |
| OT3 | -25 to +70°C | -25 to +85°C |
| OT4 | -40 to +70°C | -40 to +85°C (most common in modern fleets) |
| OT5 | -25 to +55°C, +15-min @ +85°C transient | — |
For sensors mounted near a traction converter, OT4 is the default specification — the converter ambient runs hot.
2. Vibration & shock (Section 12.2.11 → IEC 61373)
EN 50155 references IEC 61373 for vibration. The categories you'll see:
| Category | Application |
|---|---|
| 1A | Body-mounted equipment |
| 1B | Bogie-mounted (more severe) |
| 2 | Axle-box mounted (most severe) |
Most current sensors are body- or bogie-mounted, so Category 1B is the typical target — random vibration with PSD ~7.9 m²/s³ over 5-150 Hz.
3. EMC (Section 12.2.6 → EN 50121-3-2)
Railway EMC is harsher than industrial EMC. Key tests for sensors:
- Conducted emissions EN 50121-3-2 traction supply class
- ESD immunity ±15 kV air discharge (vs ±8 kV in industrial)
- Conducted RF immunity 10 V/m (vs 3 V/m industrial)
A sensor passing IEC 61000-6-2 industrial does not automatically pass railway EMC. Look for an explicit EN 50121-3-2 declaration on the datasheet.
4. Fire & smoke (EN 45545-2)
Often forgotten until type testing fails. EN 45545-2 dictates flammability requirements for materials used inside the rolling stock body. Sensor housing materials must meet hazard level HL2 or HL3 depending on operational category.
For Contisys sensors, our default housing material is rated HL3 — covering all standard rolling stock applications including high-speed and underground.
Galvanic isolation requirements
For traction circuits, isolation is governed by IEC 60664-1 overvoltage category III:
| Nominal traction voltage | Required impulse withstand |
|---|---|
| 600 V DC | 4.0 kV |
| 750 V DC | 4.0 kV |
| 1500 V DC | 6.0 kV |
| 3000 V DC | 8.0 kV |
| 25 kV AC | special — usually instrument transformer not Hall sensor |
Service life expectations
EN 50155 implies 30 years of revenue service. For sensors, this means specifying:
- Offset drift over 30 years — should be specified, not "typical"
- Gain drift over 30 years — same
- Insulation aging under continuous high voltage
- Mechanical fatigue under accumulated vibration cycles
Datasheets that don't quantify these are a red flag.
Specification template
When sending an RFQ for an EN 50155 sensor, include:
- ✅ EN 50155 OT class (typically OT4)
- ✅ IEC 61373 category (typically 1B)
- ✅ EN 50121-3-2 EMC compliance required
- ✅ EN 45545-2 hazard level (HL2 or HL3)
- ✅ Working voltage + impulse withstand
- ✅ Required accuracy at nominal and over the full OT range
- ✅ Mechanical mounting envelope (often the most constrained dimension)
- ✅ Output type — voltage / 4-20 mA / digital
- ✅ Quantity & target programme date
Anything less and you'll go through 2-3 RFQ rounds before getting a usable quote.
Common spec mistakes
- "EN 50155 compliant" without specifying OT or IEC 61373 category — meaningless
- Using industrial-grade sensor with claim of EN 50155 compliance — typically fails EN 50121-3-2
- Ignoring EN 45545-2 until material datasheet is requested by the OEM — leads to last-minute redesign