What is the focus of EN 45545-5?

EN 45545-5 focuses on the fire safety requirements for electrical equipment on railway vehicles. Unlike Part 2 (which deals with materials), Part 5 deals with design principles to prevent ignition, such as overload protection, battery ventilation, and arc containment.

What are the battery ventilation requirements in EN 45545-5?

The standard mandates that battery boxes must be sufficiently vented to prevent the accumulation of explosive gases (like Hydrogen). The concentration of hydrogen must never exceed the safety limit (typically 4% by volume) during charging.

How does EN 45545-5 handle overload protection?

It requires that all electrical circuits be protected by fuses or circuit breakers. The rating of these protective devices must be selected so that they trip and cut power before the connected cables or equipment overheat and catch fire.

EN 45545-5: Fire Safety Requirements for Railway Electrical Equipment & Batteries

EN 45545-5 establishes the fire safety design requirements for electrical equipment on railway vehicles, including Trolleybuses and Maglevs. This guide details the mandatory rules for ignition prevention, covering overload protection (fuses), battery ventilation (Hydrogen safety), and thermal isolation of braking resistors to prevent electrical fires.

December 19, 2023 11:37 pm

EN 45545-5 complements the material requirements of Part 2 by focusing on the functional design of electrical equipment. Since electrical faults (short circuits, overloads, arcing) are the leading cause of ignition on railway vehicles, this standard imposes strict rules on how electrical systems must be designed to minimize the risk of starting a fire.

It covers everything from the pantograph high-voltage line down to the low-voltage battery circuits, including specific provisions for Trolley Buses and Maglev systems. The core philosophy is “Ignition Prevention” through mandatory overload protection and separation distances.

1. Protection Against Overloads (Fusing)

The golden rule of EN 45545-5 is that the protective device (Fuse or Circuit Breaker) must trip before the cable insulation reaches its ignition temperature. Design engineers must calculate:

Nominal Current: The normal operating load.
Fault Current: The maximum current during a short circuit.
Cable Rating: The cable’s current-carrying capacity must be higher than the fuse rating, ensuring the fuse is always the “weakest link” in the thermal chain.

2. Specific Requirements for High-Risk Components

Certain electrical components generate heat by design or store massive energy. EN 45545-5 mandates specific physical installation rules for these:

Component	Risk Factor	Design Requirement
Batteries	Gas Evolution (H2) & Thermal Runaway	Must be ventilated to prevent Hydrogen accumulation > 4%. Trays must be resistant to electrolyte corrosion.
Braking Resistors	Extreme Heat Generation	Must be thermally isolated from the car body. Air outlets must not direct hot air onto combustible materials (e.g., dry leaves on track).
Power Contactors	Arcing (Sparks)	Must be enclosed in arc chutes or arc-resistant boxes to contain the plasma flash during switching.
Heaters	Overheating	Must have independent redundant thermal cut-offs (thermostats) to prevent operation if the fan fails.

3. Battery Installations (Lead-Acid & Li-Ion)

Batteries are chemically active energy stores. EN 45545-5 requires rigorous ventilation calculations. The battery box design must ensure that even during heavy charging (when gassing is highest), the hydrogen concentration remains below the LEL (Lower Explosive Limit).

For modern Lithium-Ion traction batteries, the standard also addresses “Thermal Runaway” containment, ensuring a single cell fire does not propagate to the entire passenger cabin.

4. Cable Routing and Derating

Packing too many cables into a tight duct causes heat build-up. EN 45545-5 requires:

Derating Factors: Engineers must reduce the assumed capacity of cables when bundled together.
Bend Radius: Cables must not be bent sharply, which stresses insulation and leads to cracks/arcs.
Separation: HV (High Voltage) and LV (Low Voltage) cables should be physically separated to prevent induction and flashover.

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