Wired for Safety: UIC Leaflet 626 Cable Regulations

Introduction to UIC Leaflet 626

Modern trains are essentially data centers on wheels, relying on kilometers of cabling for traction, signaling, and passenger comfort. UIC Leaflet 626, titled “Regulations regarding the use of electric cables on railway vehicles,” establishes the fundamental rules for selecting and installing these critical components.

While cable manufacturing standards (like EN 50264) focus on the material properties, UIC 626 focuses on the application: how cables should be chosen based on voltage and current, and how they must be installed to prevent mechanical damage and fire propagation.

Snippet Definition: What is UIC 626?

UIC Leaflet 626 is a technical document from the International Union of Railways that specifies the regulations for the use of electric cables on rolling stock. It covers criteria for current-carrying capacity, permissible voltage drops, mechanical protection, and crucially, fire behavior requirements to ensure passenger safety in confined environments like tunnels.

Key Technical Provisions

The leaflet acts as a guideline for electrical engineers during the vehicle design phase. Its requirements can be categorized into three main areas:

1. Fire Safety and Toxicity

This is the most critical aspect of UIC 626. In the event of a fire, cables must not become a fuse that spreads the flame through the train.

• Flame Retardant: Cables must self-extinguish when the fire source is removed.
• Non-Propagation: Fire must not travel along the cable bundlers (chimney effect).
• Halogen-Free: Materials must not release toxic gases (like chlorine) or dense smoke that hinders evacuation.

2. Electrical Sizing

Engineers must calculate the cross-sectional area of the conductor based on:

• Continuous Current: The maximum current the cable can carry without overheating the insulation.
• Short-Circuit Rating: The ability to withstand massive current spikes for milliseconds until the breaker trips.
• Ambient Temperature: De-rating factors must be applied if cables run through hot areas (e.g., near the traction motor).

3. Mechanical Installation

UIC 626 mandates that cables be protected against vibration and abrasion. Minimum bending radii must be observed to prevent insulation stress cracks.

Comparison: UIC 626 vs. EN 50264 Series

It is important to distinguish between the “Usage Regulation” (UIC) and the “Product Standard” (EN).

Environmental Conditions

Railway cables face a hostile environment. UIC 626 requires that selected cables must be resistant to:

• Chemicals: Resistance to diesel fuel, hydraulic oils, and cleaning agents.
• Weather: UV resistance for roof-mounted cables and ozone resistance.
• Temperature Extremes: Operating range typically from -40°C to +90°C (or up to 120°C for traction cables).