EN 13146-5: Measuring Electrical Insulation in Rail Fastening Systems

What is EN 13146-5?

EN 13146-5 is a critical European Standard titled “Railway applications – Track – Test methods for fastening systems – Determination of electrical resistance.” It specifies a laboratory test procedure to measure the electrical insulation provided by a rail fastening assembly between the rail and the sleeper.

In modern railway networks, the rails often serve as conductors for track circuits used in signaling and interlocking systems. If the fastening system (which connects the steel rail to the sleeper) does not provide adequate electrical resistance, current can leak into the ground or the sleeper. This leakage can cause signaling failures, “phantom” train detections, or the acceleration of electrochemical corrosion due to stray currents.

Technical Test Procedure

The standard describes a precise setup to simulate field conditions while maintaining laboratory accuracy. The core of the test involves:

• Sample Preparation: The test is conducted on a full fastening assembly (including rail pads, insulators, and clips) mounted on a standard sleeper.
• Wetting Process: Because electrical leakage is most critical in wet weather, the standard mandates a specific spraying protocol using water with a controlled conductivity to simulate heavy rain.
• Voltage Application: A specified voltage (typically 30V AC) is applied between the two rails on a single sleeper, and the resulting current flow is measured.
• Resistance Calculation: The electrical resistance is calculated using Ohm’s Law. For most standard applications, the minimum required resistance per fastening is 5 kΩ (kilohms) after wetting.

The Role of Insulating Components

The fastening system relies on specific “insulating bush” or “side post insulators” to break the electrical path between the metallic rail and the metallic fastening components (like screws or clips) that enter the sleeper. EN 13146-5 validates that these small plastic components can perform their duty under mechanical load and moisture.

Comparison: Electrical Requirements by Track Type

Significance for Signaling and Infrastructure

If a fastening system fails the EN 13146-5 test, it cannot be used on lines equipped with track circuits. A failure in insulation in the field can lead to “Red Light” failures where the system perceives a train is present when the track is clear. Furthermore, for DC-electrified railways (like many Metro systems), proper insulation is the primary defense against stray currents that eat away at utility pipes and bridge reinforcements near the track.