Mersen ERCU (Earth Return Current Unit) - axle earthing unit: brushes conduct return current from the axle to the rail. The unit performs three functions: it prevents current from flowing through axlebox bearings (a major source of bearing damage in service), equalizes rail potentials and transfers train-detection signals between track sections. Variants are available for high-speed trains >200 km/h, Intercity, metro and tram applications. Optionally, the ERCU integrates a pulse generator (gear wheel/speed sensor) for wheel-slip, direction-of-travel and standstill detection.
Current range 200–800 A, depending on the number and cross-section of copper-graphite brushes (1–4 brushes, dimensions 12.5×32 / 16×25 / 20×25 / 20×40 / 25×50 mm), operating speed >200 km/h. 100 ms surge current up to 10 kA, peak current up to 27 kA - values for the 3×20×40 mm / 600 A version; surge parameters for other versions are specified in the relevant datasheet. Standard degree of protection IP54, up to IP56 with additional seals. Three installation configurations: axial (axle end) and radial - for trains and metro vehicles - and in-wheel (“into the wheel”) for low-floor trams.
Variants by segment (datasheets attached): - High-speed trains (>200 km/h): axial 4×20×40 mm / 800 A and 3×20×40 mm / 600 A. - Intercity: axial 3×20×40 mm / 600 A (also IP65 version) and a speed-sensor variant 3×12.5×32 mm / 300 A. - Metro and tram: radial 1×10×25 mm / 65 A, 2×20×25 mm / 250 A, 2×20×40 mm / 400 A, 2×25×50 mm / 625 A, and in-wheel 4×12.5×25 mm / 300 A for low-floor trams; axial 3×12.5×32 mm / 300 A and 3×20×40 mm / 600 A. - Pulse generator (option): speed-sensor version based on the axial 3×20×40 mm / 600 A design.
Materials: corrosion-resistant bronze body, cover made of galvanized steel/aluminium/brass/stainless steel, stainless-steel springs and screws, polyester insulating ring. Mersen recommends using only its own carbon brushes - catalogue parameters are validated only for this selection.
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