Short answer: Contact wire wear is managed on two tracks: average wear over the whole anchor section is limited to about 25% of nominal cross-section - beyond that the section is renewed; local wear (pontoon strikes, arcing points) is controlled at alert and limit levels. Residual height is converted per grade from tables (CTAH-120 ~10.2 mm by common convention).
Why cross-section percentage
Wear erodes both margins: current-carrying section (resistance and temperature rise) and mechanical strength (breaking force, fatigue). Manual calipers measure residual height; inspection-vehicle laser profilometry builds a wear-versus-mileage ledger. Renewal projects should select grades per TB/T 2809-2026 (pure copper removed) and match splice and anchor clamps accordingly.