Short answer: A contact wire designation is class code + alloy code + cross-section: CT denotes copper-alloy contact wire, the following letter the alloy element - A silver, M magnesium, S tin, CZ chromium-zirconium - and the trailing number the nominal cross-section in mm². Common grades: CTA/CTAH-110/120/150, CTM/CTMH, CTS, CTCZ.
Reading a grade
CTAH-120 = copper-silver, 120 mm², high-strength condition (CTAH is the correct order, not CTHA). Stranded wires follow the same logic with J prefix: JTM = copper-magnesium stranded, JTCZ = CuCrZr stranded, JT = hard-drawn copper stranded.