Adequately made of copper Cu-ETP and copper alloy CuAg 0.10, they consist of one grooved hard profile wire. Symmetrically made grooves (notches) at the top of the round contact cable allow to connect to hanging lines. Trolleys are the most important element of the contact cable, and a combination of its typical electro and mechanical parameters limits the abilities of the railway traction, and thus performances of trains. Cooper is the most popular material used for the production of the contact cables. This metal shows great electric conductivity and has (if hard) very good strength that is reduced at increased temperatures at 80°C. Because of this fact, Djp cables cannot be loaded with too much current, which in turn influences on the reduction of the maximum speed of trains to approx. 160 km/h. The solution to this problem involved added small quantities of alloyed additives to cooper, which at all or only to a limited extent reduce cable conductivity, increasing its mechanical properties and operating temperature. For this reason, DjpS type cables have more current-carrying capacity, which translates directly to increased train speed, even up to 250 km/h. Currently in Poland, the most modern solution of a structure for railway traffic is YC150-2CS150 railway network with the variety of YC120-2CS150 with a bearing line of Cu 150 mm2 or 120 mm2 and two silver cooper wires of DjpS 150 type, approved by the Office of Railway Transport to power trains running at speeds of up to 200km/h.