The comparably light weight of aluminium wires reduc the load onto grid pylons and increases the distance of spans between them, thus reducing expenses and shortening construction time. When current passes through aluminium wires, they heat up and their surface [becomes covered] with an oxide film. This fim serves as an excellent insulator protecting the wires against external effects. Sometimes aluminium wires are covered with a protection oxide film during production, this process is called anodic oxidation. These wires have such a high chemical resistance that they can work at high humidity and temperatures ranging between 200 to +500 C without additional insulation.