Development of overhead line masts The overhead lines with their masts are the cores of the electrical power supply. The masts are mainly made of wood, concrete or steel and can have a variety of designs. For the high-voltage and extra-high-voltage grid (220kV and 380kV), steel lattice masts are usually used to allow for large heights and spans. The individual bars of these lattice-like masts are mainly made of hot-rolled angle steels, which can be