Answer:

Because transmission is typically made of aluminium alloy strands, these carry the electricity to the towers and are attached with insulators. Towers may also carry an earth wire to reduce the likelihood of direct lightning strikes. Aluminum provides a better conductivity to weight ratio than copper, and therefore is also used for wiring power grids, including overhead power transmission lines and local power distribution lines, as well as for power wiring of some airplanes. ... It has cost and weight advantages over copper wires.