Why are copper wires used instead of Steel Wires?

Every wire has some resistance to electric current. The resistance causes a voltage, and the product of voltage and current is watts, which heats the wire. That is wasted power. Copper has much less resistance than steel so it is used exclusively for carrying electricity.

In high voltage lines they use aluminum because it has almost the same resistance as copper but it's cheaper. Then they use steel cables to hold it up because aluminum does not have enough tensile strength to hold itself up.