i need ONE advantage of each, and a final reason why aluminium is used?
Copper does conduct slightly better than aluminum, but aluminum corrodes over time and the oxidized surface has very high resistance. Copper also oxidizes but is not as high a resistance. The high resistance, when in contact with another conductor, like a junction inside a box, will create heat. Those high resistance junctions create so much heat that over time a fire hazard develops. Hence, National Electrical Code disallowed the use of aluminum for safety reasons.
Copper and Aluminum are both great conductors of electricity. Aluminum is actually more dangerous than copper, as it expands/contracts a lot more with heat, and is a primary cause of house fires. Copper's advantage is that it is more reliable, it doesn't corrode as easily, and does not expand/contract much with application of heat. I believe that aluminum has an edge as a conductor, though, and is less expensive to manufacture.
