Why dc cables are thicker than the ac cables?

Question

Why dc cables are thicker than the ac cables?

Answer 1

The thickness of wire is strictly related to current. The higher the current the thicker the wire. Since DC is generally a lower voltage than AC it needs a higher current for the same power. W=E x I or watts equals voltage times current.  

Answer 2

since the electrons in a dc power system move from one charged field to another with no alternation the wire tends to be more insulated to handle a larger capacity of electrons, especially since dc is often used for larger currents. ac systems alternate the flow of electrons between generator terminals (source and appliance) with a changing field of charge.

Answer 3

DC is a direct current and AC is a not. The thing is that AC can go crazy while DC has to be kept equal... i am guessing thats the reason, people feel free to correct me, i am ONLY guessing.