Why is a thicker conductor necessary to carry a current in A.C.as compared to D.C.?

Question

Why is a thicker conductor necessary to carry a current in A.C.as compared to D.C.

Answer 1

Alternating current does not use the entire cross-sectional area of a conductor due to what is called the skin effect. This has some fairly complicated physis behind it, but essentially as one increases the frequency of the current, the current looks more like an electromagnetic wave. The metal reacts to the current as it woudl to a wave, and only permits the current to penerate to a certan depth. The higher the frequency, the shallower the depth - most of the current is carried near the surface of the conductor, hence the term skin effect.

Resistance decreases with increase cross sectional area. The skin effect effectively reduces the cross sectional area for a conductor therby raising the resistance, which is bad if you want efficient power transmission. So if you make the cross sectional area larger (thicker conductor), the effective cross sectional area due to the skin effect increases and the resistance goes down. So the increase in thickness is used to keep the effective resistance of the conductor the same or lower than it would be for a DC power source.

Answer 2

A larger conducter is required because the current density is greater nearer the surface of the conductor due to the skin effect causing the effective resistance to increase with frequency. Found this in Wikipedia who very much deserve donations for their efforts.