[snip]

> I am.
> According to my limited knowledge, current only flows on
> the skin of a conductor because a potential difference
> cannot exist inside a conductor (like a Faraday cage).
> Because we work with less-than-perfect conductors, some
> current will also flow a little deeper into the conductor,
> but the heavy current flows on the surface.
>
> This is why a ribbon can conduct more than a rod. Following
> this potentially flawed reasoning, I would expect the
> circumference of a conductor to be of more significance than
> the diameter.
>
        yes, but we are talking about wires here,
        and wires are round. until you asked, i've
        never thought about it. Here's my guess
        as to why its done this way: The skin depth
        is related to frequency, and perhaps for the
        vast majority of appliations, it doesn't
        have enough of an effect for it to matter.
        Those applications where it does matter
        may be so few (in terms of where it does
        matter) that it is not economically attractive
        for manufacturers to make a different type.

        for what it's worth, larger transformer
        applications do, in fact, use "ribbons"
        of copper instead of wires. Litz wire is
        another alternative.