A large conductor will suffer from some skin effect. Not very much at 60Hz but if you are using something like 1 kHz it will be an important factor. I'm afraid, I don't have the factors nor a good reference at hand.
Here is an article about the phenomenon. http://www.ecmweb.com/mag/electric_basics_hz_power/
[This message has been edited by C-H (edited 05-24-2004).]