How much current

[hurk27]

Actually, it applies to all frequencies from DC upwards. Increasing the frequency pushes the current towards the outside of the conductor (hence skin effect) so less of the cross-sectional area is used which increases the impedance.

Guess what I was getting at is a round conductor with a diameter of 1" or a rectangle buss 0.125" x 6.2832" both have an area of .7854"sq but at lets say at 10 mhz the buss bar will have a much lower impedance then the round conductor.

At DC-60hz (which we agree on) the bussbar will have more surface exposed to air to dissipate heat thus being able to handle more current.

These are two different reasons for the bussbar to carry more current, one is heat dissipation and the other is the skin effect at higher frequencies.

Not good with metric conversions so bare with me