Grounding an aluminum enclosure to copper pads on a PCB

since

Nope. Not always true, or even most of the time. The magnetic fields created by the very flow of current drives the flow toward the outer surface of the conductor. Maxwells law(s). The impact is low at low current densities, but causes significant issues even at power line frequencies. That is why you see quadded conductors on a few of the high voltage lines.

?-)

I seem to recall about 6% increase in resistance due to skin effect for typical power line conductors. The main reason to go with bundled conductors is to reduce corona losses (a bundle has a larger apparent radius than a single conductor of equivalent area) and a lower inductance per unit length, which allows greater power transfer.

On Sat, 22 Nov 2014 17:27:23 GMT, Ralph Barone Gave us:

Easier to hang and service too.

I wonder how they constructed the DC interlink lines.

It depends on the frequency vs. the conductor diameter. It has nothing to do with the current density. It is significant with large power lines because of the larger diameter of the conductor.