[Bored chemist]

I am not sure about that.
[/quote]
The folk who build power transmission lines are.

The inner cores of the cables strung from pylons are made from steel because the strength is important and the resistance isn't so much.
The people who build high current bus bars use strip shaped conductors, less skin effect and better cooling.
But none of that is relevant to domestic power cables.

[alancalverd]

Wikipedia:

At 60 Hz in copper, skin depth is about 8.5 mm.

so a 15 mm (around 400 amp) conductor will be conducting through most of its thickness.

Flat busbars are easier to assemble and connect than round ones - you just drill a hole and put a bolt through it. The beauty of the awful British Standard mains plug is the flat connector which (in principle) makes a more reliable contact with a simple socket than a round pin. Some other national standard plugs use the same principle but have the common sense to put the pins in line with the cable. The last thing on my bucket list is to mass-produce a plug with BS pins in line and a replaceable fuse, at a sensible price. The world will beat a path to my door.

[Bored chemist]

Wikipedia:

At 60 Hz in copper, skin depth is about 8.5 mm.

so a 15 mm (around 400 amp) conductor will be conducting through most of its thickness.

And thus anything drawing more than about 160KW at 400V or half a megawatt using 3 phase will need to use cables that are either inefficient, or flattened. Which is why bus bars are flat.

[alancalverd]

....but the transmission lines aren't. It seems odd to connect these massively efficient but relatively short bus bars  with miles of grossly inefficient round cable.