Owen Duffy wrote in news:Xns9DB5277B6263Bnonenowhere@
61.9.134.55:

....
Is "NFPA 780: Standard for the Installation of Lightning Protection
Systems" a relevant standard in your jurisdiction?

If it is applicable, it seems that for a Class 1 structure (less than 75'
in height???), the requirement for the main down conductor is 57,400
circular mils CSA if copper, that is about 29mm^2 or #2 conductor.

By contrast, #6 is 26,000 circular mils, has approximately twice the
resistance per unit length, half the mass per unit length, and somewhere
just less than 25% of the stroke current withstand of #2.

Owen