I don't see any general requirement to bond the metal siding, roofing, or incidental structural steel in the NEC. Indeed, by saying 'likely to become energized' the NEC seems pretty clear in saying "no need to bond."
Granted, that's a general requirement. Other parts of the NEC -pool areas and some agricultural buildings being examples- the NEC has another requirement that all metal be bonded. Those are special circumstances, and the requirement is limited to them.
I am curious: where do we get the #6 requirement? After all, we're not talking about the water bond - where the incoming water pipe might also become a grounding electrode.
