As others point out, a solar storm induces undesirable currents in electrical conductors, the insluation or not of said conductors is not relevant.

The voltage induced in short conductors is very small and generally of no importance.
The problems occur with very long conductors as would be found in large interconnected grid systems, the voltages can be great enough to overstress equipment and lead to large scale blackouts.
Given advance warning the risks may be reduced by isolating sections of the grid from each other, thus reducing the lengths of conductor in which voltages may be induced.

Any developed nation is at risk from solar storms, but the USA is perhaps at greater risk owing to the size of the nation and consequent very long grid lines.

Long distance telephone lines are also at risk if of copper, but most are now fibre optic which are immune.