It may come from the sun. (Read about the Carrington event)
It may be delivered on a missile from North Korea.
A lot of power grid transformers will burn out across the continent. It can take more than a year to replace a big transformer. Power companies can make defensive moves but some areas would end up without normal power for more than a year.
|More than a hundred wheels, 20 miles a day, and|
overhead wires are taken down to allow the new transformer to pass.