From what I understand about EMP’s (at least the man-made ones), if you pop a nuke about 25 miles up, the area affected is pretty localized. So long as you are over the horizon and out of line of sight, you’re fine.
But, if you biff a nuke above the ionosphere, it sets up something called the Compton Effect.
Now, I don’t even pretend to understand nuclear physics, but when a nuke of suitable size is biffed above the ionosphere, when the EMP slams into the atmosphere it gets supercharged. Some sort of cascading effect that results in something resembling a lightning storm. This is the Compton Effect. Which means the line of sight from a great altitude is a cone shape – biff one above Kansas City, depending on the height and power of the nuke, and you’ve just blown most of middle America back to the Middle Ages. Three nukes, biffed East Coast, West Coast and above Kansas City would take out all of CONUS, and even parts of Canada and Mexico…
Anything with solid state electronics in it, if it’s not protected (like your car is parked in an underground parking lot, 4 levels down… you’re probably okay), then it’s DRT (Dead Right There). Any vehicle made after 1980 or so has solid state electronics in it (which means most cars in America) will be DRT – including emergency vehicles, fire trucks, ambulances, life-flights, police cars, prime movers that bring us our Walmart crap, diesel electric trains that bring coal to our power plants, etc… ain’t that a pleasant thought?
While metals conduct electricity, some are better than others. The faraday cages I’ve seen were all made from woven copper wire. I think as long as you’ve got something that will route the electro-magnetic pulse around your stuff and into the ground, like a lightning rod, you’re good to hook…
The wicked flee when none pursueth..." - Proverbs 28:1