I’d be interested to know where as well. I’ve never read of any actual EMP blasts done over cities. The only ones I’ve heard of were the original open air blasts done before they knew about EMP. In those cases there was minor damage observed in Hawaii when the blast was in AZ.
There has been some other testing done with non-nuke EMP. The test methodology was questionable since they used borrowed vehicles to determine the damage. The vehicles had to be returned fully operational.
Link was posted
My understanding is that they didn’t have any effect because the electronics were not as sensitive as they are today.
The Soviets were aware of EMP and had studied it as a potential weapon before the US did. The US knew about EMP and considered it an undesirable side effect of a nuclear blast.
The first time they started looking at it in earnest was Operation Fishbowl. That’s worth looking up.
In the 60s we actually started working with nukes in order to do something other than burn or blow up a lot of stuff. The Cobalt bomb is an example - can we use a nuke to kill all sorts of people, but leave the buildings standing?
Turns out you can to a large extent.
A nuke that was tailored to produce a large EMP effect would not be a massive, megaton weapon. It would be something designed to shake as many electrons out of the upper atmosphere as possible. Those electrons get lensed back down to the surface of the earth where they are picked up by long transmission lines in three distinct phases.
The second one is the one that does most of the damage - destroying large transformers and the like. Solid state devices - semiconductor devices - would not cotton to a massive EMP.
The thing is, we may end up being surprised. Most big concrete structures have rebar in them and it is networked together like a faraday cage. No telling what electronics will survive in structures like that.
The electrical generation and distribution, however, is out in the open and it will be toast.
Add to this that we don’t manufacture the transformers we’d need to recover from something like that any more here in the US.