You say EMP, by which I take you mean human created?
What about a massive solar flare? Could the end result of one or even a freak storm of several (say a temporary but powerful magnetic anomaly within the Sun) be as catastrophic as a man-made EMP?
A coronal mass ejection would have to be a big one, but its already happened. In 1863 there was one so big it made telegraph lines light up, arc, and spark. The aurora it created was so bright it woke miners in California who thought it was morning, but it was o-dark 30 in the morning.
Gamma radiation knocks electrons out of the ionosphere. Because it’s spherical, it lenses those electrons down to the earth’s surface. Long conductors pick those electrons up and load up both sources and sinks. Transformers are a form of a sink. Generators are sources. Generator winding cores would melt down pretty readily too.
Nuclear EMP actually has three parts - E1, E2, and E3. E1 is the part that fries small electronics and semiconductors. E3 is called the long tail part of the pulse, and it can last up to 100 minutes after the initial detonation. I can’t remember what E2 was, but E1 and E3 were what you had to worry about.
You don’t need a big bomb to make it happen. You need a high detonation point (90 to 130 miles up). Lower yield weapons actually work better because the higher the yield the more the initial blast absorbs the gamma yield.
Thus, you should be more worried about idiot regimes getting their paws on a medium range missile than a nuke. Assume they can get a nuke, what you need is a missile that can reach the right altitude before it pops.
There is SOME fallout from a high altitude burst, but for the most part it is the cleanest type of nuclear strike you can do. It’s something you’d use if you were going to come in and colonize a foe.