Read up on EMP please. What they did was detonated it underground to contain not only the explosion but also the radiation effects. EMP is a radiating pulse from a high altitude detonation at about 60 miles. EMP’s are evident in all nuclear explosions. It is the size of the explosion that determines the area affected under it. The difference between a nuclear and a hydrogen bomb is of prime importance to the immediate concern.
http://www.onesecondafter.com/
When I see discarded microwave ovens that are thrown out because they stop working, I pick them up because they can provide a safe for protecting spares for certain electronics like my vehicle computers and sensors that I can swap out to get my vehicles running again. I also keep a radio and old notebook in one.
The size of the explosion has very little to do with the EMP effects. EMB is caused by gamma rays. Gamma rays are produced much more efficiently by atomic, i.e. fission, weapons. Further, the altitude at which such an explosion occurs is of prime importance. That part you understand quite well.
A “nuclear” bomb is commonly understood to be a hydrogen, ie fusion, weapon - though sometimes that distinction is lost on people. I have found that it is easier to compare them using similar terms. For example, either refer to them as atomic or hydrogen bombs, or refer to them as fission or fusion weapons. That way there is no confusion at all as to what you are speaking of.
Regarding microwave ovens, you have to be very careful about openings to the rest of the world. I speak specifically of where the plug enters the oven. If that is not covered up with some kind of a screen that will also filter out the EMP waves, then you have an incomplete Faraday cage, meaning that you have something that simply will not work.
o wow I threw 3 non working microwaves. Didn’t realize they could be used for protection from an EMP.