A couple of comments:
1) Asymmetric warfare: NK is practically immune to EMP itself because its infrastructure is so limited and backwards, as shown by the space photographs of NK at night. Virtually no lights.
2) The grid is a problem whose immunity I don’t know about.
Device immunity may be much different. I can tell you that even at the commercial level, EMC hardening must have a major protective effect against EMP. Hardening equipment to electrostatic discharge (ESD), and to various other radiated and powerline conducted electromagnetic insults is mandated by various international standards and is common practice.
“Device immunity may be much different. I can tell you that even at the commercial level, EMC hardening must have a major protective effect against EMP. Hardening equipment to electrostatic discharge (ESD), and to various other radiated and powerline conducted electromagnetic insults is mandated by various international standards and is common practice.”
Devices are affected by the E1 pulse, which, unlike the E3 pulse, doesn’t penetrate the ground. So it’s possible that buildings will shield computers to some degree from the E1 pulse.
Also, a very interesting feature of one of the Soviet tests was that the E1 pulse from a two-stage (i.e. hydrogen) bomb was surprisingly low:
“Interestingly, different sources concur that prompt peak E1 component of this 300-kiloton Soviet test was not excessive: between 5 kV/m and 10 kV/m. This is likely a result of the pre-ionization effect in two-stage weapons [16].”
http://www.thespacereview.com/article/1549/2
Hydrogen bombs work in two stages, with the normal atomic detonation causing a second fusion reaction. The Soviet test suggests that, in the case of hydrogen bombs, the first stage pre-ionizes the atmosphere and ruins the ability of the second fusion detonation to cause a large EMP.