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I seem to recall that the single largest atmospheric nuclear test ever conducted was by the Soviets and was a stratospheric detonation of something around 50 megatons yield. IIRC it created a second sun in the sky over the USSR for several minutes and was never tried again. The question is whether that test, which was far larger than anything that would likely be used in an EMP attack, has any relevancy since it happened before the digital age. Just don't know. But this whole "EMP will send the US back to the 19th century" sounds suspiciously like the Y2K and AGW drumbeat.

Meanwhile, owning a bicycle or an older spark plug, carburetor, and distributor function car, having a good stock of water, canned goods, and dried foods, an assortment of firearms and ammunition, firewood, and some basic hand operated tools are good planning for any eventuality. Military digital hardware was supposed to be made "EMP hardened" many years ago but who knows whether or to what extent that was accomplished? How much of that found its way for the sake of manufacturing efficiency into consumer goods? If electronics are so vulnerable to EMP why don't the things fail all the time when they are carried through all the electromagnetic fields that surround us on a daily basis?

“I seem to recall that the single largest atmospheric nuclear test ever conducted was by the Soviets and was a stratospheric detonation of something around 50 megatons yield. “

Ah, yes. The TSAR bomba, over the islands of Novaya Zemlya, in 1961:

http://www.youtube.com/watch?v=1q0hzSnKQoE

I seem to recall that the single largest atmospheric nuclear test ever conducted was by the Soviets and was a stratospheric detonation of something around 50 megatons yield. IIRC it created a second sun in the sky over the USSR for several minutes and was never tried again. The question is whether that test, which was far larger than anything that would likely be used in an EMP attack, has any relevancy since it happened before the digital age.

The Tsar Bomba was set off at an altitude of only 4 kilometers (2.5 mi). The higher the altitude the farther the EMP spreads. So at such a low altitude the blast radius was larger than the EMP radius. It doesn't matter much if your car stops running a fraction of a second before you get vaporized.

Of note the Tsar Bomba massed in at 30 tons. There aren't many launch vehicles that can put 30 tons into LEO. And Iran sure as heck doesn't have any. Iran's best launcher shown to date can put around a hundred kilograms into LEO.

Even very compact H-Bombs W-56 warhead that produces a 1.2 megaton blast is in the 300 kilogram range. Low tech enriched uranium atomic bombs of the type Iran is developing will be like the ones used at the end of WWII. So figure <20 kilo ton and the bomb masses in at a whopping 4,400 kg.

Small thermonuclear bombs (Fusion) are very hard to build. They will not be a nations first attempt. Iran hasn't even been able to fire off an atomic bomb (Fission) yet. And fission bombs are too big to loft high enough for an single shot EMP blast. So that limits you to China, Russia, France and the US. Those nations have the low mass high yield bombs and the launchers to put them at 250 km altitude.

Anything with a wire connected to electronics will be affected. Whether it is high voltage power lines or micro circuitry in your phone. The EMP/Carrington induced voltage spike is immediate. Sure fuses and circuit breakers will trip or blow but so will the transistors and other electronics that are designed into circuit boards and protection devices.
Large power transformers (and their electronics) will be harmed. IE- 138k volt to 18k volt utility transformers. Now envision that voltage increases (In one power cycle) to 240k volts on the high side and 36k volts on the other. Anything connected to this transformer will fry. Both protection devices (Digital-If they still work and Mechanical-Metal Oxide varistors used for lightning strike protection) will be destroyed. The coils of wire inside of the transformers (Specifically the insulation on the wire) will break down or fry. I have seen spectacular explosions of these transformers due to insulation breakdown.
Yep, I work in a power generation facility. Some years ago we experienced a power surge. Lightning struck a grounded fenceline on the property 150-200 yards away. It wiped out the electronics for part of our control system. We were not generating at the time, but had we been online I am positive the turbines and generators would have been harmed. On the safe side, we do monitor space weather at work. Anytime NOAA issues an alert on space weather issues we take note. I've received phone calls warning me of possible issues with solar storms while operating. A nuke/emp, well not much of a warning could be expected.
Mind that the control systems are not a typical PC but an industrial computer. The circuitry operates at either 24v DC or 120v AC. These circuits do not like any voltage excursions. We replaced the fried control circuits with spares from the shelf. It was 6 months later that we received replacements for the shelf. They had to be built from scratch at the factory. Then tested. Then shipped.
Imagine (If you can) that happening in a large geographic area. Lotsa facilities will be down. It is possible the spare parts on the shelf won't work either. EMP will be everywhere and any energy conductor will catch it. Most Intel Pentium chips operate at 3-6volts. I don't think they can survive a spike to say 25 volts. Let alone the insulation breakdown due to heat. (wire heats up as the current and voltage increase or printed circuit boards fry)
As far as the electromagnetic fields are concerned- Any device that can generate microwaves (Energy) has to be tested and registered with the FCC. Look on your cell phone for FCC information or imprinted codes. Some have wireless routers for their internet connection. Look at the packaging for the interference information. People with pacemakers avoid microwave ovens for a reason. Interference. Imagine the interference a couple orders of magnitude.
Most people wouldn't place their cell phones in the microwave oven. If the heat created didn't kill it, the microwaves would destroy sensitive electronics
Vehicles are a crap shoot.
Newer vehicles with high energy ignition systems MAY fare well. But,have you ever heard an AM radio broadcast while driving down the road. Rev up the engine and I bet you can hear the whine in the background increase. Similarly driving near high voltage power lines(EMF interference) will pick up static. Now imagine the interference increase a couple orders of magnitude.
Older cars can have issues also. The points in the distributor cap may make it but I think the the condenser will fry. The ignition coil- it takes 12v DC from your car and “transforms” it to a high enough voltage (30k to 60k) to get a spark at the plugs. Say that 12v DC increases to 36v. What voltage would you get to the plugs? Yor condenser wouldn't make the cut at 36volts let alone the saturation in the coil. It's not much current but the volts will kill it. Alternators have electronics too- Rectifiers. Zap.
The high altitude EMP testing done in the 60’s was over remote areas of the USSR and over vast areas of the pacific. Mostly uninhabited. Hawaii had issues when they blew them during Starfish Prime and the USSR didn't come away unscathed either when they did their high altitude testing. ASFAIK.
The Navy has done lower power EMP testing back east. Ships, planes, cars were all zapped. I don't know the results of those tests.
It's a long diatribe on what could happen.
Too many red-bulls.
Agree/disagree? ! ? Anyone