"..........I'm an Electronics Engineer, and I've worked inside a large number of cages over the years. There is a lot of myths about the cages running around, but almost without exception, they all neglect one single fact. For a Faraday Gage to function properly, it MUST be grounded to the earth, solidly and properly. this means multiple ground rods and heavy ground wire, NOT aluminum, but COPPER. Another myth is that an EMP will take out electric motors, this is a major fallacy, and can be seen as disproven by a quick google search for the YouTube video where a Ford Taurus is driven into laboratory pulse field, it took out the ignition system and the ECM but the electric windows still operated. Purely contact based thermostats wont be affected, electronic controllers will, but unless you have a protected generator, your AC wont work.
The North American Power Grid is not hardened, and an EMP will shut it down. What happens with an ELECTRO MAGNETIC PULSE as a current is generated across all wire (remember the electo magnets we made as kids?) well this current creates a voltage spike that is extremely high, so high that it will burn out all the solid state devices within the magnetic field of the EMP this means all microchips, transistors and diodes will burn out. A low level EMP will even burn out thyristors which are what surge suppressors are made out of. Quite literally any electronics made since the mid to late sixties and forward are susceptible. As for protecting your vehicle, two words SPARE PARTS... or a vehicle that is pre 69... with a carburetor and breaker point ignition. Military trucks are hardened, and use different alternators and are generally diesel with mechanical based injection for this reason, the electronic controlled vehicles are considered sacrificial and can be found on government auction sites with very low miles/hours because they just don't want to deal with them after an aftermath, but the hardened vehicles are either stripped for parts or rebuilt, and you will find their hulls on the sites for scrap metal only. Especially the Mraps and Hummers.
One other thing, the "frequency" of an emp is irrelevant since it is a singular event. If it is due to a Nuclear detonation it viably could throw a pulse that would equate to a frequency of a THz (terahertz)or 1000 gigahertz, and your mesh wont stop it. next the wavelength of the typical cell phone transmission is either 13 inches or 6 and a quarter inches, depending on your carrier, now with that said, all it takes is less than 1/8 wave ingress for a recoverable signal to penetrate a cage.
Meaning less than 1.6 inches or just a hair over 3/4 of an inch opening in the cage, and remember, this is to receive an intelligible signal, and that is due to the fact that our cells are digital, analog would not need that much. Now for the bad news, that one terahertz EMP single pulse? it has a FULL WAVE LENGTH of THREE millimeters so NO MESH what so ever will block it.
Ive been working in this field literally for decades, dealing with Computers, Communications and Electronic Security. Ive paid my dues as a technician who was sick of dealing with engineers who were clueless about what the tech had to deal with in the field so I moved up the ladder in order to make a mark in that respect. It didn't help. Colleges are just big sales machines and try to sell the old standards and don't care about reality."