You have the frequency spectrum chart for lightning. Each frequency is AC current. Each frequency contains some of the energy from CG lightning.
How were radio transmitters created only from DC batteries? A spark gap created AC from DC. Not very efficient. But like lightning, the discharge through a non-linear medium (the spark gap) puts energy into the AC regions - as demonstrated by that frequency spectrum chart.
If lightning were only DC, then capacitors (ie. open switches rated to exceed the breakdown voltage) would be sufficient to block lightning. Lightning cannot be stopped. Even if the breakdown voltage is not exceeded, still some current passes through the switch due to AC components of that lightning strike. If lightning were only DC, then long wires to earth would easily ground lightning. Again, it is the AC components of lightning that causes telcos to put their switching computers up to 50 meters after the surge protector AND put their surge protector right on earth ground. Wire impedance of lightning puts significant energy in AC components - as demonstrated by that frequency spectrum chart.
Either energy can be transferred by DC, or energy can be transferred by AC. Clearly much of the energy from lightning is found in AC (radio frequencies).
Wire has impedance. A sharp bend is the equivalent of increasing that inductance (and therefore impedance) by factors such as 6 times - a ballpark number. To 60 hz electricity, this impedance is trivial and irrelevant. But lightning is different electricity. We are talking about
10,000 amps with a rising edge of 8 microseconds. Anything that increases wire inductance (such as splices, sharp bends, routing through metallic conduit, etc) means a lightning transient will seek alternative paths inside the building.One trick in commercial radio stations to make lightning seek earth ground is to feed the antenna through a coiled wire or ferrite bead. That ferrite bead may be trivial to a radio transmitter. But to lightning, that ferrite bead encourages lightning to take earth ground at the antenna base rather than find earth through the adjacent transmitter shed. Again, it is the sharp rise time of that pulse combined with the massive (and short) currents that make low impedance ground wire so important to lightning protection. Generally increasing the wire gauge provides little benefit. Decreasing wire length (and therefore wire inductance) provides a much better improvement.
To provide numbers as example: the 50 feet of 20 amp electric wire may be less than 0.2 ohms resistance. That same wire could be 120 ohms impedance to lightning. Voltage difference be between a wall receptacle and earthed breaker box if a plug-in protector were earthing a tiny 100 amp surge? Less than 12,000 volts. That 0.2 ohms resistance is not the problem. That 120 ohms impedance is just another reasons why plug-in protectors are not properly earthed at wall receptacles.
To reduce wire impedance, some installations use flat ribbon wire instead of solid copper. However other problems such as weather and corrosion must also be considered which is why solid wire is often used for earthing. Military facilities are suppose to inspect this earthing system every 5 years or less. How often does the home owner do his inspection? Many home owners don't even know an earth ground exists or is necessary. Just another reason why we make compromises between lower impedance wire and corrosion resistant solutions.
Many reasons for keeping a lightning rod earth ground wire outside the building involves factors beyond the scope of this discussion. But one reason why: once inside the building, then a destructive transient has a building is chock full of conductors. The building concrete. The heating system. Linoleum tile. Etc. The point is once lightning is inside the building, then the building has too many conductive paths to create destructive and induced transients. This is but another reason why we earth transients before transients enter the building.
Analysis and elimination of those so many conductive paths inside a building is just too expensive and complicated. Earth lightning outside the building and a majority of destructive transients are eliminated. Keep lightning outside the building so that protective circuits inside appliances are not overwhelmed. Earth a transient through an adjacent plug-in protector - even a trivial 100 amp transient and the protector is something less than 12,000 volts relative to ground - ineffective protection.
BTW, we earth to accomplish two goals. First we conduct lightning to earth by the most conductive path possible. But realities say we cannot do that well enough. So we attempt to make earth beneath the building equipotential using concepts such as single point ground, Ufer or halo grounds, etc. However we can never make earth equipotential enough. So we make the earthing connection more conductive.
Effective protecti> Isn't the definition of AC electricity whose current changes direction?