I'm not saying that it's not needed, just making it clear that there are some things it can't do and protecting equipment from lightning is one of them.
After all, the arc of lightning had enough voltage to jump from about 10,000 feet to earth (lightning doesn't just fall to the earth), so jumping a small gap in a little box is simply no problem.
I have been in complete agreement with everything you have said...
I only wish to elaborate on the 10,000 feet statement.
The flashover does not require that the dielectric capability of the air be exceeded the entire length of the channel. Initiation and continuation of the bolt relies on the electric gradient at the tip of the bolt.
Dry nitrogen for example, is typically 70 volts per mil, 70kv per inch, or 27 kv per cm. A uniform infinite flat plate capacitor with a spacing of 10 cm could hold back 270 kilovolts. A van de Graf with a 10 cm spacing from the central electrode ball to the grounding ball will spark at about a quarter million volts.
This volt per distance does not scale well, but relies on there being no edges, points, corners.. At features such as this, the electric field gradient will be higher, so breakdown will occur at features first.
When a bolt initiates, the tip ionizes the air due to the gradient at the tip, and behind the tip there is no real gradient.. So the sharp "object" advances.
Liquid argon for example, flashes over at 2 megavolts per cm. A 1.2mm diameter sphere with 125 Kv on it will have a surface field of 2.08 megavolts, which will initiate flashover. A .1mm wire 10 cm from a grounded plate and 125 kv will have a surface field of 1.8 megavolts, very close. This is why all very high voltage widgits have big toroids or tubes or spheres...to prevent high surface fields that start an arc. Pass the vinyl Igor....
In general, the distance the bolt travels is not determined by the cloud to earth potential, but the gradient where the bolt initiates. The path it takes once it hits a house will be determined by the gradients at the leading point. Typically, the gradient points directly at the most expensive electronics it can find....
jn
ps. Today, I feel good..so I will not apologize for the complexity of this post...I am having fun.
