So I’m just about finished with my first read through of my 1987 copy of ‘The ‘grounds’ for lightning and EMP protection’ by PolyPhaser corporation. If you haven’t heard of them- when the big commercial outfits, governments, and the US military need tower and communications shacks to be designed as ‘lightning proof’, PolyPhaser’s products or design was likely involved. They also do design and testing of HEMP certified equipment.
Even though that book is long since out of print, I just found* the updated version written in 2000 by the same people:
Posted here for some discussion of the physics and engineering involved. It’s dispelled a lot of myths and misunderstandings about lightning and grounding that I’ve had, and as a HAM operator I consider that important. Not likely that I’m going to have AT&T’s budget to truly ‘lightning-proof’ all my stuff but it’s a good lesson in techniques that can reduce damage caused by nearby lightning strikes and, also useful, techniques that if only done half-way might actually make things worse.
If I understand this right- the voltage of a lightning strike isn’t really something that matters. It is only the current that is of utmost concern. As every conductor is an inductor, every cable, guy-wire or tower segment a lightning strike passes through on it’s way to ground represents some impedance. When a massive (80-200kA) current passes through these different inductors, it is the resulting voltage difference generated between them that causes all the spectacular destruction of equipment inside a comms shack.
So, discussed in this book is the techniques for reducing that current spike before it reaches the building as much as possible- and then shunting off what does make it inside in the proper way.
Also included is a little bit about the nature of EMP. I thought it was interesting to see where some aspects of lightning protection overlap and where they do not. An EM pulse does not deliver the current of a lightning strike, but the incredible high speed of the E1/E2 pulse and resultant high frequency ringing that occurs is what does damage differently than a lightning strike; and therefore requires different techniques when designing protections.
* if the book link ever stops working let me know, I’ve got a downloaded copy here.