A unsolicited lighting installer went up on my roof and told me that I had had a lightning strike and that the cable along the roof line (going from one rod to another) was crystallized and that I needed to have all cables replaced. I sensed a scam and sent him away. Was I right? Can these cables 'crystallize'?
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If you look at this related question
Why doesn't a lightning strike destroy the lightning rod?
The accepted answer explains that the actual energy dissipated in a lightning conductor can be expected to be really fairly modest and as such you would not normally expect a conductor to be damaged by a strike.
Crystallisation of some metals at temperatures which are a substantial fraction of their melting point is a thing but as discussed in the question I referred to this is far above the temperatures you would reasonably expect from a strike. Furthermore i can only imagine that crystallisation really refers to excessive grain growth in a metal when hot working etc and really only applies to alloys like steel where you can get phase changes rather than the relatively pure copper which is typically used for electrical conductors. As far as I am aware pure copper doesn't suffer any adverse effects from heating apart from being annealed which is not a bad thing for a conductor.
While I am certainly not an expert in lightning rods this certainly sounds bogus. I'm sure that there are many potential things which can degrade lightning conductors over time but 'crystallisation' does sound made-up.
answered Jan 19, 2017 at 19:07
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$\begingroup$ Metals are already "polycrystal". I agree that I don't think this seems like a reasonable phenomenon. I'm not sure what the intended function of the lightning rod cable is, but from my quick google search, it seems like the "crystalized" form of copper would be a better conductor. I'm not sure if thats better or worse for lightning rod cable though. $\endgroup$– JMacJan 19, 2017 at 19:45