Why should soldered joints not be used in lightning protection ground connections?

Lightning strikes carry tens of thousands of amps of electrical current. When this massive current flows through a grounding conductor, it generates extreme heat almost instantly due to electrical resistance. Because solder has a relatively low melting point compared to the copper wire it joins, the flash heat from a lightning strike will easily melt it. This destroys the protective ground connection exactly when it is needed most. For lightning protection, mechanical connections like heavy-duty clamps or exothermic (welded) connections must be used to ensure the ground path survives the strike.