On 01/11/2020 11:42, Brian Gaff (Sofa) wrote:
its obvious that there are micropores in most materials

If ordinary TV cable is permanently immersed in water the copper braid
gets discoloured, and sometimes the cable becomes very lossy. Some
installers run cables along gutters and if the gutter isn't draining
properly and is nearly always full of water that's when it can happen.
It also happens when pillocks run ordinary coax underground,
unprotected. Also when underground cable is in a duct and the duct has a
point lower than anywhere where it can drain.

This is why we have 'direct burial' cables of course.

Bill