I have not came across this myself, but have recently observed a new bank of mobile phone masts being installed in the grounds of my work place and noticed they ran there lightining conductor (which was i noticed, insulated?) straight onto there own earth rod!
I think I've seen this too. Alongside the electrical panels on this floor, there are bundles of cables going up to the roof where there are a lot of antennas. Among the wires is a thick green/yellow wire, which I assume is a lightning conductor.
Is it a good idea to introduce such high voltages towards an earthing system which is not struck?
Despite the fact that ordinary lightning conductors are bare and run close to buildings, they protect the building. I guess the insulation can be there simply to keep people from touching the wire, i.e. not introducing a shock hazard beacause of different potentials.
OTOH, the insulation on the wire can withstand a higher voltage than normal for the very short period a lightning lasts and if the lightning has a good path to earth, it is not going to jump to find another path.
(Personally, I still don't like it. I think the conductor it has to withstand hundreds of kilovolts, something which requires several millimetres of insulation. But then, I'm just a student who doesn't know this field.)
[This message has been edited by C-H (edited 05-27-2003).]