[Gllug] OT Lightning

Chris Bell chrisbell at overview.demon.co.uk
Sat Jul 6 07:34:28 UTC 2002

On Sat 06 Jul, Kevin wrote:
> Well, in theory, the lines should be protected, but I always use a modem
> line surge protector.
> They're only about 10.

   The BT termination boxes have spark gaps fitted between the two incoming
wires, but there is not normally an earth connection so they can still pass
a surge that is common to both wires. I have an underground phone line, but
I have still passed the incoming line a few times through the ferrite core
from an old TV line output transformer.
   I also have a TV tuner card in a computer, so there is a thick copper
cable direct from my TV aerial pole to an earth spike, and the aerial feeder
does a few turns through another ferrite core. The aerial then acts as a
lightning conductor, so that there is a continuous discharge which reduces
the chance of an instantaneous strike.
   The average lightning "ground" strike rate is now much lower in towns
because of the number of aerial poles pointing towards the clouds, but a
single direct strike can still do a lot of damage.

Chris Bell

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