[Towertalk] Lightning protection

[Cleeve]

Good afternoon gentlement,

	My question, after reading all the contributions with interest, is, how do
the professional broadcasters protect their facilities then. 

	My personal, and very frightening experience, of a lightning strike, occurred
some thirty years ago. I was standing, waiting for a bus beside the road, that
runs along the front of Alexandra Palace, which is built on high ground, in
North London. Alexandra Palace was the home of BBC Television, before and, for
a while, after WWII. 

	The antenna tower is incorporated into the structure of the building, and
must be about 300 ft in height. The tower was no longer in use for television
transmissions at the time, but other facilities were using it.  As I stood
awaitng the bus, about 100 feet from the building, a single big black cloud
above, appeared to be slowly making its way along the length of the building,
and as it got close to and above the television tower, there was a huge flash,
and a deafening noise, as the cloud discharged to the tower. 

	The earth strap for the tower is about 3 inches wide, by half an inch thick
copper, which runs down the tower and brickwork, to the tarmac and then
disappears under the tarmac of the car park and adjacent road. I was told that
the earth system, laid down when the television service was operational from
Alexandra Palace, around 1938 or so, consists of a very large area of copper
sheet, buried in the sloping ground, of the parkland which fronts the
palace.... if this is true, then the tower ground strap was passing under my
feet, when that cloud discharged..... the only damage to electronic equipment,
was that the colour TV receiver, in the senior engineers office, which was
about 60 feet up, inside the structure of the tower, required degausing....For
those of you outside the UK, if you are interested, then during a visit to
London, you can still see Alexandra Palace, and the very same tower, when
looking left from the railway lines leaving Kings Cross station about ten
miles out from the city....

	The replacement TV tower for London, is now on high ground, at Crystal
Palace, in  South London. This tower was manufactured by BICC, and is 750 feet
high. To the best of my knowledge, as a retired BBC engineering employee, but
not in transmitters, the transmission facilities have never been lost, as the
result of a lighting strike, although there have been many, since the tower
was erected 40 or more years ago......the actual design and building of the
tower is the subject of a film called "The Phoenix Tower", made by BICC, well
worth viewing, if you can find a copy now.... (BICC = British Insulated
Callenders Co.)

	Can anyone answer my question....thank you in advance, John Cleeve. G3JVC.