Lighting protection for TV antennas?

[Richard Freeman]

"Bazil" <nospam@spamzfree.net> wrote in message
news:425db217@news.comindico.com.au...

Franc Zabkar wrote:
On Wed, 13 Apr 2005 16:28:03 +1000, "Richard Freeman"

That is actually about as incorrect as you can get.
In fact most Lightning damage comes from sources other than Lightning
strikes to MEN mains.
ie:
Phone Lines (yes even underground ones)
Aerials
and direct strikes to houses


Hmmm, that seems counterintuitive. I would have thought that a strike
on the mains would affect several households and would take out
expensive appliances. OTOH, a strike on the phone line may take out
your phone or your modem, but not much else. Strikes on aerials would
also be localised events.

Not at all. While that does happen, when lightning enters phone lines,
look out. I saw two very dead and burnt motherboards that were connected
via modem to the phone lines. One was actually warped and twisted from the
heat. The strike was half a k up the road and just like Richard mentioned,
entered the phone lines through the ground. I don't know why mains strikes
seem to have a smaller radius of damage (maybe all the neutral grounding?
maybe the higher load presented by all the connected appliances? higher
capacitance? probably all of above),

Another thought is that Lightning damage attributed to Mains strikes are
often not the result of a strike on the AC mains at all but rather Near
strikes on nearby Trees or direct - Secondary strikes to houses, buildings
etc.
I think one of the biggest ironies is that folk are used to assuming that
equipment is susceptible to Lightning damage from the AC mains and the
'surge arrestor' industry hyes this expectation up so that when equipment
does suffer Lightning damage it is often assumed that the damage came in via
the power system so that little or no investigation is carried out as to
where the Lightning strike actually occoured.
I Believe that the main reason for the minimisation in Lightning damage from
the MEN mains is that the multiple Earths provide what is probably the best
Earthing system that it is possible to get at (relatively) low cost - in
fact Radio and Tv transmitters try to achieve the same thing by using
multiple earth stakes over often 1000 square meters or more and even they
suffer Lightning damage from time to time.

but it has always been said to disconnect your modems during electrical
storms.

Of course the reality is that a strike is going to cause damage to
whatever it hits. It's just where it goes and via what medium after that.

Yep that pretty well Sums it up !

 

[dmm]

On Wed, 13 Apr 2005 16:28:03 +1000, "Richard Freeman" <bogoff@nospam.spam> wrote:

"Bodgey" <ihate@spam.com> wrote in message
news:iSX5e.5584$5F3.169@news-server.bigpond.net.au...
That's from the lightening hitting his power supply not the aerial. Most
lightening hits come from the power supply, being hit on your aerial is
very
unlikely.

That is actually about as incorrect as you can get.
In fact most Lightning damage comes from sources other than Lightning
strikes to MEN mains.
ie:
Phone Lines (yes even underground ones)
Aerials
and direct strikes to houses

Lightning does not just strike only power lines, or only telephone lines.
Its not that selective. They typically have multiple strike points, which
are not restricted to one location. They can strike trees, power lines,
roofs, people, telephone lines, cars, etc. When you consider that millions
of volts and hundreds of thousands of amp are conducted to earth by
these strikes, it's no wonder that equipment that may be isolated by some
distance can suffer.