Lighting protection for TV antennas?

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The subject says it all - is this something that is often/ever done?



Re: Lighting protection for TV antennas?



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**Pray.

Seriously, there is not much you can do. When my antenna guy put mine up, he
offered me lightning protection. For $150.00, I figured it was cheap
insurance. He put a 7mm diameter aluminium cable from the mast to ground. It
probably doesn't work, but it is probably better than nothing. In 30 years,
I've not had a problem, but that proves very little.


--
Trevor Wilson
www.rageaudio.com.au



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The paranoid disconnect the cable from the wall.

Dave :)


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finger to keyboard and composed:

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A friend's house has been hit twice. He lost most of his electronic
equipment on the last occasion. His neighbour was worse off - his
meter box had to be replaced. Fortunately my friend was insured.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

Re: Lighting protection for TV antennas?


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.

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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.


***** The mind boggles!!!!!!!!!

Brian Goldsmith.



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   Really?  Why did I find pieces of my TV antenna more than 150 feet
from the mast after it exploded from a lightning strike?  The same
strike burnt open the underground phone line for more than a mile out to
the highway where it destroyed the electronics in the phone companies
pedestal?  it also damaged a computer and monitor that had no cables
connected when lightning hit the antenna.  Over $2000 dollars worth of
damage including battery powered items that had IC chips explode from
the EMP.

--
Former professional electron wrangler.

Michael A. Terrell
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Re: Lighting protection for TV antennas?



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That is obviously the Lightning entering the MEN mains, avoiding all those
unpopular Earth stakes and exiting out via the Antenna...... After all the
Antenna is Metal remember ! (semi-quote from one of the more Technically
stupid movies I have ever had the Misfortune to watch - Hard rain )

 The same
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But where is w_tom ? he reckons that Telco equipment is never damaged by
Lightning Strikes ....

it also damaged a computer and monitor that had no cables
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Just wait w_tom will be along shortly to tell you what really happened ;-)

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Re: Lighting protection for TV antennas?


to keyboard and composed:

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I agree. I was just making the observation that some people have a
good reason to be paranoid. In fact another friend's house (at a
different location) has also been hit more than once. His strikes came
via the power supply, too.

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- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

Re: Lighting protection for TV antennas?



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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




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Mornin,
Mains sure can bring in a lot of overvoltages - happens all the time.
True, the neutral is bonded to earth in many places (ie earth bar in
MSB, to every power pole, to high voltage earth etc). This isn't
saying stikes dont occur elsewhere but they often come in via the
mains. Its not only lighting either, tree branches can often force the
HV lines down onto the LV lines, sending 50Hz high voltage into
houses. While the lines will trip out on earth fault quickly it will
still cause damage to appliances.

Getting back to the OT, earthing the pole will help, but in the event
of a direct strike you'll still most likley do damage to your TV. What
it may do tho is prevent the many kA's coming inside and damaging lots
of other things too. Unplugging is best - I usually do that when
things aren't in use or a storm is approaching - lots of lightning
around here

Cheers
James

Re: Lighting protection for TV antennas?


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

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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.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

Re: Lighting protection for TV antennas?


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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), 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.

Bryan

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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.

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Yep that pretty well Sums it up !



Re: Lighting protection for TV antennas?



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It is largely a Conclusion I drew having Visited/Repaired many Data
communications and Computer installations following Lightning Strikes. my
observations where as follows:

Most damage to Computer systems was pretty well confined to equipment that
was connected to Data lines, Aerials and or internal building cabling (other
than AC mains) with equipment plugged into AC mains alone more often than
not surviving unscathed.
Arc tracks from Lightning consistently showed signs of arcing from unearthed
phone lines, aerials etc (line interfaces etc) typically across to chassis
and earthed equipment metalwork but I do not recall ever seeing evidence of
arcing from AC mains connections to Earthed metalwork.


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And every other Phone/modem/LI etc connected to that cable and often the
cable itself - Conterary to popular belief underground cables are just as
susceptible to Lightning damage (some people I have spoken to have argued
that they are in fact more susceptible) as aerial cables due to effects such
as EPR,EMP etc In fact I have seen Lightning strikes that have blown over
200 surge arrestors off the MDF terminating an underground cable and still
destroyed equipment in the building and this from strikes to the cable over
100m from the building.
In fact one strike I cleaned up after at the most inappropriately named
Mount Peasant (google groups search for 'mt pleasant' in aus.electronics for
the tale - and other tales of my Lightning experiences) blew the tripe out
of 50 surge arrestors, damaged faxes, modems and Eftpos machines etc and
still damaged a connector at the other end of over 5kms of cable.

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That is correct In fact most Lightning damage I have seen is localised in
nature with the exception of Lightning strikes to phone cables.

It seems counter intuitive until you realise that MEN power Distribution as
the name suggests employs a Multiple earthed Neutral (a single earth stake
is in fact inadequate during a Lightning strike as a Lightning strike
usually causes an EPR often exceeding 100,000 Volts)  is made up of
relatively low impedance cabling and often also employs lighting protection
such as earthed wires above the power lines etc.....

Regards
Richard Freeman




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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.


Re: Lighting protection for TV antennas?


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The answer is simple!

Install a 30mm steel pipe in the ground next to your house, just make sure
it's 3m higher than your antenna and at least 2m underground.

Of course, this may attract more lightning than you usually have hit your
aerial...

-mark



Re: Lighting protection for TV antennas?



The subject says it all - is this something that is often/ever done?


**** I have never seen any TV antenna fitted with a non translucent
cover.Then again I really dont understand why you want to keep the light
away from the antenna!!!!

Brian Goldsmith.




Re: Lighting protection for TV antennas?



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Way back yonder when Flintstone was just a slip of a lad, the TV aerials had
to be high. LightNing hit next doors' aerial and ran down the disconnected
300 ohm ribbon to blow a rather large hole in the concrete floor. I've been
a bit sus of bright flashes and loud bangs ever since .




Re: Lighting protection for TV antennas?


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For coax, a 90V GDT (gas discharge tube) between the inner and outer
conductors and earthing the cable screen is about all you can do.

It's a bit tricky to substantially earth the screen on RG59 though.

One of these might be the go:

http://www.novaris.com.au/images/stories/Sales%20Kit/SK05/CB12-90_high.pdf
http://www.novaris.com.au/images/stories/Sales%20Kit/SK05/pp10_high.pdf

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