Grounding TV Antenna?

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View


Hello,
I noticed in a recent thread that grounding (earthing) TV antennas was
mentioned.
I have a TV antenna on my roof and there is definitely no earth connected.
What are the implications?
Should it be earthed?
What should be earthed? (mast?screen?both?)
Does it make a difference for the reception quality?
If the mast would be earthed, wouldn't it act as a lightning rod? In
which case the gauge would have to be rather large and the earth point
of low resistance and the wire would have to run outside the building, true?
I assume connecting it to the Neutral earth point would be a nono?

Any hints appreciated:-)

Tony

Re: Grounding TV Antenna?



"Tony"

Quoted text here. Click to load it

**  Serious.


Quoted text here. Click to load it

**  Yep.

Quoted text here. Click to load it


**  Both -  usually the cable screen is grounded to the metal of the
antenna.


Quoted text here. Click to load it

** Nope.


Quoted text here. Click to load it


**  It is a grade A lightning target anyhow

 -  but earthing removes most of the risks to the householder.


Quoted text here. Click to load it


** Yep -   IIRC,  the ground wire needs to be 6 sq. mm and go direct to a
galvanised stake driven deep into in the ground.


Quoted text here. Click to load it


**  Well,  that is supposed to be the MEN ground point for the premises.

But there is obviously less risk with a dedicated ground stake.

Find a tame " roof monkey "  and ask it what the rule is.

Offer peanuts for a reward ....



.......   Phil






Re: Grounding TV Antenna?


Quoted text here. Click to load it

  The antenna is already acting as a lightning rod.  Where do you want
lightning earthed?  Via an earth ground rod, or via your TV?

  Electrical code (article 800) defines how that antenna must be
earthed and to what that earth ground rod must connect.


Re: Grounding TV Antenna?


Quoted text here. Click to load it
Thanks for all this great input!
Very interesting to hear that there is a standard  that doesn't seem to
be applied a lot. In fact I have never seen a grounded domestic TV
antenna here in Perth.
The 'roof monkeys' (do the have to be licensed?) mast know a way around
the rules. The fact that there is not much lightning damage I here of,
should indicate that the risk is not too bad. Insurance companies would
be looking into this, wouldn't they?
I could locate links to:
AS 1417.1-1987 Receiving antennas for radio and television in the
frequency range 30MHz to 1 GHz
AS/NZS 1768:2003 Lightning protection
AS/NZS 1367-2000 Coaxial cable systems for the distribution of analog
television....
Don't know what they say, is there a way to get them for free?
Is this
http://www.hdtvprimer.com/ANTENNAS/basics.html
a useful link?
I would like to have the antenna earthed anyway though. Can anyone
recommend someone in Perth?

Cheers
Tony

Re: Grounding TV Antenna?


Quoted text here. Click to load it

I wouldn't worry about it too much. The chances of being struck by
lightning is, well... about the same as getting struck by lightning.

Dorfus

Re: Grounding TV Antenna?


Quoted text here. Click to load it

---------------

I recall from about 25 years ago being told that lightning rod
conductors have to run down the outside wall of a building. A direct
lightning strike can deliver incredible voltage / amperage,
potentially more than enough to vapourise typical domestic cable
conductors instantly. Due to the amount of heat dissipated, the
possibilty of molten metal sprayed around and the explosive effects of
cable failure, and the fire hazard as well as being able to inspect
the cable visibly to see if it has failed and needs replacement,
putting it on the outside of the building is the safest option.  You
could possibly mount it behind or beside an existing drain pipe if you
dont want it visible

One lightning rod installation I have seen (on top of a town hall
clock tower) uses flat metal strap about 30mm x 5mm as a conductor to
ground.

The potential dangers just mentioned are another good reason why you
don't want to use a neutral wire inside your house for an earth
connection.
While a Neutral connection is connected to earth, it does go through
the earth leakage unit (you do have one I hope ;), and therefore its
possible that it will be disconnected if the earth leakage unit trips
(and Im sure it will if lightning strikes)

Wire and earth stake can be bought from Haymans/Turks etc.  Make sure
the cable, clamps etc are all suitable for outdoor use

Looking up the Australian standard quoted would also be an excellent
idea.








Re: Grounding TV Antenna?


Quoted text here. Click to load it

  Most all lightning has so little energy that well over 95% of all
struck trees leave no appreciable mark.  However (very rare) one
lightning strike may discharge the entire cloud.  That 200,000 amp
strike is why we install heavier wire - so that even the rarest strike
does not flay vaporized metal - create a fire.  BTW, lightning strike
only has incredible voltage when it uses less conductive materials to
reach earth.  Why do we install conductive earthing?  So that current
remains constant - and voltage is massively lower.  Therefore energy
is dissipated in earth - not in that earthing conductor where no
incredible voltages exist.

 That wire should not be behind a pipe.  It must be routed at least a
third of a meter or more from all conductive materials.  Arcing to
other conductive materials creates problems such as fire.  We want
that lightning current connected to earth without arcing.

  BTW, much energy in that earthing wire is actually outside of the
wire.  We want that wire where its surrounding volume is
electromagnetically clear and open.  Just another reason why we want
the wire outside of residential buildings and not behind a gutter
pipe.

  Relevant is a concept called impedance. Low impedance is why large
currents do not create incredible voltages.  Impedance is defined
predominately by wire length and other factors.  That earthing wire
must be as short as practical, avoid sharp bends, no splices, be
separated from other conductive materials, and separated from all
other non-earthing wires.  Neutral wire would have too much impedance,
violate those other principles,  AND may simply make an earth ground
connection in other directions, destructively, through household
appliances.

  Earth ground rod should be bonded to other ground electrodes.  When
bonded via a buried wire, then devices on one ground (ie TV,
telephone) will not become conductors of the other grounding circuit
(from cloud through antenna to earth).  That buried interconnecting
wire also improves both grounds.

  How likely will lightning strike the antenna and not the house?
Answer is found in the quality of and connection to that earthing
electrode. A low impedance connection to a better erath ground means
better protection for a building.


Re: Grounding TV Antenna?


A lot of this is good but a little is misleading. There is incredible energy
in a lightning strike. The ones that "leave no marks" on a tree are not
direct strikes at all, but up to 50m distant. Same as reports that Fred was
struck by lighting and survived. He couldn't have. He would be virtually
vaporised if he received a *direct* strike. He may have received a minor
sideflash from a close strike. The voltage necessary to promote the huge
spark (for that is what it is) is enormous. But BTW it is not DC. It is a
complex oscillatory discharge, sensitive to impedance and not DC resistance,
as the post says. All in all that post is about 1,000 times more informed
than even the so-called "scientific" reports in the media. Just needs the
concept of "hardly marked" trees to fix.

Quoted text here. Click to load it



Re: Grounding TV Antenna?


   Nothing misleading about that post.  Lightning only has incredible
energy in myths.  Lightning has high power, but not high energy.

  Nearby strikes leave no damage.  Well over 95% of direct lightning
strikes leave little indication because energy in a direct lightning
strike is only large in myths.  View a protector rated to earth 50,000
amps of direct strike lightning.  Notice how small that earthing wire
really is.  Numbers below will demonstrate why.

  Instead of speculating, we consult experts:
Quoted text here. Click to load it
Engineering":
Quoted text here. Click to load it

Martin A Uman   All About Lightning
Quoted text here. Click to load it

  Other provide numbers.  In sci.physics.electromag  on 4 Nov 2000
entitled "Oddball question" at:
  http://tinyurl.com/f495w
Quoted text here. Click to load it

  Fact that trees are struck so often without appreciable indication
comes from a US Forestry Study by Alan Taylor.  This poster does not
speculate.  A source of myths occurs when power is confused with
energy.  Lightning does not have the incredible energy that many only
know from feelings.

 Meanwhile, the OP is encouages to learn the history of his
neighborhood for at least the past decade - to appreciate his
lightning risks.  Often at greater risk are household appliances since
utility wires down the street may be struck more often.  That strike
would be a direct strike to household appliances.

Quoted text here. Click to load it


Re: Grounding TV Antenna?


Now, to my surprise, in view of my immediate reaction to this I almost
sympathise with Phil! A large amount of my professional life has been
associated with lightning and I am considered an authority on the subject. I
am afraid you are partially ill informed.

Quoted text here. Click to load it



Re: Grounding TV Antenna?


Quoted text here. Click to load it

  The rocket faciity for creating lightning tests was created by Dr
Uman. Many if not most papers that resulted from those tests have Dr
Uman's name attached. Dr Uman is considered the best if not one of the
best experts on this subject.

 Cited were facts from Dr Uman's book.  Gingre cited himself.  What is
Gingre's professional experience?  An ESE salesman?  Many whose
'large amount of a professional life has been'   was only selling ESE
devices.  What does that prove?  Nothing.  ESE devices being sold by
'lightning experts' are better called a scam.

  Those who actually learned this stuff are quoted with sources and
numbers.  Telling us that Gingre knows the experts are wrong -  and
not one technical fact from Gingre?  I smell an Early Streamer
Emission salesman who routinely claims expert knowledge.  Somehow we
should believe 'he knows' because lightning  'make a big noise'?  No
numbers.  No citations.  Gingre just knows; justifying the tone of
this reply.

  Meanwhile, Phil Allison's post is accurate.


Re: Grounding TV Antenna?


Where does Gingre say "make a big noise"?

Quoted text here. Click to load it



Re: Grounding TV Antenna?


Quoted text here. Click to load it

  Where does he say anything but "'he is the expert; automatically
believe him".   Gingre does exactly what an American president also
did.  He also knews Saddam had WMDs - "trust me".  At what point do we
say, "I'll never make that mistake again"?

  Numbers are blunt clear.  Lightning is high power and not high
energy.  Experts even note by example.  Over 95% of trees directly
struck by lightning leave no appreciable indication - Alan Taylor and
Dr Martin Uman.  People who are 'real world' experts and who learn
from those experts provide numbers and peer reviewed facts.  Those
citations contradict Gingre.

  Same reason why TV antenna is earthed - so that house and TV need
not suffer damage.

  If Gingre said he knew because "it make a big noise", then he
provided more  'whys'  than in all previous Gingre posts combined.


Re: Grounding TV Antenna?


But he didn't say that!

Quoted text here. Click to load it



Re: Grounding TV Antenna?


Quoted text here. Click to load it

  Of course not.  Did you understand the point?  Gingre did.  As he
noted:
Quoted text here. Click to load it

  Your concern is for facts.  First thing one needs in posts are
'why', 'what are the numbers', and 'where are citations for this
science'.

  Historical lessons about WMDs so important that all are sensitive
when supporting 'whys' is not provided.  No numbers.  No citations.
Reports in direct contradiction to what had been known.  Even overall
objectives completely contradicted WMD assumptions.  We are not
discussing WMDS.  We are discussing how people are taught to think so
as to be responsible.  But then that last sentence should not be
necessary; conclusion should be obvious.

  It does not matter that Gingre did not say anything about a 'big
bang' because the point of that phrase was well beyond whether the
phrase actually existed.  So many declare massive energy in lightning
strikes and then invent claims such as a 'billion volts'.  They did
not even learn from history - did not learn from the WMD fiasco and
large number of resulting innocent deaths.

  No facts.  No numbers.  No citations.  No theortectical concepts
that are confirmed by experiments.  Exactly why we teach how to do
science in junior high school.  Conditions that are necessary to have
a fact. Clearly the point of an expression about a 'big bang'.
Fixating on a phrase existence occurs when the important point is
completely misunderstood.


  Returning to the OPs original post:  an antenna is grounded so that
even the TV will not be harmed by direct lightning strikes.  However
most codes require that grounding, firstmost, so that human life is
not at risk.  An antenna must have a short, direct, etc connection to
earth.

  Not mentioned is another earthing also required to protect that TV.
Before its coax cable enters a building, that cable also must be
earthed (via a ground block) to the same earthing electrode that also
protects AC electric, telephone, etc.  That requirement also from
basic science AND from a principle demonstrated by Ben Franklin in
1752. The principles have been appreciated for that long.  The science
well proven almost 100 years ago.

  Expanding on those concepts:  at greater risk may be other incoming
paths such as AC electric that would be a direct strike if lightning
strikes down the street.  These last four paragraphs being far more
relevant to the OP's post.  Human protection must be sufficient so
that even household appliances are protected.  That antenna must be
earthed especially for human safety.  Provided elsewhere are other
conditions (ie wire not behind a gutter pipe) so that the protection
does not put humans, et al at risk.


Re: Grounding TV Antenna?


The first part of your post is as weird and incomprehensible as the second
part is spot on.  ... and you obviously haven't twigged who gingre is.

Quoted text here. Click to load it



Re: Grounding TV Antenna?


Quoted text here. Click to load it

  Sally's post is guilty of doing what is criticized in that post.
Many refuse to learn what constitutes logical thought.  Iraq war being
a classic example everyone learned from history.  Having not done so
previously means numerous innocent deaths simply because we did not
demand those supporting facts.

 Facts without numbers and 'the whys' are too frequently aspirations
of a poster - not a declaration of fact.  To have merit - to be honest
- a post must include supporting facts.  If a previous post was
incorrect, then Sally provided a detailed list  - the 'whys'.
Unfortunately her reasoning is only a soundbyte: "weird and
incomprehensible".  It only tells us one irrelevant fact - her
emotions.

  No insult here.  None intended.  None found anywhere except inside
those who know only from what they feel.  Blunt fact.  If Sally
'honestly' had a problem with that post, then Sally would detail those
reasons. She did not.  Sally's 'sound byte' response only summarizes
her feelings - is devoid of hard facts - the reasons 'why'.

 I have no idea who Gingre is - and don't care.  Only thing revelant
are facts.  As Gingre notes,
Quoted text here. Click to load it

  Why must a poster provide 'the whys' - hard facts?  For the same
reason Gingre says:
"[I] can quite see why you poured the appropriate scorn."

   Sally is right.  I have no idea who Gingre is.  Does not matter.
Topic is lightning and grounding of an antenna.  Relevant are
concepts, facts, citations, and numbers associated with the topic.
That means posts devoid of such required details lack 'honesty' -
typically contain only emotions - are best labeled pontification.
Sally's post is typical of a grudge that is too common when our Iraq
history is mentioned.

  Defined above was why an antenna is earthed and a suggestion that
significant threats may exist from elsewhere.  Each suggestion
provided with reasons why - and not using 'soundbyte' reasoning such
as  "weird and incomprehensible".


Re: Grounding TV Antenna?


Quoted text here. Click to load it
All very logical except this obsession with the Iraq war. What this has to
do with the excess voltages and currents of a lighting strike beat me. But
as Major Tom keeps dragging the war into it, I'll state my view. IMO,
America went into the Iraq war for the wrong reasons (and not the stated
ones) and may withdraw from it for the wrong reasons (nothing at all to do
with truth or a high intention). The usual arrogance was displayed and then
when *American* people got killed they want to get out. Yet in Katrina US
citizens were disgracefully treated. How's that for getting off the
subject -- and then off that one too!



Re: Grounding TV Antenna?


Quoted text here. Click to load it

  And yet "anyone's views" are completely irrelevant to the topic and
irrelevant to how Iraq applies to the topic.  The topic was about what
is necessary for reasonable conclusions.  Nobody's opinion on what is
'right'  or what politics dictate was even implied.  Discussed is
something completely different:  how so many people 'know' when
numbers, facts, citations, etc were not provided.

  Iraq is a perfect example because so many have trouble separating
the politics from historical logic.  Again demonstrates how hard it is
for some to demand and dig for the 'irrefutable fact'.  That same
problem is common in the topic of lightning because so many know - and
yet also do not first dig for the well researched facts.

  We could also cite the Challenger as an example of why failures are
not accidents. Just another lesson from history that every lurker
should have learned from.  Why do we cite major events in history?
Not for the politics attached to it.  We use history to learn.  In the
Challenger, every engineer said don't launch.  They could not find an
engineer who said it was safe to launch. So they launched anyway.  Do
you see politics in that event ... or use it to learn how people make
life destroying mistakes by violating basic logic principles?  People
murdered only because irrefutable facts - especially with numbers -
were ignored.

  Same applies to Iraq.  The 'whys' were never provided and did not
exist - from aluminum tubes to yellow cake in Niger.  Those who first
demand supporting facts accurately foresaw serious consequences and
heard numbers from responsible sources such as the weapons labs
(Sandia, Los Alamos, etc).  Actions were justified when those acts
even violated fundamental principles defined by Sze Tzu from 2500
years ago.

  But again, do you read this as a discussion of politics (which it
clearly is not) or as a lesson from a history that everyone is
familiar with.  Demonstrated is how lies and human destructive
mistakes occur when we don't first demand supporting facts.

  In the case of lightning, even ESE devices are promoted for the same
reason that so many believed presidential lies about Saddam.  And that
is the point.  How people make foolish decisions:  they don't first
demand concepts, expert research, numbers, .... they don't demand the
many 'whys'.  Once we demand those 'whys', then the scam promoted by
ESE lighting devices also becomes obvious.

  But again, this is not about the murder of seven Challenger
astronauts, the millions of refugees and dead created by America, or
ESE scams.  In every post, it is about lessons from history;  same
mistake that causes people to believe myths even about lightning.

  Some people so believe myths as to insist that grounding a TV
antenna will only attract lightning.  As Sally noted elsewhere, some
actually believe a silly little gap in a 240 volt power switch will
stop lightning.  Why do they assume this?  For the same reason why so
many blindly believed presidental lies about Saddam. Again, there is
nothing here about politics.  Obviously, its all about how people make
mistakes when 'whys' are not demanded.

  We are supposed to learn from the lessons of history.  Iraq is a
perfect example: death only because humans did not first ask for the
'whys'.    Because the facts did not exist, so many are now dead -
uselessly.  Again - why everyone is expected to learn history.

  Everyone is expected to learn why this happened - to not make that
same mistake that also created Vietnam.  Again, there is no politics
relevant in this example either.  Just another example cited because
we all know about that mistake and should also know why that mistake
was so easily avoided.  But we did not demand supporting facts.  We
immediately jumped to conclusions based only on feelings rather than
on facts.  We did not ask for or learn 'the whys'.

  Posting 'viewpoints' on Iraq is completely irrelevant to a topic -
but demonstrates how easily a point is subverted by emotion of
politics.  Demonstrated from history is how people make life
destructive mistakes only because 'whys' are not provided and not
viciously demanded.


Re: Grounding TV Antenna?



Quoted text here. Click to load it
Very eloquent! You must be a thinker and have lots of time on your hands...



Site Timeline