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Grounding TV Antenna?

Discussion in 'Hobby Electronics' started by Tony, Jul 2, 2007.

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  1. Tony

    Tony Guest

    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
     
  2. Phil Allison

    Phil Allison Guest

    "Tony"
    ** Serious.

    ** Yep.

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

    ** Nope.


    ** It is a grade A lightning target anyhow

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


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


    ** 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
     
  3. w_tom

    w_tom Guest

    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.
     
  4. kreed

    kreed Guest

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

    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.
     
  5. w_tom

    w_tom Guest

    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.
     
  6. Gingre

    Gingre Guest

    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.
     
  7. Tony

    Tony Guest

    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
     
  8. 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
     
  9. w_tom

    w_tom Guest

    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:
    Martin A Uman All About Lightning
    Other provide numbers. In sci.physics.electromag on 4 Nov 2000
    entitled "Oddball question" at:
    http://tinyurl.com/f495w
    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.
     
  10. Gingre

    Gingre Guest

    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.
     
  11. w_tom

    w_tom Guest

    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.
     
  12. Suzy

    Suzy Guest

    Where does Gingre say "make a big noise"?

     
  13. w_tom

    w_tom Guest

    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.
     
  14. Suzy

    Suzy Guest

    But he didn't say that!

     
  15. Gingre

    Gingre Guest

    Sorry not to have responded earlier. Have been away on the lecture circuit.
    No I have never been an ESE salesman and my connection over the years has
    been at the theoretical engineering level. I agree that many lightning
    associated sales people feel they are "experts" and can quite see why you
    poured the appropriate scorn. Many of your facts are spot on. I differ only
    in the concept that at the base of a strike (or the origin if such is the
    dominant polarity) there is little energy. Of course there is not
    milliseconds *after* the strike. There certainly is before. AFAIK I have
    never spoken of a "big noise" or WMD for that matter!
     
  16. w_tom

    w_tom Guest

    Of course not. Did you understand the point? Gingre did. As he
    noted:
    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.
     
  17. Sally

    Sally Guest

    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.
     
  18. w_tom

    w_tom Guest

    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,
    Why must a poster provide 'the whys' - hard facts? For the same
    reason Gingre says:
    " 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".
     
  19. Sally

    Sally Guest


    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!
     
  20. w_tom

    w_tom Guest

    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.
     
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