Grounding TV Antenna?

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

Reply to
Tony
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"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

Reply to
Phil Allison

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.

Reply to
w_tom

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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.

Reply to
kreed

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.

Reply to
w_tom

Reply to
Gingre

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

formatting link
a useful link? I would like to have the antenna earthed anyway though. Can anyone recommend someone in Perth?

Cheers Tony

Reply to
Tony

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

Reply to
Dorfus Dippintush

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:

Engineering":

Martin A Uman All About Lightning

Other provide numbers. In sci.physics.electromag on 4 Nov 2000 entitled "Oddball question" at:

formatting link

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 > A lot of this is good but a little is misleading. There is incredible energy

Reply to
w_tom

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.

Reply to
Gingre

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.

Reply to
w_tom

Reply to
Suzy

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.

Reply to
w_tom

Reply to
Suzy

Reply to
Gingre

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.

Reply to
w_tom

Reply to
Sally

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: "[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".

Reply to
w_tom

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!

Reply to
Sally

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.

Reply to
w_tom

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