TV won't turn on after lightning strike

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  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    well my tv aerial is in my loft... so hopefully it's a bit safer that way!

    A friends father was a fireman, and he absolutely wouldn't have an aerial on his roof because he's "seen so many houses with aerials struck by lightning" :p

    He couldn't seem to understand that as almost all houses have aerials, then houses with aerials are obviously more likely to be struck than those without.

    He also declined to comment on a local garage that was struck by lightning (which didn't have an aerial), yet was surrounded on all sides by taller houses that DID have aerials :D

    So by his theory you 'should' be a little safer, but I don't think the statistics would agree.

    But in any case, the chances are really pretty low, out door aerial or not.
  • [Deleted User][Deleted User] Posts: 2,151
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    Yeah I wouldn't really be worried about having the aerial on the roof.

    Its just in the loft because we didn't have a long enough ladder to put it on the roof!

    It also never gets blown down, full of water, rusty, etc.

    We can get away with it because we're in a strong signal area.. Obviously, not everyone is so lucky!
  • CaxtonCaxton Posts: 28,881
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    Yeah I wouldn't really be worried about having the aerial on the roof.

    Its just in the loft because we didn't have a long enough ladder to put it on the roof!

    It also never gets blown down, full of water, rusty, etc.

    We can get away with it because we're in a strong signal area.. Obviously, not everyone is so lucky!

    Yes, if you live in a strong signal area it really makes sense to put the aerial in the loft, it will last there indefinitely unlike one outside, so a cheap flimsy one will suffice, although aerial contractors will not tell you that.
  • [Deleted User][Deleted User] Posts: 2,151
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    Caxton wrote: »
    Yes, if you live in a strong signal area it really makes sense to put the aerial in the loft, it will last there indefinitely unlike one outside, so a cheap flimsy one will suffice, although aerial contractors will not tell you that.

    exactly. I think it was £10 from wilko's. years ago.

    still looks brand new. Never given me a spot of trouble... never needs any maintenance... (and if it does, its very easily accessible)
  • westomwestom Posts: 45
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    The 'point' is that they give a little extra protection - it won't stop a direct strike, but 'may' prevent damage from a 'near-ish' strike.
    Those adjacent protectors do so little that superior protection is inside all appliances. So tiny that that protector can also be a fire threat.

    Two completely different devices are both called protectors. One, sitting adjacent to appliances, only claims to protect from transients that typically cause no damage. The other type protects even from direct lightning strikes. And remains functional.

    A disconnected antenna cable example was understood even by 1920 ham radio operators. They would disconnect the antenna and even put that lead inside a mason jar. And still suffer damage. Damage stopped only when the antenna lead was earthed. Earthing (not a protector) defines all protection.

    That TV antenna should have been earthed. And then its lead should have also connected low impedance to the building's single point earth ground before entering. Then direct lightning strikes cause no damage. Then nobody even need disconnect anything.

    This rule applies to every wire entering a building. If any wire enters without first connecting to single point ground, then all protection is compromised. Informed homeowners typically spend tens or 100 times less money by earthing a 'whole house' protector. Because the most common source of damage to a TV's antenna connection is a surge incoming on AC electric. An antenna connection damaged because it is the outgoing path to earth.

    Remember, protection is always about the electrical path to earth. If a surge is not earthed before entering the building, then it will hunt for a damage an appliance that makes the best connection to earth.

    A TV with a properly installed antenna is, unfortunately, a best path. Because the homeowner did not earth a 'whole house' protector. A lightning strike far down the street willl hunt for and find earth destructively via the TV's antenna connection ... if a homeowner fails to earth the other completely different device - also called a surge protector.

    Two completely different devices, unfortunately, have a same name. It creates confusion causing so many to buy and recommend the other protector that claims virtually no protection. Informed consumers upgrade their single point earth ground. And install the other superior protector (that costs tens or 100 times less money). Then nobody even knoes a direct lightning strike happened. The other and superior solution even remains functional after direct strikes.

    But most consumers only know about an adjacent device with a massive profit margins and extensive advertising. It does not even claim to protect from lightning. A protector is only as effective as its earth ground. One protector can protect everything even from direct lightning strikes. As has been standard practice for over 100 years in facilities that cannot have damage. The technology is that well proven. And little known to many only informed by advertising.
  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    I'm presuming you're not involved in electronics/electrics at all?, as little in that post makes any sense - particularly the idea that all appliances have 'anti-lightning' protection inside them :p

    While cheap 'protectors' might only have cheap MOV's, most appliances don't even have those.

    Interesting idea 'earthing every incoming wire' - exactly how are you going to earth the incoming live mains feed? - MORE damage is done by lightning coming up the mains than via aerials, and also via incoming phone wires (which you're not allowed to touch, and couldn't earth anyway).

    But even rudimentary earthing (to help reduce lightning damage) requires massive expensive conductors, and an extensive earthing arrangement, presumably watered regularly to help maintain it's effectiveness?.

    Earthing aerial systems isn't a bad idea, though it isn't going to help much with a lightning strike - but there is no UK requirement for this, although there is in Germany (for example).
  • njpnjp Posts: 27,583
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    Ah. The Candyman cometh. I think it took more than 3 incantations though. He's slipping.
  • westomwestom Posts: 45
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    I'm presuming you're not involved in electronics/electrics at all?, as little in that post makes any sense - particularly the idea that all appliances have 'anti-lightning' protection inside them .
    I designed this stuff even many decades ago when internal protection was not as robust. We had to literally explain all damage. Even replaced semiconductors to prove we knew how each surge did damage. So that future damage would not happen.

    I suspect you are not involved in electronics other than at the marketing level. You know certain facts. But not others that only come from doing this stuff. For example, if you knew protection, then you know how every wire gets earthed. And why this technology is so routine in facilities that cannot suffer damage. BT must have direct lightning strikes without damage. Protection from direct lightning strikes was routine even 100 years ago.

    Earthing aerial systems is so successful (when properly installed) that electronics atop the Empire State Building are struck 23 times annually without damage. Atop the WTC, it was 40. Again, information that comes from experience, basic engineering knowledge, and underlying concepts.

    Why no requirements in the UK? Because lightning is so rare that, if proper protection was installed, then no damage would ever happen. Damage is due to virtually no effective protection. Especially the part that is so essential to protection. Single point earth ground.

    Described was how one earths every incoming wire to have no damage. Products that accomplish this come from more responsible companies including Keison, ABB, AEL Group, and Siemens. You should even know the relevant numbers.

    For example, a direct lightning strike may be 20,000 amps. So these more responsible companies market a completely different device (also called a protector) that is rated to earth 50,000 amps. Direct strike without damage even to a protector. Protectors must not be damaged even by lightning. Even spec numbers say so.

    Unfortunately, you assumed internal appliance protection is defined by MOVs. That technology was proven futile decades ago. Even ethernet ports contain protection up to 2000 volts. Without any MOVs. But again, I even designed this stuff. Had to suffer direct lightning strikes without damage. And know that damage is directly traceable to human mistakes. Simple protection that even costs less than those plug-in protectors is that routine.

    Important answer is where hundred of thousands of joules harmlessly dissipate. If that is unknown, then protection probably does not exist. Once that energy gets inside a building, then nothing protects from that transient. Protection is always about earthing that current BEFORE it can enter. Therefore BT can suffer 100 surges with each storm. Their £multi-million computer must suffer no damage - ever. Protection is that routine once basic concepts are learned.

    But then we did even more. We literally traced every surge path. Even replaced each damaged semiconductor so that every worked properly and did not fail years later. Is that someone who is not involved in electronics/electrics?
  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    westom wrote: »
    I suspect you are not involved in electronics other than at the marketing level. You know certain facts.

    I'm mostly involved in servicing, but have done a certain amount of electronics design over the decades.

    But not others that only come from doing this stuff. For example, if you knew protection, then you know exactly how every wire gets earthed.

    Again, yet another 'nonsense' term - you can't 'earth' every wire.

    And why this technology is so routine in facilities that cannot suffer damage. BT must have direct lightning strikes without damage. Protection from direct lightning strikes was routine even 100 years ago.

    BT still suffer damage, their extensive (and EXPENSIVE) lightning protection systems save most, but not all.

    Earthing aerial systems is so successful (when properly installed) that electronics atop the Empire State Building are struck 23 times annually without damage. Atop the WTC, it was 40. Again, information that comes from experience, basic engineering knowledge, and underlying concepts.

    Lightning conductors are what you have on top of buildings like that, not a simple and crudely 'earthed aerial'.

    Unfortunately, you assumed protection is defined by MOVs.

    No, I assumed nothing of the kind - only that cheap protectors have MOV's, and most domestic electronics don't even have that, hence the extra added (small) level of protection.
  • westomwestom Posts: 45
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    Again, yet another 'nonsense' term - you can't 'earth' every wire.
    Protection is routinely about earthing each wire. You are demonstrating that you do not know how surge protection works. Because protection is always about where hundreds of thousands of joules harmlessly dissipate.

    Am I being obscure? Of course. Because you are being adversarial rather than seeking to learn. You are not the only one,. Another has already wasted bandwidth posting his cheapshot.

    Start by learning how MOVs really work. What the other and destructive type of current is. Where hundreds of thousands of joules (that number is important) routinely dissipate. For example Dr Kenneth Schneider:
    Conceptually, lightning protection devices are switches to ground. Once a threatening surge is detected, a lightning protection device grounds the incoming signal connection point of the equipment being protected. Thus, redirecting the threatening surge on a path-of-least resistance (impedance) to ground where it is absorbed.

    Any lightning protection device must be composed of two "subsystems," a switch which is essentially some type of switching circuitry and a good ground connection-to allow dissipation of the surge energy. ... the need for a good ground connection can not be emphasized enough. Computer equipment has been damaged by lightning, not because of the absence of a protection device, but because inadequate attention was paid to grounding the device properly.
    Other factors applies. A connection to earth that is too long (ie 'more than 3 meters') is virtually not earthed. As a serviceman, you would understand wire resistance (ie wire thickness). But for surge protection, another completely different parameter applies. Wire impedance (ie wire must be that much shorter).

    Meanwhile, protectors used by BT are many times less expensive than what so many pay for power boards. The least expensive solution connects every wire to earth. To increase protection, they want protectors as much as 50 meters distant from electronics. That separation also increases protection.
  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    westom wrote: »
    Protection is routinely about earthing each wire. You are demonstrating that you do not know how surge protection works. Because protection is always about where hundreds of thousands of joules harmlessly dissipate.

    Am I being obscure? Of course. Because you are being adversarial rather than seeking to learn.

    I'm not seeking to 'learn' - I'm trying to correct your completely misleading claims - where I'm well versed in Electronics, most members here aren't. Claiming you have to 'earth every wire' is utter nonsense (for a start shorting every wire together would stop all of them working, and there would be a loud BANG when you earthed the incoming live mains).

    Assuming you mean "diverting lightning to ground"?, I'm in full agreement with you there - but you don't (and can't) do that by 'earthing every wire'. There are various options, such as MOV's and spark gaps etc. which will divert the energy (or at least a portion of it) to ground - but this is nothing like 'earthing every wire'.

    You're also happily talking about 20,000 amps (and higher) - which again I've no problems with, but you're not going to EVER get equipment and infrastructure domestically for handling such high values.
  • njpnjp Posts: 27,583
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    You're also happily talking about 20,000 amps (and higher) - which again I've no problems with, but you're not going to EVER get equipment and infrastructure domestically for handling such high values.
    And yet you can, very easily. Here is a selection.

    The key point is that whilst the current is very large, the time for which it flows is very short.
  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    njp wrote: »
    And yet you can, very easily. Here is a selection.

    The key point is that whilst the current is very large, the time for which it flows is very short.

    But how effective is it? - plus what kind of earth point and cabling are you going to need?.

    Short high current pulses are still subject to ohms law, so you need VERY thick earth connections and a VERY good earth.

    I'm with westom on that point, excellent earthing is crucial no matter what.
  • grahamlthompsongrahamlthompson Posts: 18,486
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    Earthing for lightning conductors requires very heavy solid copper connections. You also have to avoid sharp bends as say for instance round a projecting object. The current can easily pass through a stone sill rather than taking the copper route. They also have to very securely fastened, the bursting force caused by such high currents can easily rip the copper off the walls. Suggesting that internal domestic wiring is capable of sustaining these currents is just ridiculous. Anyone ever seen the massive cables used to connect the electrodes on a large electric arc furnace. During the refining process these thrash around like pieces of string. Take a look at the lightning conductor connections on your local church tower.

    The current generated can be in excess of 120kA not 20kA.
  • OrbitalzoneOrbitalzone Posts: 12,627
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    Most equipment brought into our old tv workshop after a storm was due to mains spikes rather than direct hits which were much rarer causes of damage - although direct hits were more catastropic usually. In those cases of non direct hits surge protectors may have helped. We had one or two folk living in villages with somewhat unstable mains supplies and again a surge protector helped sort out some odd problems here and there.

    However my main lightning protection is called household insurance...although it's not very proactive I suppose :D
  • westomwestom Posts: 45
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    Claiming you have to 'earth every wire' is utter nonsense (for a start shorting every wire together would stop all of them working, and there would be a loud BANG when you earthed the incoming live mains).
    Assuming you mean "diverting lightning to ground"?, I'm in full agreement with you there - but you don't (and can't) do that by 'earthing every wire'.
    Best protection for cable is a wire connected low impedance (ie 'less than 3 meters') from coax cable to single point earth ground. No protector required for that best protection.

    Other wires (ie telephone/DSL) cannot connect directly. But protection is always about earthing every incoming wire during a surge. So we make a same earthing connection using a protector. If any incoming utility wire does not have that earthing connection, then protection is compromised. It is done routinely where surge protection is desired.

    That connection demonstrates what a protector does. Makes a next best connection to earth ground when a hardwire cannot connect that incoming utility wire directly. It’s called earthing if by a hardwire or by a protector. Because a surge is connected directly (low impedance) to earth.

    Protection from direct lightning strikes (ie 20,000 amps) usually costs less than multiple power strip protectors. For example, Cutler-Hammer (Eaton) was selling one in big box hardware stores for about 40 quid. About one quid per protected appliance. (Unfortunately an electrician wants many times more to install it.)

    These well proven and less expensive devices typically start at 50,000 amps. Since protectors must never fail due to a surge. That means protection sufficient for all lightning strikes.

    Relevant electrical concepts are usually only known to engineers. Resistance and a thick wire is irrelevant as another has noted. Basic concepts define compromised protection if a wire is too long, with sharp bends, inside metallic conduit, with splices, or bundled with other non-grounding wires. These can increase impedance - not resistance. One term repeated often because it is so critical to the earth connection - ie 'less than 3 meters'. Every meter shorter increases protection.

    Same concepts also say why protection increases when an appliance and protector have greater separation.

    Some numbers. A one millimeter wire can conduct a surge up to 50,000 amps (as another has summarized). So we use at least 2 mm and 4 mm ground wires for signal and AC electric grounds. Worry little about wire thickness. Even a 90 degree bend can subvert the connection. Worry about impedance' not resistance.

    Another critical concept; single point earth ground. It addresses two key electrical requirements - conductivity and equipotential. Concepts that define why BT uses this less expensive and superior solution to suffer 100 surges per storm without damage.

    This post summarized key words that define protection from direct lightning strikes. A lightning strike to utility wires far down the street is a direct lightning strike incoming to household appliances. Some mistakenly refer to it as an indirect strike. But electrically, that is lightning making a direct connection to earth destructively via a TV. Another distinction that might cause confusion.

    Many ignore protection since damage rarely occurs due to so few surges and supierior protection already inside appliances.. How necessary? Well, most destructive surges occur maybe once every seven years. Less often in the UK. A ten or 20 year neighborhood history would best define the risk. Even local geology affects this risk.
  • grahamlthompsongrahamlthompson Posts: 18,486
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    westom wrote: »
    Relevant electrical concepts are usually only known to engineers. Resistance and a thick wire is irrelevant as another has noted. Basic concepts define compromised protection if a wire is too long, with sharp bends, inside metallic conduit, with splices, or bundled with other non-grounding wires. These can increase impedance - not resistance. One term repeated often because it is so critical to the earth connection - ie 'less than 3 meters'. Every meter shorter increases protection.

    .

    Seeing as how the current generated by a lightning strike is direct not alternating, how can the wire impedance be a factor ? :confused:

    At 0 frequency series inductive reactance is zero. Only the connections resistance is relevant. The heat energy produced is the current squared times the DC resistance. Your 2mm wire would be instantly vapourised by a direct lightning strike.
  • Nigel GoodwinNigel Goodwin Posts: 58,335
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    At 0 frequency series inductive reactance is zero. Only the connections resistance is relevant. The heat energy produced is the current squared times the DC resistance. Your 2mm wire would be instantly vapourised by a direct lightning strike.

    And would also drop enough voltage across it to not protect anyway (1 ohm cable resistance at 50,0000A would leave 50,000V to blow your electronics.

    He claims to be a 'designer', yet appears to have little electrical knowledge, and uses terms which no designer or engineer ever would - such as:
    Since protectors must never fail due to a surge. That means protection sufficient for all lightning strikes.

    They offer an increased level of protection, within specific limits - no one involved would ever claim total protection like that.
  • njpnjp Posts: 27,583
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    Earthing for lightning conductors requires very heavy solid copper connections. You also have to avoid sharp bends as say for instance round a projecting object. The current can easily pass through a stone sill rather than taking the copper route. They also have to very securely fastened, the bursting force caused by such high currents can easily rip the copper off the walls. Suggesting that internal domestic wiring is capable of sustaining these currents is just ridiculous. Anyone ever seen the massive cables used to connect the electrodes on a large electric arc furnace. During the refining process these thrash around like pieces of string. Take a look at the lightning conductor connections on your local church tower.

    The current generated can be in excess of 120kA not 20kA.
    I'm rather reluctant to get involved in this debate, but I feel compelled to point out that you are muddling up structural lightning protection with transient surge protection, which may be resistively or inductively coupled from lightning strikes. Such transients are of very short duration (typically 20 to 50 microseconds), and the best waveforms to simulate them for SPD testing have been endlessly debated.

    If your building needs the first, it still needs the second. And even if your building doesn't need the first, it might benefit from the second.
  • westomwestom Posts: 45
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    Seeing as how the current generated by a lightning strike is direct not alternating, how can the wire impedance be a factor ?
    1) It is not DC. Is is radio frequencies. Otherwise radio interference would not exist.

    2) Impedance is one of many reasons why wall receptacle safety ground prong obviously cannot be earth ground. Some numbers. That 2 mm ring wire to the service entrance may be well less than 0.2 ohms resistance. Due to its length (maybe 15 meters) would be something like 120 ohms impedance. A trivial 100 amp surge would put that receptacle at something less than 12,000 volts. IOW even a trivial surge permitted inside will seek other and destructive paths to earth via appliances.

    Unfortunately it involves math. Many will not even read manufacturer numbers that say an undersized protector adjacent to an appliance does not even claim to protect from typically destructive surges. It claims to protect from surges that typically do no damage. Numbers that are always required and that naysayers have never provided.

    A popular joke in engineering school was the DC spike. No such thing can exist as made obvious by secondary school math (ie Fourier Series). A spike is a sum of sine waves. IOW it is AC; not DC. Since the spike is so short (ie 20 to 50 microseconds), then that AC is radio frequencies. Impedance (not resistance) is the relevant number.

    3) Once that surge current is permitted inside, then it will hunt for earth destructively via appliances. If earthed BEFORE entering a building, then concepts of conductivity and equipotential mean everything inside is at a common voltage - no current and no appliance damage. These concepts have been understood for over 100 years. But are completely ignored when hearsay replaces science.

    4) That destructive spike is high frequency AC involving the connection of maybe 20,000 amps from a cloud to earth. And then kilometers through earth to earthborne charges. Protection means that path remains outside the building.

    5) Lightning may be as much as 100,000 amps. It is rare - probably never seen by most readers. An average lightning strike is about 20,000 amps (maybe 25K). Since a rare lightning strike can exceed 100K, then lightning rods connect to earth on wires that can conduct 200K.

    A 100K amp lightning strike is described (with numbers) in a late 1970s IEEE paper. As much as 40,000 amps may enter the nearby house. Another 60,000 amps goes to earth via other homes and utility protection equipment. So a minimal 'whole house' protector is 50,000 amps. So that direct lightning strikes (even the rare 100K strike) does not damage any protector.
  • BhaveshgorBhaveshgor Posts: 9,312
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    is it worth spending money on Surge protectors in the uk, i know the US people spend money on these since Lightning strikes are more common.
    if it is worth spending money on surge protectors, which ones are the best and cheapest.
  • westomwestom Posts: 45
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    Bhaveshgor wrote: »
    is it worth spending money on Surge protectors in the uk, .
    The least expensive solution is the one that also does the best protection - one properly earthed 'whole house' protector. About £1 per protected appliance. How necessary?
    Many ignore protection since damage rarely occurs due to so few surges and supierior protection already inside appliances.. How necessary? Well, most destructive surges occur maybe once every seven years. Less often in the UK. A ten or 20 year neighborhood history would best define the risk. Even local geology affects this risk.
  • grahamlthompsongrahamlthompson Posts: 18,486
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    njp wrote: »
    I'm rather reluctant to get involved in this debate, but I feel compelled to point out that you are muddling up structural lightning protection with transient surge protection, which may be resistively or inductively coupled from lightning strikes. Such transients are of very short duration (typically 20 to 50 microseconds), and the best waveforms to simulate them for SPD testing have been endlessly debated.

    If your building needs the first, it still needs the second. And even if your building doesn't need the first, it might benefit from the second.

    Not mixing up anything. The whole thread is based on an external lightning strike on a external antenna connected solely by a 75ohm coax cable. Only a surge diverter capable of carrying the current externally will protect the internal wiring. In the case of a spark gap arrester the voltage imposed on the coax cable beyond the arrester will be the arc voltage. Ionised air has a very low resistance so the voltage appearing at a coax plug will be relatively modest. The resistance of the connections carrying the current will not make any difference to the transferred voltage. It's resistance is largely important to prevent the conductor melting.
  • grahamlthompsongrahamlthompson Posts: 18,486
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    westom wrote: »
    1) It is not DC. Is is radio frequencies. Otherwise radio interference would not exist.

    2) Impedance is one of many reasons why wall receptacle safety ground prong obviously cannot be earth ground. Some numbers. That 2 mm ring wire to the service entrance may be well less than 0.2 ohms resistance. Due to its length (maybe 15 meters) would be something like 120 ohms impedance. A trivial 100 amp surge would put that receptacle at something less than 12,000 volts. IOW even a trivial surge permitted inside will seek other and destructive paths to earth via appliances.

    Unfortunately it involves math. Many will not even read manufacturer numbers that say an undersized protector adjacent to an appliance does not even claim to protect from typically destructive surges. It claims to protect from surges that typically do no damage. Numbers that are always required and that naysayers have never provided.

    A popular joke in engineering school was the DC spike. No such thing can exist as made obvious by secondary school math (ie Fourier Series). A spike is a sum of sine waves. IOW it is AC; not DC. Since the spike is so short (ie 20 to 50 microseconds), then that AC is radio frequencies. Impedance (not resistance) is the relevant number.

    3) Once that surge current is permitted inside, then it will hunt for earth destructively via appliances. If earthed BEFORE entering a building, then concepts of conductivity and equipotential mean everything inside is at a common voltage - no current and no appliance damage. These concepts have been understood for over 100 years. But are completely ignored when hearsay replaces science.

    4) That destructive spike is high frequency AC involving the connection of maybe 20,000 amps from a cloud to earth. And then kilometers through earth to earthborne charges. Protection means that path remains outside the building.

    5) Lightning may be as much as 100,000 amps. It is rare - probably never seen by most readers. An average lightning strike is about 20,000 amps (maybe 25K). Since a rare lightning strike can exceed 100K, then lightning rods connect to earth on wires that can conduct 200K.

    A 100K amp lightning strike is described (with numbers) in a late 1970s IEEE paper. As much as 40,000 amps may enter the nearby house. Another 60,000 amps goes to earth via other homes and utility protection equipment. So a minimal 'whole house' protector is 50,000 amps. So that direct lightning strikes (even the rare 100K strike) does not damage any protector.

    Complete rubbish, lightning is static electricity generated. A DC arc makes an excellent rf source. It's how Marconi was able to transmit radio signals across the Atlantic.

    The spark plugs in a motor car create RF interference if not adequately suppressed. Like lightning it's a high voltage dc pulse derived from the back emf of the dc current being interrupted in the spark coil by the contact points opening.

    The only effect inductance has is that it minutely delay the current from the initial voltage. If a circuit has any inductance then a pure square wave DC source will not produce a pure square wave current.

    This is basic o-level electrical theory :eek:

    I worked in the Electricity Supply Industry for years and have seen many examples of the damage that is possible.

    On one occasion a 66Kv surge diverter was struck directly and it exploded. The heavy cast iron top was found over 500yds away.
  • njpnjp Posts: 27,583
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    Not mixing up anything. The whole thread is based on an external lightning strike on a external antenna connected solely by a 75ohm coax cable.
    Well, no. If the external antenna had been struck by lightning, the OP would have had severe structural damage to their house, and a non-working TV would be the least of their worries. So (assuming that this really is lightning damage), it's a secondary effect, probably from an inductively induced transient, which has entered the TV via either the mains or the aerial lead.

    Quite a lot of research has been done into the nature of these transients, funnily enough, going back several decades. And the pulses are very short, with a very rapid rise time - so your claim that they are "DC" is about as wide of the mark as it is possible to get. I was a bit rude about the Candyman (for it is indeed he!) before I knew he was an FM and was about to show up, but he is absolutely right about the importance of impedance and short connectors when designing surge protection. And that is why the secondary protective devices that you and Mr Goodwin were so dismissive of do actually work. Surge protected extension leads: not so much.
    Complete rubbish, lightning is static electricity generated. A DC arc makes an excellent rf source. It's how Marconi was able to transmit radio signals across the Atlantic.
    No, it doesn't. An arc transmitter has a tuned circuit connected across the arc, turning it into a relaxation oscillator.
    The spark plugs in a motor car create RF interference if not adequately suppressed. Like lightning it's a high voltage dc pulse derived from the back emf of the dc current being interrupted in the spark coil by the contact points opening.
    Like the man said, there is no such thing as a DC pulse:
    The only effect inductance has is that it minutely delay the current from the initial voltage. If a circuit has any inductance then a pure square wave DC source will not produce a pure square wave current.
    A square wave is an infinite summation of sine waves.
    This is basic o-level electrical theory :eek:
    Is it? Then I think you need to move beyond O-level!
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