When Lightning Strikes

For the last couple decades, I have pushed for all computers to be on a good UPS with AVR - automatic voltage regulation. But during storms is only the minor reason. All high wattage devices in the home, office, or apartment building send anomalies down the line each time they cycle on and off. These devices include $15 1500watt made in China hair dryers, coffee pots, air conditioners, refrigerators, microwave ovens, toasters, etc. These anomalies must be "handled" by the PSU and motherboard regulator circuits, which they are designed to do. But in doing so, they generate more heat - never good. If these anomalies become extreme, then problems arise.

Surge and spike protectors can only deal with high voltage events and sadly, do so by simply chopping (clamping) off the tops of the sinewaves. They do nothing for sags and dips (which follow every surge and spike) or brownouts - extended sags. Only a good UPS with AVR can compensate for those. Note that power during a complete outage is only the icing on the cake.

I am not in the habit of disagreeing with PhDs, but he said not to plug a S&S protector into an UPS because it may damage the S&S protector. That is not the reason. The reason is because the AVR can see the load as erratic and cause the UPS to shutdown. And you should not plug an UPS into a S&S protector because it may see the supply voltage as dirty, and want to run on batteries full time.

 

S&S is a surge protector? What is the typical output of a UPS when in battery backup mode? This 120 volt UPS outputs 200 volt square waves with a spike of up to 270 volts between those square waves. Ideal perfect power for all electronics - because all electronics already contain serious surge protection. Potentially harmful to small electric motors and surge protectors because UPS power is typically so 'dirty'.

Your erratic AVR load is a popular urban myth when a majority only know what retail sales brochures and hearsay tell them to believe. These same people (often more than 70%) will believe only subjective declarations even when numbers say something completely different. Did you read the spec numbers for your UPS? Did you learn about 200 volts and 270 volts? Or just recite urban myths? The PhD was right on. That AVR myth is how UPS and power strip manufacturers avoid a damning reality to keep you deceived.

When is the UPS output cleanest? When its relay connects directly to AC mains. Another reality they hope you never learn.

The PhD is typically first confirming everything with numbers. Asking damning questions. Anyone who says a UPS does surge protection is intentionally avoiding those numbers. Believes the first thing they are told.

What is a power strip protector. A power strip. Inert. A direct connection from wall to appliance. Did you read numbers on its cardboard box that define this? A 120 volt protector is only a power strip when voltage remains less than 330 volts. It does not create erratic power. It does not do anything when voltage remains below 330 volts. It is inert - nothing more than a power strip below 330 volts.

When does it create erratic load? When a 120 volt UPS outputs voltages greater than 330 volts. And yes, some UPSes can be that 'dirty'. They need your eyes to glaze over because I just provided numbers and asked damning questions.

They need you to believe some kind of magic is performed inside a power strip that would erratically change the load. They need you to automatically believe it - not first learn the circuit. Then they need not admit to serious surges generated by a UPS in battery backup mode. 'Clean power' myth is essential to their sales. And finally they need you to not know about serious surge protection already inside every appliance.

Anything that UPS might do to block surges - a better (more robust) power supply is required to already be inside all computer.

Plug a second UPS into a first UPS. Unplug the first UPS. Its output power may be so dirty as to confuse the second UPS. Cause the second to switch over to batteries. How can this be if a UPS outputs 'clean' power? It doesn't. They need you to never ask damning questions. To ignores every spec number. They need you to remain ignorant - which the PhD did not.

The PhD was right on accurate. Power from a UPS may be so dirty as to be harmful to a power strip protector. Same power is ideal perfect for all electronics - because electronics have long been required to be that robust.

 

It all depends on the UPS, but in any event, that is better than plugging a S&S protector (and yes, I mean surge & spike) into the UPS. You may not be having any problems but it is likely your UPS kicks in more often. Since the S&S protector (regardless the price) still works by "clamping" down on the excess voltage by chopping off the tops of the sinewaves, the AVR circuits "may" still see that as dirty power and attempt to clean it up, or shut down to protect the load. I recommend you read your UPS manual. Some specifically say don't do it.

Where did you hear those fairy tales? Totally not true. Got links? That would suggest that all electronics have MOVs (metal oxide varistors) which are the main component of all S&S protectors and that is simply not true. Certainly a "quality" power supply from Corsair or Antec will have better regulation than a $15 generic power supply, but even the best Corsairs or Antec are not expected to "protect" the computer. You won't see a $200,000 replacement guarantees with any power supply. If they provided that type protection, it would be advertised all over the box!

What about spikes? Dips? Sags? Brownouts?

Where are the sources for your facts? 330Volts? That's for S&S protectors, not a good UPS with AVR. And I wasn't talking about power strips! I contend all along that S&S strips are little more than fancy and expensive extension cords - so thank you for supporting my argument. A good UPS with AVR will kick in before 330VAC (for 120VAC normal house/mains voltages).

You keep talking on surges (but not spikes) and totally ignore low voltage events, something no surge or spike protector can compensate for. They can't compensate for extended surges either, while an UPS, on the other hand, can - easily. Batteries are much more robust than any MOV.

And note in my comments above, I said repeatedly, "a good UPS with AVR". Just like power supplies, there is a big difference between a good UPS with AVR from a reputable maker and a budget, off-the-wall brand UPS.

My UPS, with a nominal input of 120VAC, boosts voltage when the line voltage drops below 89VAC and reduces voltage when it exceeds 139VAC and it does it within 8ms maximum transfer time. However, unlike any S&S protector, a "good" UPS w/AVR dumps the excess voltage into the batteries to be absorbed with aplomb - unlike a S&S protector, which uses MOVs that that get hot and wear out.

As for PC PSUs, you are only partially right, but only by a small amount. The ATX Form Factor Standard for Power Supplies is quite clear in it's requirements,

Fuses are not compensating devices. For low voltage, it says

And that table says 90VAV (when the mains are 115VAC).

Also note that a "good" UPS does NOT output a squarewave as westom would have us believe. That said, they do not output a "pure" sinewave either (but neither does the wall, for that matter). A "good" UPS with AVR typically outputs a "step-approximated" sinewave (also called "modified sinewave" or "quasi-sinewave"). And since almost all computer equipment (including peripherals) operate with DC voltages created by their power supplies, the quasi-sinewave is just fine because it provide a rest at 0V for each cycle, thus preventing the power supplies from overheating. This is different from cheap UPS with a squarewave output as squarewave have nearly instantaneous rise and fall times (sinewaves have "slopes" both up and down).

Note I said above,

Do you honestly expect everyone to believe their router, modem, external drives, monitors, PDA, phone all have "serious surge protection"? No way! Are any of them able to compensate for low voltage events? Or spikes?

westom is right, however, in that marketing weenies for very expensive "pure" sinewave UPS would have you believe spending anything less than $500 on a UPS is a waste. That is pure fairy tale stuff too - at least for digital electronics.

And note I did not say the PhD was wrong about damaging anything. I said the main reason not to plug a S&S protector into an UPS is because the UPS may see the load from the S&S strip as erratic and shut down. Besides, you don't need it. A plain old extension cord will work just fine.

 

The 330 volt number is on the box of every protector. To quote one box: "let-through voltage 330 v". Rather than make nasty accusation, go read the numbers you ignored. That includes the UPS manufacturer spec numbers that we will discuss again – and why you never quote them.

No protector clips off sine waves as myths so routinely assume. 120 volt sine waves never exceed 185 volts. You should have known that before posting the clipped sine wave myth. You should have done math that any high school student can do. 120 volts times square root of 2. Knowledge you must have before posting also says where that 185 number comes from. If you have sufficient knowledge, you knew exactly where that 185 number comes from. You don’t.

Fairy tales are accusations when one posts without learning science. Nasty is your post; accusations without quoting manufacturer specs numbers, citing facts you learning in electrical engineering courses, and no quoting professionals. Bill – that is the definition of an insult. You do none of that. You even misrepresent numbers from formfactors.org.

What is a step wave? Stacked square waves. High school math: Fourier series. What are square waves? Sum of sine waves. No, the UPS manufacturer did not lie. He is only selling myths to those who all but want to be deceived. . Step waves and square waves with spikes are so ‘dirty’ as to can be harmful to small electric motors and power strip protectors. As noted previously. Calling is a sine wave gets the naïve who want to deceived an excuse to be deceieved.

I don’t care what you believe. If you reply without numbers for those appliances, then that says you are even lying to yourself. You have no doubts or opinions until after you learn spec numbers.

How does a protector clip sine waves when it ignores voltages under 330? Only if myths and wild speculation replace science. Anyone with high school math can multiply 120 volts times square root of 2. And know why that number is relevant. Only those who ask daming questions would have done that math. How does a 120 v sine wave approach anywhere near 330 volts? It doesn't.

You don’t ask damning questions. PhD does. Explains why you were so easily scammed by a UPS lie about confused AVR. You blindly believed hearsay – never even did 120 times square root of 2. Even ignored 330 volt numbers on its box. Please. Stop insulting me. Inventing myths and not posting numbers is literally an insult to every educated American.

International design standards even in the 1970 said 120 volt electronics had to withstand 600 volt transients without damage. That sentence already lits sources than you posted in two replies. Why do I who design know that? And you who post no facts or numbers do not? You did not even know the old design numbers. Today’s design standards are even higher. Intel included 2000 volts in their ATX specs - because computers were required to be even more robust. IEC 61000-4-2 - another design standard - defines even higher numbers.
What do electronics now withstand without damage? Some now withstand 15,000 volts. Unlike you, I do not say something only because that is what a majority tell me to believe. 15,000 volts. Read the datasheet for new semiconductors that must now meet the 2000 volt and 15,000 volt requirements:
http://datasheets.maxim-ic.com/en/ds/MAX1487E-MAX491E.pdf

The PhD recommends no power strip on its output because he first learned facts before posting. Same destructive spikes are also irrelevant – not harmful – to all electronics. Electronics so robust that any protection provided by a UPS is already inside electronics.

Fact – UPS outputs power so dirty as to be potentially harmful to a 330 volt surge protector. Meanwhile electronics are designed to withstand even 600 volt spike without damage. But again, you post myths. And I reply with numbers. Including the number you intentionally ignored on protector boxes -30 volts.

Informed homeowners worry about rare surges (ie once every seven years) that can overwhelm internal appliance protection. That means earthing one protector where wires enter the building. Destructive surges that dissipate outside the building will not overwhelm tiny protection inside a UPS and superior protection already inside electronics.

How does the 2 cm part inside a UPS stop destructive surges. It doesn’t. Another damning question that the naïve never ask. That surge is incoming to every appliance. But only damages appliances that make a better connection to earth. Damage means the homeowner listened to scam artists who promote that UPS as protection. And did not learn how superior ‘whole house’ protection is earth. So effective that a direct lightning strike does not even damage the protector. A solution that costs tens or 100 times less money. And that is done in every facility that can never have damage – including munitions dumps. Why do the naïve trains by UPS propaganda sheets not know this? Only some learn by doing electrical engineering and asking damning questions. Most learn only what they are told to believe.

The UPS has only one function – to provide temporary and ‘dirty’ power during blackouts. So that unsaved data can be saved. If you learn that, you threaten UPS sales and profits. Selling a UPS for surge protection is easy when so many such as Bill know without first learning facts, numbers, electrical engineering, or international sales. So profitable when an overwhelming majority is only trained by junk science, hearsay, and what their friend told them what to believe.

You had lightning. That means the only solution – the same one used for over 100 years – is earthing that energy harmlessly outside the building. Once inside, that energy goes hunting, destructively for earth ground via appliances. No protector inside the building will avert that hunt. Some protectors can even make damage easier. No problem The protector made no protection claims in specs and still got so many to recommend it. Obscene profit margins preserved.

 

So fairy tales are nasty accusations and insults but "myths", "lying" and "wild accusations" are professional speak? You speak with forked tongue westom. I quoted the FormFactor, hard to misrepresent with quotes. And I stated the figures from my own UPS specs sheet and you continue to harp on surge and spike protectors when I've not made one claim about them, except that they are little more than expensive extension cords.

Yeah, like,

I'm done here.

 

I have some questions then since this topic is here.

You can buy power strips and surge strips. I have used quite a few ISO-BARS, and they do make a difference in the amount of 'noise' that can be communicated from one circuit to another. They claimed each circuit was isolate from the other so as to cut down on the 'noise', which is EMF or whatever.

When you buy a surge strip then, rated to withstand so many joules/watts/volts/amps/farads/whatever, will quality ones really save equipment then? I have seen what a lightning strike has done to a few computers, without any surge strip of any type, and wonder if they are really worth thier price.

What about a GFI? They are sensitive to shorts/overloads, but is something like that more beneficial if you are concerned with over/under voltages?

Earth ground to the house? You are referring to a properly placed ground rod that is tied to the buss and terminated house-wide properly? Will this alone really handle variances better than not?

I am aware of the theory that surges and slacks in voltages can be buffered by AVR technology. I haven't had many UPSs with this feature, so can't comment, but would be interested in finding out what is the truth. It seems odd to me that standard electronics now could withstand as much transients as being claimed, especially considering what little I know about electonic theories there is often not much room for error, especially with transistors and other sensitive devices.

You speak of the output possibly being a square wave, and that would not be optimum for a device. I understand the slope and square difference, but why would a "squarer" waveform be not as 'good' for a device as one with a slope? Because of the time between the top/bottom edge? It is still at a frequency though, correct? I can see a TTL signal giving no 'pause', but if a sine or square is operating at 60hz, would the time between the rise/fall not still be roughly the same, although the actual rise/fall would be much faster on a square wave?

Yes, I know only enough to vaguely understand any of this, but hey, when people who know a lot about start talking, it is a great time to learn.

Sul.

 

And all that is found in 100 years of well proven knowledge.

For example, those UPSes do not even claim protection. With or without them, same results would have happened. The surege hit every appliance equally. But only damaged appliances that made a better connection to earth. No proteector inside a building does or claims to do effective protection. Professionals do not waste money on those scams.

Protection means upgrading earthing. Munitions dumps suffer direct lightnign strikes without explosion by using Ufer grounding. Ufer grounding is routinely done when a builder is informed. An example of how a radio station suffered frequent surges - and no failures due to Ufer grounds:
http://scott-inc.com/html/ufer.htm

Orange County FL was suffering damage. So Orange County fixed the only thing that does protecton - earth ground:
http://www.psihq.com/AllCopper.htm and

An application note demonstrates the principles. Every incoming wire - even underground wires, must connect to a structure's single point ground before entering the building:
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

ARRL decribes the item always required for surge proetction in QST on July 2002:
> The purpose of the ground connection is to take the energy arriving on the antenna feed
> line cables and control lines (and to a lesser extent on the power and telephone lines)
> and give it a path back to the earth, our energy sink. The impedance of the ground
> connection should be low so the energy prefers this path and is dispersed harmlessly. To
> achieve a low impedance the ground connection needs to be short (distance),
> straight, and wide.
> ...
> The goal is to make the ground path leading away from the SPGP more desirable than any other path.

Or Sun Microsystems "Planning guide for Sun Server room":
> Section 6.4.7 Lightning Protection:
> Lightning surges cannot be stopped, but they can be diverted. The plans for the
> data center should be thoroughly reviewed to identify any paths for surge entry into
> the data center. Surge arrestors can be designed into the system to help mitigate
> the potential for lightning damage within the data center. These should divert the
> power of the surge by providing a path to ground for the surge energy. ... It is also
> necessary to protect against surges through the communications lines.

In every case, plug-in protector are not used. In very case, a protector connects short to single point ground. Or does nothing.

From the US Air Force:
US Air Force Instruction 32-1065 1 Oct 1998
> Introduction. This section covers requirements for grounding and lightning protection systems,
> including systems installed on or in areas such as explosives buildings, magazines,
> operating locations and shelters.
>
> 15. Surge Protection.
> 15.1. Entering or exiting metallic power, intrusion detection, communication antenna, and
> instrumentation lines must have surge protection sized for lightning surges to reduce
> transient voltages to a harmless level. Install the surge protection as
> soon as practical
> where the conductor enters the interior of the facility. Devices commonly used for
> this include metal oxide varistors, gas tube arresters, and transzorbs.

Telcos install their protector withing feet of earth ground. And up to 50 meters distant from electronics. Essential to protector is separaton between protectors and electronics. Nothing new.

But unfortunately too many are only taught myths in retail stores. Buy protectors that have no dedicated wire for the always required short connection to earth. Protectors that do what their numerics specs say they do - nothing. No earth ground means no effective protection. Any honest source would have posted manufacturer numeric specs. Those numbers are not provided becasue plug-in protectors claim no effective protection. Those above professionals never waste money on plug-in solutions.

Protection is always about where energy dissipates. Always. From the IEEE IEEE Green Book entitled 'Static and Lightning Protection Grounding':
> Lightning cannot be prevented; it can only be intercepted or diverted to a path which
> will, if well designed and constructed, not result in damage.

 

Read numeric specs on a power strip protector. Where does it claim protection from each type of surge? If it does protection, then numbers say so. Good luck. No plug-in protectors make those claims for a very obvious reason: no short connection to earth.

To be effective, a plug-in protector must block, absorb, or stop a surge. So how does its hundreds of joules absorb surges that are hundreds of thousands of joules? Again, those pesky numbers. Why do I ask that question repeatedly - and no one answers? Because power strip protectors do not claim protection - except when myths ignore numbers.

GFI? How does that mechanical switch that takes milliseconds to respond stop a surge that is done in microseconds? Again, a damning questions with numbers. How does its millimeter open switch stop what three miles of sky could not? Again, it does not.

A surge is a current source. From first semester electronics, a current source will increase voltage as necessary so that the current flow uninterrupted. That means voltage increase as necessary on that GFI open contact so that current arcs across it.

Same applies to power strip protector or a UPS. How do those 2 cm parts stop what three miles of sky could not. Anything that might stop a surge sees voltage increase as necessary to blow through.

Effective protection never stops surges. Effective protection means energy is not even inside the building. As the NIST says,
> You cannot really suppress a surge altogether, nor "arrest" it. What these protective devices
> do is neither suppress nor arrest a surge, but simply divert it to ground, where it
> can do no harm.

AVR does virtually nothing. Anything it might do is already done inside electronics. How does AVR that adjusts up to 139 volts magically stop surges that are 6000 volts? That AVR does nothing for surges. Even surge protectors ignore surge voltages that are less than 330 volts. Anything AVR might do is required - by numbers - to already be inside every computer power supply.

All appliances contain massive protection. Your concern are surges that occur typically once every seven years. Ie - a direct lightning strike. Install surge protection so these most destructive surges are irrelevant. Are not even inside a building. That always means a short connection to single point ground. Not just one ground rod. Earthing that both meets the post 1990 National Electrical code - and exceeds it.

Why are square waves harmful to small electric motors? Harmonic frequencies create destructive heating inside motors.

Same square waves with sharp or soft rise times are irrelevant to electronics. First the wave (square or sine) is filtered. A serious filter. Then converted to higher voltage DC. Makes no difference what the rise time is. 120 VAC is rectified to something in excess of 300 volts DC. After more filtering, that DC is converted to high voltage radio frequency AC. Now there is a far sharper rise time. That sharpest rise time is what makes perfectly stable and clean DC voltages. Electronic power supplies are so robust as to make even 'dirtiest' UPS power irrelevant. But again, a point made repeatedly with numbers.

Power supplies just keep getting better and better. Far superior to the supply allegedly designed by David Packard in 1970 when other engineers said it could not be done. Today's supplies do even so much more with so few components.

 

I live in the Florida panhandle and the best protection when the thunder starts to rumble is disconnect everything from the wall outlet and isolate it. I have surge protection from the power company that goes on my meter, phone and cable outside the house but I still isolate everything, then nothing is going to get to it. I've had my wall outlets pop like a 22 rifle shot and blue haze come thru the kitchen. I also disconnect the cable from my modem.

 

I'll keep relying on my Cyberpower AVR I've been using for the last 5-years.

 

Again, surge and spike protectors are little more than expensive extensions cords and should not be compared to a good UPS with AVR. They do not operate in the same way, nor do they have the same operating specifications, current or voltage limiting specifications, response times or, most importantly, reaction thresholds. A good UPS with AVR, for example, does not wait for a surge to reach 330VAC before reacting. As seen by this APC KB Article, it compensates for voltages up to about 150VAC for a 120VAC UPS. Voltages exceeding that cause the UPS to transfer from line to battery power. And of course, a surge and spike protector does nothing for sags, dips, or brownouts.

Whole house protectors are different as well and really are to protect from surges due to lightning - lightning arrestors, and not bad ones either, IF the facility ground connection is good. Sadly, these are often installed, then forgotten - for years and years. They should be inspected and tested regularly. When I maintained air traffic control radios systems, we tested facility grounds at least annually.

That said, nothing will protect you from a direct lightning strike, except as squid13 reports, disconnecting from the grid completely. Many mission critical systems and facilities go on battery backup as precautions before severe weather. Living in Tornado Alley in the Midwest, we have our fair share of severe weather too and the power company pushes hard to put whole house protectors on our homes. But it is important to note that whole house devices protect from anomalies from outside the home, not from within. That's an important distinction.

Contrary to what some would have us believe, household electronics and appliances do not have surge and spike protection built in. Some may have limited currently limiting devices (fuses and circuit breakers) to protect themselves from self-destruction but not surge and spike protection from other devices on the circuit or to prevent them from sending surges and spikes down the line. I'm reminded again of the $15 1500w hair dryer made in some factory in China under horrendous conditions by untrained underaged workers under the supervision of corrupt government officials, using parts from a similar factory up-river. They surely don't have surge and spike protectors - at best have a fusible link of questionable quality.

The more sophisticated devices, quality made computer PSUs for example, have limited regulation circuits to adjust for "normal" fluctuations. I say again, "normal" fluctuations.

In a perfect world, that would be good enough. But until humans can create perfection, even the best made components can fail. Devices will fail. Or they can be damaged, or abused. A failing or damaged device inside your home, office, or apartment building is capable of sending just as damaging anomalies down the line as those coming through the grid.

Apparently, it would seem some only believe in a device if it protects from every conceivable threat. That, of course, is not realistic. There is no such device. A whole-house unit will help with some problems. And a S&S protector may help with others. Short of never plugging in, the next best thing for total coverage is a good UPS with AVR.

 

Just remember, the batteries only last about 3 years.

 

Battery is always charged @ 100% and self check's always pass

 

That's great! But understand you have beaten the odds. They normally don't last that long. The real test, of course is to pull the plug from the wall and see if the UPS holds your system up long enough for you to "gracefully" shutdown.

 

How long does it test the batteries? Many batteries look 100% when first measured. Batteries require loads and time to determine their state. A 100% battery that once ran for 20 minutes may now be a 100% battery that can hardly work for one minute. Test must measure how quickly it degrades with load.

Self check and battery report is invalid without sufficient time to measure what really exists. As Bill_Bright notes, after three years, expect a standard UPS battery to be quickly dying.

Meanwhile, my car batteries in harsher environments last seven to nine years. Batteries to telco COs have a life expectancy just under 20 years.

 

Did that test also. The total time to do either a manual shut down or auto shutdown is 30-minutes. I have it set also,that if power is not resumed after 15 minutes,to automatically shut it down.

Pull the power cord from the wall,the unit powers up immediately.

 

Excellent. I would do that pull the plug test once a month. Or if your UPS came with a software component and cable interface, you may test that way.

As far as comparing UPS batteries to car batteries, that is not a valid comparison. While both are lead acid, UPS batteries are normally SLA or "sealed" lead acid designed to deliver their current for an extended period of time while car batteries are SLI (start, lighting and ignition) designed deliver maximum amperage in short bursts to start a big heavy engine. engine components). It sure would be nice, however if UPS batteries lasted 7 years, or even 20. But that would likely increase the price of an UPS considerably.

I also note we used line control units, very similar to telco equipment to control tower radios, which typically have transmitters in one facility and receivers in another. Our batteries were silver-oxide, which are very long lasting, but just don't have the current capability needed for an UPS. And they are very expensive.

This is a critical question. It must hold power to your equipment long enough to allow you (or the control software) at the very least to save any open files and shut down the system gracefully. 30 minutes is most excellent - amazing even for such old batteries.

 

Bill,

We've had an active storm season this summer,it's been put to the test many times.

It has an audible alarm that sounds when it goes into battery back-up mode. I dont even remember how much I piad for it,but if it dies tomorrow,knowing it's lasted past its life span,will make it easier to spend the $$$ on another one

 

Excellent thread! I've learned a lot in a short time Funny thing, I guess, is here I am in Calgary, AB, presently sitting at my pc plugged directly into a very old and cheap 'n cheezy surge protector while Mother nature is putting on a light show, and maybe sad to say, but I don't care one iota about the threat of a lightning strike. Maybe it's because all electrical service wiring in this very large and newer neighborhood is under ground. So, does this actually reduce the risk of lightning induced damage to home electronics, or I have just got a false sense of security? BTW, we probably get around 8-10 electrical storms, usually they're short in duration, with 2 or 3 homes in the city struck every year (~ 1 million people) during the Summer months.

 

The average event is about once per seven years. With a typically lower frequency of CG type storms, your risks would be less. But it makes little difference whether wires are overhead or underground.

This professional's application note demonstrates the concept. Every incoming wire must connect to single point ground before entering/exiting the structure. Even the underground phone wire:
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

A Polyphaser application note also discusses this in "Shielded Data Cables and Protectors" at:
http://www.polyphaser.com/techdocs/telco and dataline.pdf
It begins:
> Lightning strikes somewhere across the street close to the below grade West
> cable vault.

 

I love threads like this -- off the wall sort of stuff you don't think about often, and enough data that you don't have to worry about it being an 'advertisement'. A little muddy because of differing opinions of the primary data-givers, but still a lot of infos to cogitate on.

Sul.

 

I love the title of the thread, When Lighting Strikes and I'm here to tell you it struck last night. I live in Pensacola in the Florida pan handle just north of nine mile road and we had a storm come though yesterday about 5:30 PM that dumped 4" of rain in 55 minutes and 6 " total and our lighting here comes straight down. It was popping around here and sounded like a war zone. Lost power at 6:00 Pm when one hit my pole and took out the transformer. Got power back at 5:45 AM this morning and the power crew said they had been changing transformers all night. As I said in my previous post that when I hear thunder I disconnect everything from it's power source and I'm glad I did cause I had no damage except for no air conditioning to keep cool during the night.