Lightning Strike at my QTH

[WD5JKO]

Monday this week at 4:30pm my son calls me at work saying that there was a big storm with lightning and thunder. The last crash resulted in about 1/2 of the lights going out in the house. I came home as quick as I could. Here is what I found:

*50 amp 2-pole breaker from main breaker box to auxiliary breaker box had 1 pole popped
*15 amp 1-pole breaker for GFCI outlet popped

switching these on, and everything came up...so I thought..

Looked at my ham antenna, 38' tower with OCF dipole on top. The lead in wire to my knife switch was vaporized at the end (RG-8X) with lots of black soot nearby. I usually disconnect the lead into the house, but I forgot this time. Tried several ham rigs, all worked. Tried the ham computer, and all good. I had two levels of coax switches shorting the rigs out. Reconnect the antenna, and the SWR is way different..Ok I can deal with that later..

Then the XYL says boy it's hot in the house. Oh, Oh, yep the AC was not working. Look further and the digital programmable thermostat was scrambled. Just what I wanted to do was reprogram that thing with two females all stressed out. I sent them to the mall....Further looking, and the air handler ignition board has power, and good input but nothing works. Call AC repair guy, and $385 later I got AC, but thermostat only works in manual mode. Another $70 there.

The phone (ma bell twisted pair) was dead too. They fixed that for free.

My sons XBOX monitor and dance pad fried, PS3 fried, and computer motherboard fried.

The satellite Dish Network DVR is fried. Can do anything else but no DVR.

Today I find the water sprinkler control box scrambled. After reprogramming that (fun), zone 16 don't work. The solenoid valve reads open circuit at the controller end; all the rest are 55 ohms. More fun yet to do there.

Try zone 1, and the above ground sprinkler head was split in two. Was it that way, or did lightning hit it too?

I use CFL lights, and the bulbs all seem to have survived!

So tonight while walking with the XYL we approach a neighbor across the street to ask him if he had any lightning damage. He had a Time Warner cable box go bad. Then he said he was in his garage that Monday afternoon when I got hit. He says my antenna was struck repeatedly with a blinding flash, and deafening thunder.

Now the XYL wants my antenna taken down...

Based upon what I described, did my antenna (it was grounded until it blew out) help protect my home, or did it's presence result in a greater likelihood of damage to my home? The tower is isolated, and therefore part of the antenna. The feedline was just a piece of RG-8X center and braid together to act as a jumper to a big edge  wound coil with the low end grounded. So the antenna saw a DC short into a 8' ground rod, and about 10' of #8 wire to the cold water pipe.

Jim
WD5JKO

[ka3zlr]

Act of God nobody can answer that, I'm very glad no one is Hurt an your safe.

I had a Strike come in on my ground System.

[w3jn]

Tower needs to be grounded, for sure.  The tower ground needs to be bonded to the house service entrance.  The feedline should ALWAYS be disconnected when ever you're away - not just grounded.

Lightning isn't really DC, due to the arcing.  It amounts to a huge AC spark gap xmitter 

I've seen pics of someone's dipole that got fried by lightning; the wire was burned into 2' or so sections which implies that the frequency was ~100 MHz.  So don't rely upon "DC" grounds in a lightning strike; design low-impedance ground runs.

[KA2DZT]

Now the XYL wants my antenna taken down...

Based upon what I described, did my antenna (it was grounded until it blew out) help protect my home, or did it's presence result in a greater likelihood of damage to my home? The tower is isolated, and therefore part of the antenna. The feedline was just a piece of RG-8X center and braid together to act as a jumper to a big edge  wound coil with the low end grounded. So the antenna saw a DC short into a 8' ground rod, and about 10' of #8 wire to the cold water pipe.

Jim
WD5JKO


[/quote]

Lightning has a very fast rise time.  This fast rise time can be related to some high frequency.  At this high freq your large coil looks like an open circuit to a lightning strike.  The grounded coil does do a fine job at draining off static charges that can build up on an antenna, but, it does little to ground a direct hit.

IMO,  the tower does in fact protect your house from being struck by lightning.  Lightning strkes a spot on the ground where there is need for electrons (or it may travel from the ground upwards if there is an excess of electrons).  It is better for the lightning to strike a metal object which will conduct the current to ground rather than hit the house where it can spark a fire.

Very hard to say why some equipment survives and yet other items are damaged.  You say that you have a ground rod at the antenna location and the rod is also connected to a water pipe.  Is the electric service ground also connected to the water pipes?  If not, that may cause problems with a lightning strike.  All your grounds should be connected together with heavy wire.

With that coil isolating the tower from ground at high freqencies, the lightning probably travel on the feedline back into the house where it can cause more damage.

Fred,  KA2DZT

[WA3VJB]

Hey Jim, tough break, but glad no fires or injury.

Around here the sailboat experts point out a cone of protection that extends from the peak of the metal mast around the cabin and deck.  

"It is generally accepted that this cone of protection extends 45 degrees, all around, from the tip of the metal protrusion. This means that if the aluminum mast of the average sailing vessel is properly bonded to the vessel's other major metal masses and is given a direct, low-resistance conductive path to ground, the entire boat should fall within the protected zone."

http://boatsafe.com/nauticalknowhow/lightning.htm

Maybe you can use that concept to re-assure everyone at home that the tower (after you'll fortify the grounding) provides a place for a lighting strike that could be safer than other potential points around the house.

[flintstone mop]

There was amazing video on The Dicovery Channel of lightning bolts coming up through radio towers to the sky. Prolly HD slow motion.

Tower grounding is a must. Your situation might have been reduced if the tower was grounded......instead the strike found ground through your A/C, sprinkler system, etc.

And the cone of protection is pretty interesting to see when airlners are struck by lightning. The charge passes right through and continues and passengers or electronics never know what happened.

There is a truth to those cat whisker things, I see more and more of.

[K5UJ]

Hi  Jim, bad luck.  And I mean it.  It was bad luck period.  Here's why:

When you have a storm you have a big charge buildup in a cloud.  It is sort of like huge static electricity like what you get from rubbing your feet on carpet.  This enormous charge disparity is potential, i.e. voltage, looking for a way to dissipate, i.e. reach equilibrium.  Getting back to basics of electricity you have a surplus or deficit of electrons up above you, or both.  When it is both, you are safe because the eventual electron transfer doesn't travel to or from Earth, it is cloud to cloud.  Otherwise you have this positive or negative charge overhead looking for equalization.

This is a very unstable situation.   There is a greater chance of controlling it by presenting an earth electrode to the charge (think of it as a real big chicken stick) but that only works with some reliability when it is a real tall electrode, like a sky scraper building, TV tower, or a rocket carrying a grounded wire.  There was an experiment in Florida about 15 years ago where in thunderstorms, people shot these solid fuel rockets up about 2000 feet carrying very thin gauge wire to induce a cloud to ground strike.  The technique worked surprisingly well.   But even in these cases, there is still enough instability of the charge, which is to say randomness, that a tall electrode might get hit or some other location not far away would.   If you look at a thunderstorm with a typical commercial radio tower you see lighting all over the place--maybe the tower gets hit but often it doesn't unless it is super tall.  The charge needs a buildup of an opposite charge on the ground before the air can ionize and arc over.  That can happen anywhere--on water, a house, tree, or just bare ground.  A ham tower is just another thing down there that's part of the landscape, no big bulls eye on it.   We get lightning here hitting houses that are 25 feet tall, when there are 75 foot tall trees nearby that are untouched.   It is pretty random but as usual, it is pretty hard to convince people of that who just react to antennas and don't do any thinking about it. 

To sum up, your 38 foot tall tower is not a hazard.  It might go for years never getting a hit, even if it were out in the open on a hill  .   To put it another way, if you could magically go back in time and take down the tower before that storm, you'd probably see that lighting strike hitting the bare ground there, or jumping over to a tree or your house but the tower or anything else there did not induce anything.  It just happened to be in the way, which is why it was random bad luck, nothing else. 

I tell worried folks around here that if I took all my antennas down, there would still be lighting, it's just that my antennas would no longer have an average chance of being in the way of it.

BTW there are two kinds of lighting according to the charge in the cloud, positive and negative.  Negative strikes are much more frequent and relatively mild.  Positive strikes for some reason are an order of magnitude more intense and do much more damage.   A broadcast station can go for years taking hits then take a major positive strike and loose the rig, feedline, all kinds of stuff.

Rob

[KX5JT]

There was amazing video on The Dicovery Channel of lightning bolts coming up through radio towers to the sky. Prolly HD slow motion.

Here is a pretty wild video of that phenomenon...

http://www.youtube.com/watch?v=-bvmEYxEYiA&


Sorry to hear about the strike Jim..

[W1ATR]

Jeez. Thankfully no one was hurt. That's whats really important.

The plain truth is that lightning is going to hit wherever the hell it wants. I had a strike here about 5 years ago that I still can't explain. It missed the house, (3 family tall sucker), it missed my 80m doublet at 60ft, it missed my 10m ground plane vert, and also missed all the 80ft+ trees. What did it hit? The damn chimney cap for my oil fired Modine unit heater in my garage. The cap is only 20ft off the ground.

Why did it miss all the other tall stuff directly nearby and go after the 20ft tall chimney cap? I don't think it matters that it hit the tower or not, that's just where the streamer started. More than likely, the streamers were reaching off of everything around like the house, tress, and otherwise. The one off the tower happened to attract the return stroke first. Without the tower, it may have been a tree, the mains coming in, or even a direct strike right to the house.

That's why insurance companies call these things an act of God. That way, there's no need to explain the exact reason, (read liability), as to why an event happens.

[WA1GFZ]

Tell XYL the tower took the hit rather than the corner of the roof. It protected the house. Sounds like there could have been a fire. A guy I work with lost his house when it was hit. Fire started in the garage and family had no time to get anything out of the house by the time they noticed the garage was on fire.

[N4LTA]

A well grounded tower is a must. Grounds need to be as straight line as possible. Even a 90 degree bend is not good. Lightning is a high frequency current pulse and any inductance in a ground lead causing a high rise in voltage.

At any large discontinuity in impedance - the pulse is reflected and at the point of reflectance - the pulse can double in amplitude. That is why power line primary dead ends cause so much trouble.

I have seen cases where the power company had to extend a primary line past a customer service several spans to stop lightning problems.

Pat
N4LTA

[Bill, KD0HG]

Yes, a properly grounded tower is going to offer a zone of protection underneath. Our broadcast towers get hit all of the time, but (usually) the building and electronics inside survive without issue.

Think about solid state gear attached to a 666' tall insulated tower!

As Jared said, a strike is going to do what it wants, and sometimes a strike will also hit power lines adjacent to a tower...That's where a lot of the damage happens. Put some industrial MOVs in your load center.

The typical risetime for a stroke is about 1 uS, or about 1 MHz, so that's why you need low inductance in a tower ground. It's a huge mistake to think of a strike as a DC event. It's not.

But you can use that fact to your advantage. If you have a lot of capacitance from the tower to the earth, it's as good as the traditional DC ground. On our rocky mountaintops where a traditional ground is impossible, we lay out heavy copper radials from the base of a tower to provide one 'plate' of a capacitor to earth. We also use chemical grounds to saturate an area around the base of a tower with a conductive salt.

My own advice is to lay out a bunch of heavy-gauge copper wires or strap from the base of your tower, nothing smaller than #4. The more the better. Then plant grass or some sort of ground cover in the field and keep it irrigated in the summer. That will give you one plate of a capacitor to earth consisting of the copper and several feet of conductive, moist earth. A lot of fertilizer will help, too.

Your tower is already in place, but even better would be to line its hole in the ground with copper strap, I mean *wide* strap, like roofing copper a foot wide connected to the tower with #0 to #4-ought copper cable and big clamps. Then pour the concrete. That's the setup here.

These people are the absolute nuts for grounding copper:
http://www.gacopper.com/

There is going to be a huge current in the ground in the event of a strike, which is in turn going to induce voltage in any nearby electrical conductors, so bear that in mind when laying out a ground system. Again, think of it as RF, not DC.

Take a tip from the AM broadcasters and never run coax lines or conductors directly from a tower to your ham gear. Put a coil of two or three turns, a foot in diameter in line. Add some impedance to force a stroke into the tower ground. Since there will be a huge voltage across this inductance in the event of a strike, you need to space wind this coil. A good way to do this would be to wind maybe 4 turns of the coax or open-wire line around a big plastic bucket from Home Depot. Separate the turns by several inches.

..Good luck with the XYL.

[WA1GFZ]

I've been told the zone of protection is bull pucky. Heck I had a 20 foot sapling hit in my yard about 50 feet from the tower and the tower is 70 feet tall with a 30 by 38 foot LPDA on top.

[N4LTA]

Also - keep in mind that any NEC ground or grounding scheme is NOT for lightning protection but for handling 60Hz fault current to trip a breaker or fuse.

NEC grounding is to permit fast over-current protection tripping at 60Hz - not for lightning protection. These grounds are fine as low impedance paths for 60Hz current but can be poor to nonexistent for a fast rise time lightning pulse.

Pat
N4LTA

[N4LTA]

Well - the zone of protection has been used by every major utility since the beginning of power distribution and has served them well.

The sapling being 50 feet from a 70 foot tower is at the edge of the standard accepted 30 degree zone of protection.

[WB4AIO]

A well grounded tower is a must. Grounds need to be as straight line as possible. Even a 90 degree bend is not good. Lightning is a high frequency current pulse and any inductance in a ground lead causing a high rise in voltage.

At any large discontinuity in impedance - the pulse is reflected and at the point of reflectance - the pulse can double in amplitude. That is why power line primary dead ends cause so much trouble.

I have seen cases where the power company had to extend a primary line past a customer service several spans to stop lightning problems.

Pat
N4LTA

There are many wise words in this thread.

But I've often wondered if one's ham shack could simply "retire from the field" of ground-to-sky or sky-to-ground pulses.

That is, when not in use, completely disconnect from aerials -- and from ground.

Sky-to-ground and ground-to-sky are just reciprocals of each other, depending on whether it's a dearth or surfeit of electrons we're talking about. So I think it's useful from a safety theory standpoint to visualize all lightning strikes as energy emerging from the ground and attempting to reach a charged zone in the air.

So why not just make it (nearly) impossible for energy in the ground to pass through our ham gear? In addition to disconnecting the shack from our antennas, also disconnect it from ground -- disconnect it from anything having a DC or low-impedance connection to ground, like ground radials or AC lines -- and disconnect it from anything having a high capacitance to ground, like counterpoise systems.

Meanwhile, the trees or the grounded tower nearby would provide a current path when a path was demanded by Mother Nature.

I know such near-total isolation from ground might be difficult, especially the AC mains part. It might take some creative thinking. (For example, in my old shack in Alexandria, Virginia, I used to remove the parallel feeders from my antenna tuner and toss them out the window during storm season, many feet from the house. Could something analogous be done with the AC power feed to the shack?)

But it should be possible to make our gear no more likely to get damaged by lightning than is an unplugged clock radio sitting inside a steel box which is itself sitting on a wooden pallet.

Of course, induced currents from nearby strikes would still occur. But with nothing connected to our gear except a few short wires disconnected from the outside world in every way, even that risk would be minimized.

Just food for thought!


Kevin, WB4AIO.

[ka3zlr]

I had a strike come in through well what I thought was a good ground, everything around the house was connected
all ground rods were fairly new good ground dirt to punch ground rods into an the strike came in through the station
Ground entry an blasted away 4 Pcs of equipment.

That was quite a few years ago I have since redid everything house is on it's own as per the codes, my station runs directly
outside to my 1600 foot 3/4 inch copper water line that is broken with plastic from the wall entry into the house. The water
line is 3 feet under ground we measured all 1600 feet to the main line at the road.

An earlier strike we had hit the little plastic box on the brick wall for the phone connection, it blew off my 300 amp service
panel right off the wall an that was different, another strike hit what was then my 80 meter loop it got fryed an the strike
went straight into the ground where my ladder line turned an headed towards the house.

Interesting Hobby Electricity...


73

Jack.

[K1JJ]

Below, you're looking at a pair of 190'ers, 150' and 110' towers  from 1/4 mile away on top of an 800' hill.  Back before they were erected, we used to get slammed by lightning quite often. I lost many pieces of ham and consumer electronics due to damage.

Now this is ham anecdotal, I realize, but in over 20 years I can't remember getting a lightning strike closer than say, 1/4 mile. I haven't lost any electronic gear either.  

There is an elaborate underground ground system connecting all the towers together and also a large 160M radial field for a set of verticals tied in too. The power service and telephone/cable grounds are tied in too, which may be a major factor.

My guess is that the towers are bleeding off the charge in this area and making it less apt to be hit. The neighbors should be happy to live with this protection....

But knowing how lightning theory is still not perfectly understood, it would not surprise me if this idea was incorrect.  

However, at this point, I do not see these towers as being a lightning "attractor" at all.

T

[Bill, KD0HG]

Kevin, a corollary to your thoughts is to make sure everything is at the same potential with the use of low impedance conductors.

For example, where the ground conductivity is poor, we say the heck with a ground to earth. We bond *everything* together with strap. The tower, transmitter, equipment racks, and run a wide copper strap around the perimeter of the equipment building. In the event of a strike, everything might elevate to a potential of 100,000 volts from "ground", but it doesn't matter because everything is at the same potential. The ground strap around the structure acts as a Faraday cage, everything within is protected.

Of course, you will need to protect the phone and power lines going into the structure with impedance and varistors.  

We have a mountaintop FM site set up like this. On a pile of rock. No real earth ground but 5,000' of copper wire radials laid on the ground at the base of the tower. The 240 volt power feed to the building is routed through *big* inductors at the service entrance, 20 turns of #4/0 flexible welding cable wound on 5" PVC pipe. Similar setup for the phone lines. I have never had a single piece of equipment in the building fail, even computers, in 20 years of wicked lightning strikes.

[Todd, KA1KAQ]

I always thought it was called the 'cone' of protection, an upside-down cone shaped area covering an area around the tower or grounded structure that is proportionate to its height. The object being, to drain the charge off as it builds, before it can build up to strike potential. And yes, despite man's best efforts, it seems lightning still does as it pleases.

We have some nasty lightning here, frequent storms with frequent strikes. I can disconnect the feedlines easily enough, but getting them back outside is difficult. So my thought is to make a simple grounding bulkhead tying a few SO-239s together then to ground. Just move the feedlines to the bulkhead when not in use. That should provide a path for continuous drain. At least the gear will be isolated.

One of those times I wish I had open wire feeders running to center of a big ol' knife switch, with one side to the rig and one side to ground. Just throw the switch.

[The Slab Bacon]

The "zone of protection" theory is pure B.S. ! ! ! ! ! ! ! ! ! ! ! ! !

I got hit a few years back when the highest tip of my highest antenna on the tower was 60'+ in height. It didnt even touch the tower, It hit the pole light on my garage. (My neighbor watched the actual strike)

The "pole light" is was a 175W MV light up on a 10' pole about 25' from the tower. It hit the light (the pole is grounded as well as a NEC properly grounded and connected run of UF cable to the house. The surge rode in on the 120v line from the light and took out a bunch of totally unrelated electronics. (like the phone modem in my computer, my alarm clock and about half a dozen other things) It also fried the line bypass caps on my valiant to ashes. (All antennas were disconected)

The tower gave no protection at all. The pole light saved the tower by taking the hit for it.    

There may be some truth in the "zone of protection theory" but dont make bank on it!!
The bottom line is that lightning is gonna hit wherever IT wants!!

[K1JJ]

Todd,

At Chuck/K1KW's place, you might have noticed last time: A pane of Plexiglas window with many waterproof female connectors of military type multi's and coax SO-239's mounted on it.  In the summertime he disconnects all cables from the outside and drops them on the ground.  Excellent protection..

T

[WB4AIO]

Kevin, a corollary to your thoughts is to make sure everything is at the same potential with the use of low impedance conductors.

For example, where the ground conductivity is poor, we say the heck with a ground to earth. We bond *everything* together with strap. The tower, transmitter, equipment racks, and run a wide copper strap around the perimeter of the equipment building. In the event of a strike, everything might elevate to a potential of 100,000 volts from "ground", but it doesn't matter because everything is at the same potential. The ground strap around the structure acts as a Faraday cage, everything within is protected.

Of course, you will need to protect the phone and power lines going into the structure with impedance and varistors.  

We have a mountaintop FM site set up like this. On a pile of rock. No real earth ground but 5,000' of copper wire radials laid on the ground at the base of the tower. The 240 volt power feed to the building is routed through *big* inductors at the service entrance, 20 turns of #4/0 flexible welding cable wound on 5" PVC pipe. Similar setup for the phone lines. I have never had a single piece of equipment in the building fail, even computers, in 20 years of wicked lightning strikes.

That's an intelligent solution. With 24/7 broadcast stations, of course, you can't disconnect the feeders and toss them into the yard like we can -- but it doesn't seem to have mattered at your mountaintop site.


With my best,


Kevin, WB4AIO.

[Bill, KD0HG]

Tom and all:

Last year I had these lightning disspiators installed on a tower. (The boss told me to) The rap is that they are supposed to discharge the clouds above a structure via their razor-sharp spikes. I have no proof if this concept actually works with a charge building up a long distance overhead, and no before-and-after proof, but they're currently the hot ticket in the radio biz. Looks easy enough to homebrew.

"Lightning is the leading cause of weather related
damage to broadcast equipment. With average
lightning currents of 20 to 30 kiloamps and heat
energy in excess of 20,000°C, the need for
improved lightning protection is evident.
...Shields structure by reducing the electric
potential of the tower or structure.
..Divert the electrostatic energy away from
critical equipment and toward a safe path to
earth. Exceptional electrical dissipation
Low cost, replaceable dissipating tips.

The Lightning Spur is a very efficient hybrid
lightning dissipator. When operating as a shield
it reduces the potential between the tower and
storm cell by transferring electrical charge to the
adjacent ionizing air molecules. This
transference represents dissipation or the
controlled leakage of the charge, thus reducing
the probability of a lightning strike.
If the electric charge accumulation rate far
exceeds the dissipation rate the Lightning Spur
will divert a lightning strike away from the
protected equipment and toward a safe path to the earth." (quote)

Any physisticists out there care to comment on the concept?

[N4LTA]

The zone of protection is a 30 degree cone One each side or a 60 degree cone from the top of the tower - All electrical high voltage transmission lines are designed with grounded wires above and the three phase conductors under the cone. It is a cone as stated above  - so a pole on the ground out from the tower - probably sticks up through the "cone and is not protected................

But then it is total BS ...so why worry about it

I believe  someone on this list one said "experience always trumps science" anyway.