What will happen when and if lighting strikes my imax?Its grounded well but is there something else i should do?
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lighting and an imax
- Thread starter King Mudduck
- Start date
King Mudduck,
Doesn't matter if it's an Imax, or whatever. If it gets hit by lightning, order another one, it's history. If it isn't, buy the next lottory ticket you come across.
What's best to do when there's a potential lightning strike? Un- plug the thing and drop the coax out the window. Better yet, move it 3 feet underground (the whole antenna, not just the coax). There is no fool proof protection for a direct strike. Dropping the coax out the window does help for indirect strikes. The 'trick' is knowing which one is about to occur! If you ever find out how please let me know too!
- 'Doc
Doesn't matter if it's an Imax, or whatever. If it gets hit by lightning, order another one, it's history. If it isn't, buy the next lottory ticket you come across.
What's best to do when there's a potential lightning strike? Un- plug the thing and drop the coax out the window. Better yet, move it 3 feet underground (the whole antenna, not just the coax). There is no fool proof protection for a direct strike. Dropping the coax out the window does help for indirect strikes. The 'trick' is knowing which one is about to occur! If you ever find out how please let me know too!
- 'Doc
King, 'Doc is correct. After removing the coax to the outside, I would at least attach it somehow directly to a ground rod(s). This may cut down on the disruption somewhat, but everything in this system will likely be destroyed.
I use to watch lightning hit my grandpa's lightning rods on his barns. You could see the current ride the rod to the heavy copper lines down to the ground rods. When this happened I recall that there was not as much noise (if any) as there was when lightning hit a tree in the area.
So if you just drop the line out the window you might really hear a big bang when the lightning gets to the end of the coax and doesn't find the earth right there at the end. Even if the coax is laying on the ground there is a small air gap between the end of the coax and the earth at which point may make a loud noise.
I use to watch lightning hit my grandpa's lightning rods on his barns. You could see the current ride the rod to the heavy copper lines down to the ground rods. When this happened I recall that there was not as much noise (if any) as there was when lightning hit a tree in the area.
So if you just drop the line out the window you might really hear a big bang when the lightning gets to the end of the coax and doesn't find the earth right there at the end. Even if the coax is laying on the ground there is a small air gap between the end of the coax and the earth at which point may make a loud noise.
Had a local have his Antron 99 get hit by lightning a few years ago.The first thing he did after picking himself up off the floor and checking his underwear was call 911. :shock: Smoke was coming from the roof at the eave and from the wall where part of his kitchen cupboards were.Note I said WERE!The lightning followed the coax cable into the kitchen where the coax was behind the top corner of the cupboards and literally blew a hole in the wall and the cupboards.He had a little fire and smoke damage but a LOT of electrical damage and ended up practically rewiring the entire house.As for the antenna we did find the mounting plate and a few shards of fiberglass left. :?
now that's what I would call some kind of fire works show !!! Damned near scary if you think about it ,we really don't get much lightning striking in So.Cal where I've lived , Earthquakes (little ones) and wild fires yearly , I think I'll still take my chances out west here. Tornados and Hurracanes I can live without !! Does one truly get used to there environments ? I couldn't emagine Greenbay , Wis. or North Dakota type cold weather !! let alone 120 degrees everyday in the summer in Pheonix ,Arizona !! or the humitity of the Alabama,Mississippi states. Hell !! it gets in the 40s and IM cold !! 90s and IM hot !! must be like paradise to others.
LIGHNIN STRIKE
I use a connector off the back of the radio inserted into the window frame.
When the bad weather comes around we just unscrew the coax connector and put the end well out of the way close to ground of course.
Like the sayin goes when it comes to lightning-
"The only safe connection is disconection"
I use a connector off the back of the radio inserted into the window frame.
When the bad weather comes around we just unscrew the coax connector and put the end well out of the way close to ground of course.
Like the sayin goes when it comes to lightning-
"The only safe connection is disconection"
I was going to put a ground rod in the ground and then some how weld an antenna stud to it.That way if there is a strom coming or there calling for one that day i can just unhook it from the radio and hook it to the ground rod.
"I was going to put a ground rod in the ground and then some how weld an antenna stud to it.That way if there is a strom coming or there calling for one that day i can just unhook it from the radio and hook it to the ground rod."
that's not going to protect anything from a million volts and 4,000 amps of rf current at 2mhz. and up. everything from the antenna to the rod will be vaporized in the blink of an eye if it takes a direct hit.
if you want the capability to survive repeated direct lightning strikes then we need to look at just how this is accomplished by the big boys, the commercial broadcasters.
Do commercial broadcast stations disconnect their antennas when a thunderstorm approaches? No. Do their antennas get struck by lightning? Yes, again and again and again. Do their transmitters sustain damage? Do their transmitter buildings burn down? Are their operators killed? No. No. And no. Why? Proper installation. (Truth be told, all of the above *have* happened at commercial broadcast stations, but in every case the cause can be traced to, you guessed it, improper installation.)
Proper installation isn't cheap or easy. Make the slightest mistake, cut the smallest corner, and you open yourself to catastrophic damage. So what's a ham with limited funds and knowledge to do? Many hams just disconnect their coaxes and drop them behind the radio. Some who are a bit more savvy stick the end of the cable in an old mayonaise jar. Neither trick is satisfactory. If your antenna is struck, there's going to be around a *million* volts on that cable, that much voltage can jump 100 inches in air, and it *will* if it has to in order to reach ground potential.
The only proper way to deal with lightning is to give it a controlled way to go to ground. It's going to go to ground one way or another, your only hope is to direct it in a way that's safe for you, your equipment, and your home.
>I have a heavy ground run to the radio room for grounding the equipment. >Should the antennas be connected to this, grounding the center conductor >and sheild? Should they be grounded and a real lightning rod be installed? >Or just disconnected from the radio's?
Well just disconnecting from the radio isn't good enough. You've got to give that lightning a *low impedance* way to reach ground. And that low impedance path has got to be able to successfully handle 4,000 amperes of *RF* current. That's what lightning is, nature's own spark transmitter.
Ideally you'll have a ground window installed at your station. (I know you folks are probably tired of seeing me preach about this, but it is the best protection you can have.) That ground window will have *every* wire that enters or leaves your station passing through it via proper lightning suppressors, including power, telephone, coax, *everything*. Note, arrange the cabling so that no down lead parallels an interior station cable run. Otherwise surges will be inductively coupled from the outside cable to the inside cable bypassing the ground window.
The ground window will be connected *directly* to your ground field by a straight low inductance conductor. In no case shall the conductor be less than number 8 solid copper wire, but should really be a wide copper strap, 5 inch copper flashing is good. (The reason wide copper strap is preferred is that it's inductive only at its edges, and because skin effect limits current penetration to only a few thousandths of an inch so you want as much surface area as possible.) Ideally there will be no bends in the ground run, but in no case shall there be any *sharp* bends. That adds inductance.
Note that in *addition* to the ground window, every antenna or support whose construction will allow it should have a separate ground conductor run to the station ground field. This will relieve the downleads, and suppressors, of part of the current load they'll have to carry during a strike.
A single 8 foot ground rod is *not* an effective ground field. Ideally we'd copper plate the Earth to form an effective ground field, but that's impractical. So we make do with driven ground rods. In average soil, a single 8 foot ground rod will have a resistance to Earth of about 230 ohms. That will place a connection to that rod at 920 kV during a 4000 ampere strike. Not good. As currents start to flow into the ground, the soil becomes temporarily *saturated* with charge. This limits the amount of current that can be quickly dumped into any individual Earth connection. So we need a bunch of Earth connections. How many is a bunch? Well good practice says that the total resistance to Earth should be less than 25 ohms, so that means at least 10 rods are required. How far apart should the rods be to avoid overlapping saturation zones? The rule of thumb is that ground rods should be no closer together than the *sum* of their lengths. That means that any two rods in the ground field need to be at least 16 feet apart.
The rods should be laid out in a star pattern with the rods connected to each other by no less than 1.5 inch bare copper strap buried not less than 18 inches below grade level. Note that these straps can be considered horizontal ground rods themselves and can reduce the number of driven rods needed in the system by about a third. So assume 7 rods, one central and six radial at a 16 foot separation. Make all connections to the central rod. That's your *single point ground*. Tie power company, phone company, and CATV grounds to this point as well as attaching your station ground and separate antenna grounds to this point. Never never never daisy chain grounds. All grounds must be tied to this single point, and only to this single point. (Note, if you have a tower, it can serve as the central rod. With its base planted in concrete, it forms a Ufer ground superior to a single driven rod. Note too that if you have metallic underground plumbing, that should also be tied to your single point ground by a strap connection.)
One more caveat. If your soil is dry sandy soil, or very rocky, you'll need more rods than for the typical case above. It's OK to extend your star out beyond the first ground rod, and in this case *only* it's OK to daisy chain along a radial from one rod to another, but more than two rods along a single radial reach a point of diminishing returns. The buried radials themselves, however, make a dandy groundplane for a vertical antenna and can extend out as far as you like.
I've left out many details in the above system, such as how to deal with bonding dissimilar metals, always making a *mechanical* connection as well as an electrical connection (solder *will* melt during a strike), what constitutes a *proper* lightning suppressor, etc. Entire books have been written on proper station installations. You should read at least one, _The National Electrical Code_. And I'd recommend one more, Roger Block's _The Grounds for Lightning and EMP Protection_.
Ok, that's the *proper* way to protect your station. Now what's the cheap ham way? Install an *outdoor* bulkhead panel near ground level and bring all your antenna coaxes through it with bulkhead feedthru connectors. Drive a rod into the ground at least 100 inches from the house and bolt a bar to it that has female coax chassis fittings attached, both shell and center connected to the bar. When a storm approaches, unscrew all cables from the bulkhead and screw them to the ground bar. This will keep dangerous currents and voltages *outside* your house. But that bar is going to reach 900 kV during a strike. Make sure there's nothing conductive nearby. Obviously *don't* ground the house bulkhead panel to this rod.
(Note that this cheap approach has several faults. First you've got to be home to connect the coaxes to the ground bar. Second there is such a thing as clear sky lightning. Not all strikes occur during a well defined storm. Third, any cable that passes parallel to the grounded coaxes is going to have a large surge inductively coupled into it. And fourth not all lightning is going to come into your house via your antennas. It can also come in on the power wiring, the phone wiring, or the CATV wiring. So this method should be considered a minimum *expedient* only. It does beat a mayonaise jar.)
http://www.harvardrepeater.org/news/lightning.html
http://www.qsl.net/w8wky/reference/lightning.txt
that's not going to protect anything from a million volts and 4,000 amps of rf current at 2mhz. and up. everything from the antenna to the rod will be vaporized in the blink of an eye if it takes a direct hit.
if you want the capability to survive repeated direct lightning strikes then we need to look at just how this is accomplished by the big boys, the commercial broadcasters.
Do commercial broadcast stations disconnect their antennas when a thunderstorm approaches? No. Do their antennas get struck by lightning? Yes, again and again and again. Do their transmitters sustain damage? Do their transmitter buildings burn down? Are their operators killed? No. No. And no. Why? Proper installation. (Truth be told, all of the above *have* happened at commercial broadcast stations, but in every case the cause can be traced to, you guessed it, improper installation.)
Proper installation isn't cheap or easy. Make the slightest mistake, cut the smallest corner, and you open yourself to catastrophic damage. So what's a ham with limited funds and knowledge to do? Many hams just disconnect their coaxes and drop them behind the radio. Some who are a bit more savvy stick the end of the cable in an old mayonaise jar. Neither trick is satisfactory. If your antenna is struck, there's going to be around a *million* volts on that cable, that much voltage can jump 100 inches in air, and it *will* if it has to in order to reach ground potential.
The only proper way to deal with lightning is to give it a controlled way to go to ground. It's going to go to ground one way or another, your only hope is to direct it in a way that's safe for you, your equipment, and your home.
>I have a heavy ground run to the radio room for grounding the equipment. >Should the antennas be connected to this, grounding the center conductor >and sheild? Should they be grounded and a real lightning rod be installed? >Or just disconnected from the radio's?
Well just disconnecting from the radio isn't good enough. You've got to give that lightning a *low impedance* way to reach ground. And that low impedance path has got to be able to successfully handle 4,000 amperes of *RF* current. That's what lightning is, nature's own spark transmitter.
Ideally you'll have a ground window installed at your station. (I know you folks are probably tired of seeing me preach about this, but it is the best protection you can have.) That ground window will have *every* wire that enters or leaves your station passing through it via proper lightning suppressors, including power, telephone, coax, *everything*. Note, arrange the cabling so that no down lead parallels an interior station cable run. Otherwise surges will be inductively coupled from the outside cable to the inside cable bypassing the ground window.
The ground window will be connected *directly* to your ground field by a straight low inductance conductor. In no case shall the conductor be less than number 8 solid copper wire, but should really be a wide copper strap, 5 inch copper flashing is good. (The reason wide copper strap is preferred is that it's inductive only at its edges, and because skin effect limits current penetration to only a few thousandths of an inch so you want as much surface area as possible.) Ideally there will be no bends in the ground run, but in no case shall there be any *sharp* bends. That adds inductance.
Note that in *addition* to the ground window, every antenna or support whose construction will allow it should have a separate ground conductor run to the station ground field. This will relieve the downleads, and suppressors, of part of the current load they'll have to carry during a strike.
A single 8 foot ground rod is *not* an effective ground field. Ideally we'd copper plate the Earth to form an effective ground field, but that's impractical. So we make do with driven ground rods. In average soil, a single 8 foot ground rod will have a resistance to Earth of about 230 ohms. That will place a connection to that rod at 920 kV during a 4000 ampere strike. Not good. As currents start to flow into the ground, the soil becomes temporarily *saturated* with charge. This limits the amount of current that can be quickly dumped into any individual Earth connection. So we need a bunch of Earth connections. How many is a bunch? Well good practice says that the total resistance to Earth should be less than 25 ohms, so that means at least 10 rods are required. How far apart should the rods be to avoid overlapping saturation zones? The rule of thumb is that ground rods should be no closer together than the *sum* of their lengths. That means that any two rods in the ground field need to be at least 16 feet apart.
The rods should be laid out in a star pattern with the rods connected to each other by no less than 1.5 inch bare copper strap buried not less than 18 inches below grade level. Note that these straps can be considered horizontal ground rods themselves and can reduce the number of driven rods needed in the system by about a third. So assume 7 rods, one central and six radial at a 16 foot separation. Make all connections to the central rod. That's your *single point ground*. Tie power company, phone company, and CATV grounds to this point as well as attaching your station ground and separate antenna grounds to this point. Never never never daisy chain grounds. All grounds must be tied to this single point, and only to this single point. (Note, if you have a tower, it can serve as the central rod. With its base planted in concrete, it forms a Ufer ground superior to a single driven rod. Note too that if you have metallic underground plumbing, that should also be tied to your single point ground by a strap connection.)
One more caveat. If your soil is dry sandy soil, or very rocky, you'll need more rods than for the typical case above. It's OK to extend your star out beyond the first ground rod, and in this case *only* it's OK to daisy chain along a radial from one rod to another, but more than two rods along a single radial reach a point of diminishing returns. The buried radials themselves, however, make a dandy groundplane for a vertical antenna and can extend out as far as you like.
I've left out many details in the above system, such as how to deal with bonding dissimilar metals, always making a *mechanical* connection as well as an electrical connection (solder *will* melt during a strike), what constitutes a *proper* lightning suppressor, etc. Entire books have been written on proper station installations. You should read at least one, _The National Electrical Code_. And I'd recommend one more, Roger Block's _The Grounds for Lightning and EMP Protection_.
Ok, that's the *proper* way to protect your station. Now what's the cheap ham way? Install an *outdoor* bulkhead panel near ground level and bring all your antenna coaxes through it with bulkhead feedthru connectors. Drive a rod into the ground at least 100 inches from the house and bolt a bar to it that has female coax chassis fittings attached, both shell and center connected to the bar. When a storm approaches, unscrew all cables from the bulkhead and screw them to the ground bar. This will keep dangerous currents and voltages *outside* your house. But that bar is going to reach 900 kV during a strike. Make sure there's nothing conductive nearby. Obviously *don't* ground the house bulkhead panel to this rod.
(Note that this cheap approach has several faults. First you've got to be home to connect the coaxes to the ground bar. Second there is such a thing as clear sky lightning. Not all strikes occur during a well defined storm. Third, any cable that passes parallel to the grounded coaxes is going to have a large surge inductively coupled into it. And fourth not all lightning is going to come into your house via your antennas. It can also come in on the power wiring, the phone wiring, or the CATV wiring. So this method should be considered a minimum *expedient* only. It does beat a mayonaise jar.)
http://www.harvardrepeater.org/news/lightning.html
http://www.qsl.net/w8wky/reference/lightning.txt
Yup thats the stuff freecell, I guess I've been lucky with disconetion.
A lot of people don't think about all the other equipment in the house.
I've seen lightning explode out of a buddys tv and jump clear across the room into the guys phone only to tell him I told ya so (it was a good thing I went to the 10-100 room early-er cause my shorts would of been full).
My self I don't mind diconecting everythig and I set it up that way so it's easy to disconect and reconect and havent had any problem exept once I forgot to take the phone off line.
I could swear that my tower got nailed a few times but it didn't melt the A-99 up there. Not like a buddy of mine who forgot one day, his A-99 exploded into toothpicks and fryed
everything else along the line. Good thing it was in his shop.
It could have been worse.
Have a merry new-year everyone.
A lot of people don't think about all the other equipment in the house.
I've seen lightning explode out of a buddys tv and jump clear across the room into the guys phone only to tell him I told ya so (it was a good thing I went to the 10-100 room early-er cause my shorts would of been full).
My self I don't mind diconecting everythig and I set it up that way so it's easy to disconect and reconect and havent had any problem exept once I forgot to take the phone off line.
I could swear that my tower got nailed a few times but it didn't melt the A-99 up there. Not like a buddy of mine who forgot one day, his A-99 exploded into toothpicks and fryed
everything else along the line. Good thing it was in his shop.
It could have been worse.
Have a merry new-year everyone.