======== Newsgroups: rec.radio.amateur.antenna Subject: Re: Lightning down your aerial - ground.txt [01/01] From: garyb@psych.ualberta.ca (Gary Burchett) Date: Tue, 28 Nov 95 19:56:57 GMT In article , burkimsher@cern.ch (Paul Burkimsher) wrote: >Hi, > >I'd like to mount a long ( 7 metre ) CB aerial going up vertically from >the chimney on the roof of our house but I'm worried about lightning. > >We do get storms round here (Geneva, Switzerland) some quite fierce. What >precautions can I take? > >What do the TV companies do, I mean they have aerials on top of their >masts many hundreds of metres high, don't they? > >Your (email) suggestions gratefully received... > >Thanks, > >paul > >paul@vxcern.cern.ch >burkimsher@cern.ch Here is a nice collection of net wisdom :-) Cheers, Gary VE6BBD From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Grounding and lightning protection Date: Thu, 17 Mar 1994 06:29:11 GMT In article <1994Mar16.162143.1@clstcs> armyrman@vms4.sci.csupomona.edu (Alex Myrman) writes: > >I too have antennas up on the roof and a couple long wire (dipoles) hanging >around off the house. >What should be done when lightning comes? I understand clearly that they >should NOT be in the radio but where should the lead-in's go? 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 downlead 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.) Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | In article kcs@merc.rx.uga.edu (Ken Schroder) writes: >Hi Gary, I appreciate the info and advice. You made the point that I should >be running my AC through the ground window. I guess that what I want to be >doing is bonding both the *neutral* (white) and safety ground (green) >conductors to the station single point ground?? Since I don't want to modify >the outlet in the wall I will probably build a short, heavy extension cord >with a receptacle in a handy box to plug the surge protector into. Bonding >wires for the neutral and ground will be brought out of the handy box to the >single point. Yeah, either run from the wall outlet to a proper suppressor mounted on the ground window (Polyphaser makes several), and then run on to an outlet box for the radios, or mount your radio outlet box directly on the ground window, directly connecting neutral and ground to the ground window and using an appropriate suppressor for the hot lead to ground window. You can then plug your radios in there. NOTE: This defeats any GFI breaker protection you may have had. It would be advisable to install a GFI outlet in the box you mount on the ground window, or after the ground window, to restore GFI protection. NOTE 2: The surge suppressor boxes commonly sold for consumer equipment protection ARE NOT ADEQUATE. You need real lightning suppressors. Delta Arrestors, Polyphaser, and some others make real lightning suppressors. Don't cheap out here. >I also have a two meter antenna in the attic. I disconnect this when storms >are predicted, but I may put an Alpha Delta on it and tie that to the single >point as well. This would be for near miss induction voltage, I don't >suppose that a small attic antenna is any more likely to be hit directly than >any other attic conductors right? You are correct in assuming that a *proper* suppressor will clamp the near miss induced surge on the attic antenna. It is no more likely to be struck directly than any other wiring in the attic. With more attractive outside antennas nearby, that likelyhood is small. IMHO, the Alpha Delta suppressors have a serious design flaw, and I wouldn't use them for lightning surge protection of radio equipment. The flaw is simple, they have DC continuity. What this means is that when connected to the low impedance of a radio, the gas tube will never fire in time because the voltage will be clamped by the low parallel impedance presented by the radio until the currents through the radio have climbed to damaging levels. Polyphasor does it right. They use a DC blocking capacitor whose charging time, R*C where R is the equipment input impedance, is long enough to allow the gas tube to fire before damaging levels of current can flow through the radio input circuit. See drawing. Alpha-Delta x---------x----> to antenna | | / Gas \ R Tube / | | | GND GND If we assume a 200 volt firing potential for the gas tube, current through R will have to reach 4 amperes before the tube will fire. Polyphaser C x-----||--x----> to antenna | | / Gas \ R Tube / | | | GND GND If C is 400 pf, The RC time constant of the network will be 20 nS, which gives the gas tube time to fire before current through R rises to more than 250 mA. Note: This assumes the equipment looks like 50 ohms at the frequencies of the lightning strike. That's not necessarily true. Depending on the topology of the input network, it could look like a short or an open, or anything in between over the broad band of frequencies where lightning has significant energy. Most of the energy in a lightning pulse is concentrated below 2 MHz, but significant components exist all the way up to UHF. A worst case situation would be a cavity with a shunt loop input. It'll look like a short to the bulk of the lightning energy, so the gas tube of the Alpha-Delta will never fire. However, the heavy lightning current flowing in the cavity input loop will induce a very strong signal through the cavity at UHF and fry your radio. Using the Polyphaser design, the gas tube *will* fire and serve to limit the energy entering the cavity. >Thanks again for the advice, both in response to me and many others. This >seems like an area that is woefully under covered in most ham radio >references. I've always worried about it, never more so than since the storms >came through a few weeks back. I spent the following Saturday helping a >non-ham friend repair lightning damage to his electrical system. It could >have been much worse, but what a mess. It isn't pretty, in fact it can be lethal, or burn your house down, if you don't take the proper protective steps. Proper protection isn't rocket science by any stretch, but there are subtleties that can burn you (like the example above) unless you carefully think through what must happen for the protection to be effective. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | From: garyb@psych.ualberta.ca (Gary Burchett) Newsgroups: rec.radio.amateur.antenna Subject: Galvanized vs Cu Ground Systems Date: Thu, 30 Mar 95 15:35:10 GMT Having read with interest the postings by Coffman et al, about proper tower and station grounding, I have a question. The consensus seems to be that tower grounding should be done with flat copper strap 4"-6" width from tower legs to copper plated ground rods and continued out with flat strap in a star pattern. Galvanized tower legs should be buffered from the copper by thin stainless sheet to control galvanic corrosion. OK on all that, but I looked into the cost. Copper stock and rods and fittings are expensive and not readily available. If the tower grounding were done in the same manner, but with galvanized sheet stock and galvanized ground rods, would the net result be the same? Of course, the resistance would be a little higher, perhaps compensated by a longer run. How about corrosion on the underground galvanized stock aver a period of years? The tower legs, being galvanized, would not require a buffer to the galvanized sheet stock. The cost of the galvanized ground system would be far less than the copper, and more readily available. Opinions? Thanks, Gary. From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Galvanized vs Cu Ground Systems Yes, you can use galvanized steel in place of copper. Losses are about 5 times higher if I remember correctly, but you're grounding a galvanized conductor which is no better, and you're connecting it to soil that is much worse, so the net effect isn't really significant in many cases. If you are trying to bypass a copper conductor, such as a feed line, then that's a different story, and you can't be quite so cavalier. You want your tower base ground connection to be better than the path through the copper transmission line, any suppressors, your equipment if you've neglected ground window design, and station ground. The main concern with use of galvanized steel in contact with Earth is corrosion. The galvanizing is a *sacrificial* electrode. It protects the steel from galvanic corrosion by sacrificing itself. Sooner or later it will be eaten away and the steel will come under attack. Soil pH has a large effect on this rate, as do any currents that may be required to flow through the system. Buried galvanized steel can corrode away in less than a year in some locations. In others it may last for decades. One method to successfully use steel as a grounding conductor is the *Ufer ground*. This is rebar embedded in concrete. The pH of the concrete prevents galvanic corrosion to a large degree, and concrete is a better conductor than many soils. With the large surface area presented by the rebar containing concrete, lower actual resistances, and capacitive reactances, to Earth are possible with this method than even with the traditional copper plated rod driven directly in the soil. (Think of it as a *whole bunch* of higher value resistances in parallel versus one somewhat lower value resistor.) From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Grounding and lightning protection Date: Thu, 17 Mar 1994 03:12:19 GMT In article brett_miller@ccm.hf.intel.com (Brett Miller - N7OLQ) writes: >In article <1994Mar16.155633.14996@ke4zv.atl.ga.us> gary@ke4zv.atl.ga.us (Gary Coffman) writes: > >(snip) >> That's the principle on which lightning rods are founded. They generate >> streamers so that they are the preferred target of lightning bolts. Since >> they are installed with low impedance paths to ground, they are able to >> *divert* strike currents from harming other nearby structures. This is >> called the "cone of protection". It's diameter is equal to about 1/3 >> the HAAT of the lightning rod in most installations. (High towers have >> other problems, and a "rolling sphere" method of estimating the protective >> zone must be used.) >(snip) > >This is what I am having a hard time understanding. I am told that if >I put things on my roof like antennas and solar panels, that they should be >grounded with heavy guage wire etc. Sounds to me like I'm just turning all my >roof ornaments into lightning rods! Wouldn't it be better to leave them >ungrounded and install a lightening rod on the roof? No, it's better to ground them according to the National Electrical Code *and* install a lightning rod. The grounds are there to protect *you* in case they get struck *despite* the protection of a lightning rod. Remember their little downleads are still better paths towards ground than anything else up there other than the lightning rod, but those little leads go through your equipment to get to ground. Not good. You want to furnish lightning with a better path to ground than the one through your equipment. That's what the separate heavy ground lead is for. Lightning rods are good streamer producers because they have a sharp point. Current flow at the air terminal is always easier from a sharp point rather than from a blunt object. Everything else being equal, the sharpest point on the roof will be preferentially struck. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Grounding and lightning protection Date: Wed, 16 Mar 1994 15:56:33 GMT In article <2m4rsv$mba@bigfoot.wustl.edu> jlw3@cec3.wustl.edu (Jesse L Wei) writes: >Gary Coffman (gary@ke4zv.atl.ga.us) wrote: > >: Mobile Radio Technology had a series in the April and October 1988, >: and January 1989 issues about lightning prevention systems. They >: tried to give both sides equal time, but it's clear that the dissipation >: arrays are at best only minimally preventative, if at all. > >Now I have no technical expertise here, but I'd like to ask a couple >of questions: 1) Does the Corona effect prevent strikes, 2) do spline >balls work, 3) what about "feeler" charges? The reason I ask is that >Richardson Wireless Klub (K5RWK) had a meeting last night in which >a Richardson ham (I think) who works for TU Electric came and gave a >~1.5 hour lecture on lightning, prevention, and RF grounding. He >brought up some of the above-mentioned issues, and also said at the >end that he submitted an article to "one of the ham magazines." >Your thoughts??? First I want to note that I'm coming from the perspective of someone involved in protecting broadcast transmission systems, and as someone with lightning simulator experience. Also the local area has a thunderstorm frequency second only to Florida in the US. So I've seen a lot of strikes, and have a feel for what works and what doesn't. What I can't supply is much in the way of formal theory on the subject, only my reading of the trade press and a fair bit of other literature on the subject. With that disclaimer out of the way, I'll give you my thoughts on your questions. 1) Corona, or point dischargers, are limited to about 20-60 microamps before streamer production begins. Streamers are the main mechanism by which near Earth lightning strikes are guided. So if corona breaks over into streamer production, you're going to attract lightning. That's the principle on which lightning rods are founded. They generate streamers so that they are the preferred target of lightning bolts. Since they are installed with low impedance paths to ground, they are able to *divert* strike currents from harming other nearby structures. This is called the "cone of protection". It's diameter is equal to about 1/3 the HAAT of the lightning rod in most installations. (High towers have other problems, and a "rolling sphere" method of estimating the protective zone must be used.) 2) The idea behind "spline balls", and other dissipation systems, is to multiply the number of point dischargers so that currents can be shared so as to keep any one point's current below the streamer threshold. It's a good idea in theory, but in practice if the points are close together, their corona merges and forms streamers. Remember that a typical strike is powered by about 20 coulombs of charge, and that individual points can't exceed about 60 ua without breaking into streamer production. So even if you have widely separated points to prevent merger, you still need an incredibly large number of them, especially if the cloud is capable of multiple strikes, which is the usual case. Also remember that cloud charge zones are in constant motion, and constantly inducing "mirror" charges in the ground below, so you don't have much *time* to discharge the currents safely. The idea of a "protective space charge" is pure hokum IMHO. The winds in a storm are going to blow away any ions formed by corona as quickly as they can be produced. 3) I'm not familiar with the term "feeler charge" so I'll have to defer a response on that subject. I'll add one more thought. There's a theory that if you can cause a *lot* of *little* lightning bolts, you can avoid the big dangerous ones. These "mini" bolts are supposedly so small that you can't see their strikes with the naked eye, but can measure them on a surge counter. This idea *may* work if the storm clouds aren't very energetic, and take *minutes* to build up to a strike, but I don't think it works in practice with the big thunderboomers we typically see. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Lightning protection? Date: Wed, 17 Aug 1994 14:34:01 GMT In article <295@coutts.UUCP> wwg@coutts.UUCP (Warren Gay) writes: >In article greg@netcom.com (Greg Bullough) writes: >>In article <776689646.95snx@baker.pc.my> david@baker.pc.my (David Baker) writes: >>>What we are considering is to put up a really tall antenna (maybe 100') near >>>our transmitter, and let the lightning go for it. It can blast away at that >>>texas tower array all it likes & hopefully leave the rest alone. >[...] >>Nice thought, but not sound. First, by attracting more strikes to the area, >>you'll increase the number of surges. Lightning doesn't have to hit your >>facility directly to cause grief. >[...] >>Greg > >Another thing to consider, that I've seen written up in various places: >Put a/some sharp point(s) on the antenna(s) that you're installing. All >it takes is a pointed screw sticking out the other side of the boom for >example. The advantage of doing this is that it bleeds off any high >voltages that might collect on it. > >For most antennas, this is probably not a big deal, since mine are all >grounded boom types. But other antenna types like TV / FM / Logarithmic >may have sections that are not grounded and CAN collect high voltages >during a storm. A sharp point bleeds off the excess, before the voltage >can reach harmful levels. > >If you don't believe this, put a sharp point on the Van der Graff (sp?) >generator, and crank it up. You'll see a corona off the point, as the >charge leaks away. Alternatively, note how hard they try to avoid the >sharp edges on the Van der Graff ball to avoid bleeding away the charge. > >I know this is all small stuff when considering how to avoid strikes, >but for the price of a screw, I wouldn't do without. If you have >home brew antenna(s) with sharp edges builtin (like mine), then you >don't need to do anything further ;-) This is bad advice for two reasons. First, the sharp point will indeed bleed off charge from the antenna, as *corona discharge*. This is equivalent to a *spark transmitter* and will raise your receiver noise floor extravagantly. Second, and worse, it will promote the formation of streamers during strong atmospheric electrical activity. The formation of upward streamers is the first stage in a lightning strike. These upward streamers, when they meet a downward stepped leader, form a conductive channel for the main lightning bolt to follow. This is the principle of operation of lightning rods. They *attract* lightning strikes by the streamers that they generate. This allows them to divert the strike to themselves, and the superior ground connection they offer, instead of through the facility they are installed to protect. Instead, what should be done for ungrounded radiators is to offer them a *quiet* bleed path to ground via a 1 megohm resistor. This will appear as an open circuit to RF, but will conduct the high voltage static charge harmlessly, and quietly, away. Lightning strike protection is a more complex subject, and one which I addressed for the poster by Email. Suffice to say that the principle protective means does *not* include adding streamer producing sharp points to antenna structures you want to protect. All that does is make them a more attractive target for lightning. In general, you can't *prevent* all lightning strikes on an antenna. Instead what you have to do is to conduct the currents away in such a manner that they do no harm to sensitive components. This is not difficult in principle, but requires extreme attention to detail in facility design and implementation. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | gary@ke4zv.atl.ga.us Newsgroups: rec.radio.amateur.antenna Path: rover.ucs.ualberta.ca!news.bc.net!vanbc.wimsey.com!scipio.cyberstore.ca!math.ohio-state.edu!howland.reston.ans.net!gatech!kd4nc!ke4zv!gary From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Shack Lightning Protection (question) Message-ID: <1995Mar25.114505.3983@ke4zv.atl.ga.us> Reply-To: gary@ke4zv.atl.ga.us (Gary Coffman) Organization: Destructive Testing Systems References: <3kpcmc$hrb@newsbf02.news.aol.com> Date: Sat, 25 Mar 1995 11:45:05 GMT Lines: 29 Status: N In article <3kpcmc$hrb@newsbf02.news.aol.com> w8jitom@aol.com (W8JI Tom) writes: >Remember to avoid braided conductors for RF and lightning grounds. >Braiding has a few times the RF and "lightning" resistance of solid wire >or flashing. Think wide but not necessarily thick, and keep it smooth. >Remember skin effect, woven conductors (or twisted conductors) force the >surface currents to follow the irregular surface and rely on the poor >pressure connection from wire to wire!! Actually, woven wire has much more surface area than solid wire of equivalent gauge, and thus offers much less skin resistance, see Litz wire. OTOH, woven wire offers a somewhat higher inductance per foot than solid wire. That can be significant in a lightning protection system. Copper flashing has a larger surface, pound for pound, than solid wire, so is preferred for economy if nothing else. Routed carefully, flat strap also has a lower inductance per foot than other types of conductors. Field lines can only escape in important quantities at the edges. Round tube would seem at first glance to offer better performance because there are no edge effects, but only the outer surface of the tube actually conducts significant RF due to Faraday effects on the inside equipotential surface, IE it's a waveguide beyond cutoff, so it's only half as effective as flat strap, pound for pound. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | Path: rover.ucs.ualberta.ca!cancer From: garyb@psych.ualberta.ca (Gary Burchett) Newsgroups: rec.radio.amateur.antenna Subject: Galvanized vs Cu Ground Systems Date: Thu, 30 Mar 95 15:35:10 GMT Organization: University of Alberta Lines: 21 Message-ID: <3lepu5$1oo2@rover.ucs.ualberta.ca> NNTP-Posting-Host: cancer.psych.ualberta.ca X-Newsreader: News Xpress Version 1.0 Beta #3 Status: N Having read with interest the postings by Coffman et al, about proper tower and station grounding, I have a question. The consensus seems to be that tower grounding should be done with flat copper strap 4"-6" width from tower legs to copper plated ground rods and continued out with flat strap in a star pattern. Galvanized tower legs should be buffered from the copper by thin stainless sheet to control galvanic corrosion. OK on all that, but I looked into the cost. Copper stock and rods and fittings are expensive and not readily available. If the tower grounding were done in the same manner, but with galvanized sheet stock and galvanized ground rods, would the net result be the same? Of course, the resistance would be a little higher, perhaps compensated by a longer run. How about corrosion on the underground galvanized stock aver a period of years? The tower legs, being galvanized, would not require a buffer to the galvanized sheet stock. The cost of the galvanized ground system would be far less than the copper, and more readily available. Opinions? Thanks, Gary. Newsgroups: rec.radio.amateur.antenna Path: rover.ucs.ualberta.ca!unixg.ubc.ca!vanbc.wimsey.com!scipio.cyberstore.ca!math.ohio-state.edu!howland.reston.ans.net!swrinde!emory!cssun.mathcs.emory.edu!wa4mei!ke4zv!gary From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Galvanized vs Cu Ground Systems Message-ID: <1995Mar31.150705.1084@ke4zv.atl.ga.us> Reply-To: gary@ke4zv.atl.ga.us (Gary Coffman) Organization: Destructive Testing Systems References: <3lepu5$1oo2@rover.ucs.ualberta.ca> Date: Fri, 31 Mar 1995 15:07:05 GMT Lines: 56 Status: N In article <3lepu5$1oo2@rover.ucs.ualberta.ca> garyb@psych.ualberta.ca (Gary Burchett) writes: > Having read with interest the postings by Coffman et al, about proper >tower and station grounding, I have a question. > > The consensus seems to be that tower grounding should be done with flat >copper strap 4"-6" width from tower legs to copper plated ground rods and >continued out with flat strap in a star pattern. Galvanized tower legs should >be buffered from the copper by thin stainless sheet to control galvanic >corrosion. OK on all that, but I looked into the cost. Copper stock and rods >and fittings are expensive and not readily available. > > If the tower grounding were done in the same manner, but with galvanized >sheet stock and galvanized ground rods, would the net result be the same? Of >course, the resistance would be a little higher, perhaps compensated by a >longer run. How about corrosion on the underground galvanized stock aver a >period of years? > > The tower legs, being galvanized, would not require a buffer to the >galvanized sheet stock. The cost of the galvanized ground system would be >far less than the copper, and more readily available. Yes, you can use galvanized steel in place of copper. Losses are about 5 times higher if I remember correctly, but you're grounding a galvanized conductor which is no better, and you're connecting it to soil that is much worse, so the net effect isn't really significant in many cases. If you are trying to bypass a copper conductor, such as a feed line, then that's a different story, and you can't be quite so cavalier. You want your tower base ground connection to be better than the path through the copper transmission line, any suppressors, your equipment if you've neglected ground window design, and station ground. The main concern with use of galvanized steel in contact with Earth is corrosion. The galvanizing is a *sacrificial* electrode. It protects the steel from galvanic corrosion by sacrificing itself. Sooner or later it will be eaten away and the steel will come under attack. Soil pH has a large effect on this rate, as do any currents that may be required to flow through the system. Buried galvanized steel can corrode away in less than a year in some locations. In others it may last for decades. One method to successfully use steel as a grounding conductor is the *Ufer ground*. This is rebar embedded in concrete. The pH of the concrete prevents galvanic corrosion to a large degree, and concrete is a better conductor than many soils. With the large surface area presented by the rebar containing concrete, lower actual resistances, and capacitive reactances, to Earth are possible with this method than even with the traditional copper plated rod driven directly in the soil. (Think of it as a *whole bunch* of higher value resistances in parallel versus one somewhat lower value resistor.) Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | Newsgroups: rec.radio.amateur.antenna Path: rover.ucs.ualberta.ca!news.bc.net!torn!howland.reston.ans.net!tank.news.pipex.net!pipex!swrinde!gatech!wa4mei!ke4zv!gary From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: Antenna and lighteni Message-ID: <1995Jul25.165811.17463@ke4zv.atl.ga.us> Reply-To: gary@ke4zv.atl.ga.us (Gary Coffman) Organization: Destructive Testing Systems References: <3undve$bbb@usenet.INS.CWRU.Edu> <1995Jul23.084744.4272@ke4zv.atl.ga.us> <1995Jul24.123346.25028@nomina.lu.se> Date: Tue, 25 Jul 1995 16:58:11 GMT Lines: 53 Status: N In article <1995Jul24.123346.25028@nomina.lu.se> peter@maxlab.lu.se (Peter Rojsel) writes: >Lightning can be a strange thing. I have read some of Gary's very interesting >articles with great interest, but please explain this: > >A few years ago this happened close to where I work. >The scene is a 6 meter high tree standing 10 meters from a 20 meter high 5 >floor building with lightning protecting (copper wires of 1 cm thick) on all >corners and along the roof edges and grounded. The lightning hits the tree so >that it becomes splinters. This can only have been by a direct hit to the >tree. Why did the lighning not choose the lower impedance path to ground that >was offered by the lighning protective system of the building? The buildings >protection probably worked since it houses the computer centre of the universe >and the computers survived (they were running during the storm). > >The only explanation I can think of is that a flash can have the upper >'connecting point' in a very low cloud. You're on the right track, Peter. As you know, it takes about 4kV to arc across 1 cm of air, but the potential between cloud and ground is typically only on the order of 300 V/m. So how can the lightning bolt jump all that air? The way it does that is by streamers forming from objects on the ground, and by step leaders forming in the cloud. When a streamer finds a step leader, an ionized channel exists between Earth and cloud, and the main bolt current courses up the channel, heating it and ionizing more air so that it becomes a still better conductor, which causes more current to flow, etc. It's a runaway effect that quickly forms a low impedance channel between Earth and cloud. Ok, now the meeting of a particular streamer with a particular step leader is pretty much a chaotic event. There are lots of streamers coming up from objects on the ground, and lots of step leaders coming down from clouds. Their paths are somewhat of a random walk. Now whichever streamer and step leader first meet, that's where the bolt is going to go. A bolt is only going to "sidestep" to a lower impedance conductor if the flashover distance plus the impedance of the better path add up to less than the impedance of the original chaotic random walk path. Sometimes that's true, sometimes it isn't. If streamers or step leaders become tangled, which often happens, you may see a forked bolt, or the vast majority of the bolt current may divert to the lower impedance channel, again depending on the ratio of the impedances involved. So there's no *guarantee* that a tall low impedance object will offer a cone of protection to shorter objects in the area, but it *usually* happens that way. Which is why lightning rods mostly work. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | From: n4zr@netcom.com (Peter G. Smith) Subject: Lightning Protection (45K) Date: Mon, 5 Sep 1994 12:30:29 GMT The following summary represents inputs from a great many hams on both the CQ-CONTEST reflector and on the East Coast Mega-cluster, and has been pulled together here as a convenience. The one thing that came through to me loud and clear is that this is a VERY important matter, with significant safety and economic implications. I believe that no one should rely solely on a summary like this or on the views of individuals whose qualifications and experience he or she has not specifically investigated. In other words, take what steps are prudent to inform yourself and make up your own mind. 73, Pete Smith N4ZR On the need for lightning protection: I live on site, selected from a ham perspective,hi. It is about 15 meters higher than the surrounding fields. The self supporting tower is 24m high, the crank up is 18m and the roof of the house has 3 more antennas on it. There are no trees around for miles.... One thing I comfort myself with is that lightning always looks for needle-pointed conductors to hit. So with big HF antennas on top of my towers, I gather I have not a lot of chance to get hit . I've been living here for 9 years now.. But then again, I like to take risks.. I have 3 towers with monobanders for 10 to 40m with loads of wire antennas around. One of my towers is grounded with earth rods through the concrete. I have no lightning protection, and the wiring in my house does not have ANY electrical grounding. During the summer, we often have heavy lightning storms, and I never experienced any direct hits. Nevertheless, what I do is disconnect all antennas when I leave the house for a longer period. How about that for a solution? hi. Two of my friends who insisted in installing professional grounding for their shacks only had numerous problems with earth loops and whatever. I don't, because almost nothing is grounded. I once did get problems with a static discharge though, while there was not lightning around... -- ON6TT I'm using ICE stuff... I believe those stories they tell, but you have to remember that they are talking about COMMERCIAL sites, i.e., they are on the air to make $$$$$$$. so they STAY ON THE AIR 24 hrs a day, no matter what ... most hams I know pull the plug pretty quick when they see lightning ! -- KR0Y I am in the throes of recovering from my first lightning hit, and I am still sensitive to the hassles. I wanted to go ahead and post this to everyone NOW because summer lightning/thunderstorms here aren't nearly over. I was stupid. I had a bare minimum in station grounding and tower ground. This mistake cost me far more than buying some Polyphaser products and following their instructions. I had a secondary hit through came through the power system. At the time, all coax cables were disconnected from the HF system. Unfortunately, I still had the packetcluster 2m stuff going. The packet radio, computer, tnc, power supplies, rotors, keyers,hf transceiver -- everything got zinged to some degree. I am so fed up with all the hassle (repairs, insurance claims, etc.) I would like to forewarn anyone that lightning protection is a serious design element in your antenna system. Pay now (lightning protection) or pay later (lightning damage). -- WB4IUX You poor folks who live in the South absolutely have to plan for lightning. WB4IUX says "Pay the piper now or later". It might also be said if the ground surge doesn't get you induced voltages will. While living in Seattle with a 100 ft back yard tower lightning struck a utility transformer about 300 ft away. I suffered no ills although the houses connected to that drop had their entire panels and household wiring vaporized. I was using "modest protection". -- KG7D When the wind is howling and the lightning is booming and I am thinking about how I cheaped out on my installation I really wish that I had spent the extra money, time, and effort to do a better job. -- Bob Hale (call?) I live in S. Calif in the San Fernando Valley (on the floor of the Valley) and have never experienced a lightning hit, nor expect to. However, I used about $750 of PolyPhaser products when I installed my tower. The bottom line is that: 1) my wife doesn't worry, 2) my neighbors don't worry, and 3) the telephone RFI I was experiencing on my own 2-line phones was reduced dramatically to almost undetectable. I consider it a good investment. -- WA7BNM My QTH is on top of a mountain ridge which is 1400 feet above the surrounding terrain. The towers are 90-120 feet above the ridge top and the only thing around for several miles along the ridge line. I have had NO damage in 14 years on protected equipment. Being in a basement is NOT a shield against the lightning strike's fields. I have had only ONE instance of lightning damage. This occurred when I just moved into the new house at the QTH from my old house trailer. The shack at the house trailer was protected with all of the above systems and had no problems for 7 years. Naturally, when moving into the house, I was eager to get back on the air and did not complete the new internal station grounds. In fact, I didn't even have coax lines re-routed to the new shack yet. NOTHING CAME IN FROM OUT DOORS! I just had my radio equipments, underground power, and underground telco. To be able to listen, I had a piece of coax from my HF transceiver up to the ceiling in the basement. The ceiling was a metal grid used to hang suspended acoustic tiles. A lightning strike occured about a mile away. The induced voltage in the CEILING GRID (underground basement) was large enough to weld the alligator clip on the coax to the grid! Of course, it damaged the transceiver, went through cabling to take out a computer terminal, and went on to do other bad stuff in the house. After that, a proper protection system was installed. That was 6 years ago and no trouble since! Yes, it might cost you $400, $600, or even $1000 to put in all the protection and earthing cables. You will save this money in repairs and aggrevation very quickly and many times over. Buying $1000 worth of lightning protection, as compared to an equal amount of additional radio or computer gear, is a good investment in the performance of your station -- because your station does not perform when the equipment has been fried! -- K3NA - Lightning is a probability system ..... if you put in a $200 ground system you will likely survive the smaller strikes. If you put in a $2000 system you will probably survive the bigger strikes. It is a matter of how much voltage and current is in the strike that hits you. If you live in Los Angeles you may only get hit by a big strike once in ten years, but if you live in Florida it may be once a month. I am a believer in lightning protection. I have had $50,000 worth of equipment blown away in strikes. The lightning protection system installed after the strike only cost me $5000 ...... cheap if it had been installed first. -- WB2KMY/4 I've had some induced damage both in Los Angeles (I lived near the top of a 1300' hill) and here. And several years ago, I traded my old Kenwood 440 HT for a TR7830 2M base radio that had been damaged by a nearby strike. Initially, I had to replace several zeners, diodes and transistors in the power supply. Later, the front-end transistor died; finally, the output module gradually dropped power from 30+ watts to several watts, then all output disappeared completely. Haven't had the money to replace the module for over a year now, although I sure need the power. The moral is that although you may not see immediate degradation after a close strike, things can still gradually go away over time. And I pity the buyer of the FT1000 that is advertised on the cluster right now for $2300 with lightning damage (although the seller claims Yaesu fixed it for $170!). -- KO0U/4 Simple, Most people will not go to trouble to install all the crap, uh ground rods ground rods and more grounds called for in the instructions. So when a strike does occur and it doesn't work then it can be said, well you didn't install it like we said. that's what it sounds like to me -- WB5CRG All I can say is after seeing some major lightning damage at other hams' places, and seeing an arc in my kitchen sink one day, I am not going to skimp on the protection!! We had a bad storm here about 1 month ago. I had all coax disconnected and all the rotor cables disconnected. The flash-over in the sink was probably inductive pick up on the water line. It was not a big flash, but big enough to make me think twice about lightning protection, especially since I have a 110' tower right next to the house. One guy up here actually had a fire a couple of years ago from lightning. All I can say is ground those towers well! -- N2NU One way to look at this is that you are buying an insurance policy. How complete do you want it to be? What is your investment in tower, cable, antennas etc worth. What kind of homeowners will you have? Will it cover a total loss? I made the same analogy to someone else the other day by saying all the law requires you to have for motorvehicle insurance is 20/20/5. But that hardly covers a 5 MPH bump any more. I visited [call deleted] last week. He has done nothing special to protect his station and he has a 190' monster tower! --NX1G It really pays off. No lightning problems since, but many neighboring hams had serious hits and losses. -- K3ANS I have had no lightning problems in the house since I installed surge suppressors, even though there has been at least one lightning hit on a power pole only 3 poles from my pole with the transformer and meter. But I did have a hit a few days ago on the yard light on the barn which tookout some wiring in a conduit. I have yet had any desire to test my band-saw and cut-off saw which were plugged into the outlet that got smoked. This lightning ignored my 170 ft tower which was well grounded and on top of the hill and hit the barn which is down in a valley about 500 ft fromthe tower and just outside the "cone-of-protection" from the towers. The barn is on its own meter and I have yet to add any lightning protection to that site. (Why, I ask, does it take a direct hit before I get around to doing anything? HINT: Don't wait!) My years in radio astronomy with big HF and VHF arrays on a mountain top (8500ft) indicated that 90% of our damage was due to spikes coming in the UNDERGROUND power lines. To give you an idea of how severe this site was, suffice it to say that the building was a steel one mounted on a concrete slab and everything was well grounded, but we even had occassions where we would have corona coming off the pointed ends of the coat hangers hanging on the coat rack! --W0UN The real question is whether an amateur installation requires such measures. The answer to that one is one of "insurance". That is, once you understand that any lightning protection equipment merely constitutes an insurance policy protecting the equipment and facilities attached to an outside antenna. I feel that the replacement cost [of my equipment] is worth the one-time investment. -- N3RR What to do: A local followed Polyphaser's exact plan, never unplugs his equipment during lightning storms, and swears by it. -- WB4IUX In the least I would highly suggest perimeter grounding and specifically the dropping of all cables to ground level. Tie shields to ground at the base of the towers with mov protectors on rotor cables at the tower base and grounding rotor cables to tower base when not in use. I would stay away from antennas and or towers attached to the building. Whole house protectors at the service panel with in line cordset protectors for the most sensitive equipment. -- KG7D I used about $750 of PolyPhaser products when I installed my tower. I use a 12" x 12" x 1/4" copper plate mounted in the wall as the common point for all cable feed thrus to the shack. PolyPhaser's components are mounted on this plate. The plate is individually grounded to two 8 ft ground rods immediately adjacent, via 1.5 inch copper strap. The copper strap to one of these ground rods continues to additional ground rods, spaced roughly every 16 ft around the garage addition containing my shack, to my tower (roughly half way around). These rods, straps, and connections are all below grade. The copper strap finally terminates at my shack, to my tower (roughly half way around). These rods, straps, and connections are all below grade. The copper strap finally terminates at a connection to my electrical service ground rod. Each leg of the tower is connected via this 1.5 inch strap to a separate ground rod that is also part of the strap connected system. -- WA7BNM I have three ground rods around the standard concrete base, one attached to each tower leg. One rod is 12 inches from the concrete, the other two are 8 feet away from the tower on opposite sides. Sort of a straight line. The wires (#6 copper) to each rod are buried about 6 inches. I do not plan on plowing that patch! Next, I plan on grounding each of the guy wires, as shown in Rohn's catalog. I don't use insulators per K4VX and my own extensive computer simulations. Thus, there will be 3 more ground rods, one at each guy point, each connected to four guy wires which are connected to the tower. When I was in college I worked as an engineer at an AM broadcast station. We took our share of hits, which only tripped the overload relays in the transmitter; after you picked yourself of the floor (those spark gaps are LOUD when they fire!) and reset the relays, everything always worked fine. This was before Polyphaser (1960s). However, each tower had the usual 100+ radial buried beneath them. BUT, each tower was electrically isolated from ground; the only "connection" was through the spark gap when it fired. At the shack end, about 300 feet away from my tower (thru 7/8" Heliax) I will put a Polyphaser arrester on each coax at ground level (they are only moderately more expensive than the other brands, and a heck of a lot cheaper than our rigs!!!). My shack is on the second floor - no basements in Indiana because of our high water tables. There will be a bus at the ground level which will be connected to two ground rods driven about 5 feet apart and holding the bus. The arresters will be on the bus. Then, regular coax will cover the last 10-15 feet to the shack thru the window. Naturally, I plan on disconnecting the antennas when I'm not using things. I plan on installing a MOV across each wire going to rotors, etc, at the ground bus outside the house, using a big terminal strip mounted to the bus. That will be cheaper than the Polyphaser box, but should have much of the same effect. My cables will run in corrogated plastic drain pipe from the tower to the house. This can be moved slightly from one side to the other to mow around (I've done this at other QTHs and think it works fine), and one can add things more easily when its not buried (if something gets snagged, you can open the pipe at a junction to see what is wrong) Probably this is not quite as good as buried cable but should be better than hanging in the air! The only thing I have not decided on yet is whether to also put arrestors/MOVs at the tower. I think it makes some sense to put them at the antennas/rotators to reduce damage to the cables on the tower; but replacing these items are cheaper than replacing rigs so economics will dictate what happens here. I have decided to buy one of those computer surge suppressors which are guaranteed to $10,000 or $25,000 when the equipment blows up!!!! I always unplug all my gear anyway when I'm not using it (except the clock. I am thinking about buying a small UPS for the computer to guard against the dreaded 5 second drop during the contest which reboots the computer and then 5 minutes to get things going again. Some of these are quite cheap and maybe I can get the surge suppressor protection built in, too. I do not plan to connect the radio ground stuff to the house ground. My reasoning is that the lightning rods on the house and the electrical drop ground were installed by someone else so I don't know what I have. I am worried that if somehow the grounds were connected together and the house suffered damage (maybe even unrelated to the grounding) that the insurance may be a sticky problem. Look forward to hearing the expert responses! -- N4TZ Yep, we do all that stuff for our radio facilities here in Pacific Bell: The basic system is correct as described by the Polyphasor book. Ring ground around building Ring ground around tower connect building and tower ground in two spots bond power ground to building ring ground bond coax shields at building entrance (ala "hatchplate") use single point ground so that any energy flows down "tree" to earth - not through equipment. Now, for small radio installations, we can forgo (forego?) the ring around the building and substitute a driven ground electrode field consisting of 4 8' rods about ten feet apart. This field should be on the same side of the building as the coax or transmission line entrance. Bonding is same to tower and power ground. Be aware that Polyphasors have no DC continuity and remote antenna switches will need separate cable. Mother nature also requires that one purchases ac surge suppression for your entrance panel. This is not the MOV thing in your power strip. Check out a company called Joslyn in Spokane, Wa. They will supply you with all the info you need to protect that side of your station from being zapped. -- NV6O In an amateur station, ... the equipment is concentrated in a small area (a few square meters). AS LONG AS ALL CABLES ENTER THE BUILDING IN ONE LOCATION (very close to power and telco entrances), and the shack is small in area, there is no need to have a ring of grounding cable around the house. The following points mentioned in your message are still essential for good protection: 1. All cables coming "from the field" must have protectors: coax, rotator control lines, etc. [If you do not do this, lightning-induced voltage surges will enter the house and destroy equipment.] 2. The tower must be grounded at the base. A good system is a ground rod driven underneath the concrete base (i.e., driven into the earth before the concrete is poured, and tied into the tower), plus 3 ground rods spaced away from the tower at 6-10 feet. The ground rods should extend at least 4 feet or so below the frost line. (Frozen soil does not conduct very well; a ground rod in frozen soil is a very poor reference point.) [If you do not do this, the voltages on the tower will arc over to the cables and then travel into the house. Without a tower base ground, guy wires with also conduct. Any ceramic insulators will have the insulators carbonized and current will flow into the guy anchors; at worse, insulators can be shattered.] 3. If more than one tower, the tower grounds MUST be interconnected to each other by earthing cables. [If you do not do this, there WILL be a big voltage differential between the towers when a strike occurs near by. A current will flow over the cables from each tower back into the shack and out to the other tower(s) to equalize the voltages, damaging cables and equipment along the way.] It is helpful to install ground rods at regular intervals along the interconnecting earthing cables if the distances are large. 4. The tower ground(s) (and interconnections) must be tied back to the grounding point at the cable entrance to the house. [If you do not do this, the current which would have flowed along the lower-impedance tie-back ground cable will instead flow over your coax lines, rotator lines, etc. Once reaching the house it will find a path to earth through whatever means are available.] 5. Protectors mentioned in #1 above should be installed at the cable entrance to the house, and grounded at that point. This ground point should also be connected to telephone cable entrance ground, power entrance ground, CATV ground, and the earthing cable(s) coming from the tower(s). This ground point should also be connected to the internal station ground bus/strap/whatever. 6. All equipment (radios, coax switches, amplifiers, computers, miscellaneous little boxes like keyers/filters/etc, equipment racks) inside the shack should be individually attached (e.g., by a braid) to a shack grounding line. The shack ground line can be a piece of copper strap running along the operating desk and then out to the ground point at the cable entrance. A thick piece of copper wire is much less effective than a strap. [If you do not do steps 5 and 6, differential voltages can be induced on the equipment chassis and flow amongst the interconnecting cables in the shack. Remember, the radiated fields from the lightning strike that has just occured within a few miles of your house do not stop at the wood walls of the house! Cables and equipment inside the house will pick up induced energy from the strike in the same way as cables and equipment outdoors. The shack ground gives a common reference point and drain for all this gear. It also keeps the power line grounds (reaching your radio equipment through random lengths of house wiring) referenced to the coax and rotator cable shields; house wiring will get voltages induced on it within the house, just like every other metallic piece of equipment.] The whole objective in protection is to provide low impedance paths to earth for induced surges and high impedance paths into equipment/appliances/etc. The bottom line is that there are a lot of complicated geometrical relationships and electrical (frequency-dependent) characteristics for all the wires in your house, going out to the tower, etc etc. So you have a big messy set of equations to solve for mutual coupling in the near field (at HF at least) between the stroke channel and all this mish-mash around your house -- plus re-radiation from induced surges on everything as well -- and you have to solve it for all the frequencies from DC on up to UHF or so! This is a computationally ugly problem with widely divergent solutions depending on all these factors -- which is why the results look so erratic from one stroke to another! -- K3NA You can believe what is in the Polyphaser catalog ..... they are correct. I use their products on all my jobs here at work (Ericsson-General Electric Mobile Communications) and have never been disappointed. Some thoughts ..... - The better the ground, lower the resistance the better. This does not mean more, and more ground rods. Just a low resistance ground system. Their spec is good. - Lightning is a probability system ..... if you put in a $200 ground system you will likely survive the smaller strikes. If you put in a $2000 system you will probably survivve the bigger strikes. It is a matter of how much voltage and current is in the strike that hits you. If you live in Los Angeles you may only get hit by a big strike once in ten years, but if you live in Florida it may be once a month. - You don't have to do everything perfectly and use 100% half hard copper plates and 2AWG copper. Don't use #18!!! But there is a happy medium. If you follow the "spirit and intent" of the lightning rules you will do ok. -- WB2KMY/4 So far, I do not have any protection on my coax lines. My approach is to disconnect all wires when I'm not using them and this is probably the best practice, protection or not. I do have both my towers grounded with 3" copper strap to 8ft ground rods on each of the legs. I do like the Polyphaser tower leg clamps (fancy hose clamps) because they keep the copper strap from direct attachment to the galvanized legs (Zinc and Copper form an excellent cell which is definitely what you do not want)!!! -- N2NU I disconnect everything before it comes into the house using coax connectors and cinch jones connectors. I have loops in the cable before it leaves the tower and I have several good "earth grounds" at the base of the tower. I also have a 100% replacement rider on my homeowners policy. -- NX1G Yes the stuff does work. However some of the best articles that we as hams can equate to appeared several years ago in a trade magazine called Mobile Radio Technology. They ran a multi part article on lightning protection that I thought was very good. -- K3SKE I decided to follow Polyphaser to the letter, even installing Ufer grounds in 10 concrete bases and tower anchors for two lay over towers, 105' and 80'. I have over 1000 welds wherever the rebars intersect inside the concrete. I drove over 50 grounds into the ground, under the concrete and welded to the rebar cage, around the towers, around the concrete bases, around the anchors, around the house. I have several MILES of ground wire under ground connecting the towers, anchors, bulkhead, power ground, telephone ground, well ground, cable tv ground, radio grounds, septic ysytem, etc. Also wire in hundreds of feet of french drains, and underground drain pipe for bringing cables to the house. I ran all my cables through 20 feet of steel pipe before it approached the house, as a capacitive lightning trap. I have radials around three towers and the house. I have a ring ground inside the shack. I have a ring ground surrounding the house. And so on. Also radials around the 10 beverage ground rods. I do not regret all this work. It really pays off. No lightning problems since, but many neighboring hams had serious hits and losses. -- K3ANS A number of the utilities make available a very heavy duty surge protector for about $130 installed and it goes directly inside the meter. In my case the meter is on the utility pole and power then runs about 75 ft underground to the house. I like having my first line of defense against Mother Nature 75 ft away from the house. I have had no lightning problems in the house since I installed surge suppressors (Joslyns) in the two main breaker panels and the utility installed one in the meter, even though there has been at least one lightning hit on a power pole only 3 poles from my pole with the transformer and meter. My personal experiences with a number of hits are that well-grounded towers with lots of grounded Yagi elements do tend to drain away the charge build-up that provides a track for the stepped-leader pre-cursor of the main stroke. I would take advantage of any utility program that will install surge suppression directly in the meter, then add my own suppressors in the main breaker box, use power strips with surge suppression, and put my own MOVs in any homebrew equipment and any commercial equipment that didn't already have them. -- W0UN My 75 ft tower has been in 4 years. Until recently I had one 8 ft rod off each leg of the tower, and ran 75 ft "radials" off each leg just below gnd surface (used an edger for the slit). According to their formula, my tower shoud be hit once every 3 years. I think it was hit once, but not sure. Coax was disconnected from station at time. No damage anywhere. This summer I upgraded the grounding by installing a bulkhead where the lines come in (to coax and control lines). Also followed their suggestion for a common ground point. I di not go as far as a perimeter ground - too much work. I did all this for safety. I hear hams getting hit all the time with big wipeouts. -- W2UP I have 2 runs 1/2 hardline, 6 runs of RG 214 plus 2 runsof 8 conducter rotor cable. It runs from here in the shack into the basement out the basement wall about a foot off the ground and into the ground with 4 in pvc. Then about a foot underground to the tower 55 feet in back of the house. It comes out about 8 feet from the tower into a homemade box with a panel of various PL 238's or whatever you call the ones that are about 1 1/2" long with a nut on either side. Its all taped up and coax comes from tower and is manually connected and disconnected. We have not lost anything since going this way about 8 years ago. The rotor cable breaks with an 8 pin Jones plug, becoming very hard to find now. I look every ham fest. The other thing that helps in my opinion, is the 8 foot ground rods out from each leg of the tower (Rohn 25 70' with 11' mast out) which are connected with #2 wire around and then up to the tower legs with "Hotline' connectors. The wire is cad welded at all the wire rod joints. I swear my receiver got quieter and I have not had a hit since this was done abt 5 years ago. So there you are, plugging and unplugging and don't take chances. -- N3UN I spoke to [name deleted], who is a local guru on radio communications (he does the tower and radio for the Connecticut State Police) and he feels that the only absolute protection is to shunt the antenna leads directly to ground....that may not protect the antennas, but it will protect the radios....Other than that, he recommends, and installs it this way on the towers he does, #8 copper cable on each leg of the tower to eight foot copper clad steel sunk BELOW the base of the tower....even at that, if your ground resistance is more than five ohms, you've got problems. -- NM1Q After many hits on my 170 ft tower , I installed 10 more ground rods and this seemed to help a lot....no problems in more than one year, except a couple of popped breakers. -- W3WFM For what it's worth, what I recall [call deleted] saying he does in Co where he has BIG antennae, is he puts one ground rod abt 6 ft from each tower leg, connects to the tower with heavy ga copper in a broad sweep...not a sharp bend. He then puts two more ground rods in a triangle abt ten feet from each of the first three, so there are three per leg, all tied together. He has seen lightning approaching his QTH, stopping when it gets there, and starting agn when it gets past him. He feels his good grounding discharges the clouds ard him. You can buy ground rods for less than $300. I have 100 ft with several ground rods...I unplug power and antennas in storms. -- W1WEF The best policy is to leave your antennas disconnected when they are not in use during the T-storm season. Better yet do what I don't do - dis-connect everything from the AC mains. If you get a direct hit NOTHING will help - some of your equipment will be toast no matter what you use for protection. The Polyphasers can't hurt but they will only reduce the amount of damage not eliminate it if the hit is close enough. A well grounded tower and disconnecting everything is the best way. -- W3ZZ Lightning protection is something that can be taken to any extreme you care to, but the most basic of things may be enough. What is the minimum? One ground rod at the base of the tower. That may be enough. Next step...three ground rods at the base of the tower. The one thing that comes to mind from Dayton is putting the tower ground rods 10' away from the base, spread 'em out. I know [name deleted] (regional tower guru) has suggested two or more ground rods close in can crack the concrete foundation as lightning goes underground from one to the other. That's an argument for more distance between them. Next, buried coax gives lightning a ready path to ground. Next, stripping the black insulation of the coax and grounding the braid to a ground rod before it leaves the vicinity of the tower, and doing the same again just before it enters the house is sometimes done. Using a metal plate where the coax enters the house is a nice touch. The plate is grounded directly to a rod (or household plumbing pipe if it's handy). This is nice in station design anyway because all your long runs can come to a bulkhead connector at that plate, and end. On the other side of the plate, the inside of the shack, you can have quick-disconnect coax connectors so when a storm approacheth, boom, boom, boom, you can have all those antennas hard disconnected within seconds. The one thing to purchase from Polyphaser when you want to go an extra step is the DC blocking whatever-they-call-em, one in each coax run, and one (or is it one at each end of the run) for your rotator cable. -- KE3Q I'm a little skeptical when they promote the use of flat conductors vs round wire for grounding - not what I learned in school. Round conductors have MUCH less rf resistance than a flat conductor which only conducts along the edges. I use ICE's recommendations and have installed a bulkhead grounding chassis on my basement wall on which protectors for ALL wires are installed. The chassis is grounded to an 8' rod through less than 12" of 3/8 dia copper cable. I made my own protectors with MOVsand disc caps for the rotators. I used 32v MOVs, I think. I have an 8' rod at each tower leg connected to the leg with some #4 AWG round wire. I gooped the connection with conductive paste and clamped it with brass clamps. I used pieces cut from SS hose clamps in between the tower leg and clamp to lower the potential difference but it may be overkill with the paste. One more thing on the tower, I clamped and soldered a ring of #4 bare wire to each rod and each leg connects to that. I also have a 10' circle of hardware cloth soldered to the ring and numerous radials. I also have a nonconductive patch panel at the operating position fitted with bulkhead connectors which lets me easlily disconnect everything just in case. Also installed large MOV protectors in my service panel. Got them for $35/set of 3 at a hamfest. -- N6CQ/3 On the addresses and merits of various suppliers: [for AC line suppressors] The complete name of the company is: Joslyn Electronic Systems Corporation Building N-1, Sppokane Industrial Park Spokane, Wa 99216 (509) 922-0483 (509) 922-0686 fax The catalog I have lists a 3 wire, 120,240 volt, 120 volts each line to neutral model 1250-33. specs: Surge current: 10,000 to 20,000 amps on lightning waveform of 8 to 20 microseconds rise time (this is a pretty close spec to nominal 50% probability lightning waveform and current) Life expectancy: heavy duty units 2000 operations of 10,000 amps no mention of life of medium duty units, but I'm sure its sufficient Load Rating: Unlimited (these things are in parallel with AC line so no current flow except during, you know) We have used these things in our outdoor electronics for years, I've only seen 1 go and that was when a 60 kv conductor dropped on a 12 kv conductor which supplied power to a transformer that fed our stuff. The arrester smoked, the electronics didn't. -- NV6O In a work enviroment the past 15+ years I have used devices from Poly-phaser and Fisher Custom Communications. Both under the area of protection from EMP (Nuclear War) to Lightning. I have written technicial responses to proposals from NATO, DND Canada, and for use by the National Park Service in the Flordia Everglades. Polyphaser does spend a lot of money promoting the name and all, however the firm that I feel offers the best product is Fisher Custom Communications in CA. Polyphaser internally uses internal chip capacitors. This does two things to the device. It makes them frequency and power level sensitive. If you read the side of any Polyphaser device, you will see specific rated power levels as the intended frequency of usage increases. In short if you're in the business of needing to use them, you could have have several models on hand and it makes ordering them a pain as well. Fischer Custom Communications Manhatten Beach, CA (310) 545-4617 -- K3SKE As far as surge suppressors I installed a GE type. It was a 5 minute job. The suppressor mounted in one of the holes on the main panel. I had the electric company come out to disconnect the meter to remove the power. They did that for free. Took my hex wrench installed the 3 wires from the surpressor and it was done. By the way the unit cost me $45. Shipping was extra. We went to a local electrical supply house to place the order. Its a GE part. Tranquell Secondary Arrestor, 9L15FCB001. -- WB5M A number of the utilities make available a very heavy duty surge protector for about $130 installed and it goes directly inside the meter. In my case the meter is on the utility pole and power then runs about 75 ft underground to the house. I like having my first line of defense against Mother Nature 75 ft away from the house. I have had no lightning problems in the house since I installed surge suppressors (Joslyns) in the two main breaker panels and the utility installed one in the meter. -- W0UN I have talked with Polyphaser and read some of their literature but I'm a little skeptical when they promote the use of flat conductors vs round wire for grounding - not what I learned in school. Round conductors have MUCH less rf resistance than a flat conductor which only conducts along the edges. Give I.C.E a call and ask for their tech sheets on the subject and see if it makes sense to you. They also have product comparisons of their arc tube protectors vs Polyphaser and others. The Ph. No. for ICE is (800) ICE-COMM and fax is (317)545-9645. -- N6CQ/3 ...The probable difference [between I.C.E. and PolyPhaser] is that the Polyphaser unit stands a chance (if properly installed in a well engineered system) of protecting the equipment in the shack from the consequences of a direct hit to the tower structure to which the equipment is connected via feedline and the I.C.E. protector as described probably won't. PolyPhaser doesn't have a ham station to generate anecdotes about but they do have a complete test facility capable of simulating lightning bolt magnitude voltages and currents for testing their devices. The above statement is strictly opinion based on a large amount of experience with mountaintop installations protected by PolyPhaser and other suppressors. I have no direct experience with the I.C.E. stuff but the NE-2 style gas tube with small round leads is inadequate in my opinion. I have pulled duplexers apart which were hit through inadequate protectors that had coupling loops made of 3/8 inch wide solid copper strap (.032" thick) folded flat against the top of the cans due to magnetic forces. I'm sure the same fault would have vaporized the NE-2 leads. That leaves the choke to dissipate the brunt of the current. Unless this is a seriously large toroid (possessing some magical properties not found in other inductors) I don't see how this can protect the leads of the NE-2 style tube from catastrophic damage. How is this supposed to work? The inductance suddenly goes to zero due to core saturation during a fault? If so, what happens to the core material? What happens to the core material when transmitting 1.5 KW output on 160 M with a 3:1 or 5:1 SWR? What is the function of the shunt cap? Are these suppressors limited to a particular band? Why would I tolerate a series resistance (I assume in series with the center conductor) in my feedline unless I was feeding a MAXRAD dipole? I'm sure there must be something I'm missing here. Someone please post a rational description of how the I.C.E. protector is supposed to work. What is its insertion loss when driving a 3:1 SWR (loadimpedance low compared to line impedance)? Maybe we can all learn a bit of magic. -- N7CL -- 73, Pete N4ZR@netcom.com "Better, faster,cheaper -- choose any two"