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Grounding Tower & Shack (Advice Needed)
Disconnecting coax, wire, etc. from the house with at least 10 ft spacing,
before storms arrive is a good idea in any case... |
-- Listen to Alternative News and Conversation You Won't Hear On Commercial Radio. Visit http://live365.com/stations/pascoradio YOU HAVE BEEN WARNED! First Time Users May Be asked To Do A 1 Time Setup. "Jack Painter" wrote in message news:r4_Rc.12079$Yf6.1279@lakeread03... "Harry Conover" wrote (Private) wrote in message . com... Hello, I am looking for some advice on if the ground system featured below is sufficent or should be upgraded. It consists of: - 3 ground rods 10' each around the tower (bonded together) - 2 ground plates (one outside, one in the shack, also bonded together) - lightning arrestors and/or feedthrough adapters - tower to mast ground - interior coax switch (not shown) I provided some pictures below: http://www.telusplanet.net/~homac/exteriorground01.JPG http://www.telusplanet.net/~homac/exteriorground02.JPG http://www.telusplanet.net/~homac/exteriorground02a.JPG http://www.telusplanet.net/~homac/exteriorground03.JPG http://www.telusplanet.net/~homac/exteriorground04.JPG http://www.telusplanet.net/~homac/interiorground01.JPG http://www.telusplanet.net/~homac/interiorground02.JPG I am looking for constructive feedback..... Thank-you.... Lloyd Hi Lloyd, Looks like a nice installation, although your grounding rods might be placed farther apart, or augmented by some heavy gauge radial wires (depending on your local ground condictivity). What I did note missing was the mention of 'lightning chokes' wound in the coax lines decending from the tower. These are basic to lightning protection for broadcasting towers, but I've rarely seen them implemented by hams. The idea of a lightning choke is to add a small amount of inductance to the coax so that if a direct lighting strike happens, the instantaneous current flowing though the outer jacked of the coax into your lightning arresters will at least have some amount of impedance limiting the current magnitude, thus reducing the probability of destruction of both the coax and the the arrester itself. These chokes are more often than not implemented by winding a dozen or more turns of coax around a form (say a 4" diameter phenolic tube) prior to the arrester or spark gap. Harry C. Harry, that winding of coax may be useful as an RF choke, but it is most certainly not a lightning choke, and will act more like an air-wound transformer than anything else. Not only is this not specified for any lightning protection systems, it is specifically warned against in many. Jack Painter Virginia Beach VA Hello All. First let me comment that the lightning mitigation techniques used are better than many ham installations. That being said, I would increase the conductor size between the tower legs and the ground rods. When I saw these, I thought a "fast acting fuse." The amount of current that the tower can handle cannot be safely terminated to ground with smaller conductors. Also, the screw terminals need to be checked periodically because they will loosen themselve due to "cold flow." Why not repace them with crimp types and then solder the crimp with a torch as a back up? I am asuming that this device is covered by something to protect it from rain, etc? John-WA4JM, Dade City, FL, home to some of the most ferocious lightning activity in the western hemisphere. |
"Jack Painter" wrote in message news:r4_Rc.12079$Yf6.1279@lakeread03...
"Harry Conover" wrote (Private) wrote in message . com... What I did note missing was the mention of 'lightning chokes' wound in the coax lines decending from the tower. These are basic to lightning protection for broadcasting towers, but I've rarely seen them implemented by hams. The idea of a lightning choke is to add a small amount of inductance to the coax so that if a direct lighting strike happens, the instantaneous current flowing though the outer jacked of the coax into your lightning arresters will at least have some amount of impedance limiting the current magnitude, thus reducing the probability of destruction of both the coax and the the arrester itself. These chokes are more often than not implemented by winding a dozen or more turns of coax around a form (say a 4" diameter phenolic tube) prior to the arrester or spark gap. Harry C. Harry, that winding of coax may be useful as an RF choke, but it is most certainly not a lightning choke, and will act more like an air-wound transformer than anything else. Not only is this not specified for any lightning protection systems, it is specifically warned against in many. Jack Painter Virginia Beach VA Jack, while I'm sure that you believe this, I really can't guess where you obtained such IMHO such massive misinformation. First of all, it is the purpose the the coiled coax to act as an inductor (r.f. choke) because this is how it resists the very rapid di/dt common mode characteristic associated with a lightning hit, thus limiting the peak discharge energy that the following spark-gaps and lightning suppessors must absorb and reducing the overall peak impulse power damage potential. It's basically a brute-force version of the common computer technique of placing a ferrite torroid around cables to attenuate their common mode impulse transmission/conduction ability. Realize that with sufficiently low SWR, currents through both the inner conductor and outer shield of a coax are equal, summing to zero, hence there is no net electromagnetic field produced. The same is not true for a common mode impulse traversing the transmission line. The bottom line is that only the common mode impulse resulting from a lightning strike will experience the results of the "choke". I'm not sure why you would believe that a coil of coax would act like a 'transformer' of any type, unless the SWR is truly enormous, a probem in itself. A case in point is that in both proton synchrotrons (typically operating in a swept frequency range of roughly 3-30 Mhz), and in large phased array radars (some of which operate in the UHF range) employ multiple feeder coax transmission lines that are cut the the same electrical length, with the cable lengths in excess of the required physical run length being coiled up somewhere in the system. There is no net significant electrical effect on the cable's transmission characterists in either case. Prior to completing my degree work at Drexel, I spent 8-years installing and maintaining broadcast transmission systems ranging from 5-Kw to 50-Kw. This included 5 years as chief engineer in one station (WBUD in Trenton, NJ) plus part-time work for WFIL, WCAU, and KYW in Philly. (Additional work in 4 or 5 smaller stations.) Quite honestly, I can't remember a single one of these that did not protect their very costly antenna installations, transmitters, and on-air reliability without lightning chokes employed in their transmission lines. Still, these broadcasters use equipment that, in general, nothing more sophisticated than your average ham station, but on steroids! True, the average AM broadcasting tower usually exceeds 200-feet, but in an intense lightning storm, a 40-foot ham tower is fully capable of experiencing the same energy lightning hit! I purchased my first ham receiver, an SX-71 from a ham named Bob Rutkowski (sp?) in Trenton, NJ. A day or so before I picked it up from him he took an evidently direct lightning hit on his 40-some foot crank up tower holding a 2M beam that was attached to his house. He had grounded the outer shield of the RG-8U coax at the based of the tower, but without a lightning choke in the coax, the hit simply vaporized the majority of his RG-8U, his grounding connection, and most of the final tank circuit in his rig in the basement! Not a pretty sight! Realize that a commercial radio broadcaster has to survive episodes like this without disruption of their operations. Hams don't. Still the emulation of the broadcaster's time proven protection techniques involves only a small additional cost to an otherwise excellent installation. For more information, see: Edmund LaPort, "Radio Antenna Engineering", McGraw-Hill Book Company, New York. (My issue carries a 1952 copyright, still it's an 'oldie but a goodie' with many subsequent editions -- and AFAIK is still the bible of the broadcasting industry.) IIRC, early editions of the ARRL Handbook also described this protection technique (likely pre-1970) in the days when most hams built their own rigs. Harry C. p.s., Jack, I'd love to hear a citation where "it is specifically warned against", and why. |
Thank-you for the advice to this point. I think I will invest in the
rotator cable ground. Not sure what to do about the lightning choke. I don't mind replacing the antenna/mast if I receive a direct lightning hit, I just dont want to turn be fried to a crisp..... Lloyd (Harry Conover) wrote in message om... "Jack Painter" wrote in message news:r4_Rc.12079$Yf6.1279@lakeread03... "Harry Conover" wrote (Private) wrote in message . com... What I did note missing was the mention of 'lightning chokes' wound in the coax lines decending from the tower. These are basic to lightning protection for broadcasting towers, but I've rarely seen them implemented by hams. The idea of a lightning choke is to add a small amount of inductance to the coax so that if a direct lighting strike happens, the instantaneous current flowing though the outer jacked of the coax into your lightning arresters will at least have some amount of impedance limiting the current magnitude, thus reducing the probability of destruction of both the coax and the the arrester itself. These chokes are more often than not implemented by winding a dozen or more turns of coax around a form (say a 4" diameter phenolic tube) prior to the arrester or spark gap. Harry C. Harry, that winding of coax may be useful as an RF choke, but it is most certainly not a lightning choke, and will act more like an air-wound transformer than anything else. Not only is this not specified for any lightning protection systems, it is specifically warned against in many. Jack Painter Virginia Beach VA Jack, while I'm sure that you believe this, I really can't guess where you obtained such IMHO such massive misinformation. First of all, it is the purpose the the coiled coax to act as an inductor (r.f. choke) because this is how it resists the very rapid di/dt common mode characteristic associated with a lightning hit, thus limiting the peak discharge energy that the following spark-gaps and lightning suppessors must absorb and reducing the overall peak impulse power damage potential. It's basically a brute-force version of the common computer technique of placing a ferrite torroid around cables to attenuate their common mode impulse transmission/conduction ability. Realize that with sufficiently low SWR, currents through both the inner conductor and outer shield of a coax are equal, summing to zero, hence there is no net electromagnetic field produced. The same is not true for a common mode impulse traversing the transmission line. The bottom line is that only the common mode impulse resulting from a lightning strike will experience the results of the "choke". I'm not sure why you would believe that a coil of coax would act like a 'transformer' of any type, unless the SWR is truly enormous, a probem in itself. A case in point is that in both proton synchrotrons (typically operating in a swept frequency range of roughly 3-30 Mhz), and in large phased array radars (some of which operate in the UHF range) employ multiple feeder coax transmission lines that are cut the the same electrical length, with the cable lengths in excess of the required physical run length being coiled up somewhere in the system. There is no net significant electrical effect on the cable's transmission characterists in either case. Prior to completing my degree work at Drexel, I spent 8-years installing and maintaining broadcast transmission systems ranging from 5-Kw to 50-Kw. This included 5 years as chief engineer in one station (WBUD in Trenton, NJ) plus part-time work for WFIL, WCAU, and KYW in Philly. (Additional work in 4 or 5 smaller stations.) Quite honestly, I can't remember a single one of these that did not protect their very costly antenna installations, transmitters, and on-air reliability without lightning chokes employed in their transmission lines. Still, these broadcasters use equipment that, in general, nothing more sophisticated than your average ham station, but on steroids! True, the average AM broadcasting tower usually exceeds 200-feet, but in an intense lightning storm, a 40-foot ham tower is fully capable of experiencing the same energy lightning hit! I purchased my first ham receiver, an SX-71 from a ham named Bob Rutkowski (sp?) in Trenton, NJ. A day or so before I picked it up from him he took an evidently direct lightning hit on his 40-some foot crank up tower holding a 2M beam that was attached to his house. He had grounded the outer shield of the RG-8U coax at the based of the tower, but without a lightning choke in the coax, the hit simply vaporized the majority of his RG-8U, his grounding connection, and most of the final tank circuit in his rig in the basement! Not a pretty sight! Realize that a commercial radio broadcaster has to survive episodes like this without disruption of their operations. Hams don't. Still the emulation of the broadcaster's time proven protection techniques involves only a small additional cost to an otherwise excellent installation. For more information, see: Edmund LaPort, "Radio Antenna Engineering", McGraw-Hill Book Company, New York. (My issue carries a 1952 copyright, still it's an 'oldie but a goodie' with many subsequent editions -- and AFAIK is still the bible of the broadcasting industry.) IIRC, early editions of the ARRL Handbook also described this protection technique (likely pre-1970) in the days when most hams built their own rigs. Harry C. p.s., Jack, I'd love to hear a citation where "it is specifically warned against", and why. |
"Private" wrote in message om... Hello, I am looking for some advice on if the ground system featured below is sufficent or should be upgraded. It consists of: - 3 ground rods 10' each around the tower (bonded together) Lightning likes to go straight. Try to have at least one ground rod connected to the tower base at the base; the rod should be directly under the base or as close to touching the base as possible. A 10' ground rod is good if in conductive earth. In sandy Florida, where I tood several hits, it took over a 20' length of ground rod (1/2" steel water pipe) to hit conductive "hard pan". I just washed it in until it hit some solid clay, and then washed it into the clay as far as I could. - 2 ground plates (one outside, one in the shack, also bonded together) - lightning arrestors and/or feedthrough adapters - tower to mast ground - interior coax switch (not shown) The coax switch should be a grounding switch. Floating elements on an antenna could actally attract a lightning hit. Also, for induced hits (not a direct strike, but with enough voltage to damage equipment due to a nearby strike), the grounding of the antenna lines gives the charge a nice safe path to follow. That's better than letting the current find its own path by arcing somewhere. I like to turn off the AC power to my entire equipment setup when not in use. So, with the power switch on the transceiver and the main "shack" ac power switches off, a lightning surge on the power line can only get me or the equipment when I am actually operating. One last suggestion: put a big (3 or 4' diameter) vertical loop (preferably near the ground) in all tower cables going into the house. (Right over your ground plate might be a good place.) The inductance of the loop, and the fact that lighting likes to ionize paths in a more or less straight lines, will keep the main current surge of a direct hit from entering your house and finding its "home" in your power line or telephone line. I survived operating for many years in the lightning belt of Florida and have the burn marks on my mast to prove it. The only known damage in Florida was some induced power that killed a couple of ICs connected to a printer ribbon cable. That was just from the current going down the tower on the outside side of the wall. Lightning protection is still as much art as science, Lloyd - but what you have done so far should fairly well protect folks in the house. If lightning is going to hit, just let it find a nice safe home - and try not to be operating when it does. HI HI In Florida, a house one block from us burned to the ground when lightning started a fire in their attic. That couldn't have happened at our house, as the lighting had a 70' tower to hit first, and a 23' ground rod to give the current a safe place to go. We were hit - several times. So, look at your well grounded tower as an asset for true lightning protection - not a liability. 73 ak |
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Reasons not to create a coiled-coax "choke"
http://www.comm-omni.com/polyweb/hamradio5.htm Even though inductive properties of the coax cable appear to be beneficial, and some extra inductance can be created by adding a few turns to the coax; don' t do it. The added turns can also act like an air wound transformer that can couple more energy into the line. This is just the opposite of the desired effect. Instead, make sure that coax lines leaving the tower remain at right angles to the magnetic field surrounding the tower. http://www.wrblock.com/Papers/Amatue.../APARS_P09.htm Neatness counts - cables (transmission lines, power (ac and dc), speaker, microphone, computer, control) should be cut to length and routed neatly and cleanly between boxes using the most direct practical route. The coiling of excess cable length on the protected side should be avoided since it could act as an air-wound transformer coupling magnetic energy from a nearby lightning strike back into the protected equipment. http://www.marcspages.co.uk/tech/2100.htm Some in the RF industry would have seen coils used as static drains. The theory is the coil is high impedance at RF and so looks open circuit, whilst still presenting a short to the DC and draining it to deck. The problem with them is they too can start reacting ('scuse the pun!) with the capacitance present on the system, especially at the lower ends of the band. 24hr ops FULL COVERAGE PROTECTION (no "chokes") http://users.erols.com/n3rr/lightningprotection/ http://www.alvarion.com/RunTime/Mate...arch31_R41.pdf ALVIRON SUBSCRIBER SYSTEMS TOWER LIGHTNING PROTECTION (no "chokes") And one major US communications company which drawings and specs are confidential and proprietary information - but they do NOT use any kind of coiled-coax and prohibit same from all systems. Here's one exception - from an Amplifier and relay company - they are NOT in the lightning protecton business and this is very outdated advice, but shown anyway becasue we're honest! http://www.ameritron.com/ameritron/man/pdf/RCS-4.pdf We strongly recommend the use of lightning retarding loops in the coaxial cables near the relay box (see illustration). Remember that lightning travels through the path of least resistance. Station ground leads should be solid, large surface area conductors. Do not use braided or stranded wire for the ground leads. Avoid sharp bends in the ground leads. Use multiple ground rods and/or radials to provide the earth termination. --- Recommend you ignore this and maintain direct paths - JP Finally, Richard Clark's mention of "code" is pretty important. Reference the NEC-70 and NFPA-780 for US installations. Jack Painter Virginia Beach VA http://members.cox.net/pc-usa/station/grounding.htm |
Thank-you so much for the feedback and information thus far.
Although I really appreciated the information, I do not want to get too hung up on the coiling of the coax. This weekend I plan to upgrade the gauge of the wire from #8 to #3. Also I have now bonded the cold water pipe entering in the basement floor to the exterior ground plate. Any other feedback on the pictures below are appreciated...... Lloyd - 3 ground rods 10' each around the tower (bonded together) - 2 ground plates (one outside, one in the shack, also bonded together) - lightning arrestors and/or feedthrough adapters - tower to mast ground - interior coax switch (not shown) I provided some pictures below: http://www.telusplanet.net/~homac/exteriorground01.JPG http://www.telusplanet.net/~homac/exteriorground02.JPG http://www.telusplanet.net/~homac/exteriorground02a.JPG http://www.telusplanet.net/~homac/exteriorground03.JPG http://www.telusplanet.net/~homac/exteriorground04.JPG http://www.telusplanet.net/~homac/interiorground01.JPG http://www.telusplanet.net/~homac/interiorground02.JPG "Jack Painter" wrote in message news:9WQSc.16277$Yf6.6584@lakeread03... Reasons not to create a coiled-coax "choke" http://www.comm-omni.com/polyweb/hamradio5.htm Even though inductive properties of the coax cable appear to be beneficial, and some extra inductance can be created by adding a few turns to the coax; don' t do it. The added turns can also act like an air wound transformer that can couple more energy into the line. This is just the opposite of the desired effect. Instead, make sure that coax lines leaving the tower remain at right angles to the magnetic field surrounding the tower. http://www.wrblock.com/Papers/Amatue.../APARS_P09.htm Neatness counts - cables (transmission lines, power (ac and dc), speaker, microphone, computer, control) should be cut to length and routed neatly and cleanly between boxes using the most direct practical route. The coiling of excess cable length on the protected side should be avoided since it could act as an air-wound transformer coupling magnetic energy from a nearby lightning strike back into the protected equipment. http://www.marcspages.co.uk/tech/2100.htm Some in the RF industry would have seen coils used as static drains. The theory is the coil is high impedance at RF and so looks open circuit, whilst still presenting a short to the DC and draining it to deck. The problem with them is they too can start reacting ('scuse the pun!) with the capacitance present on the system, especially at the lower ends of the band. 24hr ops FULL COVERAGE PROTECTION (no "chokes") http://users.erols.com/n3rr/lightningprotection/ http://www.alvarion.com/RunTime/Mate...arch31_R41.pdf ALVIRON SUBSCRIBER SYSTEMS TOWER LIGHTNING PROTECTION (no "chokes") And one major US communications company which drawings and specs are confidential and proprietary information - but they do NOT use any kind of coiled-coax and prohibit same from all systems. Here's one exception - from an Amplifier and relay company - they are NOT in the lightning protecton business and this is very outdated advice, but shown anyway becasue we're honest! http://www.ameritron.com/ameritron/man/pdf/RCS-4.pdf We strongly recommend the use of lightning retarding loops in the coaxial cables near the relay box (see illustration). Remember that lightning travels through the path of least resistance. Station ground leads should be solid, large surface area conductors. Do not use braided or stranded wire for the ground leads. Avoid sharp bends in the ground leads. Use multiple ground rods and/or radials to provide the earth termination. --- Recommend you ignore this and maintain direct paths - JP Finally, Richard Clark's mention of "code" is pretty important. Reference the NEC-70 and NFPA-780 for US installations. Jack Painter Virginia Beach VA http://members.cox.net/pc-usa/station/grounding.htm |
Richard Clark, KB7QHC wrote:
"(don`t fall for the monster under the bed stories of gazillion volts at a bajillion amps)." Good point! It`s akin to: "You can`t protect against a direct hit!" Oh yeah? How about 10,000 medium-wave broadcast stations struck by nearly every charged cloud passing overhead? Sometimes several times a minute for a long time period. The listener is often unaware of the instantaneous carrier drops to extinguish the arcs initiated by the lightning strikes. And, one of the most important lightning opponents is a large coil of large wire in each tower lighting wire at the base of the tower. It keeps lightning as well as R-F out of the electrical service to the station. If tower lighting chokes stepped up the lightning, they would all be replaced with Austin transformers or some other technique such as shunt feed of the radio towers to eliminate the base insulator. Truth is, lighting chokes are very effective at keeping lightning out of the power supply. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
Richard Clark, KB7QHC wrote: "(don`t fall for the monster under the bed stories of gazillion volts at a bajillion amps)." It's not a monster under the bed. But it is a heaven of a blast! The actual USAF specification for lightning strikes is based on a probability model. It's been 20 years since I read the actual wording, but the values are; 90% of all lightning strikes in the USA are described as falling within the spectrum defined by a strike with the following characteristics: 1) Double strike. First peak 100,000 amperes with a second strike of 50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth] of 100 useconds for each peak. 2) Rise time from 0 to peak is 1 usecond on both strikes. 3) Fall time is a decaying exponential from peak to approximately 500 amperes sustaining current in the lightning channel for 300 milliseconds. 4) Electric field intensity prior to prestrike is greater than 10,000 volts per meter. Conclusion: Lightning has lots of energy. Systems have been designed to not only survive a direct strike but to operate through the direct strike. All it takes is $$$$$$. Note: 50% of all strikes use the same pulse width model but with a reduced amplitude of 20,000 and 10,000 amperes for the peak values. W1MCE Program Chief Engineer, retired USAF MX MIssile RS/RV, WS-118 |
"Richard Harrison" wrote in message ... Richard Clark, KB7QHC wrote: "(don`t fall for the monster under the bed stories of gazillion volts at a bajillion amps)." Good point! It`s akin to: "You can`t protect against a direct hit!" Oh yeah? How about 10,000 medium-wave broadcast stations struck by nearly every charged cloud passing overhead? Sometimes several times a minute for a long time period. The listener is often unaware of the instantaneous carrier drops to extinguish the arcs initiated by the lightning strikes. And, one of the most important lightning opponents is a large coil of large wire in each tower lighting wire at the base of the tower. It keeps lightning as well as R-F out of the electrical service to the station. If tower lighting chokes stepped up the lightning, they would all be replaced with Austin transformers or some other technique such as shunt feed of the radio towers to eliminate the base insulator. Truth is, lighting chokes are very effective at keeping lightning out of the power supply. Best regards, Richard Harrison, KB5WZI Hi Richard, really glad to see you chime in. Even ignoring the few examples I found that argue against the choke concept, what was more relevant to me was that in poring over hundreds of documents lately, I can find no modern specification for coiling the coax at any point, high or low. Not in the NEC or NFPA, not in the descriptions and specs to nationwide antenna tower systems, and not in National Lightning Safety Institute, University of Florida or other acedemia writings of such protection systems. So what seems to remain, is its record of use, perhaps prominently at one time, without evidence that the design was ever effective. Remember that for 230 years science seemed to support the pointed lightning rod without really testing it against other attachment points. Now it is fairly well agreed that blunt-tip rods were sceintifically tested to do a much better job of attracting the leader that was headed for a given area anyway. Perhaps the colied coax chokes are just fading away due to no real evidence that they work, and some theory and maybe even feeble arguments that they could do harm. From an EMI standpoint, it's hard to argue the concerns. And from direct attachment, only a massive winding of very heavy conductor could slow down lightning (providing there was an arc-gap for it to take as an alternate to that slowdown). Might be why the modern lighter cabling of todays proliferant towers find little usefulness for the concept - just as a possibility. Best regards, Jack Painter Virginia Beach VA |
So to those that think a simple Transorb or air gap device will protect their 5
v CMOS circuitry... |
On Sat, 14 Aug 2004 01:08:12 GMT, Dave Shrader
wrote: Richard Harrison wrote: Richard Clark, KB7QHC wrote: "(don`t fall for the monster under the bed stories of gazillion volts at a bajillion amps)." It's not a monster under the bed. But it is a heaven of a blast! Hi Dave, The point of the monster is that it is NOT under the bed, but in the heavens. Let's look at the numbers you provide: First peak 100,000 amperes with a second strike of 50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth] of 100 useconds for each peak. Expressed as power into a section of tower where the cumulative resistance is 1 mOhm (not unreasonable) and giving the stroke a full second sustained current flow (I've never seen such a long one) so we can round the numbers into watt-seconds (never mind KWH); and figuring a duty cycle of 0.01% based on your pulse width, but let's get extravagant and say 0.1%; then both strikes express all of 150 milli-watt-seconds of power. 500 amperes sustaining current in the lightning channel for 300 milliseconds. Again, expressed in watt-seconds (sneering KWH) this probably doubles the power burden another 150 milli-watt-seconds. Total power: less than half a watt-second or as much heat as 1/10th of a Christmas tree bulb held for the same time as the strike. For those who remember NE-2 bulbs in their radio's front end, these are rated at 1/4 Watt. The paranoid may wish to parallel several, but such devices exhibit what is called current hogging - one will fire to destruction before the others light up. To demonstrate the catastrophe that is so often associated with a strike, divert the same strokes to a nearby tree that shows all of 10 Ohms resistance in its sap: 3 KW-Seconds. Try holding three clothes irons for 1 second. :-) Even this is barely remarkable given the heat is spread over a considerable bulk. What makes the difference so destructive? That same time element. The heat does not have the leisure of dissipation in 100µS and concentrates. This accounts for the scoring of a strike on metal, or the steam explosion in a tree trunk. 4) Electric field intensity prior to prestrike is greater than 10,000 volts per meter. Conclusion: Lightning has lots of energy. Energy is a strange thing, sunlight has vastly more energy than radio waves at HF (or VHF or UHF or SHF or....) No one worries about their radio at the beach, but they put sun screen on their skin. Walking across a wool carpet generates far more energy than a pre strike, but hardly enough power for a pinwheel. Separating two sheets of typing paper is about the same risk. This does not diminish the liability to sensitive components. The electric fields created by the casual separation of paper can destroy a transistor IFF it is not in a circuit. The power absorbed by common, resistive components in relation to that same transistor protect it simply. There are some circuit designs that seek a high input resistance that easily fail to this assault. I should note that in this day and age of surface mount that there are also resistors that can be destroyed by these casually generated potentials. Systems have been designed to not only survive a direct strike but to operate through the direct strike. All it takes is $$$$$$. Well, for the amateur (not working through a strike) perhaps $$. The risk is: "Do you maintain 0.001 Ohm or better strike paths?" 73's Richard Clark, KB7QHC |
"Richard Clark" wrote wrote: Richard Harrison wrote: Richard Clark, KB7QHC wrote: "(don`t fall for the monster under the bed stories of gazillion volts at a bajillion amps)." It's not a monster under the bed. But it is a heaven of a blast! Hi Dave, The point of the monster is that it is NOT under the bed, but in the heavens. Let's look at the numbers you provide: First peak 100,000 amperes with a second strike of 50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth] of 100 useconds for each peak. Expressed as power into a section of tower where the cumulative resistance is 1 mOhm (not unreasonable) and giving the stroke a full second sustained current flow (I've never seen such a long one) so we can round the numbers into watt-seconds (never mind KWH); and figuring a duty cycle of 0.01% based on your pulse width, but let's get extravagant and say 0.1%; then both strikes express all of 150 milli-watt-seconds of power. 500 amperes sustaining current in the lightning channel for 300 milliseconds. Again, expressed in watt-seconds (sneering KWH) this probably doubles the power burden another 150 milli-watt-seconds. Total power: less than half a watt-second or as much heat as 1/10th of a Christmas tree bulb held for the same time as the strike. For those who remember NE-2 bulbs in their radio's front end, these are rated at 1/4 Watt. The paranoid may wish to parallel several, but such devices exhibit what is called current hogging - one will fire to destruction before the others light up. To demonstrate the catastrophe that is so often associated with a strike, divert the same strokes to a nearby tree that shows all of 10 Ohms resistance in its sap: 3 KW-Seconds. Try holding three clothes irons for 1 second. :-) Even this is barely remarkable given the heat is spread over a considerable bulk. What makes the difference so destructive? That same time element. The heat does not have the leisure of dissipation in 100µS and concentrates. This accounts for the scoring of a strike on metal, or the steam explosion in a tree trunk. 4) Electric field intensity prior to prestrike is greater than 10,000 volts per meter. Conclusion: Lightning has lots of energy. Energy is a strange thing, sunlight has vastly more energy than radio waves at HF (or VHF or UHF or SHF or....) No one worries about their radio at the beach, but they put sun screen on their skin. Walking across a wool carpet generates far more energy than a pre strike, but hardly enough power for a pinwheel. Separating two sheets of typing paper is about the same risk. This does not diminish the liability to sensitive components. The electric fields created by the casual separation of paper can destroy a transistor IFF it is not in a circuit. The power absorbed by common, resistive components in relation to that same transistor protect it simply. There are some circuit designs that seek a high input resistance that easily fail to this assault. I should note that in this day and age of surface mount that there are also resistors that can be destroyed by these casually generated potentials. Systems have been designed to not only survive a direct strike but to operate through the direct strike. All it takes is $$$$$$. Well, for the amateur (not working through a strike) perhaps $$. The risk is: "Do you maintain 0.001 Ohm or better strike paths?" 73's Richard Clark, KB7QHC Hi Richard - can you please explain this "duty cycle of 0.1%" ? I thought it was expressed as a 10% duty cycle - but then a 50kva strike would be expressed as 5kva sustaining current in the lightning channel, not 500 amperes. Dave - was that 500 amperes a typo or the figure used by the USAF for protection design? My internal surge protection is designed for 10kva max, and the rooftop downconductors would certainly be expected to carry at least 5x that much for a short time from a direct attachment. Even internal AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which does incidentally happen from those 100kva strikes. It just happened less than half a mile up the beach from me last month. Thanks, Jack Painter Virginia Beach VA |
On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter"
wrote: Hi Richard - can you please explain this "duty cycle of 0.1%" ? Hi Jack, Duty cycle is a simple ratio of on time to off time. It would be presumptuous to offer that the strike off time for any particular spot on earth is hundreds of years, so the choice of one second is suitably long enough given strike components have long since faded, but are easily recent both. The shape of the pulse complicates the estimate because Duty Cycle is often expressed in the expectation of a square wave. What is the on time? When you get into pulse work, most in the field arbitrarily assign the width of the half-power, or half-voltage points. For Dave's numbers, this would be some 100µS which, when compared to 1 second is actually 0.01%. Being generous, and given the shape of the decay I simply threw in a 10X fudge factor. I thought it was expressed as a 10% duty cycle 10% of what? Lightning current flows for 100µS and is off for 1mS? Dave clearly expresses lingering current flow out to 300mS so that is clearly wrong. - but then a 50kva strike would be expressed as 5kva sustaining current in the lightning channel, not 500 amperes. Where did the volts come from? If the pre strike fields are running 10KV then your strike has only 5A in it. This is the pencil whipping that comes with lightning: the voltage description. ALL of that voltage is dropped across 10000 feet of discharge length, not in the last 3 inches from the tip of the bolt to ground. In normal, settled air, in the most benign weather without any disturbance, the potential gradient from earth to sky is 180V/M. That is to say, your head is at an elevated potential of 300V with respect to your feet. At an altitude of 10000 feet the potential is 1,800,000V without any inducement to discharge. Dave - was that 500 amperes a typo or the figure used by the USAF for protection design? My internal surge protection is designed for 10kva max, and the rooftop downconductors would certainly be expected to carry at least 5x that much for a short time from a direct attachment. Even internal AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which does incidentally happen from those 100kva strikes. It just happened less than half a mile up the beach from me last month. You need to look at those surge protection ratings again. My experience is that they are rated in Joules capacity which is NOT the same thing as v-amperes. The two may be equivalent, but your reference for volts is missing altogether. As I offered in other postings: where did the voltage come from? If your tower is of the standard design, you are not going to develop any appreciable voltage unless you introduce resistance or impedance to develop it from the current flow. 100,000A through 0.001 Ohms may give you 100V at best, and only if you can reach the top of tower where the strike hits. For those who want to multiply this voltage with Z, calculate the impedance of a 12" diameter wire 50' tall at a frequency of 1MHz. Perhaps this will make an NE-2 glow, if its leads are long enough. It just happened less than half a mile up the beach from me last month. No doubt, but what exactly was "It" that happened? Stick 50 feet of tower up into the air, and interrupt it with insulation and YES! arcs will spark. No one needs an insulated $$$$$$ tower - thousands of commercial installations typically discard that feature in favor of simple $$ lightning protection. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
. . . You need to look at those surge protection ratings again. My experience is that they are rated in Joules capacity which is NOT the same thing as v-amperes. The two may be equivalent, but your reference for volts is missing altogether. . . A joule is a watt-second. Roy Lewallen, W7EL |
On Sat, 14 Aug 2004 16:20:49 -0700, Roy Lewallen
wrote: Richard Clark wrote: . . . You need to look at those surge protection ratings again. My experience is that they are rated in Joules capacity which is NOT the same thing as v-amperes. The two may be equivalent, but your reference for volts is missing altogether. . . A joule is a watt-second. Roy Lewallen, W7EL Hi Roy, Quite so. Still missing the volt reference (and no mention of Ohms). 73's Richard Clark, KB7QHC |
"Richard Clark" wrote
On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter" wrote: The shape of the pulse complicates the estimate because Duty Cycle is often expressed in the expectation of a square wave. What is the on time? When you get into pulse work, most in the field arbitrarily assign the width of the half-power, or half-voltage points. For Dave's numbers, this would be some 100µS which, when compared to 1 second is actually 0.01%. Being generous, and given the shape of the decay I simply threw in a 10X fudge factor. Thanks Richard. - but then a 50kva strike would be Meant to say "ka" sorry. Dave - was that 500 amperes a typo or the figure used by the USAF for protection design? My internal surge protection is designed for 10kva max, and the rooftop downconductors would certainly be expected to carry at least 5x that much for a short time from a direct attachment. Even internal AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which does incidentally happen from those 100kva strikes. It just happened less than half a mile up the beach from me last month. You need to look at those surge protection ratings again. My experience is that they are rated in Joules capacity which is NOT the same thing as v-amperes. The two may be equivalent, but your reference for volts is missing altogether. Only the those destructive MOV power strips get rated in joules ;-) My normal-mode silicon diode surge suppression is rated in KA (not kva, sorry again). http://www.transtector.com/documents...s/1451-001.pdf the 10ka model has a 12,000 amp surge rating. I located one at the main AC entrance panel (load side) and one on the station's 240v branch panel. Transtector also produces "power strip" surge protection that is all silicon with NO MOV's and NO L-G references. My station has no AC surge protection references to ground, and all equipment is connected to L-N surge protection power strips. Except the computer which runs through an Amer.Pwr.Con. UPS - which although it has an unavoidable L-G MOV, it is first protected by the two Transtector Fortresses. It just happened less than half a mile up the beach from me last month. No doubt, but what exactly was "It" that happened? Stick 50 feet of tower up into the air, and interrupt it with insulation and YES! arcs will spark. No one needs an insulated $$$$$$ tower - thousands of commercial installations typically discard that feature in favor of simple $$ lightning protection. 73's Richard Clark, KB7QHC A strike on a home and/or power lines in which the surge was so powerful that it blew the electric meter clean off the wall of the home (burning the powerline and the service panel inside the home). I visited when it was still smoking but they discouraged my camera. I did get a good picture of my neighbor's pine tree striped from 75' in the air to 6' above the ground, where it jumped to and split a wood fence. That was about 50' from the end of my 60 meter dipole which was operating at the time. I'm thinking the surge protection is working as advertised this summer. At this rate I'll soon have more examples that just nearby strikes......but hopefully not. 73, Jack Painter Virginia Beach VA |
"Roy Lewallen" wrote - A joule is a watt-second. ========================== The only trouble with Richard (Clark) is his abuse of the English language. ;o) ;o) ;o) Punchinello, G4FGQ |
On Sun, 15 Aug 2004 02:26:15 +0000 (UTC), "Reg Edwards"
wrote: The only trouble with Richard (Clark) is his abuse of the English language. Glad to observe you don't challenge my technical language. Figured out mud yet? :-P 73's Richard Clark, KB7QHC |
Richard Clark wrote: On Sat, 14 Aug 2004 01:08:12 GMT, Dave Shrader SNIP h, but let's get extravagant and say 0.1%; then both strikes express all of 150 milli-watt-seconds of power. Richard, I'm not going to try to out calculate you. But, please tell the group what the junction temperature of any semiconductor device is at transient thermal failure at 0.1 and 1.0 useconds. Twenty years ago the USAF test data indicated that failure occurred at 0.5 microjoules!!! That's 300,000 times more sensitive than your numbers. Note, it is extremely difficult to really achieve a 0.001 ohm mechanical interconnect. Secondly, the major electronic failure mode is from the coupling of the magnetic field. A di/dt of 10^5/[1E-6] yields a value of 10^11 amperes/second. A one foot length of wire has a self inductance of approximately one nanohenry [1*10^[-9]] and the di/dt impact is ... 100 volts peak from one end of the wire to the next. Back in the olden days, twenty years ago, the action integral, that you calculated was sufficient to burn a 0.5 inch diameter hole right through titanium that was 0.1 inch thick. Note: the titanium alloy we used melts at slightly below 2000 degree F. The design issue is TRANSIENT THERMAL EFFECTS not average heating. At 1 microsecond the heat flow from the stressed area has not started. The USAF required adiabatic heating as the peak temperature for the starting condition for the transient thermal analysis. Restated, all the energy is converted to instantaneous heat and then the thermal stress analysis would be performed under that constraint. Conclusion, lightning is a highly stressful environment. |
On Sun, 15 Aug 2004 11:39:30 GMT, Dave Shrader
wrote: Richard, I'm not going to try to out calculate you. But, please tell the group what the junction temperature of any semiconductor device is at transient thermal failure at 0.1 and 1.0 useconds. That was covered in another posting. Twenty years ago the USAF test data indicated that failure occurred at 0.5 microjoules!!! That's 300,000 times more sensitive than your numbers. Current USAF lore holds, rightly, that it is the power supply that fulfills the failure, junction penetration energy is insufficient to accomplish this. Turn off the equipment, disconnect leads and NOTHING HAPPENS! Same pulse = no damage. Damage is not found in the miniscule power it is found in poor practices. Shielding is rather simple to accomplish, and taking care of front door and back door paths is not Rocket Surgery. It takes very little imagination to withstand these pulses; unfortunately it takes even less imagination to succumb. The stories of 1 idiot's plight make the news, not the 1 million survivors' success. Note, it is extremely difficult to really achieve a 0.001 ohm mechanical interconnect. For you perhaps, and certainly others who experience lightning's catastrophic failure, but 1mOhm is no big deal - measuring it is however. It is simple to enumerate poor examples, but that does not pass as careful accomplishment being impossible or unlikely. Secondly, the major electronic failure mode is from the coupling of the magnetic field. A di/dt of 10^5/[1E-6] yields a value of 10^11 amperes/second. A one foot length of wire has a self inductance of approximately one nanohenry [1*10^[-9]] and the di/dt impact is ... 100 volts peak from one end of the wire to the next. You are pencil whipping yourself, Dave. You are off by at least 1 order of magnitude in inductance. As current USAF lore to this matter reveals (and it is nigh on to 25 years stale), huge pulse coupled currents at low frequencies do a ****-poor job plain and simple. Saying coupling and making it happen are two different things (per current USAF lore) and trying to fit 1MHz into a 1 foot wire is loath to considerably less potential. This is called overplaying your hand, a direct strike is enough to argue. Back in the olden days, twenty years ago, the action integral, that you calculated was sufficient to burn a 0.5 inch diameter hole right through titanium that was 0.1 inch thick. Note: the titanium alloy we used melts at slightly below 2000 degree F. I've already commented to this specifically. The design issue is TRANSIENT THERMAL EFFECTS not average heating. At 1 microsecond the heat flow from the stressed area has not started. I've already commented to this specifically. The USAF required adiabatic heating as the peak temperature for the starting condition for the transient thermal analysis. Restated, all the energy is converted to instantaneous heat and then the thermal stress analysis would be performed under that constraint. Conclusion, lightning is a highly stressful environment. Stress also encompasses primitive fear and probably far more so than the actuality of failure. This is called the probability of big numbers. In a nation of 280 Million, any individual's once in a million experience like lightning striking them or near them happens 280 times a year (5 times a week or more) - it misses the other 279,999,720 times tho'. Thus such hair raising stories inordinately color the topic and are suitable for selling insurance and amulets. Hence the advertising and $$$$$$ suggested retail cost for "peace of mind." At that price, if only 0.01% of those 279,999,720 pushed their credit cards across the counter, that makes for a very profitable living second only to ENRON. Moral: "Don't use insulated towers." Risk: "How well can you reduce R?" 73's Richard Clark, KB7QHC |
All about grounding and lightning protection at PolyPhaser -- URL:
http://www.polyphaser.com/ppc_pen_home.asp -- One Watt To steal ideas from one person is plagiarism; to steal from many is research. -- Comedian Steven Wright "Private" wrote in message om... Hello, I am looking for some advice on if the ground system featured below is sufficent or should be upgraded. It consists of: - 3 ground rods 10' each around the tower (bonded together) - 2 ground plates (one outside, one in the shack, also bonded together) - lightning arrestors and/or feedthrough adapters - tower to mast ground - interior coax switch (not shown) I provided some pictures below: http://www.telusplanet.net/~homac/exteriorground01.JPG http://www.telusplanet.net/~homac/exteriorground02.JPG http://www.telusplanet.net/~homac/exteriorground02a.JPG http://www.telusplanet.net/~homac/exteriorground03.JPG http://www.telusplanet.net/~homac/exteriorground04.JPG http://www.telusplanet.net/~homac/interiorground01.JPG http://www.telusplanet.net/~homac/interiorground02.JPG I am looking for constructive feedback..... Thank-you.... Lloyd |
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