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Antenna mast grounding question
I will be puting a intenna mast up on the roof, and I plan on
running a wire from the mast to a grounding rod. My house is grounded via just the water pipe, as far as I can tell, no grounding rod connects to my electrial service. Do I need to run a wire from the grounding rod to my water pipe to prevent a grounding loop? What size wire should I use from the mast to the rod? and from the rod to the water pipe, if it is required? Thanks! -Mike Ekholm -- Mike Ekholm, UNIX Sys Admin - web: http://www.ekholm.org ham: kc0mpu irc: Nalez ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UNIX - The Swiss army knife of software. |
Mike, Putting the mast grounding aside for a minute, I think I'd have a talk with whoever supplies your electrical power about the ground that should be there and isn't. 'Doc |
On 27 Nov 2003 17:02:33 GMT, Mike Ekholm wrote:
I will be puting a intenna mast up on the roof, and I plan on running a wire from the mast to a grounding rod. My house is grounded via just the water pipe, as far as I can tell, no grounding rod connects to my electrial service. Do I need to run a wire from the grounding rod to my water pipe to prevent a grounding loop? Based on my personal experience: I would verify that you don't have a electrical system ground. If you don't, then add one post haste. The number, size, and spacing vary according to soil conditions and the size of your electrical service. It's for your own safety. The water pipes/system should be considered as a safety backup. " Check the electrical codes for your area", or get to know an electrician. Here the code required I have two, 8' ground rods six feet apart connected with #6 wire for the electrical service for *both* the house and the shop. Although fed from the same transformer they have their own meters and breakers. The TV mast and small satellite dish required their own 8' ground rod and only a #10 wire for grounding. BTW we are also required to tie the electrical service ground to gas pipes and water pipes. Which in our case is strange as the water system is all plastic except for the water meter. What size wire should I use from the mast to the rod? and from the rod to the water pipe, if it is required? You didn't say what type of soil you have in your area, but most would be using bare, solid (or stranded), #6 or #8. As I noted above, the TV antenna mast and satellite dish use only a #10. I use #2 and have everything tied together for the ham station, but I have a large antenna system that gets struck by lightening fairly often. You'll have to fix the return add due to dumb virus checkers, not spam Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Thanks! -Mike Ekholm |
I will be puting a intenna mast up on the roof, and I plan on
running a wire from the mast to a grounding rod. My house is grounded via just the water pipe, as far as I can tell, no grounding rod connects to my electrial service. Do I need to run a wire from the grounding rod to my water pipe to prevent a grounding loop? No, Earth ground is earth ground is earth ground, That's true, _if_ you happen to be living on a solid sheet of copper, or a superconductor. The actual DC resistance of "earth ground" across the width of a house can be quite substantial. This can lead to a significant voltage potential developing across "ground" under certain circumstances. For this reason, the U.S. National Electric Code states that each building may have only a single "grounding system". If you have two or more ground points (ground rods, grounded water pipes, etc.) the NEC says that you must "bond" them together with heavy-gauge wire, precisely to overcome this resistance. 8-gauge is usually required, and I believe that some municipalities require even heavier wire such as 6-gauge. If you don't do this, then under certain circumstances, an electrical fault can have some very unfortunate effect. Let's say you have a grounded antenna mast, with its own ground rod, but that you haven't bonded it to your electrical service-panel ground. Let's also assume that: - You've got a DC-grounded antenna (e.g. a copper-pipe J-pole) attached to the mast - Your rig is plugged into an outlet, whose ground wire happens to come loose, and - Your rig develops an internal hot-to-chassis electrical short. At this point, you're probably going to be in a world of hurt. The "hot" current is going to flow into the rig's chassis, through the coax braid to the antenna, down the mast to the ground rod, and through the soil to the service panel. The soil resistance is going to have two very bad effects: - It can limit the current flow through ground to below the circuit breaker's trip limit. - It'll allow the rig chassis, and the antenna and mast, to remain at a fairly high voltage above neutral. As a result, you can end up with both a shock hazard, and a risk of severe heating and fire. 10 amps through your coax could spoil your whole day. You only need to ground the antenna to the grounding rod, the water pipe and antenna ground rod are both on the same circuit. Just think of the earth ground as a very large negative terminal on a car battery. Nope. The two ground points could very well have tens to hundreds of ohms of soil resistance between them. For purposes of electrical safety, bond 'em together! As Bob Pease of National Semiconductor said (in a different context, also having to do with ground impedance): "You may be able to trust your friends. If you're very fortunate, you may be able to trust your government. You cannot trust your ground." I'd strongly encourage the OP to check the his local electrical codes to find out what the ground-bonding requirements are in his area. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
As Bob Pease of National Semiconductor said (in a different context, also having to do with ground impedance): "You may be able to trust your friends. If you're very fortunate, you may be able to trust your government. You cannot trust your ground." A very smart guy. My rule for current: "Always put it back where you got it from." If you let it find it's own way home, it will usually make a mess. |
"Keith" wrote in message link.net... On Fri, 28 Nov 2003 05:58:38 -0000, (Dave Platt) wrote: Nope. The two ground points could very well have tens to hundreds of ohms of soil resistance between them. For purposes of electrical safety, bond 'em together! They are bonded together by earth ground. The antenna is not going to carry any AC load if your station is grounded. Who knows maybe a 747 will clip the guys antenna at the same time as lightening hits the 747 knocking the ground wire from the antenna and creating a huge fireball above his house. Keith, In this case you are not providing helpfull advice as it is very important that a wire bond exist between grounding systems. It is impossible to predict the direction that the fault will eventually come from there fore it is important to project from an many senarios as possible. Lightning hitting a nearby object, like a tree, will raise the ground potential around the tree by many thousands of volts and this voltage may vary greatly a few feet away. One ground rod many be at a 5,000 volt potential while the other rod is at a 3,000 volt ground potential. In this case the 2,000 volts will look for the easiest path to equalize themselves. It could be the bonding wire or, without the bond, the radio equipment. 73 - Mike - K9JRI |
On 27 Nov 2003 17:02:33 GMT, Mike Ekholm just had to say:
: I will be puting a intenna mast up on the roof, and I plan on : running a wire from the mast to a grounding rod. My house is grounded : via just the water pipe, as far as I can tell, no grounding rod connects : to my electrial service. Do I need to run a wire from the grounding rod : to my water pipe to prevent a grounding loop? Thanks for the responses folks. I will run 10ga from the mast to the ground rod, and I will also run a wire from my house ground system to the ground rod to prevent a ground loop. I will need to do some code reading to find what size wire I need to run from the house gound system to the rod. Thanks! -Mike Ekholm -- Mike Ekholm, UNIX Sys Admin - web: http://www.ekholm.org ham: kc0mpu irc: Nalez ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UNIX - The Swiss army knife of software. |
Nope. The two ground points could very well have tens to hundreds of
ohms of soil resistance between them. For purposes of electrical safety, bond 'em together! They are bonded together by earth ground. The National Electric Code says otherwise. Earth ground is *not* considered adequate bonding for the purposes of electrical safety. The antenna is not going to carry any AC load if your station is grounded. Who knows maybe a 747 will clip the guys antenna at the same time as lightening hits the 747 knocking the ground wire from the antenna and creating a huge fireball above his house. The whole purpose of proper electrical *safety* grounding is to ensure that when things go wrong (short circuits, open neutrals, etc.), they go as *little* wrong as possible. Failing to bond ground rods together would be one of those things which would make no difference *normally* (in the absense of faults in the building wiring). If a wiring fault, short circuit, etc. were to occur, proper ground-rod bonding could make the difference between a tripped circuit breaker (if you're run a heavy-gauge bonding wire), and a burned-down building (if you didn't bond 'em, and the current flow through the soil wasn't enough to trip the breaker). The bonding rule is there for a very good reason... safety. As a very practical matter: if you fail to follow the Electrical Code (or your own local rules, if different), then your home may fail inspection if you try to sell it, and (if a fire occurs) your insurance company may refuse to pay your claims if they find a not-to-code electrical installation/modification. Bonding the grounds together will cost maybe $10 worth of wire. It's cheap insurance. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
That is not a wise idea. If your mast takes a direct hit, or if there is one
nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. |
Antenna grounds should always be isolated from
housewiring grounds. ============================== Unless your antenna is under another distant thundercloud you must have suicidal tendencies. ;o) |
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On Sat, 29 Nov 2003 05:23:05 GMT, Roger Halstead
wrote: On 29 Nov 2003 02:25:58 GMT, (K9SQG) wrote: That is not a wise idea. If your mast takes a direct hit, or if there is one nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. Here I have everything tied together, but it's not a normal installation. There are 30 ground rods connected by over 600 feet of bare #2 copper. All ground rods are bonded (CadWelded) together forming a network which should keep any particular ground and equipment at the same potential no mater where which tower would be hit. Although the likely hood of anything other than the main tower getting hit is unlikely. It's 130 feet, the top of the multi band vertical on the shop is 60 feet and the mast at the other end of the house is only 25 feet. Nice work Roger, ever work for the telephone company? Russ |
On Sat, 29 Nov 2003 15:05:07 GMT, Russ wrote:
On Sat, 29 Nov 2003 05:23:05 GMT, Roger Halstead wrote: On 29 Nov 2003 02:25:58 GMT, (K9SQG) wrote: That is not a wise idea. If your mast takes a direct hit, or if there is one nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. Here I have everything tied together, but it's not a normal installation. There are 30 ground rods connected by over 600 feet of bare #2 copper. All ground rods are bonded (CadWelded) together forming a network which should keep any particular ground and equipment at the same potential no mater where which tower would be hit. Although the likely hood of anything other than the main tower getting hit is unlikely. It's 130 feet, the top of the multi band vertical on the shop is 60 feet and the mast at the other end of the house is only 25 feet. Nice work Roger, ever work for the telephone company? Nope! I had to purchase everything. Hence the reason for me doing all the work:-)) Welll...come to think of it, way back in the early 50s my dad was a lineman on one of the old privately owned rural lines. I got to do a lot of pole climbing. I still have the old portable test set... and memories of splinters. You'll have to fix the return add due to dumb virus checkers, not spam Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Russ |
On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote:
(K9SQG) wrote in message ... That is not a wise idea. If your mast takes a direct hit, or if there is one nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. If all grounds are at the same potential, no current can flow between them. Not to mention the NEC requires it in the U.S. MK When you figure the rise time there can easily be several thousand volts between the base of the antenna mast and the electrical system ground. IE the voltage could be 50,000 at the tower and not even have started to rise at the electrical ground. It's not just a simple CD circuit. I've seen tower strikes where there was such a strong current and fast rise time, the magnetic field quenched the current flow and the lightening got off part way down and jumped sideways to something else. You'll have to fix the return add due to dumb virus checkers, not spam Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com |
Roger Halstead wrote in message . ..
On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote: (K9SQG) wrote in message ... That is not a wise idea. If your mast takes a direct hit, or if there is one nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. If all grounds are at the same potential, no current can flow between them. Not to mention the NEC requires it in the U.S. MK When you figure the rise time there can easily be several thousand volts between the base of the antenna mast and the electrical system ground. IE the voltage could be 50,000 at the tower and not even have started to rise at the electrical ground. In my case, those are pretty much the same place. All my grounds tend to rise in potential at the same time, being they are all tied together at the base of the mast. Nothing is perfect of course, but you sure don't want any large potential differences between grounds. It's not just a simple CD circuit. I've seen tower strikes where there was such a strong current and fast rise time, the magnetic field quenched the current flow and the lightening got off part way down and jumped sideways to something else. If I remember right, the original poster was going to mount an antenna on a roof. That has the potential for even more serious problems if the antenna acts as a lightning rod. He'd want as few turns or sharp bends in the ground wire to earth. This is why I much prefer using a metal mast on the side of the house to support verticals or other high risk antennas, rather than a mast attached to the roof of the house. And then hoping a ground wire will safely direct the charge to earth...It usually will, at least much better than the house itself, but it's kind of scary if it has turns or bends. The important part at the house is making sure that everything rises together so there's no lower resistance path for the charge to take through the shack or house. At the mast, I always tape all coaxes or wires to the mast, and run them all the way down to earth to try to avoid flashing problems. So far in two strikes to the mast, I haven't noticed any, and I have a breaker box, elevated power lead in, phone lines, cable lines, all within 5 ft of that mast. MK |
Consider:
The National Electric Code says otherwise. Earth ground is *not* considered adequate bonding for the purposes of electrical safety. The bonding rule is there for a very good reason... safety. Bonding the grounds together will cost maybe $10 worth of wire. It's cheap insurance. My main pannel's nutral bar is attached to a stranded 2AWG wire attached to the cold water pipe (from 1963). Other work done in 2001 by a contractor has a solid 6AWG wire on the nutral bar, going out to a stake in the back yard. He tied the gas line in the house, to the cold water pipe, and also, in another area of the basement, tied the copper sewer line to the cold water line. Am I good-as-gold with this setup? alex batsonaatcomcastdotnet |
The National Electric Code says otherwise. Earth ground is *not*
considered adequate bonding for the purposes of electrical safety. The bonding rule is there for a very good reason... safety. Bonding the grounds together will cost maybe $10 worth of wire. It's cheap insurance. My main pannel's nutral bar is attached to a stranded 2AWG wire attached to the cold water pipe (from 1963). Other work done in 2001 by a contractor has a solid 6AWG wire on the nutral bar, going out to a stake in the back yard. He tied the gas line in the house, to the cold water pipe, and also, in another area of the basement, tied the copper sewer line to the cold water line. Am I good-as-gold with this setup? I can't speak for the legalities of the situation (only your local code inspector can), but it sure sounds good to me! Keep up this approach with any new grounding points/rods you add, and I think you'll be in very good shape. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Though in practice you are correct to express concern, your reason is
not properly stated. You further the lighting rod myth. Actually, "if the antenna acts as a lightning rod." He'll have little problem. The purpose of a true lightning rod is to blead off the charge, defeating a strike, not to attract it. A lightning srtike will blow any lightning rod system to smithereenes. When a charged object has a sharp corner or point, the charge tends to collect there. Because there is more charge at that p[oint it will have a higher concentration and therefore a higher voltage. It builds to the point of forming a corona/plasma and will discharge it. That's why the van De Graf (sp) generators have the round ball on the top. They WANT to build up the charge and not loose any more than necessary.. I all fairness, I do not know if lightning rod systems work in practice.They do wear out due to the discharge corona and should be sharpened periodically. Apparently the points of the typical beam are not sufficient or they wouldn't get struck, no? 73, Steve K,9.D;C;I "Mark Keith" wrote in message om... Roger Halstead wrote in message . .. On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote: (K9SQG) wrote in message ... That is not a wise idea. If your mast takes a direct hit, or if there is one nearby, there is a possibility that some of the energy will go into the house via that ground rod. Antenna grounds should always be isolated from housewiring grounds. If all grounds are at the same potential, no current can flow between them. Not to mention the NEC requires it in the U.S. MK When you figure the rise time there can easily be several thousand volts between the base of the antenna mast and the electrical system ground. IE the voltage could be 50,000 at the tower and not even have started to rise at the electrical ground. In my case, those are pretty much the same place. All my grounds tend to rise in potential at the same time, being they are all tied together at the base of the mast. Nothing is perfect of course, but you sure don't want any large potential differences between grounds. It's not just a simple CD circuit. I've seen tower strikes where there was such a strong current and fast rise time, the magnetic field quenched the current flow and the lightening got off part way down and jumped sideways to something else. If I remember right, the original poster was going to mount an antenna on a roof. That has the potential for even more serious problems if the antenna acts as a lightning rod. He'd want as few turns or sharp bends in the ground wire to earth. This is why I much prefer using a metal mast on the side of the house to support verticals or other high risk antennas, rather than a mast attached to the roof of the house. And then hoping a ground wire will safely direct the charge to earth...It usually will, at least much better than the house itself, but it's kind of scary if it has turns or bends. The important part at the house is making sure that everything rises together so there's no lower resistance path for the charge to take through the shack or house. At the mast, I always tape all coaxes or wires to the mast, and run them all the way down to earth to try to avoid flashing problems. So far in two strikes to the mast, I haven't noticed any, and I have a breaker box, elevated power lead in, phone lines, cable lines, all within 5 ft of that mast. MK |
On Sun, 30 Nov 2003 22:26:31 -0500, "Alex Batson"
wrote: Consider: The National Electric Code says otherwise. Earth ground is *not* considered adequate bonding for the purposes of electrical safety. The bonding rule is there for a very good reason... safety. Bonding the grounds together will cost maybe $10 worth of wire. It's cheap insurance. My main pannel's nutral bar is attached to a stranded 2AWG wire attached to the cold water pipe (from 1963). Other work done in 2001 by a contractor has a solid 6AWG wire on the nutral bar, going out to a stake in the back yard. He tied the gas line in the house, to the cold water pipe, and also, in another area of the basement, tied the copper sewer line to the cold water line. Am I good-as-gold with this setup? Here the answer would be no, but YMMV depending on location (local codes) Although tied together the Neutral and ground are not considered the same. Neutral is the return to the power transformer on the pole and is normally the same size at the hot wires. (220 VAC). There should be a ground at the pole and one (or two) within 6 to 12 feet of the service entrance. *Here* and I emphasize here, that ground varies with the size of the service, but for a 200 amp service I believe it was #6. It had to be "Green" and tie to the ground clamp in the breaker box. In the breaker box is a jumper that ties the neutral and ground together. My electrical service for the house has two 8 foot ground rods, one with in 6 feet of the entrance and the other at 12 feet. The shop with the same size service (200 amp) only has one ground rod. BTW, although the ground wire is #6 the feed wires are 2 ought, or (#00) for both the house and shop. It takes pipe benders to get that stuff around the bends in the meter sockets and panels. Both the house and shop are fed with underground runs of about 130 feet. Some where I have some photos of me running the "trencher" across the driveway to install the PVC conduit. The gas line should have another Green wire (insulated except at the connectors) of the same size tieing back to the ground in the breaker box. Each of the other lines should also have it's own green wire going back to the breaker box ground. Only one ground wire from the box to the ground rod(s). This puts all of those metallic systems tied to the same potential. We were not allowed to "daisy chain" grounds. Each had to be a separate run and all tie to the buss where the green from the ground rods ties in. Again, I emphasize *here* is quite likely different than *there* although I'd assume they'd be close. Everyone has to meet the national electric code, but some areas are more strict. (I make no claim to being an expert on the national code, but having just rewired our home including installing a transfer switch to a 9 KW generator I am up on the local requirements) Part of this is still under way. Here being, Homer Township, in Midland County, Michigan. You'll have to fix the return add due to dumb virus checkers, not spam Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com alex batsonaatcomcastdotnet |
Steve,
Sorry, you are the one who is furthering the lightning rod myth. There is no way a "true lightning rod" bleeds off enough charge to avoid a strike. That idea is about 99% urban legend. I suggest perusal of the Polyphaser web site. There is a lot of good information there. One relevant comment is: "The real solution for lightning protection is to have control of the strike energy. To do this, a well-designed ground system will be a better investment than cluttering up the top of the tower." The cluttering refers to a bottlebrush arrangement of multiple sharp points, but the same idea applies to a single sharp point. As usual, Mark is right on target. 73, Gene, W4SZ Steve Nosko wrote: Though in practice you are correct to express concern, your reason is not properly stated. You further the lighting rod myth. Actually, "if the antenna acts as a lightning rod." He'll have little problem. The purpose of a true lightning rod is to blead off the charge, defeating a strike, not to attract it. A lightning srtike will blow any lightning rod system to smithereenes. When a charged object has a sharp corner or point, the charge tends to collect there. Because there is more charge at that p[oint it will have a higher concentration and therefore a higher voltage. It builds to the point of forming a corona/plasma and will discharge it. That's why the van De Graf (sp) generators have the round ball on the top. They WANT to build up the charge and not loose any more than necessary.. I all fairness, I do not know if lightning rod systems work in practice.They do wear out due to the discharge corona and should be sharpened periodically. Apparently the points of the typical beam are not sufficient or they wouldn't get struck, no? 73, Steve K,9.D;C;I "Mark Keith" wrote in message In my case, those are pretty much the same place. All my grounds tend to rise in potential at the same time, being they are all tied together at the base of the mast. Nothing is perfect of course, but you sure don't want any large potential differences between grounds. It's not just a simple CD circuit. I've seen tower strikes where there was such a strong current and fast rise time, the magnetic field quenched the current flow and the lightening got off part way down and jumped sideways to something else. If I remember right, the original poster was going to mount an antenna on a roof. That has the potential for even more serious problems if the antenna acts as a lightning rod. He'd want as few turns or sharp bends in the ground wire to earth. This is why I much prefer using a metal mast on the side of the house to support verticals or other high risk antennas, rather than a mast attached to the roof of the house. And then hoping a ground wire will safely direct the charge to earth...It usually will, at least much better than the house itself, but it's kind of scary if it has turns or bends. The important part at the house is making sure that everything rises together so there's no lower resistance path for the charge to take through the shack or house. At the mast, I always tape all coaxes or wires to the mast, and run them all the way down to earth to try to avoid flashing problems. So far in two strikes to the mast, I haven't noticed any, and I have a breaker box, elevated power lead in, phone lines, cable lines, all within 5 ft of that mast. MK |
On Wed, 03 Dec 2003 19:56:06 GMT, Gene Fuller
wrote: Steve, Sorry, you are the one who is furthering the lightning rod myth. There is no way a "true lightning rod" bleeds off enough charge to avoid a strike. That idea is about 99% urban legend. I suggest perusal of the Polyphaser web site. There is a lot of good information there. One relevant comment is: "The real solution for lightning protection is to have control of the strike energy. To do this, a well-designed ground system will be a better investment than cluttering up the top of the tower." I'd be a bit careful about that statement on a site for a company who makes their money from attempting to control the energy when lightening strikes, rather than preventing the strike. There are two distinct camps. The one that says the solution is to control the strike and the other says to prevent the strike. Lightening strikes are unpredictable in most cases, but if you have the tallest structure around the odds are that it will get hit before lower nearby structures. The cluttering refers to a bottlebrush arrangement of multiple sharp points, but the same idea applies to a single sharp point. According to our electrical inspector it's not a myth, but I don't know one way or another. However I do know that it would take little to bleed a charge and a lot to control a strike. I also know that every tall structure at the chemical company where I used to work had lightening rods Bleeding supposedly does just that. I prevents the charge from building up to a potential that will help bridge the gap to the feeders. The last class I had at work on electrical safety was pro lightening rods AND ground systems. (as was the one for skywarn from the NWS) I do use polyphasers and end up replacing one every now and then. My tower gets hit on average of three times per year. Since the tower went up there have been no strikes to any home within about 5 lots from me. There haven't been any really close strikes that didn't hit the tower. (of which I am aware). The neighbors are quick to tell me, "Man you shouldda been home this afternoon when the lightening hit your tower". That happened in August this year. They were really impressed and more so in that we had no damage even to the radios which do not get disconnected. My antenna ground system has over 600 feet of bare #2 copper wire with 30 grounding rods, not counting the two ground rods for the house electrical system and the one for the shop. They have separate feeds, but as my computer network ties it all together, I'm thinking of bonding the grounds for both services together and to the system ground. I have visions of a lightening strike to one system and reaching ground in the other by going through the 130 feet of cat-5 cable. There's a reason I back up everything on CDs and DVDs. You'll have to fix the return add due to dumb virus checkers, not spam Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com snip |
Roger Halstead wrote:
The cluttering refers to a bottlebrush arrangement of multiple sharp points, but the same idea applies to a single sharp point. According to our electrical inspector it's not a myth, but I don't know one way or another. However I do know that it would take little to bleed a charge and a lot to control a strike. I also know that every tall structure at the chemical company where I used to work had lightening rods Bleeding supposedly does just that. I prevents the charge from building up to a potential that will help bridge the gap to the feeders. I don't know if I would call it a total myth, but I call it fairly risky none the less. I know I sure wouldn't trust one to protect me from a strike. I don't think they can bleed the charges from constant hard wind and rain fast enough to do any good. It's like taking a whiz in a whirlwind. :( The last class I had at work on electrical safety was pro lightening rods AND ground systems. (as was the one for skywarn from the NWS) I agree there, if he is talking about the traditional pointy lightning rod used to protect other gear or buildings. I'm of the opinion strikes can never be totally avoided, and the brush things are a waste of time. I've heard of many reports of them being struck. Sometimes spraying hot metal around and causing a fire hazard. And you still should have a good ground even with those. To me, the only sure thing is expecting the strike to happen, and safely controlling it's path to ground when it finally does. So I'm firmly with polyphaser on that one. MK -- http://web.wt.net/~nm5k |
There is a short video available (saw in a search of lightning arrestor
systems) that shows the Empire State Bldg being struck several times, and not once does the lightning "visibly" hit, follow, or otherwise act impressed with the elaborate grounding system on the building. Taken as a whole though, it must be effective, because the strikes do no apparent damage, and they obviously get to the ground somehow. JP "Mark Keith" wrote The last class I had at work on electrical safety was pro lightening rods AND ground systems. (as was the one for skywarn from the NWS) I agree there, if he is talking about the traditional pointy lightning rod used to protect other gear or buildings. I'm of the opinion strikes can never be totally avoided, and the brush things are a waste of time. I've heard of many reports of them being struck. Sometimes spraying hot metal around and causing a fire hazard. And you still should have a good ground even with those. To me, the only sure thing is expecting the strike to happen, and safely controlling it's path to ground when it finally does. So I'm firmly with polyphaser on that one. MK |
Jack Painter wrote:
"Taken as a whole, though, it must be effective, because the strikes do no apparent damage, and they obviously get to ground somehow." True. I`m skeptical of claims of lightning avoidance by discharging the earth beneath the thunder cloud. I think the protection is from substituting a more attractive target to the lightning than the one you want to protect. I`ve worked with too many radio towers. Many had inverted Copperweld ground rods bolted to the tower tops with the pointed end aimed up. Function of the rods was protection of beacons and other appurtenances atop the tower. The towers still get lightning strikes but the beacons don`t get damaged from the tower hits when there`s a Copperweld lightning rod up there. I`ve seen broken and burnt beacons from towers that didn`t have the rods. A radio tower with a sharp-pointed lightning rod is very salient and should discharge the earth under and around the tower, if this is a prctical course. From what I`ve seen these lightning rods do not prevent lightning strikes but they do prevent some of the damage that lightning causes. Best regards, Richard Harrison, KB5WZI |
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