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Author Topic: Station ground question.  (Read 6602 times)
W2WDX
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Posts: 188




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« Reply #15 on: November 16, 2012, 11:27:30 AM »

Dave, you are really putting yourself in the line of fire so speak to say things like, "There is now no lightning path through the wiring or the coax to the station then to ground. The lightning current though the house wiring problem is solved." Simple question. How have you dealt with the center conductor of your coax? Do you really think lightning is gonna follow the complex path you laid out after it has already managed to travel hundred feet or more through an air dielectric we call "the atmosphere". Add a Polyphaser?!!! Making assumptions is how people get killed or gear turns to molten globs of nothingness. :-)

Dave, you're gonna get zorched regardless of what spice tells you. Stop running software and use common sense instead.

BTW I'm not sure you understand the magnitude of energy we are talking about and I don't think spice can deal with numbers this high. An average return stroke of lightning carries an electric current of 30,000 amperes (30 kA), and transfers 15 coulombs of electric charge and 500 megajoules of energy. Large bolts of lightning can carry up to 120 kA and 350 coulombs. And remember the dielectric strength of damp air is about 3 million Volts/m, so in order to get cloud-to-ground lightning the electric field has to exceed this.

Like I said grounding for lightning protection ... NO SUCH THING! Ground for function of the station is the only practicable thing one should discuss. No matter how good your grounding is, your gear and you will be damaged if you get a direct hit. At least your house will not be the path to ground, which is why we had lightning rods before all the plumbing (with stand pipes) was added to structures. Without it lightning passed right through the wood structure of the house and it burned. But protecting your gear and yourself during a storm when you get a direct strike, nope sorry ... not gonna happen on almost any Hams budget.

John

« Last Edit: November 16, 2012, 11:58:22 AM by W2WDX » Logged

WX7G
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Posts: 6056




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« Reply #16 on: November 16, 2012, 11:54:42 AM »

Interesting. Commercial transmitter sites and military communication installations are designed to take direct hits and keep on working. Aircraft are designed to take direct hits and keep on flying. BTW, I design EMP and lightning protection circuits.

I think you are alluding to the lightning channel (the conductive path for charge through the air) and whether it ceases when a ground system is encountered or if the lightning channel continues along the ground system. I have found no papers (so far) that mention the continuation of the lightning channel.

Here are some useful military publications detailing lightning protection:

http://www.wbdg.org/ccb/FEDMIL/std188_124b.pdf


http://www.everyspec.com/MIL-HDBK/MIL-HDBK-1000-1299/MIL-HDBK-1004-6_7896/


http://www.nautel.com/wp-content/uploads/2011/04/Lightning-Protection-Radio-Stations-Oct-1998.pdf

See figure 5 for the best way to ground a station and figure 6 for the worst way to ground a station. Figure 6 is what the initiator of this thread is starting with. Figure 5 shows a system where the station is hanging off a single point ground (and yes additional grounding can be placed between this ground and the antenna). There is no path from the single point ground through the station to another ground. As the single point ground rises in potential during a strike the station goes up with it. Placing connected ground rods around the house minimizes the potential difference between the AC wiring inside the house and the ground under the wiring. And all of this can be modeled quite nicely in SPICE. Lightning is not magic, it's electricity.

And here are some articles by a well known ham whose station is hit by lightning regularly
http://www.w8ji.com/lightning.htm

If you're an IEEE member you might have access to this article on using SPICE to model lightning effects
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=692371&tag=1

And for a laugh read "The Lightning Rod Man" by Herman Melville.
http://www.melville.org/lrman.htm

Another paper where SPICE is used to model lightning effects
http://teide.cps.unizar.es:8080/pub/publicir.nsf/codigospub/0140/$FILE/cp0140.pdf

here is a fascinating paper on modeling lightning effects
http://www.iclp-centre.org/pdf/Invited-Lecture-Ametani-2010.pdf


« Last Edit: November 16, 2012, 12:48:19 PM by WX7G » Logged
N4NYY
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Posts: 4758




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« Reply #17 on: November 16, 2012, 12:18:43 PM »

I have my station grounded to a shack ground rod, which is connected to a single point entry box. That is then bonded via 4 ga to electrical service panel ground. 
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W2WDX
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Posts: 188




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« Reply #18 on: November 16, 2012, 12:43:10 PM »

Most commercial communications systems use extensive systems including technologies like lightning rods, early streamer emission (ESE) and static dissipation used in concert. These include things like streamer preventing terminals on towers, large conductive core systems to dissipate the energies involved quickly, ground charge collector systems that are low resistance and low impedance grounding systems which let the charges move without much resistance, as well as Transient Suppressors (which are involved in different applications and locations like Service Entrance SPD, Distribution Panel SPD, Branch Panel SPD, as well what we use most often which are Point of Use SPD like Polyphasers).

These systems cost as much as most peoples homes, and still do not guarantee 100% protection, they only mitigate downtime. Some of the devices used in commercial systems individually cost out at thousands of dollars a piece. For instance, you mention lightning protection for aircraft. One of most common ones used are made by JOSLYN, and its HF antenna arrestors cost about $3000 each on the open market, and those aren't even the military versions.

To take isolated small parts of these costly complex systems, and then apply them to a home amateur station isn't a bad idea, just not something one should gamble on. Especially when the systems has not been calculated to handle the energies involved as an overall system. If the entire system is not able to dissipate the charges involved, they will go elsewhere. So taking bits and pieces is not advisable, both in terms of safety and property protection. If you are in this line of work you should know this.

Like I said, take your lead-ins and move them away from the shack when you know weather is on the move. Unplug your stuff, preferably at a location remote to your station.

John
« Last Edit: November 16, 2012, 12:57:05 PM by W2WDX » Logged

WX7G
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Posts: 6056




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« Reply #19 on: November 16, 2012, 12:57:53 PM »

My expertise in the field of lightning/EMP is calculating/simulating what voltage/current is inducted inside system cables (DC to 1 GHz) and designing circuits to protect sensitive circuits.

But back to ham antennas and lighting protection. W8JI has designed his antenna farm and station (in Georgia) such that the station suffers no lightning damage during frequent direct strikes to the antennas. The antennas don't always survive.

The lighting stress on a ham station/house can examined using Ohm's law as described. From this the number and placement of ground rods, wiring schemes, power/coax entry and how to hang the station off the side of a single point ground can be explored. Good and bad systems can be identified.

It's not rocket science and anyone with a basic knowledge of electricity can examine various scenarios and design a good system. How good that system ends up being depends on how much money and time they want to invest. By proper design better performance can be achieved for less money and time.

One more good paper on home lightning protection. See page 30 for a discussion of Ground Potential Rise and page 32, Fig. 7 for how not to bring communication cables into a house
http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
« Last Edit: November 16, 2012, 01:22:36 PM by WX7G » Logged
W2WDX
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Posts: 188




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« Reply #20 on: November 16, 2012, 01:25:14 PM »

Ha ... I'm sure his antennas do take a beating.

BTW, that Spanish paper you quoted has been peer reviewed and the findings in his comparisons between Spice and and EMTP have shown to be inconclusive. Even EMTP is being questioned now since it relies on TEM mode wave propagation assumptions. I didn't check your link but I think the last paper you quoted goes into to that, if it's the paper I think is (if it's the one by Akihiro Ametani).

I still think the best approach for an amateur is to disconnect with distance, something not practicable in commercial installations. Mitigation through some of your suggestions is certainly advisable, though not a panacea, if you cannot disconnect because you are not home for example.
« Last Edit: November 16, 2012, 01:29:53 PM by W2WDX » Logged

W5WSS
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Posts: 1728




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« Reply #21 on: November 16, 2012, 07:48:53 PM »

The best place for arresting a stroke is up above the antenna using a Porcupine looking device that functions exactly as, but better than; a lightning rod and using a large diameter copper wire such as a 1/0 conductor connecting directly straight down to a circular ring of Earthing rods nearby apx 6ft out from the base but not within the base structure. This also applies to dissipating the static build up to be more neutral as compared to the Earth surface acting to within the umbrella of protection formed by the system. Helping to avoid the stroke by dissipating the build up to be more UN- noticed by surface to cloud using the air channel in the first place.

I would not omit this technique above a horizontal beam for example.

The aluminum elevated vertical atop the pole or tower poses a different set of problems but can BE the lightning rod since it is somewhat a sharp point and can lend itself for the same end by Bonding attachment via it's mounting bracket then on down as previously described.

The Fibreglass, or PVC, or whatever one uses for rigidity utilized to house the soft wire these types are especially problematic because the conductor embedded within vs the outer material forms a potential difference with respect to Earth ground below while the fibreglass can not be grounded even though it builds up a static charge of it's own and dissipates at it's own dielectric constant consequentally little can be done with thevarious materials such as fibreglass etc all of these materials not limited to Fibreglass and all which behaves separately from the embedded interior antenna.

In every case a large section of the feedline can be opened or shorted to ground or both at the surface below the antenna and again at the shack entry outside by using perhaps fibre optic(will listen to others thoughts on the optical idea) switches prior to thunderstorms this automates and eases the physical burden to disconnect of the feedline and control lines that stay outside.

These techniques are very useful to the ham with an outdoor set of antennas on a single tower while striving for the economical solutions.
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N1RND
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Posts: 69




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« Reply #22 on: November 17, 2012, 06:52:14 AM »

Well first of all, thanks for all the replies and information from everyone.
This is an intense subject.
I suppose I could tie the two points together. 
The easiest path would be through the cellar, BUT THIS IS PROBABLY A NO NO, RIGHT?
I can run the bonding conductor outside along the perimeter of the house, it will just be more work.

Dave
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WX7G
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« Reply #23 on: November 17, 2012, 10:04:44 AM »

The NEC requires that antenna ground rods be bonded to the AC service ground using #6 or larger copper wire routed outside the house.

Additional ground rods placed at shack end of the house and spaced 2X their length will reduce the lightning current through the house. A second #6 wire routed around the other side of the house will further reduce the lightning current through the house.

To eliminate lightning current through the radio gear:
1. Route the coax and ground wire to one AC outlet in the shack. Connect these wires to the outlet GND.
2. Route the coax from there to the radio.
3. Power the radio from this outlet.

To protect the radio RF I/O a coaxial shorting switch is better than a polyphaser.

I built a nice SPICE simulation of all this today but there's no way to post it here.
« Last Edit: November 17, 2012, 10:07:13 AM by WX7G » Logged
N1RND
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Posts: 69




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« Reply #24 on: November 17, 2012, 12:22:19 PM »

While on the subject, I noticed today at the local home center, galvanized ground rods.  When and why would you use a galvanized rod instead of copper clad?
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N1RND
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Posts: 69




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« Reply #25 on: November 17, 2012, 01:03:21 PM »

Here is some http://www.ecmag.com/index.cfm?fa=article&articleID=5794great info ground rod types and historyhttp://www.ecmag.com/index.cfm?fa=article&articleID=5794.
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N1RND
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Posts: 69




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« Reply #26 on: November 17, 2012, 01:04:42 PM »

and, http://www.transorbelectrical.com/pq/technical/NECCompliantGndRodR8.pdf
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WD4ELG
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Posts: 873




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« Reply #27 on: November 17, 2012, 05:55:29 PM »

At the risk of looking like an idiot, I am going to ask so that I can learn:

OK, so I am an electrical engineer but I am NOT an electrician. 

My station is multiple wires and inverted L antennas.  Property surrouned by 70-90 foot trees.  Pines, oaks, maples.  The antennas are within the trees (insulated wire) and in some cases, between them.  Antennas are 200 feet from the house, which is NOT in the woods.  I have the AplhaDelta polyphaser discharge devices (which won't do a thing for a direct hit, I get that point).  Shack is on the second floor (not that this matters much, but I added the detail anyway).

The house/trees have not been hit in the 3 years we have been here.  But there have been close calls (across the street in the tall sweetgum trees, the 50kVA high voltage 150 foot towers about 300 yards north of the house).

I DEFINITELY understand the point #1: the only sure way to be safe is to disconnect the feed line and move it AWAY from the house.  Not 2-3 feet, but 50 to 100 feet.  Here's the challenge: in North Carolina, lightning is quite frequent (actually, the second state to FL in terms of lightning deaths).  I may not be at home to do the disconnect.

W8JI has a wealth of suggestions on his pages.  But exactly WHAT should I be looking for (visually) to confirm that my house has the single-point ground?  Should this be encompassing the entier foundation of the house?  Is a single point ground just a sytem of several ground rods that include the phone, tv cable, electrical ground?  The home was built in 2000, does it already have what I need if it complies with NEC code?  What do I need to do with all the feedlines (which come in through a common location point)?

SPECIFIC, DETAILED guidance with actions would be greatly appreciated.  I am not a gambler, and this topic keeps me up at night, especially in the spring and summer months.
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N1RND
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« Reply #28 on: November 17, 2012, 06:23:45 PM »

Welcome to the thread that I have created, kind of like a monster.  Tomorrow I will attempt to add an 8 ft. ground rod to my service entrance, after discovering that the sparkies who installed it only used a 4 ft. rod due to rock ledge issues!
Then I will attempt to bond the service ground to the station/antenna ground system with a continuous run of heavy copper wire.
After this I will be done.  This will be the most involved ground that I have ever used.  I feel that it is better than what I used in the past.
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WB6DGN
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Posts: 619




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« Reply #29 on: November 17, 2012, 11:17:16 PM »

Another "country" heard from.  I have a small house, aluminum siding, single story with breaker panel in a partial basement.  The electrical entrance/meter panel is about five feet (horizontal) away and above the breaker panel.  I have not been able to find a ground rod at the meter panel but find one outside the basement at the breaker panel location.  I am not concerned at the moment about a ham station but, instead, a rather nicely equipped service bench with some rather pricey (at least for me) test equipment.  The breaker panel is about 20 feet from the proposed bench location and the service entrance/meter about 25 feet away.
My thought is that the first step would be to circle the house perimeter with 8' ground rods about 16' apart and tied together with copper strap cad welded to the ground rods.  Of course, those rods would be bonded to the breaker panel and to the meter base.  My question is (and I have not seen this discussed) about how far away from the base of the foundation should that circle be spaced?  Would I place that ring of ground rods as close to the foundation as possible or is that critical?  Problem is that there is an elevated deck at the rear of the house which would have to be partially dismantled in order to put the ground rods next to the foundation at that location.  Worst part is that that deck is located just outside where my service bench would be.
I hope my description makes sense; I've tried to explain it as clearly as I could.  In any case, any comments and/or advice would be much appreciated.
Tom
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