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eHam Forums => Antennas and Towers and more => Topic started by: N1RND on November 13, 2012, 04:50:02 PM



Title: Station ground question.
Post by: N1RND on November 13, 2012, 04:50:02 PM
Before I get into any detail,

Who DOES NOT have their station/antenna ground and service entrance ground bonded together?


Title: RE: Station ground question.
Post by: LA1BRA on November 13, 2012, 06:32:41 PM
You ask a real loaded question, be perpared for an onslaught of pro's and con's.

My station in Texas is grounded at the top of the tower, at the base of the tower and at the entrance to the metal building, all of this grounding is bonded to a ring of 6awg copper around the building, the common point is the ground round where my utility drop is....

On some web sites, I have seen where Ham's have stated they have no ground and are quite happy without....

However, I don't suppose they have ever been hit by a direct strike.

I was once, my ground setup was marginal at best, however all I lost was a fiberglass antenna on top of the tower.

Now, at my location where I am today in Mexico, the only ground I have is the ground lug on on 120 volt wall outlet.....

My radio room is on the second floor of this rent house......

I am not experiencing any issues with not having a permanent station ground....however I wish I had one, just to be on the safe side, I un-plug everything when I am not on the air....

I saw a video in a high voltage safety school a few weeks ago, they had a video of a test with about 50kv into a ground rod...wow is all I can say, the ground round literally jumped out of the ground.

now imagine that hitting your antenna....the whole idea of a station ground is safety, you want the strike to return to earth by the path of least resistance, if your path is your home and or your radio equipment, be prepared to argue with you insurance company on the replacement. If you follow good engineering practice, you can shunt the strike to ground and minimize the collateral damage..Nothing short of a full blown commercial type grounding scheme will keep the strike out of your equipment. There are tons of info out there, do find the Motorola handbook on there recommendation they follow for cell tower sites.

Ground your station is the bottom line.

regards
tom
XE3 / KB5VWZ   aka LA1BRA  old Mexico today...


Title: RE: Station ground question.
Post by: N1RND on November 14, 2012, 06:14:23 AM
Hi Tom
Thanks  for all  that  info.  I agree also that  you  cannot  have too much ground.  I am aware that everything requiring a ground in a dwelling should  be at the same  potential.
My problem  is the service and station grounds are at opposite ends of the house.
My station ground consists of 6 ga copper from the roof mounted vertical to a ground rod, an AlphaDelta transitrap for the coax on another ground rod, short heavy braid from equipment to another rod, and then all rods bonded together with 6 GA.
As of now this is the most I can do.  Everything gets unplugged when I'm not  on the air


Title: RE: Station ground question.
Post by: W2WDX on November 14, 2012, 02:34:26 PM
Yeah ... real loaded question.

Regarding lightning protection? No such thing. It's gonna go where it must regardless. It can only be mitigated (or even problematically increased) by grounding. I had a huge (and I mean huge) knife switched I used for disconnecting my ladder-line from my station which grounded the ladder-line. I got hit by lightning and it took out the switch, the 1" copper sheet strap going to the  two ground rods 2' below it, and still it jumped across the switch and zorched the tuner. The ladder line itself turned to vapor. I last used gold binding posts and spades (corrosion resistance) on my ladder-line outside and disconnected the ladder line and tossed it away from the house into the yard when not using the station. Grounding for lightning protection? No such thing.

The real issue is a matter of the two most relevant ground types for our operational uses. DC ground and RF ground. The latter being the most important for performance, the former being more important for noise and AC line protection.

I always use a ground designed for RF, no matter what. Mainly to improve antenna performance and radiation efficiency. I also use a DC shunt of some type for static noise abatement.

There is a school of thought that says "single point grounding". But this thinking is derived from the "star type" or similar grounding schemes used in the audio world. In those circumstances a single point is best, however in the amateur application you have a need for low impedance grounding necessary for a good RF ground as well as protective grounding. Sometimes one may not be compatible to the other. Or better put, protection grounding while good for safety may not be a good path for RF and be problematic for station performance.

One should not go binding grounds willy-nilly. There should be a reason. You should measure whether there is a potential across the grounds. If there isn't one, binding may not be needed and in some cases doing so can actually create problems with RF. Sometimes ground is not always ground. You can take one ground rod, clip a test lead to it and take another ground rod and clip another lead to it and actually measure a potential difference (voltage) between the two. So by not binding the two together you may actually have a voltage floating between whatever is connected to one and whatever is connected to the other. You will have all sorts of currents flowing around in this situation. However, in some cases where you have bonded, having all this wire going all over the place may actually create impedance issues that make for a poor RF ground and actually causes the various RFI issues ground is supposed to mitigate. The point is, the situation dictates the methodology.

As far as binding, I do this if there is a substantial potential between my AC safety ground and my RF ground. But also sometimes this can lead to station ground loop issues, especially in audio circuits or conversely it can help eliminate them. I use a ground bar at the station and ground all of the hardware, mainly for AC protection, which is bound to the earth ground of my AC. I do sometimes lift the ground on the edison jacks going into the outlets if I have a ground loop issue, but ONLY if the chassis is grounded to the bar. I also had a separate grounding system for my antennas, designed with RF in mind. The two were not bonded, but there was little or no potential between the two ground points since I had very high ground conductivity in that location. There was no reason to bond them, so I could use separate grounding designs optimized for each ones application - safety vs. RF.

So what I say is ... it depends on the situation.

John, W2WDX


Title: RE: Station ground question.
Post by: LA9XSA on November 14, 2012, 03:33:40 PM
When talking about lightning protection, it's a lot easier to protect coax than ladder line. If you have a ladder line fed antenna, consider putting the balanced tuner outside and only bringing coax (with ground kits and protectors) inside.
My problem  is the service and station grounds are at opposite ends of the house.
While the ideal situation is to have a common entry point, if you bind the grounds together with an outdoor buried ground wire it can be close to what you get with a common entry point.

The electrical code usually demands that all grounds are bonded together, so it might be illegal or against insurance terms to not do it. What you have to decide is how and where you bond RF ground with safety ground and lightning ground - when using unbalanced antennas the exact "tuning" of the ground system matters. I think the good way to do this would be to attend to safety and lightning ground first, and then tune the RF ground by adding radials, counterpoises and "artificial ground". For example, a tower may have three or four buried radials made of different lengths of heavy copper wire for lightning protection; on top of the soil there might be a large number of thin RF radials. Not only would putting on the lightning radials last mean digging up the RF radials - they could be detuned.

If you look at the Motorola grounding guideline, they indeed recommend a common entry point, but to bond the entry points together through the outdoor ground ring if there are more of them.


Title: RE: Station ground question.
Post by: WD8KNI on November 14, 2012, 05:30:06 PM
Ladder line is very easy to protect.  Two spark plugs to create a spark gap and a tapped copper plate and you are in business 4/6 bucks if you buy new ones.

Not so hard, coax costs more and you can not look at the protectors to see if they are still good... Fred
 


Title: RE: Station ground question.
Post by: W2WDX on November 14, 2012, 07:57:23 PM
Like I said. Grounding for lightning protection? No such thing. The lightning will always take the path of least resistance. If that means taking a route through your gear instead of an air gap on a spark plug, if that has the least resistance that's were it will go first. And most likely both paths will do. A spark gap is great for high level static discharge, although a shunt inductor (choke) to ground on each leg is a more effective static drain.

But ground for lightning protection? Do not depend on it.

The NEC does state that any antenna masting on a building be bonded directly to the electrical service ground to prevent omnipotential ground situations that can cause shock injury or fire. However, do not confuse this with RF grounding, which can be a separate thing. The NEC only concerns itself within the scope of safety in AC and ground potential and not the function of RF. Furthermore, Section 810.21(J) clarifies that the bonding requirement applies only to electrodes at the same building or structure. This means a free standing tower, a separate structure, is not required to be bonded to the house ground. This also includes a dipole strung between two trees for instance. It is also a separate structure. However any lead-in wires to the house, should they happen to be grounded in some way before entering the house (a good idea) that grounding should be bonded to the house AC ground. So if you use a gas discharge or a DC shunt system on your feedline its ground should bonded to you house AC ground for NEC compliance. An air gap discharge device (spark-plug or spark gap), which is not electrically connected to the feedline in any way does not need this bonding for NEC compliance. In fact, not only is it not a good way to bleed of static (if it makes a spark static has already built up and not been bled prior, and its noisy), it is also not NEC compliant with regard to balanced feeders.

If you want to be really compliant, you must use a DC static drain on any open wire feeder, like twin-lead, window-line and ladder-line. That means a spark gap is not to code. You must use some type of shunt effectively grounding the lead-in wire to ground at DC. The only exceptions to this are using coax where the shield is grounded, or if the antenna is directly grounded. So a dipole with ladder-line must have high impedance inductors shunting to ground on each leg of the lead-in wires to truly be compliant, according to Section 810.57 of the NEC.

But again, if you have a ground at your tower and one in your building that are at different potentials you should bond them just as good practice, and if the potential is the same it is not required by NEC.

An RF ground can be separate, like the radial system on your ground mounted vertical. Basically signal grounds for electronic circuits do not have to be bonded to the AC grounds nor required by the NEC. Electronic signal grounds are sometimes not related to or even referenced by AC ground and may be at an inherently different state. A balanced antenna system is a good example of this. A loudspeaker is another. Its also one of the reason digital grounds and analog grounds are isolated from each other in some circuits.

BTW, if you are concerned about NEC then you cannot also use anything smaller gauge than 14ga copper-clad steel wire for things like HF dipoles (12ga if over 150' span) and 14ga CC steel for ladder-line or window-line. That's in the code too.

So you can be code totally compliant, but that shouldn't stop you from thinking beyond the code. After all, it only deals with safety at DC or ULF and does not take into the account the affects of ground on circuit function and efficiency in RF.

John


Title: RE: Station ground question.
Post by: W2WDX on November 14, 2012, 09:32:48 PM
One other point. True lightning protection is physically disconnecting your lead-in wires and moving them some distance from your shack. That's it.

A Polyphaser discharge unit (or any other similar unit) will turn into a molten mass of metal within seconds of a direct hit. Your lead-in wires, whether coax or ladder-line, will turn to vapor, that vapor then providing a path of charged particles to ground BTW for the lightning. So do not depend on devices to protect from an arc that can travel hundreds or thousands of feet across air in the first place. The potential is so astronomically high, no device will impede, deflect or stop it. (Well in all honesty, there are some but no amateur station has them nor could we afford them).

Gas discharge units are good (for a limited time BTW) for discharging near hit impulses. They are technically EMP protection, not lightning protection. However they are good for this application. Spark gaps for ladder-line should be thought of in the same way. Good impulse protection. Neither bleeds off static to ground directly though, except for the grounded shield on the coax. (Except for the I.C.E. brand devices, which do have a DC shunt in addition to a gas discharge tube.) And on balanced lines spark gaps do nothing but make noise in your receiver, especially once the static builds up enough to discharge across the gap. SNAP!!! POP!!!

I use large chokes on my ladder-line to bleed of all static and impulses on my ladder-line. If you do use them they have to be able to choke below your lowest operating frequency, but will still make a DC path to ground. I was amazed how much noise that I thought was atmospheric or man-made noise was actually static from things like wind, rain and snow and distant lightning EMP, which completely disappeared in my receiver once I began using DC shunts to ground on my ladder-line.

However, always physically remove your feed-lines a good distance from the house or shack. That's the only truly effective lightning protection from a direct hit.

I remember one circumstance of a friend who had his feed-line tied to his house at a corner, then down the side to his ground devices then into the house. He had a direct hit on his dipole which then ran down the feed-line, jumped to his aluminium siding on the corner where he had fastened the feed-line and burned a hole straight down to his foundation through his siding. It also arced the two feet from his disconnected feed-line, up to the connectors on his house and through his station inside, running across the chassis and through his station grounding bar and the AC ground. The point is get the feed-line off the house so you can remove it and move it away into the yard. A few million volts doesn't see wire insulation, ignores tiny electronic circuits like gas discharge devices and just roars toward ground which ever way it chooses.

John


Title: RE: Station ground question.
Post by: LA9XSA on November 15, 2012, 03:12:31 AM
For commercial sites that can be operated safely during a thunderstorm, we're basically talking installing the radios themselves in a special equipment room/building with heavy duty protection, but that is also electrically separate from the shelter that the operators sit in, with fiber optic cable being the only connection, right? Even if the strike turns out to be too much for the equipment room to handle, none of the strike energy makes it into the shelter. Such an installation would be out of reach for most hams.

If you're happy to sacrifice your TS-2000, I guess you could install it in a box at the bottom of the tower with its own battery, and use your HT and skycommand to operate it remotely.

For N1RND though: Bury a ground ring of heavy copper wire around your house, bonded to the ground rods on both sides. You already said you unplug when not on the air - but I'd consider grounding the coax outdoors too. If you leave the coax "floating" and a nearby strike induces current in the vertical, it could jump to the electrical system through the wall or something?


Title: RE: Station ground question.
Post by: K1CJS on November 15, 2012, 04:05:27 AM
One of the big differences between commercial sites and most ham radio shack installations is this--at commercial sites, top of the line equipment and cabling is used.  Not so at most ham stations.  Then those hams wonder why their stations are hard hit by any lightning strike nearby....

To the first question--Anybody (in the US, anyway) who does not care what the NEC states about grounding.  People like that ought not to have any sort of ham radio station--or ANY radio receiver with an external (outside the building) antenna.


Title: RE: Station ground question.
Post by: M6GOM on November 15, 2012, 05:21:57 AM
Before I get into any detail,

Who DOES NOT have their station/antenna ground and service entrance ground bonded together?

Me. Living in the UK there is absolutely no point whatsoever.


Title: RE: Station ground question.
Post by: LA9XSA on November 15, 2012, 08:50:51 AM
The Norwegian electrical standard - NEK 400 - requires all protective ground leads, metallic pipes (even non-metallic drain pipes in some cases), and coax shields to be connected to a common ground terminal.

What does BS 7430 and EN 62305 say?


Title: RE: Station ground question.
Post by: KH6AQ on November 15, 2012, 10:51:48 AM
Hi Tom
Thanks  for all  that  info.  I agree also that  you  cannot  have too much ground.  I am aware that everything requiring a ground in a dwelling should  be at the same  potential.
My problem  is the service and station grounds are at opposite ends of the house.
My station ground consists of 6 ga copper from the roof mounted vertical to a ground rod, an AlphaDelta transitrap for the coax on another ground rod, short heavy braid from equipment to another rod, and then all rods bonded together with 6 GA.
As of now this is the most I can do.  Everything gets unplugged when I'm not  on the air

You have the worse situation one can have; the AC service ground at one end of the building and the station at the other end.

Let's take the example of a 30 kA lightning strike. You have three ground rods at the station and one at the AC service. Assuming zero impedance between grounds the current will divide with 1/4 of the 30 kA taking the path to the AC service ground. That is 7500 amps through the house AC wiring. The AC wiring (three #12 wires for GND, Line, and Neutral is about equal to a #6 wire. Add a #6 wire from the station ground to the AC service ground and the current divides equally between the house wiring and the #6 wire. Now the current is 3750 amps through the house. Note that 2/3 of this must find its way from the station ground to the Line and Neutral wires.

But you don't have the added wire around the building and that is one place where things can be improved. And additional station ground rods spaced twice their length will help. But, there is the situation where the power pole can take a lighting strike. From that direction most of the current will take the path through the house wiring to the station ground rather than the AC service ground.

My station is 10' from the AC service ground. I route the coax from the antenna ground to the AC service ground. Then it's routed to the station. 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.

What is left is differential voltage induced in the coax by lightning current X the coax shield transfer impedance. At lighting frequencies the transfer impedance is about 0.01 per meter. I have 20 meter of coax giving a total transfer impedance of 0.2 ohms. A 30 kA strike, giving my antenna grounding will send about  5 kA along the coax. That will induce 5 kA X 0.2 ohms = 1 kV into the coax. That is in addition to the lightning voltage directly into the antenna. I think a direct strike will not burn down my house but the ham equipment will be destroyed. If I thought I'd ever have a lightning strike I would add Polyphasers.


Title: RE: Station ground question.
Post by: LA9XSA on November 15, 2012, 04:24:35 PM
WX7G, I still think your lightning calculations look suspiciously simplistic. They do not take into account the cone of influence of a ground rod, physical distance between rods, the area of influence around the buried ground wire itself, bends in the wire, the local ground resistance, etc.

It's easy for me to understand the rule of thumb that the ground conductor should be at least the same gauge as the sum of the other conductors (they limit the incoming current by their limited current carrying capacity, though there is the added complication of skin effect and and their continued conductivity after transition to vapor form though). But I still can't understand how you figure that a cluster of three ground rods will receive exactly 3/4 of the energy while the fourth ground rod at the other end of the house gets 1/4 of the energy no matter what the impedance between them is.

Are you still claiming that you could hang the bonding conductor on the wall and it would be as good as burying it? (I apologize if I misunderstood last time.)

Have you reconsidered the possibility for arching through walls? (As in, I think it's not a good idea to hang the coax on the exterior wall when you route it to the AC entry point. I think the coax should approach the house at a right angle to prevent flashing through the wall or inducing current in the wiring inside the house, while you said it was fine to hang the coax on the exterior wall all along the house if you want?)


Title: RE: Station ground question.
Post by: KH6AQ on November 15, 2012, 05:09:12 PM
First we must understand the simplified case before developing a more complex model. Then SPICE can be used.

When modeling lightning in SPICE I build the ground as a grid of resistors. Wires are represented as inductors with series resistance. The lightning is modeled as a current source having a defined rise/fall time and amplitude. SPICE allows us to probe points to see potential differences.

For now let's do a paper calculation to see what happens when connecting the station ground rods and the AC service ground together.

Let's say the station ground is not connected to the AC service ground. Ignore the earth resistance between the station and AC ground. A lighting strike of 30 kA occurs and has a rise time of 20 kA/us. The three ground rods at the station present 33 ohms. In a little over 1 us the ground rods are at a potential of 1 MV. We now connect a 10 meter wire between the station and AC ground. The inductance of this wire is 5 uH.

di/dt = V/L = 1MV/5us = 200kA/us.

From my previous post the AC service current was 7.5 kA. In 25 ns the current would be achieved. The 10 meter wire does allow the current divide as predicted by the simplified method.

Another check is to look at this in the frequency domain. The 1 us rise time is equivalent to 350 kHz. What is the impedance of the 5 uH wire at 350 kHz? It is 11 ohms. The 100 ohm impedance of the AC service ground dominates the current through this path and so again the simplified method yields a good answer. If the wire connecting the ground rods were long enough it would dominate and there would not be (at least not during the high di/dt portion of the lightning) the 3/1 division of current.

An exact paper model uses differential equations. I prefer to put it in SPICE and let it do the work.

Conclusion: A simple model yields numbers good enough to design a lightning ground system. But to do a design we need a number to design to. All of this hinges on how much current we will allow though the house. Once that is decided the number of ground rods and their placement is simple. The potential difference between ground rods can be calculated to determine if there could be arcing from a rod/wire outside the house to a wire inside the house.









Title: RE: Station ground question.
Post by: W2WDX 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



Title: RE: Station ground question.
Post by: KH6AQ 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




Title: RE: Station ground question.
Post by: N4NYY 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. 


Title: RE: Station ground question.
Post by: W2WDX 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


Title: RE: Station ground question.
Post by: KH6AQ 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


Title: RE: Station ground question.
Post by: W2WDX 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.


Title: RE: Station ground question.
Post by: W5WSS 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.


Title: RE: Station ground question.
Post by: N1RND 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


Title: RE: Station ground question.
Post by: KH6AQ 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.


Title: RE: Station ground question.
Post by: N1RND 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?


Title: RE: Station ground question.
Post by: N1RND 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.


Title: RE: Station ground question.
Post by: N1RND on November 17, 2012, 01:04:42 PM
and, http://www.transorbelectrical.com/pq/technical/NECCompliantGndRodR8.pdf


Title: RE: Station ground question.
Post by: WD4ELG 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.


Title: RE: Station ground question.
Post by: N1RND 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.


Title: RE: Station ground question.
Post by: WB6DGN 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


Title: RE: Station ground question.
Post by: K1CJS on November 18, 2012, 07:50:26 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.

The cable should be run outside the house, but if it can't be, the inside route can be used.  The main reason for tying the two ground points together is to equalize the potential between the two ground points.  In other words, the bonding together of the two is to prevent anyone who is in your shack from becoming that interconnection--and getting killed in the process.


Title: RE: Station ground question.
Post by: LA9XSA on November 18, 2012, 03:16:46 PM
Thanks for the links guys - I have some reading to do. I think I might make some CAD drawings of the various home station grounding scenarios to have something more concrete to run calculations on.
early streamer emission (ESE)
I did some literature searching about ESE couple of months ago, and as far as I can find, there's no evidence that ESE actually can prevent lightning strikes from happening - as is often claimed by ESE proponents - or that they work better than regular air electrodes like points or balls. The only possible exception might be ground-to-cloud strikes from towers more than 300 feet high, for which there is simply insufficient evidence to show anything conclusively. The strike is going to come somewhere in the area - but with a lightning protection system you can try to help it strike where you want it to go.
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?  
It should be outside the drip line of your roof - you want the ground ring it in wet ground. Or something like that. Here in Norway NEK 400 specifies 0.5 m away from the foundation.


Title: RE: Station ground question.
Post by: W2RWJ on November 18, 2012, 04:31:44 PM
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?

Tom,
The Motorola R56 Site Standard referencess in Chapter 4 Part 4.4.1.6 the following:

1)   Ground rings shall be installed in direct contact with the earth at a depth of 30 inches below grade, or below the frost line, whichever is deeper (ANSI T1.334-2002, section 5.3.1 and NFPA 70-2005, Article 250.53).

2)   Building ground rings shall be installed at least 3 feet from the building foundation and should be installed beyond the drip line of the roof (MIL-HDBK-419A and MIL-STD-188-124B).

3) Tower ground rings shall be installed at least 2 feet from the tower foundation (ANSI T1.334-2002, section 5.3.1)

Martin


Title: RE: Station ground question.
Post by: K5LXP on November 19, 2012, 12:45:49 PM
I have the AplhaDelta polyphaser discharge devices (which won't do a thing for a direct hit, I get that point).

A popular misconception is that surge arrestors somehow have to divert, direct or dissipate a lightning surge.  Thinking like that, it's not surprising many do not believe their survivability.  The majority of the surge energy is on, and through the coax *shield* and antenna support structure to ground, not "through" the arrestor to ground.  The function of the arrestor is to clamp or isolate any surge coupled to the center conductor of the feedline, which is small in comparison. 


Mark K5LXP
Albuquerque, NM


Title: RE: Station ground question.
Post by: LA9XSA on November 19, 2012, 01:25:12 PM
Yeah, more exactly the surge arrestor only has to deal with the voltage difference between the center and shield that remains when the strike comes to the entry panel. I suspect there's not much point in over-designing Polyphaser EMP arrestors to handle higher voltages than they already do since at one point the differential will spark through the coax dielectric, or jump acros the feed point anyway. Or turn it into a fluid.

A long run of (preferably buried) coax will work to limit strike energy all on its own, and is hopefully augmented by ground kits (connection from shield to the grounding system) along the way, so the arrestor only has to deal with any differential that remains.

On the flip side, if the lowest impedance path from the antenna to ground goes through the arrestor and into the house, it doesn't matter if you had the world's best arrestor there since the most of the strike will enter the house anyway - through the shield.

Now theoretically, even if you have the strike going through your station, if you have a ground system that ties everything together with low enough impedance, everything should rise in potential at approximately the same time, but I sure don't want to be there to test it out if it happens.  ;)

PS: I'm an engineer, but not an electrical engineer, so take the above with some salt.


Title: RE: Station ground question.
Post by: WB6DGN on November 19, 2012, 07:16:09 PM
Thanks Martin,
I found a place to download the R-56 manual; now I've got some heavy reading to do.
The spacing from the building is a mixed blessing for me as that substantially increases the perimeter (and number) of the rods but, thinking about it, it should have been obvious to me.  I can see that this is going to be a lot more work that I had thought but I guess I can take it a little at a time.  I do want to keep my GPS frequency standard powered 24/7 so it needs to be done.
Again, thanks for the reply and reminding me of that very useful reference.
Tom


Title: RE: Station ground question.
Post by: N1RND on November 23, 2012, 06:46:43 PM
UPDATE!
I ended up running heavy gauge stranded wire( from the outside station/antenna grounds) to the water main connection which has the same run going to the load center panel.  I then added a ground rod to the already existing service entrance ground rod.

Here is a link to w8ji's very good website on station grounding.  Now my set up is pretty much close to the "best buy far" part of his site.

  http://www.w8ji.com/house_ground_layouts.htm

It was alot of work considering the rocky soil I have and the outdated logistical layout off my house.