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Author Topic: lightning protection  (Read 419 times)
VE3BWA
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Posts: 31




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« on: June 29, 2004, 11:17:45 PM »

Hi folks,

I'm getting ready to install a Force 12 C3SS beam on my roof, using a 4.5 foot Glen Martin base with a 5 foot mast, Yeasu rotor (total height is about 40 feet). I've got a lightning rod at the top of the mast with a ground wire that ties to a lug on the little tower, then continues to an 8 foot ground rod in the earth. It makes sense to me that I also want lightning protection for the rotor cable and the coax feed line. How do I do this? Please be specific - I'm new at this

Thanks de Chuck VE3BWA  
 
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K6AER
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« Reply #1 on: June 30, 2004, 12:34:57 AM »

General Lightning Protection -

The DC and RF component must be addressed in setting up a lightning firewall suppression system. In commercial systems, the building has installed a ground halo around the perimeter with an internal ground halo and a suppression demarcation point for all outside wiring and coax entries. Homes are built to a different standard and we must adapt where possible. The often misunderstood NEC code for grounding is not applicable when you are protecting your HAM radio equipment from external surge potential. Grounding your equipment to the AC panel ground will not protect your equipment from high current surges coupled on the antenna lines. This will only prevent AC ground loops should you lose your primary AC return ground. Because lightning has a great amount of RF contained in the strike, any long ground leads will not ground off RF energy and at may best delay grounding of DC spikes due to lead inductance. The best way to prevent RF and DC surges from entering the Shack is at the cable entrance or at the base of the tower. Each of these points can be considered a surge firewall demarcation point. This ground point must be as short as possible. Even a nearby strike can inductively or capacitively couple thousands of volts into your antenna coax system.

Typical Installation-

Let’s follow the proper grounding procedures from the antenna down to the radio. The antenna lines should be grounded at the top of the tower when possible. Should your tower be a crank-up, you will only be able to ground at the tower base. A fixed, guyed tower represents the greatest conductor to ground. Running a ground wire up to the tower top, although popular,  is a waist of time unless the conductor is larger than the tower. For guyed towers, all guy points need to have at least two ground rods.  Always place ground rods into the soil around the tower and not through the concrete base. The concrete of an ungrounded tower base will shatter when hit by lightning. The tower should have at least three ground rods spaced about five feet apart out from the tower with connections to each leg of the tower base.

Use copper or brass when connecting to the tower base. Other metals can cause corrosion on galvanized metal and can weaken the tower base. Three would be a minimum number of rods in good conductive soil for a ground halo. In poor soil such as in the mountains and in the western U.S., you might need up to fifteen 8-foot ground rods all interconnected to provide a good coupling to earth. Use stranded copper wire of at least 2 gage and connect all ground rods with brass or copper ground clamps. All connections should have a coat of Ox-Gard paste to maintain the connection integrity.

The coax cables need to have their outer conductors grounded at the tower base and attached to the tower ground halo system. At this point surge protectors need to be installed in series with the coax lead before routing antenna feeds into the home and to the radio equipment. It is best, when ever possible, to protect the surge protectors from weather by enclosing them in a NEMA or weather resistance box. If this is not possible use a moisture protector barrier tape over the connections and surge protectors.

The surge protection box would be the best location for all other surge protectors such as those needed for Rotors and remote control line. The surge protectors should be attached to a mounting strip with copper conductivity (flat ribbon or cable) to the tower base ground halo system.

Inside the radio room all coaxes should be attached to a grounded routing switch with a common grounding position for all entries. This grounding location must be attached to the operating station grounding buss bar. All coax and radio connections should be grounded at this point. A separate ground halo should be used if the distance to the tower halo or outside antenna/building ground halo is more than ten feet away. Remember we are also grounding RF energy as well as DC potential and long ground runs are self defeating due to series inductance. A 33-foot ground run will present a high impedance connection at 7 MHz during a lightning strike.

Other Potential Sources-

Many times radio amateurs will assume that a lightning strike came into the radio room via the antenna connections. This may not be the case. Often electronic damage is via the phone, cable and AC lines in search of a good ground. It is also imperative that surge protectors be mounted on all entry conductors. A typical home AC mains will only have one ground rod. Though this may satisfy the NEC and local building codes is not adequate for lightning surge grounding. Several ground rods must be added for AC lightning protection. Your grounding solution and protection will be only as good as the weakest link.

If you have othe rquestions feel free to contact me at QRZ.com.

73's,

Mike - K6AER
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W8JI
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« Reply #2 on: June 30, 2004, 08:14:33 AM »

Chuck,

I'd look at the polyphasor site for grounding tips.

I'm in the second to the highest area for lightning in the USA, and have a 318 ft tower as well as shorter towers along with many acres of receiving antennas (about 30-40 receiving antennas most of which are over 700 feet long).

Everything stays connected all the time, and I take hits on the tower at least several times a year. I don't have a single polyphasor or other exotic suppressor in my system, and I never have problems inside the buildings. Even my modems live through strikes.

The reason I never lose anything is because I use single point grounding and ground the shields of all cables by using bulkhead feedthroughs. The power, telco, TV antenna, and my feedlines and control wires all are grounded to one common point.

Suppressors help a little, but 99% of the cure is making sure EVERYTHING entering the house is grounded together with a very low impedance connection. As a matter of fact, the national electrical code down here requires power, telco, and everything else to share ONE ground.

By all means disconnect if you can and use lightning suppressors, but ALWAYS be sure everything ground to the power main ground with a very low impedance connection!!!! That common ground is 99% of what you can do to save things inside the house.

73 Tom
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W9OY
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« Reply #3 on: June 30, 2004, 09:06:11 AM »

The discussion is very interesting but it does not address this man's specific question regarding how to ground a roof top antenna structure.  What are the constraints specific to this kind of structure?  You can't have 3 ten foot ground rods connected by 5 foot of #2 from the tower legs when the leg of the tower is 25 feet in the air in the middle of the roof.

So what is the experience regarding this kind of installation?

By the wayt I thought "Halo" was what those jokers on 75 say into their mics when they are tuning up!!

73

W9OY
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KB9CRY
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« Reply #4 on: June 30, 2004, 10:31:03 AM »

First make sure that you use a large, low resistance/impedance wire from your tower down to the ground.  I'd use solid(not stranded) #4 or larger or even better would be wide copper strap or #4 welding cable or larger.  Is that ground rod near the cable entrance to the house/shack?  If so then this will be your SPG, single point ground, to which you'll also connect the grounds from your coax and rotator cable lightning arrestors.  IMHO there are only two players, Polyphaser and ICE.  Each of their websites has ton's of info on how to do it, etc. (ICE via the Array Solutions website). Personally I use ICE but both are about the same.  Then you'll also want to run the same large wire from your shack equipment ground out to the SPG.  Finally run the same large wire from your electrical service ground rod around the house to this same SPG.  Now all your grounds are tied together and in a surge event all the voltage potential on all of various types of grounds will rise and fall together.  If they don't then the difference usually does so inside of your equipment and may make some smoke!  Don't forget to install surge arrestors (not surge strips from WalMart!) on your electrical and phone lines that connect to your equipment or computers.  I use ICE here also.  Some folks go the extra route and install a whole house electrical arrestor but personally I like mine right near the equipment.  Gd luck; the lightning rod at the top can be lost, if you properly ground the tower, static buildup will be constantly bled off and the strike will find another target.  Hope this helps.  Phil  KB9CRY
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K1CJS
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« Reply #5 on: July 01, 2004, 08:56:29 PM »

K6AER--

Could you repeat that in plain simple English?  I forgot how to read Technicalese!  ;-)
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VE3BWA
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« Reply #6 on: July 04, 2004, 06:02:40 PM »

Thanks to all the Elmers who responded - you folks are a dependable source of thoughtful experience I have learned to count on

KB9CRY - I checked the ICE product line and likely will go that way for rotor remote connector and coax arrestor for my feedline - the one additional question I have on the latter is: ICE products are rated for 1 KW, 8KW and 15KW - how do I decide which one makes sense for me?

Chuck Rachlis
VE3BWA
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