grounding 2 masts far from ground - scenario/questions

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AZhummer

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Going to go very in depth on my scenario just to explain :)

I'm about to setup my first scanner antenna "farm" at a home in Phoenix, AZ. Nothing crazy and its receive only for me. Just purchased two 10ft 16gauge masts and plan to put 2 antennas on each mast (2 log periodics with rotators, 1 omni discone, and a yagi.. I plan on putting the 2 masts in different areas on the roof - 40 foot apart on flat roof (adobe style).. I will mount the masts on the parapit wall at roof level (25 ft).. So antenna would be about 35-40ft off ground.. Ground elevation at my home is 2500ft and its desert landscaping around, no higher trees than my roof level. I have 100 ft distance to my chosen grounding frame/plate & grounding rod location from mast #1, and 60 ft from mast #2.. I plan on running #2 copper from the masts to the grounding rod..

My questions.. with one major point.. I plan on disconnecting all my radios and tossing the interior coax lines down to the outside of the house during any electrical storms.. My main concern is keeping the house safe from roof fire etc. onto the questions..

1.. is it ok to fasten/bond mast #1 to mast#2 with 2ga. copper, then mast #2 across the flat roof 60 more ft to the grounding rod? or do i need 2 guage copper from mast #1 to grounding rod, and a totally separate 2 guage copper from mast #2 to grounding rod? I guess a simpler way of putting it, for grounding the masts, can I daisy chain the copper run?

2.. I am debating between the 8ft copper clad rods found at major hardware stores and the 6ft solid brass rods at ICE: Industrial Facility Hardware
Rumor has it the 8fts copper clad rods will flake off in about 5 years from being underground while the brass holds strong.. But I've also read that the extra 2ft deeper is better in managing potential lightning strikes. Which way should I go for my setup?

3.. related to the above.. What if I get two rods and plant them twice their depth apart? Better? or waste of time & expense in my scenario?

4.. if two rods is suggested, is copper #2 sufficient to link them together?

5.. I plan on buying ICE coax surge suppressors for my LMR400 runs.. I will get a rotator cable suppressor for those lines.. but I'm debating between ICEs more amateur "mounting frame" shown here:
Chassis Enclosures
and ICEs more professional bulkhead frame shown here:
Industrial Facility Hardware

I like the first more only because it mounts DIRECTLY on top of the grounding rod and I've heard the shortest distance from arrestors to rod is best (what better than direct?) but... with the number of antennas and rotators I plan on installing ICE doesnt make a mounting frame big enough for up to 6 arrestors.. I guess I could could install 2 smaller frames, one on each ground rod if I bury 2 rods? or is that a big no no to have 2 grounding plates to 2 bonded ground rods? If I get a bulkhead frame, what gauge wire to link the rod to the frame? again #2 wire?

Thanks in advance!

-Mike
 

AK9R

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1. ... I guess a simpler way of putting it, for grounding the masts, can I daisy chain the copper run?
My gut feeling is that you can daisy chain, but don't break the ground wire at the second mast. In other words, run a continuous length of wire from the first mast to the second mast to your ground rod.

2. I am debating between the 8ft copper clad rods found at major hardware stores and the 6ft solid brass rods at ICE...
Copper clad steel ground rods have been an industry standard for years. I would think that if there was a legitimate problem with them, the NEC or NFPA codes would have addressed it by now.

But I've also read that the extra 2ft deeper is better in managing potential lightning strikes. Which way should I go for my setup?
In your area, I would think soil conductivity would drive your ground rod decision. Have you looked into this?

3. related to the above.. What if I get two rods and plant them twice their depth apart?
In my area, it is standard practice in new residential construction to drive two ground rods about 8-10 feet apart and bond them together and then bond them to the electrical service entrance.

By the way, you didn't mention this, but are you bonding your new ground rods to your existing electrical service ground rod(s)? I believe it's required by NEC that all ground rods connected to a structure be bonded together.
 

prcguy

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I suggest you purchase the lightning book from Polyphaser and read it several times, that will answer all your questions.

I won't tell you how to do the job but will mention how survivable lightning ground systems are usually built.

Every air terminal (lightning rod) or small antenna in your case would have a separate large conductor to a ground rod or cluster of three ground rods at a specific spacing. All ground conductors must be as straight as possible to the ground rod or ground ring (more on that later) with no bends or kinks. If you have to run the cable around something it must be a gentle sweeping bend.

All ground rods are bonded together and if the system covers a large area you end up encircling the antenna farm or house with a very large buried conductor or ground ring. Then the central building ground is bonded to the ground ring or in a smaller system to the cluster of bonded ground rods.

The goal is to have the antennas, building electrical and all equipment inside at the same potential during a lightning strike. After the ground system dissipates most of the strike the ground system may still be thousands of volts above the power companies neutral but everything is at the same potential in your house and damage is reduced.

If you ground your antennas separately and not to the building ground and the coax is connected to the equipment, everything in the house will probably get smoked in a direct hit from the huge difference in potential between grounds.

This is how I see major repeater sites and satellite broadcast centers built and our mountain top repeater sites survive direct hits year after year and I'm not aware of any damage.

Get the book.
prcguy
 

jackj

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I worked for a company that used microwave radios to carry long distance phone calls. Our dish antennas were on 150 to 300 foot tall towers. Our standard was to install a ground rod at all four corners of the hut and connect them together with #6 or #4 copper wire, cad-welded the rods. The top of the rod was buried below the frost line and the rods were 10 feet long. Each leg of the tower had a ground rod as well as each guy wire anchor. All of the ground rods were bonded together using copper wire cad-welded to the rods. All of the grounds were bonded together and entered the building at one point only. The AC ground along with the equipment racks were each bonded to the site ground entry point. The goal was to eliminate any current flow through the equipment during a lightning strike.

Remember that the current flow from a lightning strike will have a very fast rise time. Anything that introduces inductance into your ground system will result a very large voltage difference across that inductance during the current spike. Your goal is to eliminate damage to your equipment, not keep the lightning out of your equipment. If no current flows through your equipment then it doesn't matter how much voltage in on your equipment, there will be no damage.

There are several good books available on the subject. Go to your public library and check out one or two of them.
 

AZhummer

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thx for all the replies. books shnooks.. :( I want to have this up in a few days :-( What if I go with one mast instead (3 antennas on it).. Can I run #2 from the mast to the grounding frame/block/plate, and then run the 3 coax lines to the coax suppressors on that same plate? and just use one ground rod?


Interesting one of you said to connect the rods to electrical service panel.. yes NEC but I read a few others posts in history that said to AVOID connecting the ham/scanner antenna grounding rods to anything in the house grounding or you risk a direct hit taking out the "other stuff" in the house.. why so many mixed opinions?
 

prcguy

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Just the opposite is true. Follow the NEC and look over the Polyphaser book or Google some legitimate info on the subject from professionals.
prcguy

Interesting one of you said to connect the rods to electrical service panel.. yes NEC but I read a few others posts in history that said to AVOID connecting the ham/scanner antenna grounding rods to anything in the house grounding or you risk a direct hit taking out the "other stuff" in the house.. why so many mixed opinions?[/QUOTE]
 
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