[TowerTalk] Ground resistance

Thu Jun 8 15:11:46 EDT 2006

Hello Gary,
Thanks for the response and information. Like you, I have been reading 
various mail regarding lightning protection and effective grounding....I 
came to the conclusion that the answer was "as long as a piece of string" 
and that is why I decided to "bite the bullet" and call in the professionals 
to resolve my problem. Prior to their visit, I went along to their offices 
and was given a very interesting mini lecture on providing lightning 
protection, for tall structures, church steeples etc. and half buried 
structures, such as explosives magazines (stores) from lightning strikes. 
The specified ground resistance for such an installation is just 1 ohm, or 
less.......It was also pointed out, that there appears to be an increasing 
incidence of lightning strikes in the UK, with at least three in my area, in 
the past five years or so, each one causing  structural damage to property. 
After a discussion, it was agreed that the company would send a team of 
people to look at my location, tower/garden, and carry out some measurements 
for me......My location, Long Ditton, in Surrey, is about 50 feet above sea 
level, and about a quarter of a mile south of the river Thames, at Hampton 
Court. This is about 15 miles up river from Central London, and is at the 
London end of the Thames Valley. My house is located about half way down a 
small hill, the ground sloping to the river, and with a ground water table 
of about 12 ft below the surface. The ground is made up of layers, fine sand 
and clay, with the ground water filtering between and through the layers to 
end up in the river. It was when the lightning protection people got down 
into the ground water region, that the measured ground resistance took a 
huge dive. So, I am very pleased with the end result. My tower is a three 
section, 60ft steel lattice, by Strumech, and because it is made up of 
moveable sections, the lightning protection professionals used a length of 
stranded flexible copper, to make the connection between the tower head 
unit, and the newly installed ground rods and interconnecting strap. This 
flexible copper is about five eighths of an inch in diameter. The copper 
rods, straps etc. together with the various clamps used, are all designed to 
carry the huge current of a lightning strike, the clamps are bronze 
castings, and the clamping bolts are half an inch in diameter! I also use 
the new ground system as my "clean earth" connection for my shack. The base 
of the tower is not connected to the ground system, and the tower lightning 
protection system is not connected to the domestic AC supply 
ground.........But, thats another story, but I have chosen to isolate myself 
from the domestic AC supply, and in so doing,  I have reduced receiver noise 
levels on 80 metres from an average of S7, back down to those of some 40 
years ago, when they were around S1, or 2.... I wish you success with your 
grounding, and would recommend that you talk with a professional, lightning 
protection company, get their advice, and perhaps assistance...your 
insurance company will be impressed!!   best of luck, John G3JVC.

----- Original Message ----- 
From: "Stone, Gary R." <Gary.Stone at va.gov>
To: <g3jvc at jcleeve.idps.co.uk>; <TowerTalk at contesting.com>
Sent: Thursday, June 08, 2006 3:15 PM
Subject: RE: [TowerTalk] Ground resistance

TT and John,

Thanks John - that is very interesting.  I have 9 (nine) 8 foot ground
rods around the base of the tower.  I do NOT have them connected with a
large outer circle but may do that.  I do have them all connected to the
tower and groups of 3 are connected to each other with bare # 4 cooper
wire - solid:  1 ground rod (8 feet) at each leg of the tower with 2
more connected to each of those for a total of 9 ground rods.  I then
have a large wire going from one of those ground rods about 35 feet over
to the house electrical entrance and connect to the ground rod there -
and during the length of that 35 feet I have 3 (three) 6 foot ground
rods spaced evenly.

So, a total of 13 ground rods connected with #4 bare cooper.  I hope
that provides some protection.  In addiction I have an I.C.E. rotator
cable 8 conductor arrestor mounted at the base of the tower.  And I use
an Array Solutions RatPak remote switch which has MOV protection.

I have just ordered a coax surge protector (one for HF and one for
VHF/UHF) that I will probably install near the shack on the one hf line
coming from the rat pak and the one VHF/UHF coax coming into the shack.
I ordered the I.C.E. coax protectors designed to mount directly to a
ground rod and I have another 6 foot ground rod for that purpose I plan
to actually make a hole in the floor to the side of my shack and put it
into the ground there with the coax protectors mounted directly on the
ground rod.

So, am I ready for a strike?  I don't know - and I would like to get the
ground resistance measured but don't know of anyone in rural north Texas
that would do that reasonably.   Other than the ground resistance I am
thinking about putting in two circles with #4 wire connected the first 3
ground rods from the tower and then the 6 ground rods with a larger
circle.  The 8 foot ground rods are spaced 16 feet apart.  Ideas
appreciated?

Gary, N5PHT
-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of John E.Cleeve
Sent: Thursday, June 08, 2006 8:27 AM
To: TowerTalk at contesting.com
Subject: [TowerTalk] Ground resistance

----- Original Message ----- 
From: John E. Cleeve <g3jvc at jcleeve.idps.co.uk>
To: 'Stone, Gary R . ' <Gary.Stone at va.gov>
Sent: Thu Jun 8 14:34
Subject: Fwd: Re: [TowerTalk] Ground resistance

Hello Gary,
I asked the same question. The answer was that the measurement device
cost around 1400 pounds sterling, so I decided to ask a company that
specialised in installing lightning protection for church towerers
etc. They came to my house and measured the ground resistance by means
of a bridge type meter, putting out test leads around the site etc.
They came up with a reading of 19 ohms, between my own "earth rod",
and the site boundarys, and said that figure could be improved on. I
agreed that they should continue the work, and they proceeded to drive
three copper ground rods into the soil, using a Kango hammer, at the
corners of an 8ft triangle, where my tower base is in the centre of
the triangle. They measured the ground resistance as each length of
copper went down, and once the three ground rods were driven to a
depth of 4 metres, the measured ground resistance was just 2.1 ohms, I
saw the meter reading, and I have a certificate to prove it. The
surface ends of the copper rods were then tied together, using 1 inch
wide, thick copper strap, and the top of my crank up tower, connected
to this ground system by means of a flexible copper conductor of an
equal cross section. The entire job took about 1 hour, and the cost,
about one third the price of the test equipment required to do the
measurement......I hope this may be of some interest to you and the
group....sincerely,
John. G3JVC.

On Wed Jun 7 19:09 , 'Stone, Gary R.' Gary.Stone at va.gov> sent:

>Greetings,
>
>
>
>I imagine I have missed the obvious but my question is how do you
>measure ground resistance? Does it take a special meter (I suspect it
>does). I am writing this in reference to ground rods and grounding of
>towers.
>
>
>
>Thanks,
>
>
>
>Gary, N5PHT
>

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