[TowerTalk] Adding ground rods, effect on ground resistance..

[Alan Zack]

Question please,
I have three 8 ft ground rods at the base of my tower, connected to 
each tower leg, tied together by a nr 2 wire plus tied to my rebar 
cage in the concrete (the rods are outside the concrete base) per my 
city bldg code.  My coaxes pass through I.C.E. devices that are 
connected to the very bottom of the tower.  The coax runs underground 
through a PCV tube to the house.  At the house they pass through 
Polyphaser devices before entering the wall that are connected to 
another 8 ft single ground rod.  There is 25 ft of coax between the 
base of the tower and where it enters the house.
Question, should these two grounds be connected (the tower ground rods 
and the house ground rod).  Presently they are not.  I was told by the 
Cel Tower installer who helped me with my tower installation that I 
should not connect them, that the rods at the tower base would handle 
any strike I had and I might make things worse by providing another 
path to the house by an additional ground wire between the tower and 
house.  OK experts, what's your opinion?  I can do it ether way, what 
is best?
TIA & 73

Jim Lux wrote:

> ----- Original Message -----
> From: "Keith Dutson" <kjdutson at earthlink.net>
> To: <towertalk at contesting.com>
> Sent: Monday, January 17, 2005 9:32 AM
> Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
> 
> 
> 
>>I read Polyphaser's technical note before installing my system.  There is
> 
> a
> 
>>lot of discussion about soil conductivity and how adding more rods will
>>improve conductivity.   Do you have an idea of HOW MUCH impedance would be
>>reduced?
>>
>>Keith NM5G
> 
> 
> There's a heck of a lot of details that can go into this, but, it's easy to
> establish the BEST that you can do, in a relative sort of way.
> 
> If the rods are "far" apart (basically on the order of 2 rod lengths), then
> they're essentially independent, so the resistance of N rods in parallel is
> the resistance of one rod divided by N.  (assuming same soil conditions,
> etc.)
> 
> If the rods are closer together, you get less improvement, culminating in
> the situation where the rods are right next to each other, when the
> resistance isn't much lower than a single rod.
> 
> The other factor to consider is the inductance of the wire(s) going to the
> rod(s).  1 microhenry per meter is a nice rule of thumb number to use for an
> isolated conductor... it might be twice or three times that, or half or a
> third, but it probably won't be 10 uH/meter or 0.1 uH/meter..
> 
> You can also bury rods horizontally...  To a first order, it's surface area
> in contact with the soil that's the important thing.
> 
>
> 

-- 
__________________________________________________________________________ 

Alan Zack
Amateur Radio Station K7ACZ
Las Vegas, Nevada, USA
Quality Engineer, The Boeing Company, Retired
Aviation Chief Warrant Officer, U.S. Coast Guard, Retired
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