[TowerTalk] Grounding

[Dale Sanders]

> Over the years of being an electrical engineer and a "ham", I've heard 

> so many stories about how this ham or that ham was grounding his 

> station to prevent lightning strikes or handle a lightning strike.  

> Let me go on record that if "the finger of God" decides it your turn 

> to be touched, nothing, I repeat, NOTHING will stop damage from a 

> strike.  I work in the broadcast and wireless industries where 

> grounding is literally a science.  We use established standards for 

> grounding systems at the towers and there is still damage from lightning
strikes.

> 

> In any lightning strike, even a 2" solid piece of copper takes on the 

> characteristics of a light bulb filament.  I see all this discussion 

> of all the capacitances and impedances, and all these highly technical 

> discussions when the people that install grounding for these 

> commercial facilities use the following guidelines.  These are time
proven, well researched solutions that are in use worldwide by engineers
responsible for million dollar equipment and sites.

> 

> 1.         Single point grounding.  Use one ground field or system and

> everything gets grounded to it.

> 2.         You put enough copper in the ground to get to a <25 ohm, and in
the

> case of telecom, <5ohm resistance at the ground field connection 

> point.  I doesn't matter what type of soil you have or where you are.  

> You still have to put enough conductor into the ground to get to those 

> low resistance figures. ...and it doesn't matter if it's simple or 

> something exotic.  It's all about the resistance.  A difference of as
little as 5 ohms can divert the energy in a lightning bolt.

> 3.         Measure the resistance into the ground with a "Megger" or with
a

> clamp-on type ground meter.  I realize these are expensive tools but 

> there are guys in your area that probably have them and use them on a 

> regular basis.  Ask around amongst the local hams, the wireless 

> companies, the telephone companies, or any local tower companies.  

> There are even grounding companies out there that would take a reading 

> on a system for little or nothing.  Seek and ye shall find.

> 

> BTW -- You do not have to use exothermic welds exclusively for your 

> ground connections.  One of the companies that make crimp on grounding 

> connectors is "Burndy".  These clamps are designed to get away from 

> Cadwelding but still require the use of a 12 ton crimper to bond the 

> connection.  Again, these can be rented.  Since I work in this 

> industry, I have access to all of this stuff and I'm sure there are 

> others that you can find that can assist you in your system.  I've 

> helped many hams in my area by loaning them a crimper or a CadWelder 

> and the associated "shots" that are required to make a connection.

Whatever you use, DO NOT scrimp on the connections in your grounding system.
The old

Clamp on grounding connectors from Home Depot "ain't" gonna cut it.

> 

> The key to a ground system is the conductor connecting the tower, 

> radios, whatever to the ground field.  It MUST be of a lower resistance 

> than any other piece of conductor in the system.  In most systems 

> where we install an MGB (Main ground bar) we utilize one or 2 pieces 

> of 750 or larger grounding conductors to connect to the ground field.  

> This gives you the low resistance path to ground for EMP, a nearby 

> strike, or a strike that takes place miles away but still can energize 

> the ground or neutral conductor coming from the utility (remember that the
ground cable is a conductor too).

> 

> 

> In my set up, I have 14 ground rods driven into the ground 8 ft deep 

> under the concrete base of my tower.  The bottom section of my tower 

> is bonded to those rods (which are bonded together) with a 4 pieces of 

> copper braid that are cadwelded (exothermic) to the tower legs.  From this
point, I have an 8"

> x 3" x 1/4" ground bar mounted with a piece of 750 cable running 

> inside to my MGB (see above). It is cadwelded to the braid and to the
tower leg.

 

Everything in my shack is grounded to 

> that MGB, including the negative of the battery bank and the utility 

> ground.  This places the grounds in my home, shack, and tower on the 

> same ground plain electrically (single-point grounding).  In other 

> words, if you do not tie all the grounds to a single point, then you 

> run the risk of having varied resistances at each grounding point.  

> Remember now, that lightning will take the lowest resistance path to 

> ground....make sure that, if your tower is the target, then the ground 

> directly below it has the lowest resistance path of any path in your
system. 

 If you don't then  the lower resistance path will be the one that the
lightning will follow.

> 

> Remember that we're not always able to eliminate lightning strikes, but
we're 

> trying to manage the path of the lightning so that it doesn't come 

> into your shack or home.  If you need further clarification, Google
"P.A.N.I."

> grounding.  It's the grounding system that is used in critical systems 

> worldwide.  P=Producer, A=Absorber, N=Non Isolated, and I=Isolated.

> Remember to ground your radios to the "I" or isolated side of the MGB.

> The large, low resistance cables connecting the MGB set up in the PANI 

> manner will always be connected dead-center between the A and N 

> sections of the ground bar.

 

There's not enough room here to explain the PANI theory, you'll have to
research that on your own.

> 

> If you have any questions, feel free to ask.  I'll answer and help out 

> as time and work allows.

> 

> '73

> Dale - WD4IFR