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Re: Lightning hits



Yes, Jon, you are exactly right about the differing potentials at different locations (the further apart, the greater the potential).  This situation causes both ground loops (especially at RF) and the reliance on a long conductor with an unknown reactance at the RF frequencies of a lightning strike.  

My point is that the safest thing you can do is thoroughly ground the tower at the base, with as short and straight vertical a bonding jumper you can manage to as large a ground grid as practical (three 8' copper rods arranged in a 10' triangle with # 2 bonding jumpers would be ideal).  Adding a jumper to your house's safety ground does not offer better protection AND it does offer the opportunity of lightning-induced RF (at very high voltages) to enter your home.  Your compliance with the NEC is required only if you are a contractor or if your installation is subject to inspection by some authority.  Something you could do is add a jumper for inspection and then remove it for operation.

A couple of other minor points:  your equipment should be grounded to your buidling safety ground and your coaxial cable shields should be grounded at the point where they enter your house.  I have a triad of rods right outside my shack where the coax cables are all grounded.
73,
Jerry, K5OE


 Jon Ogden <na9d@mindspring.com> writes:

<< on 12/11/00 5:38 PM, K5OE@aol.com at K5OE@aol.com wrote:

> The NEC also stipulates the antenna must be grounded at the nearest accessible
> location.  If that location is not the building power service safety ground,
> then a bonding jumper is required between the antenna and the safety ground.
> 
> All that said, a far more practical (and most likely safer) method is to
> ground the tower immediately at the base with a triad of rods, interconnected
> with large bonding jumpers.  Running a long lead to the house's ground is not
> something I would recommend.

So which is it, Jerry?  The code states that you must jumper between the
antenna and safety ground.  Yet you say to skip running a long lead to the
house.  So which is it?

The whole reason behind connecting all the grounds is that "ground" is not
necessarily "ground" and that you can have different potentials at different
points.  Tying them all together eliminates that.

A long lead between tower and the power company ground *should* not cause
any problems, IMHO, IF your tower is well grounded.

1.) Lighting will take the shortest path to earth possible
2.) A long piece of wire will tend to be inductive.  To a DC impulse and
inductor looks like an open circuit.

Therefore, if your tower is very well grounded, the long line to the power
company ground should not even be seen by lighting.

Now I'll admit I am not an expert on this, and Jerry, you seem much more
knowledgeable so perhaps I did not understand what you were saying.

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Member:  ARRL, AMSAT, DXCC, NRA

http://www.qsl.net/ke9na

My President is George W. Bush -> The legal winner in Florida

 >>


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