First, you should probably learn what a "single point ground system" is as
it is referenced to in the discussion of lightning protection for radio
equipment. It is NOT the service entrance panel.
It is NOT true that "a direct hit will get stuff fried". Proper grounding
and protection devices can prevent most of the damage commonly caused by
lightning. It does not take a second mortgage on your house to do. Of course
nothing is 100% but most damage can be eliminated.
Jim is correct in stating that "lightning energy peaks around 1 MHz" with
significant energy going as high as VHF frequencies.
Inductance is the enemy of all lightning ground leads.
Yes we want to divert lightning energy directly to ground and not thru our
equipment or building. We also want all of our equipment to be at a common
potential during a strike for that amount of energy that we are unable to
divert directly to ground. The ground lead in our house wiring is not going
to get that job done!
A 100 foot long #6 wire is next to useless for diverting a lightning strike
to ground. However it will help in equalizing voltage difference between two
points but it is even much too long for that purpose.
A few ground rods is not a sufficient ground for lightning protection. It
takes many, along with radials.
A single point ground (SPG) needs to be close to the ground system and
connected to it by a very short path of wide copper strap. All antenna
cables, power and phone lines come thru this point before entering the
shack.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Mickey Baker
> Sent: Thursday, June 17, 2010 2:20 PM
> To: Jim Brown
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Shack ground
>
> All choices in life are driven by the evaluation of the criteria at hand.
> Some of the choices people make seem eccentric to others. Non-hams wonder
> why we erect towers and antennas.
>
> As an engineer, this is an exercise in economics vs. probability.
>
> The grounding discussion here seems to rotate around diverting a direct
> lightning strike to ground.
>
> Emotionally, we all want our families, ourselves and our "stuff" to be
> safe.
> Unfortunately, the reality is that we can't engineer a solution to many
> things, including the dissipation of the energy of a direct hit from
> lightning. There is some validity to almost every post here, but you must
> ask yourself what you can do in your situation to come to reasonable
> accommodation of risk and keep yourself and your household safe.
>
> A direct hit = you're going to get stuff fried, maybe wires are going to
> vaporize anyway. I have seen aluminum service drops - 5/8" aluminum
> conductors - vaporized and leave only shards of insulation. Goodbye ham
> radio station, computers, televisions, just about anything connected to AC
> power if your breakers don't trip immediately!
>
> The object (and original discussion) was how to provide a better path from
> your communications ground to the SPG than through the household
> appliances
> - from one point on earth to another.
>
> Every electrical outlet in every house with single phase service is
> connected to the SPG through the ground lug on the outlet, both of which
> should be bonded to neutral at the SPG. When you connect your ground wire
> from your ground rod to your rig, you then are connecting your ground rod
> to
> the SPG through your rig's cabinet.
>
> The bonding REQUIRED by the NEC provides that multiple ground systems be
> bonded directly for a number of safety reasons as well as a direct
> lightning
> strike. I'll allow the group to ponder this - I can think of one case
> related to measuring 100 Ohms to ground from an outlet!
>
> For almost all cases, a #6 solid wire from the SPG ground to your tower
> ground rod system will be fine to keep your home safe. Certainly it is
> compliant with NEC. Compliance with code is my reasonable accommodation of
> risk. It is what is required of a contractor or engineer, legally.
>
> You can build a Faraday cage around your house and ground it with 512
> ground
> rods if you like, but it just doesn't make economic, technical or legal
> sense!
>
> Spend your money as you like, but let's not insult each other with
> half-truths and old wives's tales about lightning.
>
> Jim's statement about lightning having "its energy centered around the AM
> broadcast band" is factually incorrect. Even if it were correct, nothing
> passive has a lower impedance than a large, straight conductor in a line
> between two points.
>
> If you want to know what electrical characteristics of lightning have been
> measured, here is some actual science:
> http://www.lightning.
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>
> ece
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>.<http://www.lightnin
> g.ece.ufl.edu/PDF/cotisonrtl.PDF>
> ufl
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>.<http://www.lightnin
> g.ece.ufl.edu/PDF/cotisonrtl.PDF>
> edu
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>/<http://www.lightnin
> g.ece.ufl.edu/PDF/cotisonrtl.PDF>
> PDF
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>/<http://www.lightnin
> g.ece.ufl.edu/PDF/cotisonrtl.PDF>
> cotisonrtl
> <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>.<http://www.lightnin
> g.ece.ufl.edu/PDF/cotisonrtl.PDF>
> PDF <http://www.lightning.ece.ufl.edu/PDF/cotisonrtl.PDF>
>
> Follow the NEC and bond! If you want to install a 4" copper pipe to do so,
> good for you - but it isn't necessary to be safe and it could cost more
> than
> a house full of ham gear.
>
> My interest in this topic...
>
> On July 20, 2000, I was in my back yard when lightning hit a tree about
> 15'
> away. It split the tree and eventually killed it. Energy through the (dry,
> solid) ground injured my leg muscles - I spent the next 5 days in the
> hospital and have had 4 surgeries on the leg.
>
> As a result, I became a bit obsessed by the topic of lightning. As an
> electrical engineer (who now works for a storage technology company) I
> have
> found, read and understand most of the literature. I believe I could make
> a
> living as a lightning protection engineer, but fortunately, I'm having a
> good time doing something else that I know even better.
>
> Mickey, N4MB
>
>
>
> On Thu, Jun 17, 2010 at 12:09 PM, Jim Brown
> <jim@audiosystemsgroup.com>wrote:
>
> > On Wed, 16 Jun 2010 22:08:24 -0400, Mickey Baker wrote:
> >
> > >K7DD is right. Bond to your SPG with as big a wire as you feel you can
> > >afford.
> >
> > Right.
> >
> > >Longer path = bigger wire.
> >
> > WRONG! Lightning is NOT a DC event. It is a TRANSIENT, with its energy
> > centered around the AM broadcast band and extending for several octaves
> > either side (that is, from about 200 kHz to about 5 MHz). INDUCTANCE is
> > what matters, and that is proportional to length. The only benefit of a
> > bigger conductor is that the conductor can discharge more of the event
> > before it vaporizes. :)
> >
> > 73, Jim Brown K9YC
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
>
> --
> Mickey Baker
> Fort Lauderdale, FL
> "Tell me, and I will listen. Show me, and I will understand. Involve me,
> and
> I will learn." Teton Lakota, American Indian Saying.
> _______________________________________________
>
>
>
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