[TowerTalk] Sparky Pays a Visit

Wed Aug 3 13:17:00 EDT 2005

About all you can do in that case is:
1. spread out the energy as much as possible, bury radials just below the
surface out to about 50' or so... they don't have to be straight, and they
don't all have to be the same length, just bury what you can as long as you
can.
2. do the ring around the house with radials running out from it.  You don't
need to use tubing, heavy wire is adequate. Attach it solidly to the tower.

3. Make sure the service entrance is connected to the ring and tower
grounds.
4. have service entrance mov installed, make sure there are protectors on
the phone and cable tv entrance if you have that also.  And of course use
protectors on the coax and control cable entrance which must be tied to the
ring as well.

the idea here is not to stop lightning, you can't do that... but first to
spread it out a bit with the radials.  And second, to have everything rise
and fall together when you do get hit.  As long as everything is at the same
voltage nothing should be the weak link to get fried.

It is important to know what the purpose of the mov lighting 'arresters' are
in this application.  They are not to take voltage off the power or signal
lines and put it into the ground, they are to actually keep the voltage
difference between the ground and power or signal conductors below the
flashover voltage.  This prevents the phenomena knows as 'backflashover'
where the lightning raises the ground voltage above the power or signal wire
voltage and flashes over to the other wires, often through your equipment.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Steve London
> Sent: Wednesday, August 03, 2005 20:41
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Sparky Pays a Visit
> 
> So, just for amusement, let's see what folks would do in my situation...
> 
> I live on a very dry hilltop in SW New Mexico.  There are large limestone
> boulders at the surface, or within a few inches of the surface. You don't
> dig in
> this stuff with a shovel or backhoe - it takes a jackhammer or excavator
> with a
> jackhammer attachment. There is no moisture in the ground, except for a
> few days
> after a monsoon rain event.
> 
> For what small good it might do, I have ground rods at each end of my
> beverages.
>   The deepest I could get them was about 2 feet. The resistance between
> the
> ground rods (which are about 500 feet apart) is around 5M ohms.  We're
> talking
> DRY here !
> 
> Frankly, what the local power company does for grounding seems worthless.
> They
> drill a hole in the ground for their pole, run their copper ground wire to
> the
> bottom of the pole, loop the copper wire in a spiral around the bottom of
> the
> pole, and plop the pole in the ground.  With no moisture in the ground, I
> can't
> believe that does anything.  When my house was built, they didn't even try
> to
> drive in a ground rod, they just used the rebar and concrete in the
> foundation
> as a Ufer ground.  I understand that is okay for safety grounding, but
> completely worthless for lightning protection.
> 
> Now, as far as radio goes, I have a 105' guyed tower, about 100 feet from
> the
> house, and two 30' guyed towers about 30 and 50 feet from the house.  The
> tall
> tower has the typical Rohn-approved concrete base and guy anchors.  No
> ground
> rods, buried copper wires, etc.  All of the cables, from all of the towers
> run
> on top of the ground, and terminate at an aluminum plate ("bulkhead")
> located
> about 30' from the house.  There is a separate set of cables that can be
> connected to the bulkhead connectors, running underground, through plastic
> conduit, to the ground-floor hamshack.  When the hamshack cables are not
> connected to the bulkhead, they sit in a covered plastic bucket, about 3
> feet
> from the bulkhead. The bulkhead is not intentionally grounded or connected
> to
> the house Ufer ground.  My strategy is simple - I don't care what happens
> on the
> tower, but keep the lightning out of the house.
> 
> I haven't had a direct hit yet, but that's only a matter of time on this
> hill.
> It does make me feel like I'm playing with a loaded gun !
> 
> So, short of doing a major excavation to lay a circle of copper tubing
> around
> the house and bonding everything to it, what might make sense to protect
> the house ?
> 
> 73,
> Steve London, N2IC/5
> _______________________________________________
> 
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
> 
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