[Antennas] Radials

[David Robbins]

Really read some of those reports you find with that google search... then
go look for real world examples of lightning exploding tower bases.  Most of
the dramatic reports I have seen on line are of 'foundation' damage, usually
showing on the inside of a basement, and if you look closely you normally
either see signs of rusted rebar, or very little rebar at all, both bad
situations as it is really the rebar that spreads the lightning charge out
so it can dissipate safely through the concrete.  Signs of rusting around
the rebar show that the foundation was already compromised.

Lightning doesn't have enough energy to blow up a properly connected (all
the steel tied together) tower base, nor will it melt rebar or even properly
sized copper ground wire.  Most of the examples shown in the on-line reports
of lightning damage are buildings where the lightning strikes the exterior
of the building and spalls the surface due to local heating.  There may be
some other examples where lightning arced out of rebar to another external
conductor and spalled that point above ground.  

But in a concrete foundation the current is spread over a relatively large
area and concrete is itself a better conductor than the soil it is in.  When
designing lightning and protective grounds for high voltage power lines if
you use just rods or radials you have to account for the ionization of the
soil around them due to the high surface gradients... when using ufer
grounds they are so big they don't cause further ionization and are
considered linear resistances.  It is also a common practice in poor soil or
rock areas to encase ground rods and radials in bentonite or concrete to
improve the ground.

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


-----Original Message-----
From: Antennas [mailto:antennas-bounces at mailman.qth.net] On Behalf Of
Riichard Neuman via Antennas
Sent: Saturday, April 18, 2015 04:26
To: nf4l at comcast.net; antennas at mailman.qth.net
Subject: Re: [Antennas] Radials

Do yourself a favor...Google "lightning concrete damage" ...get the
lightning off the tower by other means than THRU the concrete.

Richard


 


Hi Richard - 
  
 
 
According to the electrician, whose company does a lot of grounding work
here, rods would add nothing to the protection afforded by the Ufer ground.
But that wasn't the question. 
 
  
 
 
73, Mike NF4L 

 

 

 

-----Original Message-----
From: Mike Reublin NF4L <nf4l at comcast.net>
To: Riichard Neuman <secopsys at aol.com>
Sent: Fri, Apr 17, 2015 9:03 pm
Subject: Re: [Antennas] Radials


Hi Richard - 
  
 
 
According to the electrician, whose company does a lot of grounding work
here, rods would add nothing to the protection afforded by the Ufer ground.
But that wasn't the question. 
 
  
 
 
73, Mike NF4L 
 
  
  
   
    
On Apr 17, 2015, at 20:51, Riichard Neuman <     secopsys at aol.com> wrote:

    
    
     You want to get the possible lightning strike off and away from each
leg before the concrete.   Clamps on each leg with heavy duty gently
sweeping wires out to driven ground rods...one at each leg driven into the
ground NOT thru the concrete.  In addition possibly further ground rods
heading away from each leg.
       
        
       
       
        
       
       
-----Original Message-----       
 From: Mike Reublin NF4L <       nf4l at comcast.net>       
 To: antennas <       antennas at mailman.qth.net>       
 Sent: Fri, Apr 17, 2015 8:04 pm       
 Subject: [Antennas] Radials       
        
        
         
I have a 70' tower with an inverted-L for 160M and a 1/4 w sloper for 80M.
The tower base has 8 yards of concrete and a lot of rebar. There are 3 #4
copper wires, with one end attached to each tower leg, then into the
concrete, attached to the rebar then exits the concrete just under ground. 

The original plan
was to put 3 ground rods along each wire. My electrician told me that as far
as safety grounding goes, there was no benefit. The tower/base megged at 4
ohms.

The wires are currently rolled up at the base of the tower. If I straighten
them out and staple them to the lawn, do they then act as radials?
Would it be feasible to attach more radials to these where they emerge from
the concrete, so as to avoid having the top of the concrete pad awash in
wire?

73, Mike
NF4L
______________________________________________________________
Antennas
mailing list
Home: http://mailman.qth.net/mailman/listinfo/antennas
Help:
http://mailman.qth.net/mmfaq.htm
Post: mailto:Antennas at mailman.qth.net

This
list hosted by: http://www.qsl.net
Please help support this email list:
http://www.qsl.net/donate.html

        
       
     
   
  
  
 

______________________________________________________________
Antennas mailing list
Home: http://mailman.qth.net/mailman/listinfo/antennas
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Antennas at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html