[Top] [All Lists]

[Towertalk] creating ground "surround" of house: Obstacle

To: <>
Subject: [Towertalk] creating ground "surround" of house: Obstacle
From: (Glenn Little)
Date: Wed, 18 Sep 2002 18:00:53 -0400
If the grounds are not tied together, you will get a difference in 
potential between the two grounds. If the grounds are tied together, the 
difference of potential will be minimum. If everything is tied together and 
a lightning strike occurs, everything elevates to the same level and 
everything is happy. If the grounds are not tied together and a strike 
occurs, the two "grounds" will elevate to different points. A difference of 
potential and current flow. Not at all good. If the tower takes the hit 
(probable) and is connected to the house by anything conductive and the 
house is not at the same ground potential as the tower, dammage will occur 
as the energy attempts to equalize. To ground the tower to the house 
requires ground rods placed along the path at twice the distance of the 
ground rod length. The ground wire should be bonded to the rods along the 
path. To be done properly, the rods are driven to about 18 inches below 
grade and the ground wire (#2 AWG or larger) is trenched to the depth of 
the rods and welded. References for this are Motorola's R-56 manual for 
site selection and MIL-HDBK-419A.

In my past job, I evaluated sites for lightning probabilities.  If 
everything is bonded together, minimum damage during a strike. I anything 
was not attached to the system bonded ground, it was usually toast after a 



At 06:42 AM 9/18/02 -0500, Jon Ogden wrote:
>on 9/16/02 11:56 PM, Bill Hider (N3RR) at wrote:
> > Now, sometimes the tower is located so far from the shack (house) that the
> > impedance in the coax shield
> > over that long run (say several hundreds of feet) is so large that you'd
> > think the lightning would dissapate before
> > it got to your shack.  Well, maybe it would and maybe it wouldn't.  Why not
> > be safe and provide a path for the lightning
> > that YOU know is the one you want it to take?  Add that measure of
> > protection.  In your case, 70 ' just doesn't come
> > close to being far enough to ignore this, in my opinion.
>This whole thing seems to be a bit of debate between people.  To connect the
>tower to the house ground or not to.
>Most people I have talked to do not connect the tower ground to house
>ground.  The simplest reason, is you want to keep lightning strike energy
>AWAY from the house.  A big, long wire connecting 70 feet or more of length
>is going to have a lot of inductance to lightning and won't do much good
>The reason for tying electrical grounds together is for safety reasons as
>you want all "ground" points to be at the same potential relative to the hot
>wire in the electrical circuit.  Otherwise, you can create major problems as
>ground is not always "ground."  Tying electrical grounds together fixes
>This is a different purpose for the tower ground.  In fact, I personally
>think that keeping the ground separate is a very good thing as you want to
>keep al lightning strike AWAY from your house electrical system.
>The best protection of shack and equipment is as one person said to
>disconnect everything.  Sure, but it's not always practical.  So the
>alternative is to bite the bullet and drop the big bucks for surge
>suppressors.  One of the guys that helped me put up my tower told me in no
>uncertain terms to do this.  He said EVERY line coming from the tower going
>into the house needs to be protected.  The surge arrestors should be as
>close to ground as possible and grounded right near the tower.
>So yesterday I ponied up the big bucks and spent the money to get the
>arrestors for every line.  Cable Experts sells the ICE, Alpha Delta and
>Polyphaser models.  The ICE ones that I bought cost $40 to $46 each and look
>to have a pretty good design.
>Jon Ogden
>NA9D (ex: KE9NA)
>Life Member: ARRL, NRA
>Member:  AMSAT, DXCC
>"A life lived in fear is a life half lived."
>Self Supporting Towers, Wireless Weather Stations, see web site: 
>Call 888-333-9041 to place your order, mention you saw this ad and take an 
>additional 5 percent off
>any weather station price.
>Towertalk mailing list

Glenn Little                  QCWA  LM 28417
Amateur Callsign:  WB4UIV     AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)                      ARRL  TAPR

<Prev in Thread] Current Thread [Next in Thread>