[TowerTalk] Fwd: Grounding connection to tower legs

[Keith Dutson]

Charles,

Basically, what you are saying is that a solid connection to ground is
sufficient.

Tests with lightning have shown there is impedance to ground through various
connections.  The greatest impedance was found where the connection
presented reactance to the RF frequency of the lightning strike (yes, it has
RF frequency across a wide band).  It seems that flat copper strap presented
the least impedance.  Large diameter copper wire was also a good RF
connector.  Copper braid exhibited higher impedance as it got older.  I have
heard this is caused by surface oxidation over time.

Use Ohm's Law to calculate the power consumed by the impedance during a
lightning event.  I do not have information on lightning strikes handy, but
it is fairly easy to predict high power consumption in a braided connector,
compared to copper strap or solid copper wire.  So, you are looking to
handle a ultra-high current and voltage with the least impedance.  This is
why braid is not the best connector for lightning mitigation.

Looking at commercial installations of lightning mitigation, observe the
grounding of the top wire (ground) on a typical power line pole.  There is a
solid copper wire connected to this stranded wire, down the pole, to the
ground.  Recently, I was able to observe a maintenance crew digging around a
pole to inspect the pole for rot.  I could see the ground wire coiled around
the pole starting at ground level and going down, out of site.  I saw no
ground rod.  During a trip to the local electrical supplier, I asked if they
had any of this wire used on power line poles.  Yes, they had 500 foot
rolls.  I purchased a roll.  The guy at the counter yelled to the back "roll
of two ten."  I asked what this means.  He said two gauge tinned solid
copper wire.  Then I saw the price: $500.  Ouch.  After payment, he directed
me to the pickup area.  The roll came out and was placed in the bed of my
truck.  At home, I picked up the roll to carry into the garage.  It was too
heavy to carry.  So I used a dolly.

 Hope this helps understand the need for a good tower ground.

73, Keith NM5G

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
Charles Gallo
Sent: Monday, October 16, 2017 3:26 PM
To: Gary Schafer <garyschafer at largeriver.net>
Cc: 'Reflector' <towertalk at contesting.com>; 'Ward Silver'
<hwardsil at gmail.com>; 'Billy Cox' <aa4nu at comcast.net>
Subject: Re: [TowerTalk] Fwd: Grounding connection to tower legs

On Mon, October 16, 2017 2:27 pm, Gary Schafer wrote:


>Never use braid

I keep seeing this said.  I think we need to define braid

When I was a kid, I used to hang out at a barn that had an extensive, and
very very OLD "Lightning rod" system, and it had "braided cable" running to
the ground

The reason I use quotes was this braid was made out of what (from 40 year
old memories) was about 16-18 gauge strands, and a LOT of them, the braid
when in an oval was about 2.5 inches wide, and 1 thick, and as a teen, I
know we could not bend it aside to pain under it

Basically it was BIG FAT litz wire




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