This conversation comes up at an appropriate time for me. I had just
previously downloaded the Burndy Grounding Catalog, a hundred plus pages of
everything re grounding and even an illustration (P11) of what appears to be
a commerical broadcast station grounding plan. Additionally, there is a
wealth of additional reference info at the end plus a well illustrated
section on exothermic welding.
I know my grounding system is flawed and inadequate and intend to fix this
issue. Although cloud to earth lightning strikes (sheet lightning from time
to time) along the coast at this location is a a very rare occurance I know
it can happen.
Lots of opinions offered but also a lot of good solid experiences of those
who have had to deal with the issue. As to electricians, I have to wonder
how some of the local folks ever passed the tests required to be licensed,
Too many of them 'cut corners' from what I've seen in previously installed
wiring, requiring cleanup when encountered. Doubt many know the current
codes except to the extend that can get an inspector to sign off.
Don W7WLL
-----Original Message-----
From: Bob Shohet, KQ2M
Sent: Monday, October 16, 2017 10:20 AM
To: Billy Cox ; Ward Silver
Cc: Reflector
Subject: Re: [TowerTalk] Fwd: Grounding connection to tower legs
Ward’s and others comments on this remind me of an experience that I had at
my qth a few years ago. After what I thought was a direct hit on one of my
towers, we lost cable (no surprise there). Turns out that it was not a
tower hit, but rather a case of lightning coming in via the cable lines
(which has happened twice before). What was interesting was when the cable
guy came out he could not locate the cable splitter into which the cable
feed from the utility pole was connected. He also could not locate the clamp
used at the cable ground! Hmmm.... What happened to them?
I find them in two different places about 15’ away from the side of the
house where the cable feed was connected. I lost cable because of the surge
that literally blew out the splitter and cable ground (and the connection on
the utility pole). There was no clamp on the splitter it was just screwed
into the side of the house before it was literally “blown away”. Both the
splitter and the ground clamp (VERY flimsy) showed damage and black scorches
on them. This incident nicely illustrates what Ward and others are talking
about.
I then watched him attach a flimsy hoseclamp for the cable ground, on its
own ground rod NOT connected to the house utility ground connection (equally
flimsy). I remarked on this and he said “that was the code”. I
subsequently went out and improved the ground. In another storm, lightning
came via our well pump and it had to be replaced. After the installation,
the guy made a solder connection on an extremely thin wire to make a
“ground”. It was a cold solder joint and completely useless. I pointed it
out whereupon he resoldered it. I then asked him about the ridiculously
flimsy wire ground and he said it was code. I was appalled.
I don’t know whether or not these two examples were up to code or not but if
they were then the codes here are grossly inadequate and guaranteed to cause
more damage in the future to my property (not that they care – they don’t
live here!). If they weren’t up to code then the cable company and the well
installer were either lazy or incompetent or both. A problem either way.
Moral of the story- be prepared to make BETTER ground connections than
code – it is your property and safety and the only person that will care
about it is you!
I use the Bronze heavy duty two hole compression clamps on the legs of each
of my two towers. Although they have taken multiple intense hits over the
years, including FIVE in one “storm from hell”, they have never been
scorched or loosened. I know that it is not the best ground possible, but
mechanically it has repeatedly stood the “lightning tests”.
73
Bob KQ2M
From: Ward Silver
Sent: Monday, October 16, 2017 12:56 PM
To: Billy Cox
Cc: Reflector
Subject: Re: [TowerTalk] Fwd: Grounding connection to tower legs
A quick reply - yes, the stainless steel shim clamps can be used *in
some circumstances* but my understanding from Polyphaser folks was these
are not to be used as primary grounding clamps for heavy conductors.
These are just to attach some kind of light-duty strap or wire (or
braid!) to a galvanized pipe, tube, or rod. For the main ground
connection that is intended to handle the lightning surge, you have to
use the heavy-duty clamps.
A good source of information is usually an electrician or tower
installer who knows what the local codes are and any special
circumstances that require particular hardware, coatings, etc.
73, Ward N0AX
On 10/16/2017 11:13 AM, Billy Cox wrote:
Good Morning All, and I am reading along this with interest given past
posts
as to the what/where of properly using worm-gear type clamp products.
Ward ... please note that some suppliers DO seem to suggest their use?
http://www.polyphaser.com/products/grounding-and-bonding
On the other hand, and from the daily calls/email here as to "can I do
this or
should we do that?" with various clamp products, there are many many
design
factors that really need to be properly considered with this topic.
So given the various present unknowns here (clamp type, bandwidth,
thickness,
type of materials and so on) I can't fully agree or disagree with your
statements
as to the use of worm-gear clamps for such applications. But it is
interesting ...
Basically this topic comes down to risk management. And as one who in
times
past did things poorly and suffered the consequences in the form of
canceled
insurance, and extra work/time/investments to overcome the root causes
....
I would suggest each person understand their specific risks, study
appropriate
sound technical information (such as Ward's book!) to decide what to
do there.
73 de Billy, AA4NU
Disclaimer if needed: Product Manager - Ideal Clamp Products.
------------------------------------------------------------------------
*From: *"Ward Silver" <hwardsil@gmail.com>
*To: *"Reflector" <towertalk@contesting.com>
*Sent: *Monday, October 16, 2017 7:26:02 AM
*Subject: *Re: [TowerTalk] Fwd: Grounding connection to tower legs
> Why would the hose clamp blow apart? I have used this method for decades
and have had multiple direct lightning strikes.
The mechanical forces on a conductor carrying kilo-amp currents from a
lightning strike can be extreme - many pounds per foot of conductor. (This
is described by Ampere's Force Law.) That's why codes require ground
conductors for lightning rods and antennas to be secured to a building or
support structure. (This was news to me, too.)
Basically, the conductor experiences a huge jerk which would destroy
either
the conductor or whatever is trying to secure it - like a hose clamp. So
it would be more accurate to say that the hose clamp is not rated to
withstand the force experienced by the ground conductor and is not blown
apart by the current. It's the mechanical force.
If hose clamps have been used and the tower has taken hits without
damaging
them, then the ground conductors are not for whatever reason carrying
enough of the current pulse to generate damaging forces. Or maybe the
configuration of the conductor was such that the force was weaker than it
could be. i.e. - you got lucky :-)
I'm no different in that I've used hose clamps over the years for similar
applications and got away with it. No more. As long as we're in True
Confessions mode, I've used braid from old coax (outdoors, even!) and
soft-soldered strap and braid to ground rods. No more of that, either.
Live and learn, especially now that I live back in the lightning zone
(Missouri) with towers on a high spot.
So the advice is just to use the right stuff for the job. It's not that
expensive (a lot less than your insurance deductible, that's for sure) and
has been engineered to minimize corrosion and handle the mechanical
requirements of the application.
I also got a question about CadWeld and those are great for ground
electrodes but I would never use them on the tower itself. It may be
possible to safely weld a connection to a tower but I wouldn't do it to a
tubular load-bearing leg, not to mention the dissimilar metals
involved and
all that. I wouldn't want to weaken a cross-brace either, especially when
there are other options designed for that exact application. Maybe someone
with broadcast tower experience could weigh in on that. I repeat, for us
hams, just buy the right stuff and and do what the manufacturer says.
73, Ward N0AX
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