[TowerTalk] Fwd: Grounding connection to tower legs

[Ward Silver]

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 at gmail.com>
> *To: *"Reflector" <towertalk at 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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