Why? Prime Directive: Always follow the Manufacturer's instructions.
The manufacturer recommends using strap and clamps. Polyphaser and ICE
both, that is. Polyphaser is out to sell things, sure. However, they'd
probably sell the non-strap solution for just as much as the strap
solution, so I'd tend to trust their engineering over guesswork about
what a few microhenries might or might not mean to my house and gear.
That way, when the insurance agency comes around to settle a claim, I
don't have to justify why I didn't follow the manufacturer's
recommendations for ground system. ICE doesn't sell the strap at all,
but discussions on the phone with them indicate that they strongly
recommend using strap over wire or braid. Therefore, the probability of
there being a conflict of interest in their case is pretty much nil.
Besides, a coworker used to design ground systems for broadcast towers
before he discovered he enjoyed programming and the higher paycheck it
brought more than he enjoyed designing ground systems. He recommended
copper straps over wire or braid, based upon the skin-effect of the
high-frequency components of a lightning strike. You have way more
surface area on the strap than you do on any of the braids or wire.
More surface area means less resistance/impedance to the energy, meaning
more gets diverted to ground and less makes its way into your shack.
Considering it's a relatively inexpensive addition to the overall cost
of the tower project means I'll stick with the Manufacturer's
Recommendations.
However, it's your shack. Do what you think best.
--JohnK
73 de W5NNH
10X 75371/M&M 117/SMIRK 6185/Six Club 285/TRA 2499/Norcross 228 F&AM
jimlux wrote:
> John Kemker wrote:
>
>> Polyphaser has stainless steel hose clamps that have a section that fits
>> underneath the ground strap/wire/braid and protects from bimetallic
>> corrosion. (not the exact term for it, I know, but I can't recall the
>> exact term off the top of my head)
>>
>> Georgia Copper (www.georgiacopper.com) sells them and also sells wide
>> copper strap to connect them with and Polyphaser strap-to-ground rod
>> clamps. Only problem I've found is coming up with any sort of cadweld
>> or other brand of mold to attach strap to ground rods with.
>>
>
>
> Then why not use what most people use for lightning grounds: stranded or
> solid copper wire/cable. There's already plenty of inductance in the
> whole tower, so adding a fraction of a microhenry by going from strap to
> wire for few foot run isn't going to make a significant difference. If
> you're worried, use a bigger cable.
>
> The cable is more rugged, to boot.
>
> I'm not sure I see the value in using a copper strap for a tower ground.
> Yes, you'll see copper bar stock used as a tie point or as a ground
> reference at the back of a bench, or on the wall behind a row of racks,
> but that's mostly because it's easy to drill and tap a hole to connect a
> wire to it where needed, rather than some sort of wire/wire tap or
> splicing. And that's something like 1"x1/8" bar stock, typically.
>
>
> Yes, folks will be happy to sell you thin copper ribbon. After all, if
> YOU were in the copper business, you'd encourage folks to buy it.
> Copper ribbon in sizes like 1"x0.02" is used in applications like
> transformer windings for switching power supplies.
>
> And sure enough, it might be lower RF impedance at 1 MHz than a 4/0
> cable (maybe, maybe not.. 4/0 is almost half an inch in diameter, so the
> circumference is 1.5". Skin depth at 1 MHz in copper is about 0.002", so
> the AC resistance of the 4/0 and a 1" wide copper strap is about the
> same. Inductance is going to be pretty close, too.
>
> Copper strap will probably be cheaper (there's less copper than in the
> same length of 4/0 or 2/0), but if you're going through gyrations trying
> to find a connector to bolt it all together, maybe you're solving the
> wrong problems?
>
> Or, you could use a thicker piece of copper, and just drill a hole and
> bolt it to the tower (with appropriate hardware, and suitable washers..
> probably stainless steel would be a good idea). Somehow, a hoseclamp
> style clamp doesn't strike me as a good long term solution. Hoseclamps
> are designed to go on something resilient (hose?) that can provide a
> constant spring force. The clamp itself isn't elastic or springy, so
> over time, it WILL loosen from temperature cycling. If you look at the
> compression clamps used for ground rods, you'll see they're a very
> different design. A couple bolts squeeze the rod between the jaws of a
> clamp. And even those need to be inspected and retorqued every year.
>
>
>
> By the way, you don't need 4/0 or 2/0 to carry the lightning current.
> AWG 6 or 8 is probably big enough. The current is high, but doesn't
> last very long. Look at the grounding conductor on a wooden power or
> telephone pole. They're not running 2" wide copper strap or big 1/2"
> copper cables.. It's a solid AWG 10 or AWG8 (guestimating by eye from
> the last time I saw one a few weeks ago). The reason for a physically
> large conductor is for mechanical strength.
>
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