Interesting statement from Rohn: Rohn "no longer supports" .
I have seen tower failures of sharply bent guy cables about a anchor point, and
many other tower failures when people "cut corners" upon installation.
Decades ago - I was taught an old proverb "Never put a saddle on a dead horse".
I only use Big Grips, a bit more costly... but never have seen one fail.
Thanks N 73,
James
ki5dq
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On Sun, 6/7/15, Donald Chester <k4kyv@hotmail.com> wrote:
Subject: [TowerTalk] Guy Wire Cable Clamps
To: "towertalk@contesting.com" <towertalk@contesting.com>
Date: Sunday, June 7, 2015, 2:56 PM
It's tower and antenna season once again.
For tower guying I prefer Big Grips, but for some applications I still use old
fashioned cable clamps, for example, to attach guy wires to ground anchors,
allowing for easy re-adjustment as necessary, months or even years after the
initial installation. Another is for strain insultors and other hardware whose
contour won't allow it to fit snugly against the U-shaped bend of the Big Grip.
An engineer at PLP verified that this has caused failure,
particularly with offshore manufactured strain insulators. He strongly
recommended against using Big Grips for such applications, knowingly
discouraging potential sales.
For a recent project I ordered a bag of 3/16" clamps from Rohn through one of
their distributors, under the same part number as listed in the Rohn catalogue.
Originally, these were part # 3/16 CCM, but the Rohn catalogue now lists them
as 3/16 CCF. The old style were "malleable", while the
new style are said to be "forged". I have found the newer style to be all but
worthless. One would be better off buying cheap wire rope clips from Ace
Hardware.
The older CCM clamps had a deep channel in the body of the saddle, which
positioned the dead end to overlay the live cable under pressure from the
U-bolt, so that all compression was exerted between the two sections of cable.
Instead of a real channel, the newer CCF clamps have four bumps on the body of
the saddle, laid out in a rectangular configuration. The channel formed between
the bumps is too shallow to hold both segments of cable in place so that one
rides on top of the other; the dead end tends to ride over to one side at about
a 45 degree angle, wedging partly against the body of the saddle instead of
pressing 100% against the live cable. In addition, the older clamps had a
series of diagonal grooves at the bottom of the channel, designed to grip the
cable over the full length of the channel. The newer ones have a single
diagonal ridge, which pinches the live cable in exactly the same manner as the
U-bolt does when clamps are installed the
wrong way and the U-bolt b ears down on the live cable. I did a test run with
some newer clamps, a piece of scrap cable and a come-along. I was able to pull
the cable tightly enough to cause it to slip through three clamps with the nuts
firmly tightened. I suspect this would have been impossible with the older
clamps; some piece of hardware would fail or the cable would break before it
would slip through the clamps.
Furthermore, the U-bolts that come with these clamps are no better than the
saddles. The older ones were heavily galvanised, like marine hardware. The
newer ones are merely zinc-plated, just like the aforementioned Ace Hardware
product. About six months ago I used some of the newer
clamps for a less critical application, to attach some pieces of guy cable
anchoring the end insulators of a wire antenna. Now, in little more than half a
year, the U-bolt nuts are completely rusted with no remaining sign of zinc
plating at all; in fact the nuts on these clamps are already rustier than the
older ones on a nearby tower that has been up for more than 30 years.
I called this to the attention of a Rohn engineer, and his only comment was
that Rohn "no longer supports" the use of cable clamps with guy wires; they
now solely recommend Big Grips. He said they only list clamps in the catalogue
because they still occasionally get orders for them. The illustration in the
catalogue clearly shows a picture of the older style clamps, not the junk they
sell now.
Does anyone know of a vendor who stocks original style heavily galvanised
clamps similar or identical to the older 3/16CCM? Based on what I paid in 1980
and on-line inflation calculators, these should now run a little over $1.00
apiece.
Don k4kyv
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