Topband: Fwd: cable clamps on old Phillystran
HAROLD SMITH JR
w0rihps at sbcglobal.net
Fri May 30 11:21:01 EDT 2014
Hi Grant and Carl,
About 20 years ago, I replaced my steel guy wires on my 80 ft of Rohn 45G with
6700lb Phillystran. At that time the end kits were 4 galvanized cable clamps and a plastic end cap.
Their instructions said to torque the cable clamps to 25 ft/lbs. I also used RTV on the end caps.
I have had no problem and the installation has been through winds over 80 mph. The Phillystrand
did improve my shunt feed performance on 160. I did have to re-tune my Omega Match.
I also use 1200 lb Phillystran for the overhead guy on my Telrex 20M456
73 Price W0RI near St. Louis
On Thursday, May 29, 2014 10:44 PM, Grant Saviers <grants2 at pacbell.net> wrote:
Ice is an interesting question. I'll speculate that it doesn't matter
much since the sheath is pretty flexible and the Kevlar has a small
sensitivity to moisture. The Kevlar demonstrated very high crush
strength, I think about the same as its tensile strength, so to me that
is not a concern. However, if the sheath is degraded to expose Kevlar
to UV then it is a whole different ballgame. I also think it takes a
bit of faith that the factory recommended plastic endcaps on current
production Philly keep all moisture out.
On 5/29/2014 7:45 AM, Carl wrote:
> What about ice forming inside the sheath from those breaks?
> ----- Original Message ----- From: "Tree" <tree at kkn.net>
> To: "160" <topband at contesting.com>
> Sent: Thursday, May 29, 2014 9:48 AM
> Subject: Topband: Fwd: cable clamps on old Phillystran
>> Forwarding from KZ1W:
>> ---------- Forwarded message ----------
>> From: Grant Saviers <grants2 at pacbell.net>
>> Date: Wed, May 28, 2014 at 9:56 PM
>> Subject: cable clamps on old Phillystran
>> To: topband at contesting.com
>> Cc: tree at kkn.net
>> Per prior topband posts and discussions about this topic, I've
>> concluded a
>> round of testing of cable clamps on parallel strand (old style)
>> Phillystran. Here is the Conclusions and Summary I wrote:
>> A hydraulic jack H frame press was modified to provide tension in
>> excess of
>> 20,000 lbs. Tension was applied to a 4 foot long 5/8” od parallel
>> (old) Phillystran cable terminated with four 5/8” cable clamps and ¾”
>> thimbles at both ends. Clamp nuts were torqued to specific values
>> and the
>> holding capacity of the cable assembly was measured over periods of
>> There is significant creep of the plastic sheath from the cable clamp
>> forces between the clamp and the Kevlar core. In the first test
>> the residual torque of the clamp nuts reduced by 65% in 21 days.
>> tightening of the clamp nuts showed smaller sequential reductions of
>> residual torques. Five cycles of tightening were demonstrated as
>> over a period of weeks to achieve sufficient residual torque of the
>> A conclusion at 66 days since initial assembly was that four 5/8”
>> wire rope
>> clamps, torqued in 5 cycles over weeks to a 50 ft-lb value, will
>> support a
>> long term tension without significant slippage at the desired holding
>> strength of 6600 lbs, about 25% of the cable rated strength. After
>> of the cable sheath, there was no visible damage to the Kevlar core
>> at the
>> clamps or at the thimble. It is speculated that a slightly higher
>> value than 50 ft-lbs would improve the slip strength. Adding a 5th
>> would further improve the slip strength.
>> The core around the thimble showed evidence of small differential
>> of fibers. The test sequence was such that the fibers could slip
>> each other as tension and clamp nut torques were increased
>> sequentially. Thus,
>> the test process was not the same as tightening the clamps and then
>> installing the guy. However, the Phillystran tested is to be used at
>> of its rated strength, so the risk seems minimal in this case. Note that
>> wire rope is expected to hold at least 80% of rated strength when
>> terminated with cable clamps, and is not sequentially pre-tensioned when
>> put into service. Whatever unequal forces exist in the individual wire
>> strands around the thimble are equalized in some manner.
>> From this testing, it seems unlikely that parallel strand Phillystran
>> be reliably terminated with cable clamps at more than 1/3 of rated
>> strength. The simplified conclusion is that the cable will slip
>> unless the
>> clamp has extruded out most of the plastic sheath in the clamping area.
>> The planned tower has maximum pretension in the guys of 600 lbs.
>> Thus, the
>> average long term tension is substantially below the measured slip value
>> produced in these tests, so it seems unlikely that the preload
>> tension will
>> cause slip over a period of years.
>> Since the plastic sheath was breached by at least one clamp, water will
>> intrude into the core. Moisture does slightly reduce the strength of
>> Kevlar fiber. The clamp fully covers the split area so degradation from
>> sunlight seems unlikely, although UV degradation is a major concern with
>> Although the tests were successful in achieving a stable termination at
>> 6600 lb tension, doubts remain in my mind about the long term
>> of using cable clamps. Hence, I plan to assemble and test a Phillystran
>> cable terminated with the standard Crosby Spelter sockets for 5/8” wire
>> rope using epoxy potting.
>> A pdf of the full report is available, contact me offline for a copy.
>> Grant KZ1W
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