[TowerTalk] Preforms

[Jim Thomson]

Date: Mon, 29 Aug 2011 18:41:52 -0400
From: "Dick Green WC1M" <wc1m73 at gmail.com>
Subject: Re: [TowerTalk] Preforms
To: "'Gregg  Seidl'" <k9kl at centurytel.net>, <TowerTalk at contesting.com>
Message-ID: <002501cc669c$d9f11ad0$8dd35070$@com>
Content-Type: text/plain; charset="us-ascii"

Preforms are an industry-standard product that doesn't loosen up over time
if correctly sized and installed. You must have had the wrong size,
defective grips, or they weren't installed correctly. I've got a friend with
preforms on his tower and they haven't loosened up in 20 years. Mine show no
sign of loosening up, either. Personally, I think grips are far superior to
cable clamps, which can deform the cable, can be installed incorrectly and
the screws can loosen up over time.

73, Dick WC1M

-----Original Message-----
From: Gregg Seidl [mailto:k9kl at centurytel.net] 
Sent: Monday, August 29, 2011 10:44 AM
To: TowerTalk at contesting.com
Subject: [TowerTalk] Preforms

I personally don't like the preforms. I have tried some and I feel they do
loosen up after time. I took them all off and now only use cable clamps.
Cable clamps are cheaper and can be reused or retightend.  Just my opinion.

Gregg K9KL

##  I worked for the local telco for 34 years..and never even heard of one loosening up.  I saw one instance where a 
D-9 cat hit the pole and snapped the ehs cable in the middle...and didn't put a dent in the preforms. The preforms are 
usually 4 x strands..and formed into a 'U'.   You effectively end up with  8 x strands, 4 in and 4 out...which is one more strand than the
7 x stand ehs guy wire you have the preform attached to. Where the pre-form loops around the egg, turnbuckle etc, is actually stronger than the ehs cable. 
The more tension you put on it, the tighter it grips, just like those chinese finger devices.   Now they are only supposed to be used once.
They have to be installed correctly, and no gunk, grease, debris, etc, on the ehs cable. The ehs cable has to stick out the end of the 
preform a bit...so it doesn't quite touch the egg insulator, etc.  

##  the real old style cable clamps the power co's  used consisted of a 2 x piece steel double trough clamp assy..with 2-3 bolts  compressing the 2 x halves
together.   I know of one KL7 ham that used those things, the bolts loosened up on him, and the ehs cable slipped out, and he lost a 100' tower.   We still
have a lot of them in use around town, but they are rare these days.  Telco's and power co's  will use preforms at BOTH ends of the ehs cable.. and no turnbuckles used
anywhere.   They use a different technique to get the slack out of the cable [ they actually grab and bend the wooden pole over a bit in the process] , then attach the lower
preform.   Of 100's of thousands of preforms in use, they are the most reliable thing going. 

##  If you do insist on using U style cable clamps,  typ 4 x are used, and they have to be spaced correctly, with the U bolt bearing down on the  dead end of the cable [ short pig tail portion].
The saddle of course, bears down on the live end of the cable [ long portion].   "you can't saddle a dead horse"    Every time I see a ham tower using cable clamps, I have yet to see one
that's actually done correctly. They either don't have enough clamps, or ham will alternate the clamps 180 degs..or have em spaced too far apart, too much slack between clamps,
bolts not lubricated, nuts not tight enough, too tight, etc.   Don't get me started on guy anchors, esp elevated ones.  Samll diam steel tubes, with thin walls, sticking  out of
the concrete by 5'-8'  are semi useless  at best.  Then they don't typ construct the concrete base correctly either.  If you do use a steel tube, at least fill it with concrete, or it will
fill with water, freeze, and then split, or rust from the inside inside out. 

later... Jim  VE7RF