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Re: [TowerTalk] Tram rope

Subject: Re: [TowerTalk] Tram rope
From: Eric Scace K3NA <>
Date: Tue, 19 Dec 2006 23:50:11 -0500
List-post: <>
Dick --

Addressing your questions (to the best of my limited knowledge):

A snatch block is a pulley (block) whose frame opens so that the rope 
can be laid into the block; i.e., one does not have to thread the end of 
the rope through the block.  Either a snatch or normal block can be used 
at the base of the tower.

Wire rope clip data:  One minute on Google yielded:

   For 5/16" rope, the smallest size on page 2, two clips are required 
with 30 ft-lb torque on unlubricated bolts.  That's bigger than your 
rope size, so we go to the next site... a wire rope hardware manufacturer:

Here it states that for drop forged wire rope clips for 1/4" rope, two 
are required with 15 ft-lb torque.  The rope turnback distance is 4.75" 
(see the drawings from the other site above for explanation of turnback).

There are other sites that say the same.  For more complex question, 
refer to "The Lineman's and Cableman's Handbook" or "Handbook of 
Rigging", both excellent references.  The later discusses wire rope 
clips and installation on pp 229-231.  (Thanks to John W0UN for tipping 
me off to these books many years ago.)

Use of dead-end guy grips:
   Note:  Preformed Line Products' website states: "[Dead end guy grips] 
should not be used as tools; that is come-alongs, pulling-in grips, etc."
   The site also states the grip is made of the same material as the 
strand to which it is applied.  So applying a galvanized EHS 
large-diameter strand to a small-diameter strand wire rope sounds wrong.

Wire rope is very different construction from the 7-strand guy wire.  
"6x19" rope contains 6 strands made up of 15-26 wires, of which no more 
than 12 wires are "outside" (lay on the outside surface of the rope).  
The wire diameters vary and the cross-section layouts differ (Seale, 
Warrington, or filler are common layouts).  The key point is that the 
outside surface of wire rope does not resemble guy cable -- so I would 
be skeptical that a dead-end grip desired for guy cable will work 
properly on wire rope.

Furthermore, the PLP catalog shows the grips as having left-hand lay.  
Guy cable is also left-hand lay.  But most wire rope is right-hand lay!  
(The lay of a line can be determined by looking at the line from above, 
with the line stretched out to run straight away from your waist.  If 
the outer strands on the top of the line wrap toward the left as they 
recede away from you, that is left hand lay.)  (And in most wire rope, 
the lay of the individual wires within each strand are opposite to the 
lay of the rope -- that's called "regular".  So most wire rope is 
Regular Right Lay.  The opposite design, called "lang", results in more 
flexible rope that has greater resistance to abrasion and fatigue ... 
but it kinks & untwists much more easily.  You don't want Lang lay 
(either right or left) on a rope that's lifting anything because the 
rope untwists under tension, lengthening and causing the load to spin.)

-- Eric K3NA

on 06 Dec 19 Tue 21:38 Dick Green WC1M said the following:
>> turning pulley near the base of the tower, and then 
> Isn't this known as a "snatch block"?

>    Wire clips of correct size, number, spacing and 
> installation (nuts tensioned according to manufacturer's 
> instructions) will have greater holding strength than the 
> breaking strength of the wire cable.
> Where is the published data on that? Where is the information on proper
> torque for tightening the nuts on, say, 1/4" wire clips?
>>    I'd feel comfortable using a guy grip on 7-strand steel 
>> cable tram line, since that's what it was designed for.
> I don't doubt that, but take a look at the Preform website. The literature
> for dead-end guy grips doesn't say anything about 7-strand steel cable. The
> only spec is the cable diameter. Now, the word "cable" is used, not rope or
> wire rope, so perhaps that's enough to rule out wire rope. But they don't
> specify the number of strands.
> <snip>
>> I don't know how the 
>> manufacturer feels about using a guy grip designed for 
>> 7-strand cable on wire rope of the same diameter; the 
>> manufacturer's Prime Directive applies here.  Maybe there are 
>> grips designed specifically for wire rope.
> My wire rope happens to be 7-strand as well, though of course it's 7x19.
> It's clearly softer than EHS, which may very well make it unsuitable for use
> with guy grips. Does anyone know?
> 73, Dick WC1M

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