[TowerTalk] ratings on wire rope

[K7LXC@aol.com]

In a message dated 9/3/01 4:32:46 PM Pacific Daylight Time, 
n2tk@earthlink.net writes:

> I am using 1/4" wire rope to tilt over my tower. When my tower is near the
>  ground I have a maximum pull of 2900 lbs. on the pulley. Since I am going
>  through a single sheave on the gin pole from a winch, I assume that the
>  maximum pull on the pulley is 2900/2 = 1450 lbs.

    Picture a pulley up on your tower and you want to pull a 1,000 load with 
a rope that goes through and down to the ground where you're going to pull. 
The load on the pulley is 2,000 pounds - 1,000# on the load side and 1,000# 
on the pull side. 
>  
>  I understand that 1/4" wire rope has a breaking strength of 7700 lbs. I 
have
>  heard that you should take the breaking strength and divide it by 3.5 for
>  the load rating - 7700/3.5 = 2200 lbs. I would think this would give me an
>  okay safety rating?? Comments?

    The ultimate breaking strength of 1/4" EHS (Extra High Strength) wire 
rope is 6700#. ALL other grades of wire rope (of which there are 6-7) have 
LESS UBS. You need to find out which grade of wire rope you have and what its 
UBS is in order to know what its specs are and how you can use it.

    The safe working load for a wire rope (or rope for that matter) is 
typically around 20% of UBS. A wire rope having a UBS of 6000# will have a 
SWL of 1200#.

Cheers,    Steve    K7LXC
Tower Tech 

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