[TowerTalk] RE: ratings on wire rope

N2TK n2tk@earthlink.net
Wed, 5 Sep 2001 18:53:22 -0400

Oops. I made a mistake on the rating of the wire rope. According to the
distributor it is rated at 7000 lbs. Breaking strength. I have recalculated
the numbers below. Looking for comments if my margins are good or marginal.

-----Original Message-----
From: N2TK [mailto:n2tk@earthlink.net]
Sent: Monday, September 03, 2001 19:32
To: 'towertalk@contesting.com'
Subject: ratings on wire rope

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.

I understand that 1/4" wire rope has a breaking strength of 7000 lbs. I have
heard that you should take the breaking strength and divide it by 3.5 for
the load rating - 7000/3.5 = 2000 lbs. I would think this would give me an
okay safety rating?? Comments?

However, one wire rope company told me that when you use cable clamps on the
end of wire rope it reduces the strength by 20%. Was also told if you have
the end of the wire rope "weaved" over a thimble, then strength of the wire
rope is reduced by only 5%. Is this correct?

If I am losing 20% strength of the wire rope then,
7000 x .8/3.5 = 1600 lbs. Is this cutting it too close? Comments please.

If I have the cable company weave the end then,
7000 x .95/3.5 = 1900 lbs.

Is either method sufficient, or should I be looking at 5/16" wire rope?


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