Wire Rope Strength

In order to know the strength of your wire rope, you need to know it's class and material.  For example, is it 6x19 Improved Plow Steel, or is it 7x19 Galvanized (aircraft) cable?  Most winches sold for the 4x4 market come with 5/16" or 3/8" diameter 7x19 galvanized wire rope.  Below is a table listing the specifications for  7x19 Galvanized - the most common type supplied with and replaced on 4x4 winches.  Also shown is 7x19 Type 304 Stainless Steel.

It's easy to see the potential for problems when taking into account the factors described above.  If your Warn HS9500 winch came with 5/16" wire rope, it has a nominal breaking strength of approximately 9,800 lbs.  Remember, that's at 100% efficiency under laboratory conditions ONLY.  Add some fittings, wind it on a drum, and use it a couple of times and the breaking strength can be way below the force the winch can generate.....which can be very dangerous if not understood and respected.  Also, remember that's BREAKING STRENGTH, not Safe Working Load with a design factor.  Just for illustrative purposes, if one were to apply hoisting industry guidelines and use a design factor of 5, that brand new 5/16" rope would have a safe working load of 9,800 / 5 = 1960lbs under ideal conditions.  If the cable was well used, not particularly well maintained, and had a less than optimal end termination (sound like any you've seen?) that could drop it's efficiency to 70% or less, so keeping the same design factor (although admittedly the purpose of the design factor is to account for such losses in efficiency) would mean a SWL of 1960 x 70% = 1372 lbs !!!!!!

Add the fact that you totally stuck rig could easily have a rolling resistance of up to 10-15,000 lbs, is it any wonder these things fail and people get hurt!

Bottom line - understand your gear and it's limitations, maintain it well, replace when worn, and treat it as lethal, and you're much more likely to have an effective and SAFE winching experience.

7 X 19 GALVANIZED CABLE
Size Approx. Wt. per 1000 Ft. in Pounds Nominal Breaking Strength in Pounds* 3/32" ** 17.4 1,000 1/8" 29 2,000 5/32" 45 2,800 3/16" 65 4,200 7/32" ** 86 5,600 1/4" ** 110 7,000 5/16" ** 173 9,800 3/8" ** 243 14,400	7 x 19	All 7x7 and 7x19 galvanized cable is in accordance with proposed A.S.T.M. National Standard on Wire Rope for General Purposes, as applicable.
*Listed for comparison only. Actual operating loads may vary, but should never exceed recommended design factor or 20% of catalog Breaking Strength. ** According to Federal Specifications RR-W-410D. "Meeting dimensional and strength requirements of MIL-W-83420E.
7 x 19 STAINLESS STEEL CABLE, TYPE 304
Size Approx. Wt. per 1000 Ft. in Pounds Nominal Breaking Strength in Pounds* 3/32" ** 17 920 1/8" ** 29 1,760 5/32" ** 45 2,400 3/16" ** 65 3,700 7/32" ** 86 5,000 1/4" ** 110 6,400 5/16" ** 173 9,000 3/8" ** 243 12,000	7 x 19

Typical Drum Layered Power Loss
12,000 lbs. Winch Example