We have had many questions over the years on properly determining the working load limit for cargo control devices like the Original BEDNET® Cargo Restraint.
The Federal Motor Vehicle Safety Administration defines WLL this way: “The working load limit (WLL) of a tie-down, associated connector or attachment mechanism is the lowest working load limit of any of its components (including tensioner), or the working load limit of the anchor points to which it is attached…”
US DOT FMVSA Regulation § 393.108
This means the weakest point on any assembly is used to determine working load; the stronger components are irrelevant in this initial determination.
So we start with the smallest tensile rating for any component in our device
WLL is typically calculated by dividing the ultimate break strength of the weakest component by a safety factor: for tie-down applications is typically 3 or more, for sling applications it is 4 or more.
We divide that smallest tensile by a safety factor of 3 or more to get our WLL (BEDNET® uses 3 1/3)
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Let’s look at three examples where we divide the lowest rating by 3 to derive WLL
A tractor trailer freight cam strap
- E-Clip 8000 lbs tensile
- Cam Buckle 2500 lbs tensile
- Polyester Webbing 6000 lbs tensile
2500lbs / 3= 833 lbs WLL
A tractor trailer ratchet strap
- E-Clip 8000lbs tensile
- Ratchet 5000 lbs tensile
- Polyester Webbing 10000 lbs tensile
5000 lbs / 3 = 1733 lbs WLL
Original BEDNET® Cargo Restraint
- Steel Hook 2000 lbs Tensile
- Quick Tite Buckle 1500 lbs tensile
- Polyester Webbing 6000 lbs tensile
1500 lbs / 3 = 500 lbs WLL
BEDNET® uses a slightly higher safety factor of 3 1/3 to derive a WLL of 450 lbs
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