Working load limit (WLL), safe working load (SWL) and minimum and maximum rated loads explained
The term safe working load, (SWL) was the cornerstone of engineering, particularly with regard to loadcarrying equipment, for many years. It was generally considered to be the breaking load of a component divided by an appropriate factor of safety giving a ‘safe’ load that could be lifted or becarried1 . About 20 years ago, however, the USA ceased using this term, because of legal implications. The European and ISO Standards followed suit a few years later. However, while this was a clean-cutmove, for some time there has been indecision as to exactly what replacement terms could be used. Over the past two or three years, both the Americans and Europeans have agreed that working load limit(WLL) should replace safe working load (SWL) in describing the capacity of items such as hooks, slings and shackles etc. A general definition of WLL was: the maximum mass or force which a product isauthorized to support in general service when the pull is applied in-line, unless noted otherwise, with respect to the centreline of the product i.e. the WLL of a component is specified by themanufacturer. However, while the definition for working load limit was originally confined exclusively to the manufacturer’s specified maximum load that the item could lift, it is now generally extended toinclude both of the following: • • the maximum load that an item can lift; the maximum load that an item can lift in a particular configuration or application.
If the WLL is thought of as anassessment of the maximum load an item could lift under ideal conditions, the SWL (if the term is going to be used) can now best be thought of as being a derating of WLL, following an assessment by a competentperson of the maximum load the item can sustain under the conditions in which the item is being used.
If a 3 tonne (t) sling hook is attached to the bottom end of a 3 t single-leg wire...
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