WLL — Working Load Limit
Definition
The working load limit (WLL) is the maximum load that a lifting component is designed to carry in normal use, as marked by its manufacturer. It equals the minimum breaking load (MBL) divided by a safety factor (design factor) that depends on the component and on the standard it is built to. Examples are 5:1 for steel wire rope slings (EN 13414-1 in Europe, ASME B30.9 in the United States) and 7:1 for textile slings (EN 1492-1 and EN 1492-2). When loads hang over people, some national rules add a further margin. In Germany, DGUV Regel 115-002 doubles the working coefficient by limiting rigging equipment to half its rated capacity, and in the United Kingdom the guidance of the National Rigging Advisory Group (NRAG) loads industrial chain hoists over people to 50% of their rated capacity. Every component in a rigging system is rated at the same WLL or higher, because the weakest component sets the WLL of the whole system.
In the field
Mixing components of different WLL does not give the assembly the highest rating, because the whole chain is limited by its weakest link. The WLL of each component is recorded, and the total suspended load is checked against it before anything is flown.
Related lessons
Sources
- EN 13414-1 (Steel wire rope slings — slings for general lifting service) et ASME B30.9 : coefficient d'utilisation 5 pour les élingues câble · cargorigging.com
- EN 1492-1 (élingues plates) / EN 1492-2 (élingues rondes) : élingues textiles, coefficient de sécurité 7:1 · h-lift.com
- DGUV Regel 115-002 et DGUV Information 215-313 « Lasten über Personen » : accessoires limités à la moitié de leur capacité au-dessus des personnes (doublement du coefficient) · unfallkasse-nrw.de
- PLASA / NRAG, Guidance: load suspension using electric chain hoists over stages and auditoria (janv. 2021) : palans industriels (D8, D8+) au-dessus du public à 50 % de leur capacité nominale · plasa.org