What is the working load limit?
The working load limit (WLL) is the maximum load that a piece of lifting equipment, such as a sling, chain, wire rope or shackle, is allowed to carry in normal use. The manufacturer sets the value and marks it on the item. Safe working load (SWL) is the older term and is still used in UK regulations; in practice it describes the same limit. The Dutch term is ‘veilige werklast’.
WLL and breaking load
The WLL sits well below the minimum breaking load (MBL), the load at which the item fails in a destructive test:
WLL = minimum breaking load / safety factor
The EU Machinery Directive (2006/42/EC) gives these factors (working coefficients) as a general rule:
- wire rope with its termination: 5
- lifting chain: 4
- textile slings: 7
- metal components of a sling: 4
A wire rope with a breaking load of 10,000 kg therefore has a WLL of 2,000 kg. The margin covers wear, shock and small deviations. It is not spare capacity to plan with.
Marking and examination
In Great Britain, the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) require lifting equipment to be marked with its safe working load. HSE guidance says lifting accessories need a thorough examination at least every six months, unless a competent person has drawn up an examination scheme. Webbing slings also carry a colour code, for example violet for 1 tonne, green for 2 and yellow for 3, but the label always takes precedence.
Common mistakes
- Ignoring the angle: the WLL on the label applies to a straight vertical lift. In a choke hitch or with legs at an angle, the permitted load drops. Use the manufacturer’s load table.
- Forgetting the weakest link: a 4-tonne chain on a 2-tonne shackle is a 2-tonne assembly.
- Using unlabelled gear: a sling without a legible label should be taken out of service.
- Shock loading: jerking or dropping a load creates forces far above its weight.
Related terms
- Lifting sling
- Winch
- Load test
- Point load
- Occupational health and safety
- Load-bearing capacity
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