WLL, SWL and marking of lifting gear
To read the device's capacity and understand what the marking tells
PLACEHOLDER_83
§WLL and SWL — what is the difference
WLL (Working Load Limit) is the maximum permissible working load that the gear is designed and marked to carry under normal conditions. SWL (Safe Working Load) is used for the same basic concept, but can be a safe working load set for a specific setup or use — and therefore can be lower than the general WLL if conditions require it. In practice, WLL is the fixed, marked limit, while SWL can take into account how the gear is assembled and used.
§Fracture strength and safety factor
WLL is not the same as the load at which the gear breaks. The gear's breaking strength is far above WLL, and the ratio between breaking strength and WLL is called the safety factor. The built-in margin takes into account jerks, wear, uneven loading and material uncertainty. For this reason, you must never rely on the margin as extra lifting capacity — it is the safety reserve, not a buffer you draw capacity from.
§How to read the label
The marking or label on the equipment bears the information that makes it safe to use: the capacity (WLL), an identification that links the equipment to its documentation, and often material or class. Fiber slings are also color-coded according to capacity, so the right sling can be quickly identified. If the marking cannot be read, the capacity is unknown — and then the equipment must not be used until it is clarified.
| Equipment | The marking typically tells this |
|---|---|
| Chain | WLL, chain class and an identification for the certificate |
| Wire strap | WLL and an identification; capacity depends on suspension |
| Fiber sling (roundsling/band) | WLL, colour code for capacity and material |
| Shackles | WLL and size/type stamped in shackle and bolt |
§Capacity depends on usage
The marked WLL applies to a specific use — typically a straight, simple pull. If the device is used differently, the capacity changes. If a strap is laid double or wrapped around the load, and hung from multiple points with spread, different figures apply than the simple WLL. The manufacturer's table states how the capacity is reduced for the way the device is actually used — and you use the table rather than guessing.
§When the equipment doesn't have valid marking or documentation
Equipment without legible marking and without documentation has no known capacity. This also applies to homemade lifting devices and improvised brackets. Such equipment is taken out of service — not because it is necessarily weak, but because you do not know what it can bear, and therefore cannot safely lift with it.