In the modern lifting and rigging industry, precise terminology is essential for maintaining safety standards. Standards bodies in the developed world have updated the way we define load capacities to eliminate ambiguity. This guide breaks down the correct usage of Maximum Rated Capacity (MRC) and Working Load Limit (WLL).
Rated Capacity is the maximum gross load which may be applied to the crane, hoist, or lifting attachment while in a particular working configuration and under a particular condition of use. It is often called the Manufacturers Rated Capacity or Maximum Rated Capacity (MRC) to avoid any confusion with maximum gross load.
When used on a crane, hoist, or winch, the Rated Capacity includes the weight of any attachments, spreader beams, or lifting devices below the crane hook.
* Note: The MRC must be clearly labelled on both sides of the crane beam or boom.
A Working Load Limit is the maximum Working Load for an accessory under a set configuration for expected or normal working conditions. The "Working Load" for any component is the load on the component plus the mass (weight) of the component itself.
It is calculated using the Minimum Breaking Load (MBL) required to fail or permanently deform that piece of equipment, divided by a Factor of Safety (FoS).
* Note: The WLL is set by the manufacturer. Any requirement to "derate" a piece of equipment should only be done by a qualified engineer after consultation with the manufacturer.
When designing a lifting configuration, it is critical to remember that the lifting system is only as strong as its weakest link:
