The rated load is the heaviest load which a piece of equipment has been designed to deal with. Rated loads can consist of several different types of loads, including energy, weight, and speed. Most equipment is marked with informational plates which indicate the rated load along with other parameters for use so that people can use the equipment safely and avoid situations which could pose a threat to health and safety.
Manufacturers determine the rated load. This is done in part with the use of standardized equipment which has known tolerances, and in part by testing the equipment to see how much of a load it can bear or produce. For example, electrical equipment may be rated in terms of the energy it generates or in terms of the amount of energy it can handle as output. Likewise, equipment can be laden to see how much weight it can bear, with the equipment being utilized in test conditions in a way similar to the way it is used in the real world. An elevator, for example, would be moved vertically to determine the rated load.
It is usually recommended to use equipment with a rated load which exceeds the potential maximum capacity, and to avoid actually pushing the load limits of equipment. For example, when installing tires on a vehicle, people would choose equipment with a tire rating load which exceeded the laden weight of the vehicle. This would reduce the risk of equipment failure and increase safety for users.
Rated loads can be determined for structures as well as equipment, as for example when people study rated loads of bridges to find out how much traffic they can handle safely. In the case of something like a bridge, the load may be quite unique, because the bridge itself is not necessarily standardized. This makes it important to perform a wide variety of calculations to ensure that the bridge will be safe and usable.
With many types of equipment, companies are required by law to determine the rated load and disclose it truthfully. Failure to do so can result in legal penalties, especially if someone is injured by improperly tested or labeled equipment. Many companies make their testing methods and results public so that people can understand exactly how the equipment was tested and peruse the outcome for themselves. Proprietary testing techniques may have obscured details when they are published so that the manufacturer can maintain its market share.