When working with cranes, it is more than likely that you’ll be operating heavy loads, with multiple workers onsite and present. It is absolutely crucial that you adhere to guidelines and lifting capacities at all times to keep all of those around you safe. Below we have explained one such guideline, a rating capacity, in more detail, as well as how you read rated capacity charts properly.
What is a rated capacity?
Before defining this term, it is important to distinguish between two terms that relate to this; safe working load (SWL), also known as the working load limit (WLL) and minimum breaking load (MBL).
The MBL is used to define the minimum point at which a crane will break. Lifting at this capacity, or any capacity higher, is unsafe and must be avoided at all times. The SWL, on the other hand, is a limit that will have been issued by the manufacturer from which you purchased your crane. This will be set way below the MBL, and is the limit that you should be working to, or under, at all times.
It’s important not to exceed the weight limit of your crane
Coming to “rated capacity” then, the definitions for the term differ. Generally, it is accepted to mean the maximum allowable lift for a crane in any given configuration. So, if a crane is utilised with different accessories or is placed in different positions, this capacity may change. This tends to be the broader view for the term.
Others believe that the definition needs to be more specific than this. They argue that this capacity limit is just one figure for the maximum allowable lift of a crane. They say that a crane is only safely operating at its rated capacity when:
- It is set at the minimum lifting radius. This must be at a horizontal distance from the middle of the crane’s rotation, and to the middle of gravity of the load being lifted
- It must also be set at minimum boom length
So, for example, a 30 tonne crane is only able to lift a 30 tonne load when set at the shortest boom section, and when it is as near to the crane as is possible. If this radius increases, then the allowable lift must decrease at the same time. Or, increasing the boom length, but at the same radius, can also reduce this allowable lift too.
For the sake of this article, we’ll stick with the broader definition of rated capacity, as the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) refer to multiple configurations within their guidelines.
LOLER states that the rated capacity will change for different configurations. For example, the hook of a hoist may be moved into different positions, which may change the SWL. In cases such as these, each possible rated capacity must be specified. It is also recommended that each of these varying capacities should be fitted to the crane, so anyone operating can easily see what the limits are.
Reading rated capacity charts for cranes
Each crane will have its own specific rated capacity chart specifying its capabilities. This chart will detail the lift capacity of your product when considering factors such as distance and angles. These are the factors to look out for in a rated capacity chart:
Dimensions and weight
Any chart will show the dimensions and weight of your crane. This is crucial information to know how to move your crane, and how well it can operate in your workspace.
This details the actual lifting capabilities of your crane. This will vary depending on the weight of the load, and the distance from which it is being lifted from the crane. For example, the closer a lifting hoist is operating towards the supporting structure of a jib crane, the higher the capacity that it will be able to lift.
The lift range refers to the maximum range at which a crane can operate. Some cranes will operate within a fixed range, for example gantry cranes which don’t have extendable arms, meaning this factor doesn’t come into play.
Some cranes can operate at different angles, and this will play a part in any lifting operation. When using a higher angle of lift, you will find a decrease in the maximum load capacity of your crane.
It’s important that your chart contains all the crucial information
Would you like to speak to us directly?
If you are interested in finding out more about the range of cranes and crane accessories that we stock here at Cranes Direct, or you have any other questions about rated capacity charts, then we would be more than happy to speak. You can get in contact with us here.