Crane duty classifications are important to select and install a lifting crane that is appropriate for your application and facility. Selecting the appropriate lifting crane classification will help to ensure the working condition and longevity of your overhead system. Pushing your system beyond its duty rating is both dangerous and counterproductive. Using an overhead crane in accordance with its duty classification will not only protect your long-term investment and ensure worker safety—it will also provide valuable insight about the maintenance and inspection requirements of your overhead crane system.
Multiple standards exist to rate the duty class of a crane and hoist, including those developed by the Crane Manufacturers Association of America (CMAA). CMAA classifications are established based on a lifting crane’s average load intensity and number of lift cycles. Simply put, crane duty classifications are established by how much weight the system will need to lift, how high the loads will need to be lifted, and the frequency within an hour that the lifting crane will need to perform those works.
Two lifting cranes with the same capacity, span, and size can differ in the average load intensity and loading cycles. That’s because a lifting crane’s components experience various short-term and long-term loading conditions, which is why it’s important to choose a system that matches the duty class of your application.
Short Term Affects impact the functionality of your lifting crane and its components under full lift conditions. When crane manufacturers design structural components, they must take strength and rigidity into consideration. Long Term Affects impact the durability of the lifting crane and its components. Durability is assured by selecting mechanical, structural, and electrical components designed for the working load (average load intensity) and number of load cycles. Long term and short term affects must be considered during the design phase of a lifting crane to assure the safety and proper function of the system throughout its lifetime. During the design phase, engineers consider factors like system fatigue and component durability to ensure the working condition of a system. Crane duty classifications exist for that very reason.
The CMAA developed crane duty classes to help users determine the safest and most economical crane for their operation. In doing so, you must consider how much weight and how frequently the crane will be lifting and transporting materials. Once you have determined what needs to be moved and how often, a crane can be selected. The following is a list of crane classifications according to the CMAA.
Class A cranes are used as standby or infrequent duty cranes. These are systems intended for use at slow speeds and with long periods of idling between each lift. This class often includes installation and maintenance cranes for applications involving public utilities, motor rooms, and transformer stations.
Capacity loads might be handled for the installation of the equipment and for infrequent maintenance.
Class B cranes are designed for light duty requirements at slow speeds. Duty cycle and loads may vary from no load to an occasional full load with two to five lifts per hour, averaging ten feet per lift. Cranes in this class are often used in light assembly facilities, repair shops, duty buildings, and warehousing where duty requirements are light and slow.
Class C cranes are designed for moderate duty in an environment where the crane will need to handle loads averaging 50 percent of the rated capacity, with five to ten lifts per hour. The lift height for Class C cranes averages 15 feet. Most cranes are designed to meet Class C duty requirements. This duty often includes cranes used in manufacturing, machine shops, or papermill machine rooms.
Class D cranes are designed for heavy duty applications. In other words, 50 percent of the crane’s rated capacity is handled constantly throughout the workday. The crane will need to perform an average of 10 to 20 lifts per hour, with heights averaging 15 feet. Class D cranes are designed to move loads quickly and are usually installed in locations where heavy equipment must be moved constantly. This duty is often used for applications in heavy machine shops, foundries, fabricating plants, steel warehouses, container yards, and lumber mills.
Class E cranes are designed to handle loads approaching rated capacity throughout their lifetime. In other words, Class E cranes should lift their rated load capacity at an average of 20 lifts per hour. They can operate at any height, and they have few limitations for their workload per hour. These systems are often installed in scrap yards or production mills, and are usually used when heavy items need to be transported regularly throughout the workday. Applications often include cement mills, lumber mills, fertilizer plants, and container handling. Class E and F cranes require more frequent maintenance and provide the highest reliability possible.
Class F cranes are the most powerful cranes available. These systems are similar to Class E cranes because they are designed to handle severe duty. They also require the ability to handle loads approaching their rated capacity—throughout their entire lifetime. The main difference between the two is that Class F cranes are designed for continuous severe duty.”
Oftentimes, Class F cranes are custom designed for a specific function within a particular facility. They are built for ultimate performance and reliability, no matter how often they are used and regardless of their weight capacity. The most important factor for Class F cranes is that they can handle high capacity loads with constant frequency. Class F cranes are often used in industrial settings, although very few industries need to meet a Class F duty rating. These systems are difficult to design because they require the ability to handle the most extreme working conditions.
