Two cranes with the same rated capacity and span may differ in their average load intensity and/or expected loading cycles. There are different standards which classifies cranes based on the service class. The Crane Manufacturer Association of America (CMAA) classifies bridge cranes according to average load intensities and number of cycles. On the other hand, the classification of hoists by the International Organization for standardization (ISO), European Federation Standard (FEM) and Hoist Manufacturer Institute (HMI) is according to more rigorous requirements, which include number of starts and maximum running time per hour. CMAA Crane classification and its comparison with other classification are given below. There are six different classifications of cranes by CMAA based on the duty cycle of crane.
Class A (Standby or Infrequent service)
This crane is the lightest crane as far as duty cycle is concerned. This service class covers cranes where precise handlings of equipment at slow speed with long idle periods between lifts are required. Capacity loads may be handled for initial installation of equipment and for infrequent maintenance. Example of the use of Class A cranes are transformer station, power houses, turbine halls, motor rooms and public utilities etc.
Class B (Light service)
This service class covers cranes where service requirements are light and speed is slow. Loads may vary from no load to occasional full rated loads with 2 to 5 lifts per hour, averaging 10 feet (3 meters) per lift. Examples of class B cranes include service buildings, light assembly operations, repair and maintenance shops and light ware housing etc.
Class C (Moderate service)
Class C cranes are those cranes whose service requirements are deemed moderate. These cranes handle loads which average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet (4.6 meters) with not over 50 percent of the lifts at rated capacity. Examples of class C cranes are the cranes usually used in paper mill machine rooms and machine shops etc.
Class D (Heavy service)
In class D crane service, loads approaching 50 percent of the rated capacity is handled constantly during the work period. High speeds are desirable for this type of service with 10 to 20 lifts per hour averaging 15 feet (4.6 meters) with not more than 65 percent of the lifts at rated capacity. Typical examples of cranes with heavy service are steel warehouses, foundries, fabricating shops, heavy machine shops container yards and lumber mills etc. Cranes may be with standard duty buckets or magnets operations where heavy duty production is required.
Class E (Severe service)
Cranes with class E service are capable of handling loads approaching the rated capacity throughout its life with 20 or more lifts per hour at or near the rated capacity. Application of canes with class E include magnet, bucket, magnet/bucket combination cranes or fertilizer plants, cement plants, scrap yards, lumber mills and container handling etc.
Class F (Continuous severe service)
Cranes with class F service are to be capable of handling loads approaching rated capacity continuously under severe service conditions throughout its life. Typical examples of such cranes include custom designed specialty cranes essential for performing the critical work tasks affecting the total production facilities. This type of crane must provide the highest reliability with special attention to ease of maintenance features.
Comparison of Various Classifications