Crane duty classifications of USA

There are six (6) different classifications for overhead cranes, specified by the Crane Manufacturers Association of America (CMAA). Overhead crane duty classification were established so that the manufacturer and end-user could design the most economical crane for the application, based mostly on the average rated load that the crane will lift, and how often the crane will be performing lifts.
Below we’ll identify and define the six types of overhead crane classes and provide types of businesses or industries that match up the best with each overhead crane classification.

Duty Class A1 (STANDBY SERVICE)

This duty classification covers cranes where precise handling of valuable machinery at slow speeds with long idle periods between lifts is required. Rated loads may be handled for initial installation of machinery and for infrequent maintenance.

Cranes of this duty class are usually used in power houses, public utilities, turbine rooms, nuclear reactor buildings, motor rooms, nuclear fuel handling and transformer stations.

• Bearing Life: 1,250 hours
• Number of Lifts: Up to 2 per hour
• Motor Starts/Stops: 75 per hour

Duty Class  A2 (INFREQUENT USE)

These cranes will be used in installations where the loads are relatively light, the speeds are slow, and a low degree of control accuracy is required. The loads may vary anywhere from no load to full rated load with a frequency of a few lifts per day or month.

Cranes of this duty class are usually used in small maintenance shops, pump rooms, testing laboratories, etc.

• Bearing Life: 1,250 hours
• Number of Lifts: Up to 2 per hour
• Motor Starts/Stops: 75 per hour

Duty Class  B (LIGHT SERVICE)

This duty classification covers cranes where service requirements are light and the speed is slow and loads may vary from no load to occasional full rated loads.

• Average load is 50% of the rated capacity
• 2 to 5 lifts per hour
• Average lift distance of 15 feet
• No more than 50% of the lifts at rated capacity

Cranes of this duty class are usually used in repair shops, light assembly operations, service buildings, light warehousing, etc.

• Bearing Life: 2,500 hours
• Number of Lifts: 2-5 per hour
• Motor Starts/Stops: 75 per hour

Duty Class  C (MODERATE SERVICE)

This duty service class covers cranes where service requirements are deemed moderate.

• Average load is 50% of the rated capacity
• 5 to 10 lifts per hour
• Average lift distance of 15 feet
• No more than 50% of the lifts at rated capacity.

Cranes of this duty service class are usually used in machine shops, paper mill machine rooms, etc.

• Bearing Life: 5,000 hours
• Number of Lifts: 5-10 per hour
• Motor Starts/Stops: 150 per hour

Duty Class D (HEAVY SERVICE)

In this type of duty service class, heavy-duty production is required but with no specific cycle of operations.

• Average loads approaching 50% of the rated capacity will be handled constantly during the work period
• High speeds are desirable for this type of service with 10 to 20 lifts per hour
• Average lift distance of 15 feet
• No more than 65% of the lifts at rated capacity

Cranes of this duty class are usually used in heavy machine shops, foundries, fabricating plants, steel warehouses, container yards, lumber mills, etc., and standard duty bucket and magnet operations where heavy-duty production is required.

• Bearing Life: 10,000 hours
• Number of Lifts: 10-20 per hour
• Motor Starts/Stops: 300 per hour

Duty Class  E (SEVERE SERVICE)

• This type of service requires a crane capable of handling loads approaching the rated capacity continuously, in repetition throughout a stated period per day, in a predetermined cycle of operation.
• Average load at or near the rated capacity
• High speeds are required with 20 or more lifts per hour
• The complete cycle of operation should be specified

Typical examples of this duty class are magnet, bucket, magnet / bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handlingเป็นต้น

• Bearing Life: 20,000 hours
• Number of Lifts: 20+ per hour
• Motor Starts/Stops: 600 per hour

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