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Duty Cycle / CMAA Classifications

Selecting the right class and duty cycle for an overhead crane is critical for a customer who is trying to balance the initial investment of a crane system with the cost of future maintenance that will be required.

What Is An Overhead Crane: Determine Duty Cycle

These four factors are the most important requirements that you should identify to make sure that your crane is specified for the correct duty cycle and classification:

  1. Rated Load — Estimation of the loads lifted at or near capacity
  2. Service — Total hours in operation per day
  3. Number of Lifts — Average lifts and trolley and bridge movements made each hour
  4. Distance — Average length of each movement

Other factors that may not directly affect the overhead crane classification, but should still be taken into consideration when designing and specifying an overhead crane, are:

  • Speed — how quickly can the crane transfer materials or equipment? How many lifts per hour can the crane perform?
  • Maintenance Requirements — will the crane need to be serviced regularly and how will maintenance or repair affect production and downtime?
  • Operating Environment — In what type of environment or conditions will the crane be operating?
  • Future Needs — Any changes or increases in production requirements down the road? If you design a Class C crane, but know that down the road you be lifting heavier loads or using your crane more frequently, you may need to consider a Class D range crane.

Why Do You Need to Classify Cranes by Duty Cycle or Service Class?

Crane service classifications allow you to select and build an overhead crane that is the most economical and safest design for your lifting application. Selecting the right duty cycle or service classification of an overhead crane helps ensure that the components of the overhead crane are durable enough to withstand the load and usage requirements.

Two cranes with an equal capacity and span could vary in price as much as $100,000 because high duty cycle cranes (Class D, E, or F) require specialized components like the hoist, end trucks, motor, bearings, and controls. Low duty cycle cranes can get away with more standardized and economical components—resulting in significant cost savings.

When designing an overhead crane, you’ll also want to give special consideration to any future usage requirements. If you think that your production may expand down the road which may result in higher capacity lifts or an increase in the number of lifts per day, then you may want to spec out the crane and components so it can accommodate your future growth.

Different Types of Duty Cycles and Crane Classifications

There are six (6) different classifications for overhead cranes, specified by the Crane Manufacturers Association of America (CMAA). Overhead crane service classifications 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.

What Is An Overhead Crane: Crane Class A

CLASS A1 (STANDBY SERVICE)

This service class 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.

Typical examples are cranes 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

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.

Typical examples are 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
What Is An Overhead Crane: Crane Class B

CLASS B (LIGHT SERVICE)

This service class 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

Typical examples are cranes 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
What Is An Overhead Crane: Crane Class C

CLASS C (MODERATE SERVICE)

This service 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

Typical examples are cranes 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
What Is An Overhead Crane: Crane Class D

CLASS D (HEAVY SERVICE)

In this type of service, 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

Typical examples are cranes 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
What Is An Overhead Crane: Crane Class E

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 are magnet, bucket, magnet / bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc.

  • Bearing Life: 20,000 hours
  • Number of Lifts: 20+ per hour
  • Motor Starts/Stops: 600 per hour
What Is An Overhead Crane: Crane Class F

CLASS F (CONTINUOUS SEVERE SERVICE / STEEL MILL AISE SPECIFICATION)

In this type of service, the crane must be capable of handling loads, approaching rated capacity continuously under severe service conditions throughout its life. Cranes in this class are covered by the current issue of The Association of Iron and Steel Engineers’ Standard No. 6-1969, Specification for Electric Overhead Traveling Cranes for Steel Mill Service.

Typical examples are custom-designed specialty cranes essential to performing the critical work tasks affecting the total production facility, providing the highest reliability, with special attention to ease of maintenance features.

How Load Class and Load Cycles Affect Crane Service Class

In both CMAA #70 and CMAA #74, there is a table that shows the relationship between the Load Classes and Load Cycles and how those affect the CMAA Crane Service Classification.

Load Classes:

  • L1 = Cranes which hoist the rated load exceptionally and normally—very light loads.
  • L2 = Cranes which rarely hoist the rated load and normal loads of about 1/3 of the rated load.
  • L3 = Cranes which hoist the rated load fairly frequently and normally—loads between 1/3 and 2/3 of the rated load.
  • L4 = Cranes which are regularly loaded close to the rated load.

Load Cycles:

  • N1 = 20,000 to 100,000 cycles
  • N2 = 100,000 to 500,000 cycles
  • N3 = 500,000 to 2,000,000 cycles
  • N4 = Over 2,000,000 cycles

Calculate the Average Daily Operating Time

t = (2 x H x N x T) / (V x 60)

Where:

  • t = average daily operating time, hours/day
  • H = average hoisting height, feet
  • N = number of work cycles per hour, cycle/hour
  • T = daily working time, hours
  • V = hoisting speed, m/min or feet/min

CMAA Crane Classifications vs. European FEM Classifications

You should know that some overhead crane manufacturers use FEM Hoist Duty Classifications when specifying the service class and duty cycle of their crane systems. FEM is the European Federation of Materials Handling and they are responsible for publishing standards for the material handling industry. FEM standards use load spectrum and average daily operating time to determine their duty classifications.

It’s possible that you may even receive some quotes for a crane project with components specified to FEM standards. In the table below, we compare CMAA crane service classifications to the FEM hoist duty classifications and HMI hoist duty classifications (which we will touch on in more detail later).

Crane Classification

Hoist Classification

Use

Typical Shift Operation

Load Spectrum

Approx. Lifts Per Hour

Typical Application

CMAA

FEM

HMI

ISO

Class A

1Cm

H1

M2

Light-duty

Single shift

Very light

Up to 2 per hour

Standby service or infrequent service cranes used in public utility facilities, small maintenance or machine shops, testing laboratories, etc. for initial installation or infrequent maintenance of equipment.

Class B

1Bm

H2

M3

Light-duty

Single shift

Maximum load lifted occasionally

Up to 2 per hour

Cranes used in repair shops, light assembly operations, fabrication, service buildings, light warehousing, etc.

Class C

1Am

H3

M4

Light to medium-duty

Single Shift

Maximum load lifted occasionally

2-5 per hour

Cranes used in machine shops, paper mill machine rooms, etc.

Class D

2m

H4

M5

Medium to heavy-duty

One or two shifts

Medium to heavy loads

5-10 lifts per hour

Cranes 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.

3m

H4

M6

Heavy-duty

Two shifts

Heavy loads lifted regularly

10-20 lifts per hour

Cranes 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.

Class E

4m

H4 or H5

M7

Extremely heavy-duty

Two to three shifts

Heavy loads lifted regularly

20+ lifts per hour

Typical examples are magnet, bucket, magnet / bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc.

Class F

6

N/A

M8

Extremely heavy-duty continuous operation

Two to three shifts

Loads lifted continuously

Continuous

Custom-designed for a specific function within a particular facility. Built for ultimate performance and reliability. Example: Hot metal crane in a steel mill.

Lesson tags: duty cycle, CMAA service classifications, European FEM Crane Classifications, HMI hoist duty classifications, Class A cranes, Class B cranes, Class C cranes, Class D cranes, Class E cranes