The duty class (service class) is one of the most important decisions when specifying an overhead crane. The wrong class increases safety risks and leads to breakdowns, high maintenance costs and production stops.
FEM mechanism groups
FEM classifies cranes by load spectrum and average daily operating time. The most common groups are:
- 1Bm – very light duty
- 1Am – light duty
- 2m – medium duty, typical factory use
- 3m – heavy duty production lines
- 4m – very heavy, continuous operation
These correspond to ISO 4301 groups M3–M7.
Average daily operating time
t = (2 × H × n × T) / (60 × V), where H is the average hook travel (m), n the number of cycles per hour, T the working hours per day and V the hoisting speed (m/min).
Which class for which plant?
- 1Bm / 1Am: maintenance workshops, assembly, rarely used warehouse cranes, power plants.
- 2m: standard production plants and general workshops, 4–8 hours of medium use per day — the most common class in Türkiye.
- 3m: steel plants, foundries, heavy machinery lines, port warehouses.
- 4m: 24-hour steel service centres, scrap processing, automated lines.
Why it matters
A crane designed for its real duty can run for 15–25 years; an under-specified crane can show serious wear within 2–3 years. Over-specifying increases the investment unnecessarily.
Calculate your class in minutes with our FEM classification tool.
