This series are used for Crane Duty applications / Lift duty applications where movement of inertia of the load is maximum equal to movement of inertia of motor. For S3 series the duty cycle is designated as S3-40%, S3-60%. The no. of starts is also less, either 45 or 60 starts per hour. For S4 Series the duty designation is mentioned as S4 – 60% CDF, 150 starts per hour Extra.