# Understanding Motor Duty Rating

By on December 12th, 2011

One of the comments on my Motor Starting Series was asking for something on duty cycles.  Here it is.

As a purchaser of a motor, you have responsibility to let the manufacturer know the anticipated duty of the motor.  To assist in the communication of this information, the standard IEC 60034-1 (Rotating electrical machines) defines several duty characteristics, denoted S1 to S10:

Thermal Equilibrium is the state reached when the temperature rise of the machine does not vary by more than 2K per hour.   If you don't specify the duty cycle, the manufacturer will likely assume S1. Click on the image to see a larger version, illustrating the duty cycles.

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Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

#### View 1 Comments (old system)

1. sabari nath says:
5/24/2013 2:51 AM

Can you help me understand the relation between Motor duty cyce and Starts per hour?

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