# The 10 Motor Types Every Engineer Should Know

When selecting a motor, it is important to ensure the motor meets the needs of your application. Here we provide a basic introduction to the 10 motor types every engineer should know. Once you have identified the type of motor your machine operates, contact us at [email protected] to see how our team of experts can find the best solution for your specific application.

**1. Continuous running duty (type S1) **

For a motor suitable to this duty type, the rating at which the machine may be operated for an unlimited period is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S1.

DEFINITION – The duty type S1 can be defined as operation at a constant load maintained for sufficient time to allow the machine to reach thermal equilibrium.

**2. Short-time duty (type S2) **

For a motor suitable to this duty type, the rating at which the machine, starting at ambient temperature, may be operated for a limited period is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S2.

DEFINITION – The duty type S2 can be defined as operation at constant load for a given time, less than that required to reach thermal equilibrium, followed by a time de-energized and at rest of sufficient duration to re-establish the equilibrium between the machine temperature and that of the coolant temperature. A complete designation provides the abbreviation of the duty type followed by an indication of the duration of the duty (S2 40 minutes).

**3. Periodic duty (type S3-S8) **

For a motor suitable to this duty type, the rating at which the machine may be operated in a sequence of duty cycles is specified. With this type of duty, the loading cycle does not allow the machine to reach thermal equilibrium. This set of ratings is linked to a defined duty type from S3 to S8 and the complete designation allows identification of the periodic duty. If not otherwise specified, the duration of a duty cycle shall be 10 minutes and the cyclic duration factor shall have one of the following values: 15%, 25%, 40%, 60%. The cyclic duration factor is defined as the ratio between the loading period, including starting and electric braking, and the duration of the duty cycle, expressed as a percentage.

Duty type S3 (Intermittent periodic duty)

DEFINITION – The duty type S3 is defined as a sequence of identical duty cycles, each including a time of operation at constant load and a time de-energized and at rest. The contribution to the temperature-rise given by the starting phase is negligible. A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor (S3 30%).

**4. The duty type S4 **

(Intermittent periodic duty with starting) DEFINITION – The duty type S4 is defined as a sequence of identical duty cycles, each cycle including a significant starting time, a time of operation at constant load and a time de-energized and at a rest. A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor, by the moment of inertia of the motor JM and by the moment of inertia of the load JL, both referred to the motor shaft (S4 20% JM = 0.15 kg m2 JL = 0.7 kg m2).

**5. The duty type S5 **

(Intermittent periodic duty with electric braking) DEFINITION – The duty type S5 is defined as a sequence of identical duty cycles, each cycle consisting of a starting time, a time of operation at constant load, a time of electric braking and a time de-energized and at a rest. A complete designation refers to the duty type and gives the same type of indication of the previous case.

**6. The duty type S6 **

(Continuous-operation periodic duty) DEFINITION – The duty type S6 is defined as a sequence of identical duty cycles, each cycle consisting of a time of operation at constant load and a time of operation at no load. There is no time de-energized and at rest. A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor (S6 30%).

**7. The duty type S7 **

(Continuous-operation periodic duty with electric braking) DEFINITION – The duty type S7 is defined as a sequence of identical duty cycles, each cycle consisting of a starting time, time of operation at constant load and a time of electric braking. There is no time de-energized and at rest. A complete designation provides the abbreviation of the duty type followed by the indication of both the moment of inertia of the motor JM and the moment of inertia of the load JL (S7 JM = 0.4 kg m2 JL = 7.5 kg m2).

**8. The duty type S8 **

(Continuous-operation periodic duty with related load/ speed) DEFINITION – The duty type S8 is defined as a sequence of identical duty cycles, each consisting of a time of operation at constant load corresponding to a predetermined speed of rotation, followed by one or more times of operation at other constant loads corresponding to different speeds of rotation.

There is no time de-energized and at rest. A complete designation provides the abbreviation of the duty type followed by the indication of the moment of inertia of the motor JM and by the moment of inertia of the load JL, together with the load, speed and cyclic duration factor, for each speed condition (S8 JM = 0.7 kg m2 JL = 8kgm2 25kW 800rpm 25% 40kW 1250rpm 20% 25 kW 1000 rpm 55%).

**9. Non-periodic duty (type S9)**

Duty with non-periodic load and speed variations. For a motor suitable to this duty type, the rating at which the machine may be operated non-periodically is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S9. DEFINITION – The duty type S9 is defined as a duty in which generally load and speed vary non-periodically within the permissible operating range. This duty includes frequently applied overloads which may greatly exceed the reference load.

**10. Duty with discrete constant loads and speeds (type S10) **

For a motor suitable to this duty type, the rating at which the machine may be operated with a specific number of discrete loads for a sufficient time to allow the machine to reach thermal equilibrium is specified. The maximum permissible load within one cycle take into consideration all parts of the machine (the insulation system, bearings or other parts with respect to thermal expansion). The maximum load shall not exceed 1.15 times the value of the load based on duty type S1. Other limits as regards the maximum load may be given in terms of limits of the temperature of the winding. The minimum load have the value zero when the machine operates at no-load or is de-energized and at rest. This class of rating corresponds to the duty type whose appropriate abbreviation is S10. DEFINITION – The duty type S10 is defined as the operation characterized by a specific number of discrete values of load maintained for a sufficient time to allow the machine to reach thermal equilibrium. The minimum load during a duty cycle may have value zero and be relevant to a no-load or rest condition.

The above is just a snapshot guide providing a brief overview of motors. Our friendly sales team are on hand and would be delighted to speak with you and elaborate further on your motor requirements.