What exactly is S3 rating on IEC motor spec label

[naxat]

Have a single phase 240v motor single cap. With S3 duty rating how long can this motor run for, before requiring rest period i.e. what is the duty cycle. Unusual oddball motor frame 80D 1.3kw/1.8hp 4pole 1420rpm

 

[stardelta]

S3 is Intermittent periodic duty. S3 motors generally state on the nameplate the max period of time they can run for or the max temperature they can safely reach before a rest period is required. The rest period is the time taken for the motor to cool to ambient and it should not be less then the run period.

 

[petronila]

Hello naxat,

The S3 is a Periodic Intermitent Service.
For S3 the motor works secuencially in identical cycles, each cycle have two periods, In the first the motor runs at constant load and the second period is for rest.In this services type, the cycle is calculate in order to the starting current don´t affect the motor´s heating.

For This Service Type the name plate will indicate in percent the cyclic duration factor = CF

Example: S3 25%.

CF is (N/(N+R))x100%.

N is the Run Time at constant load and R is the rest time.

Note: In a periodic Service the thermal equilibrium is not reached during the runnig period at constant load.

Regards

Petronila