What is reason for the percent difference of measured electric motor no load rpm compare with name plate data.

Question

What is reason for the percent difference of measured electric motor no load rpm compare with name plate data.

Answer 1

Basically there should be no difference so to speculate constructively on a reason, it would be useful to know how much difference you are seeing.  Some reasons for possible small variations would be:

High bearing friction

High ambient temperature (leads to increase of resistance)

Damaged or rubbing fan or other parts.

Answer 2

Most likely, the name plate lists only the RPM at rated full load. The difference between no load RPM and full load RPM will be determined by the motor's specific design details.

Exactly what is on the name plate will be determined by the type of motor and the standards to which it conforms.