It is normal for the frame of a motor running at full load to get too hot to hold for long, and that alone does not mean a fault. The frame surface is cooler than the winding, where the heat originates. The catalogue's reference values are for the winding and bearing area: winding temperature about 110 °C maximum, bearing area about 80 °C, temperature rise target below 75 K. No separate limit is given for the frame surface, and exact values are in the model test report.

So the question “how many degrees is normal” is answered more safely by comparison than by a single number:

  • Measure the temperature at the same spot each time with a non-contact thermometer and record it.
  • Take the reading together with the current; if the current is below the nameplate value and the temperature does not rise over time, the situation is most likely normal.
  • A clear rise compared with earlier readings at the same load, one bearing much hotter than the other, or a burning smell are signs that need investigation.

Where the winding temperature must be known directly, a PTC or PT100 sensor embedded in the winding is the preferred solution.