The basic rule: the setting is the rated current (In) shown on the motor nameplate for the voltage you run on. On the 11 kW 160M-4 model running on a 400 V supply this is 20.4 A; with direct-on-line starting, the thermal relay is set to 20.4 A. If the nameplate gives separate currents for 380, 400 and 415 V, use the value closest to the actual voltage you measure.

Caution in star-delta panels: the thermal relay is usually connected at the output of the main contactor, i.e. in the same branch as the motor winding. The current through it is the winding current, not the line current, and equals 1/√3 of line current, about 0.58 times. For the same motor, the setting becomes 20.4 × 0.58 ≈ 11.8 A. If the relay is connected at the supply input, the setting is again the nameplate current; confirm the connection point from the panel diagram.

Other points:

  • For loads with long starts (large fans, flywheel machines), the relay's trip class must suit the starting time; otherwise the relay trips before the motor accelerates.
  • If the relay trips often, measure the current instead of raising the setting: if the current really exceeds the nameplate value, the motor is overloaded or the supply is faulty.
  • After setting, check with the relay's test button that it actually opens the contactor.

For details, see our article on thermal relay and fuse selection.