Thermistor Motor Protection

Product Details

Thermistor Motor Protection 3RN1

Order No: 3RN10..-…..

Thermistor motor protection devices are used for direct monitoring of the motor winding temperature. For this purpose, the motors are equipped with temperature-dependent resistors (PTC) that are directly installed in the motor winding and abruptly change their resistance at their limit temperature.




  • Thanks to direct motor protection, over dimensioning of the motors is not necessary
  • No settings on the device are necessary
  • Solid-state compatible output thanks to versions with hard gold-plated contacts
  • Rapid error diagnosis thanks to versions that indicate open and short circuits in the sensor circuit
  • All versions with removable terminals
  • All versions with screw or spring-type terminals




Direct motor protection through temperature monitoring of the motor winding offers 100% motor protection even under the most difficult ambient conditions, without the need to make adjustments on the device. Versions with hard gold-plated contacts ensure, in addition, a high switching reliability that is even higher than an electronic control.

Motor protection:

  • At increased ambient temperatures
  • When switching frequency is too high
  • When start-up and braking procedures are too long
  • Used together with frequency converters (low speeds)