Thermistor Motor Protection Relay

This product is used in conjunction with an external PTC thermistor which is typically embedded in motors. It will monitor the resistance of the thermistor and if increases above the fixed threshold (due to an increase in measured temperature), the relay will de-energise. The resistance must decrease below the “release” threshold before the relay re-energises again.


  • Compact 17.5mm DIN rail housing.
  • Used in conjunction with PTC (Positive Temperature Coefficient) thermistor typically embedded in motor windings.
  • Detects when the resistance of thermistor exceeds the fixed Operate threshold and de-energises internal relay.
  • Auto-resets (relay re-energises) when resistance returns below the Release threshold.
  • Isolated Auxiliary Supply (100 – 230V AC/DC).
  • 1 x SPDT relay output 5A.
  • Green LED indication for supply status.
  • Red LED indication for relay status.