Electronic device technology / thermal machine protection


The electronic thermistor motor protection relay monitors thermally relevant positions in conjunction with PTC sensors. When used correctly, safe protection against thermal overload is guaranteed.

The areas of application are:

  • Difficult start-up (overload)
  • Excessive switching frequency
  • With rapidly increasing winding temperature due to blocked rotors
  • Phase failure and resulting rise in winding temperature
  • Heating and ventilation
  • Operation with frequency inverters
  • Transformer protection
  • Surface temperature control of power semiconductors

The trigger device analyses the temperature of a PTC sensor element. The relay is energised in normal operation, i.e. there is no impermissible temperature increase. In the event of exceeding a specified temperature (PTC NAT), which is equivalent to an increase in resistance (> 4000 Ohm), the relay drops out. If the temperature drops or the restart resistance (1650 to 750 Ohm) is reached, the relay energises again automatically. Independent switching on and off is guaranteed by the switching hysteresis specified in DIN VDE 0660.

  • Internationally standardised switch-on and switch-off points
  • PTC thermistor sensors can be replaced as required
  • PTC thermistors of all standardised nominal trigger temperatures can be connected (DIN 44081 and DIN 44082)
  • Sensor cable break is detected
  • Device operates according to the closed-circuit current principle, i.e. safe switch-off of the electrical machine even in the event of a power failure
  • Excellent price-performance ratio
Product information

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