Auxiliary, trip and supervision relays

2TD770 700 Series Temperature Sensing Relay



  • Ten year factory warranty
  • Plug in measuring module
  • Double insulated high impact polystyrol case
  • Termination socket included for surface mounting enabling front or rear connection with optional DIN rail mounting
  • Proven circuit designs based on over 15 years of field service in hundreds of varied & demanding applications
  • Easy to set calibration scales
  • Tolerance to shock & vibration for generator, compressor & mobile applications


The 2TD770 Series relays are solid state temperature sensing relays for use in motor protection applications where sensors are located in the stator windings. Heavy duty industrial motors are prone to catastrophic failure. If overheating occurs due to such circumstances as locked rotor, restricted cooling or heavy starting conditions.
The 2TD770 can be used to effectively monitor the motor temperature and switch its mechanical output relay to indicate an alarm condition or isolate the power supply.
The 700 Series range of electronic measuring relays are manufactured as a modular approach to electrical system protection & control. Designed to meet rigid Australian & international specifications the 700 Series provide a flexible, cost effective & extremely reliable solution for a multitude of applications under electrically hostile conditions.



Three PTC thermistors (one for each phase) are connected in series to the input terminals of the relay. An increase in local temperature of the motor causes an increase in resistance in the corresponding thermistor. The relay senses the change in resistance and picks up when the temperature increases beyond the preset setting. A visual indication is given by a red LED n the front panel when the output relay is energised.

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Railway rolling stock
Railway signalling