Electrical Schematic – Motor Protection – Against Overloads – PTC Thermistor Probe Relays

These protection relays control the actual temperature of the motor to be protected.
Probes are imbedded into the motor and because they are small, their thermal inertia is very low, ensuring a very short response time and hence a very accurate temperature reading.
They directly control the temperature of the stator windings so can be used to protect motors against: overload, increase in ambient temperature, ventilation circuit faults, too frequent starting processes, inching, etc.







An electronic device powered by alternating and direct current for continuous control of the resistance of the probes linked to it.

Depending on the probes chosen, this protection mode can be used to:

  • set off an alarm without stopping the machine (NOT of the probes lower than the maximum temperature set for the element to be protected)
  • or order the machine to stop (the NOT has reached the maximum level)