for protection against overheating
Thermistor motor protection relays provide decisive advantages wherever current-dependent protection by means of circuit breaker or overload relay does not offer the perfect monitoring solution: In some cases, mostly as a result of external effects, overheating can occur without being detected by the thermal image in the circuit
breaker or overload relay. Examples include heavy-duty starting (e.g. centrifuges), operation with frequency converters or frequent switching, braking operations or impeded cooling, e.g. due to dirty environment.