Functions
7.4 Motor protection
SIRIUS 3RW52 Soft Starter
100 Manual, 01/2019, A5E35630451002A/RS-AD/004
7.4.2 Thermistor motor protection with temperature sensor (optional)
Operating principle
The temperature sensor of a motor can be connected to the soft starter and evaluated. If a
specific motor-dependent temperature is exceeded, the soft starter recognizes this and
reacts accordingly. The sensor cables can be monitored for open-circuit and short-circuit.
Two different types of measuring sensor can be connected to the soft starter:
● PTC thermistors type A
This type of sensor describes a temperature-dependent switch.
● Thermoclick
This type of sensor describes a temperature-dependent resistor.
When the thermistor motor protection has tripped, the 3RW52 soft starter cannot be
restarted until the sensor installed in the motor has cooled down. The recovery time varies
according to the temperature state of the sensor.
You will find more information on the connection of the temperature sensor in Chapter
Connecting the temperature sensor (Page 175).
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