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PTC thermistors are semiconductor elements with a very high positive temperature coefficient. They are embedded directly in
the phase windings of the stator. In contrast to the thermal overload protection that responds to the load current, the thermis-
tor protection responds to the change in thermistor resistance due to temperature change in the motor windings. The thermis-
tors are selected to have a rated operating temperature that corresponds to the insulation class, type and construction of the
motor. At the rated temperature the thermistor resistance increases sharply up to the hot temperature resistance value.
The UMC senses this abrupt change in the resistance. When thermistor protection is activated there is also an internal supervi-
sion which detects open or short-circuit faults from the thermistor circuit.
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Connect the PTC to the T1/T2 terminals of the UMC
Relevant Parameters:
• PTC
Motor with
PTC sensors
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