PTC Thermistors should be placed as near as possible to the hot spot. In three phase motors, one PTC Thermistor should be embedded in each phase. Good thermal contact between PTC Thermistor and winding is essential. The PTC Thermistors should be embedded parallel to the winding.
In this way the mechanical stresses on the PTC Thermistors during forming the end turns of overhang winding can be minimized. Shrink cap is especially well suited for this because of its mechanical stability. At ambient temperature, resistance of one thermistor is between 20 ohms to 250 ohms. The resistance increases sharply in the region of the nominal response temperature. Response times > 5 sec. are achieved with Thermistor. This signal can be used to switch off power circuit of electric motors/ transformers by using Thermistor Protection Unit.