Where would a thermistor be located in the overcurrent protection circuit of a 3-phase induction motor?

Where would a thermistor be located in the overcurrent protection circuit of a 3-phase induction motor?

• A. In the winding of the motor and connected to a control relay
• B. In the motor housing
• C. On the external cooling fan
• D. In the power supply line

Answer: (B)

Temperature sense in motor protection is used to detect winding overheating caused by overcurrent or overload. A thermistor is placed where it can read the actual heat of the windings, which is inside the motor housing. By mounting it in the housing, the sensor sees the true winding temperature and feeds that information to the protection relay, which can trip before insulation or windings are damaged. Placing the sensor elsewhere wouldn’t give an accurate reading of the winding heat, so the housing is the proper location to ensure effective protection.

Temperature sense in motor protection is used to detect winding overheating caused by overcurrent or overload. A thermistor is placed where it can read the actual heat of the windings, which is inside the motor housing. By mounting it in the housing, the sensor sees the true winding temperature and feeds that information to the protection relay, which can trip before insulation or windings are damaged. Placing the sensor elsewhere wouldn’t give an accurate reading of the winding heat, so the housing is the proper location to ensure effective protection.