A PTC device is used
A. to start a hermetic compressor. B. as a motor protector. C. to protect against low oil pressure. D. to protect against high oil temperature.
The Correct Answer and Explanation is :
The correct answer is B. as a motor protector.
A PTC (Positive Temperature Coefficient) device is typically used in electric motor protection, specifically as a motor protector. It is designed to prevent motor damage by providing overcurrent protection through its self-regulating nature.
Explanation:
A PTC device works by utilizing a thermistor that increases its resistance significantly when it reaches a certain temperature. In normal conditions, the PTC thermistor has a low resistance, allowing current to flow freely to the motor. However, when the motor experiences an overload or excessive heat, the temperature of the PTC device rises. As it heats up, its resistance increases sharply, which limits the current flowing to the motor. This action helps prevent further heating and potential damage to the motor by interrupting or limiting the current flow when it reaches unsafe levels.
The self-regulating feature of the PTC device makes it particularly useful for protecting motors from overheating. Unlike traditional fuses, which must be replaced once they blow, a PTC device resets itself once it cools down and returns to its original low-resistance state. This reset capability makes it an effective and low-maintenance solution for overcurrent protection in electric motors.
In contrast, PTC devices do not perform the functions listed in the other options:
- A. Starting a hermetic compressor: PTC devices are not used to start compressors. Typically, starting devices like relays or capacitors are used for that purpose.
- C. Protecting against low oil pressure: PTC devices do not measure or protect against low oil pressure, which requires specific sensors and monitoring systems.
- D. Protecting against high oil temperature: While high temperatures may affect the PTC itself, the device is not specifically designed to protect against high oil temperatures. Systems like thermostats or oil temperature sensors are used for that purpose.
In conclusion, PTC devices are valuable in providing motor protection, ensuring that motors are safeguarded against potential damage due to excessive heat or current.